Dr Gernot Frenking
email: frenking@chemie.uni-marburg.de

Nicole Holzmann

Bernhard Neumüller

Kurt Dehnicke
email: dehnicke@chemie.uni-marburg.de

Bernd Harbrecht

Geburtstag

2 PPh 2 ) 2 ] -ein Donor-Akzeptorkomplex des Berylliums mit dem Bis(diphenylphosphino)methan-Liganden

Keywords: Beryllium, Bis(diphenylphosphino)methane, Donor-acceptor complex, X-ray diffraction, IR spectra, DFT calucations Beryllium, Bis(diphenylphosphino)methane, Donor-acceptor complex, X-ray diffraction, IR spectra, DFT calculations

The donor-acceptor complex [BeCl 2 (Ph 2 PCH 2 PPh 2 ) 2 ] (1•2CH 2 Cl 2 ) was prepared from beryllium-dichloride and bis(diphenylphosphino)methane in dichloromethane suspension to give colourless single crystals, which were characterized by X-ray diffraction, IR spectra, and DFT calculations. Compound 1•2CH 2 Cl 2 crystallizes monoclinically in the space group C2/c with four formula units per unit cell. Lattice dimensions at 193(2) K: a = 2339.5(2), b = 916.7(1), c = 2415.4(2) pm, β = 97.15(1)°, R 1 = 0.0386. The structure of 1 consists of distorted tetrahedral molecules with site symmetry C 2 and bond lengths Be-Cl of

196.8(2) pm and Be-P of 220.6(3) pm. Quantum chemical calculations at the RI-BP86/SV (P) level give a structure of 1 which is in very good agreement with the experimental one. The calculations predict that the bond dissociation energies of the first and second Ph 2 PCH 2 PPh 2 ligand from 1 are D e = 16.8 kcal/mol and 24.3 kcal/mol, respectively. Wir haben die Bindungsdissoziationsenergien (BDE) der Reaktionen (2) und (3) berechnet:

[BeCl 2 (Ph 2 PCH 2 PPh 2 ) 2 ] (1) → [BeCl 2 (Ph 2 PCH 2 PPh 2 )] + Ph 2 PCH 2 PPh 2 (2)

___________________________________________________________________________ 1 Einleitung 2 Ergebnisse

 12 Eine Bilanz der Kenntnis von Donor-Akzeptorkomplexen der Berylliumhalogenide vom Typ [BeX 2 (L) 2 ] mit L = monofunktionellen Donormolekülen mit Stickstoff-oder Sauerstoffatomen als Donoratomen weist eine ansehnliche Anzahl auch kristallographisch gut belegter Beispiele auf [1, 2]. Dagegen sind mit den Ligandmolekülen L und dem Donoratom Schwefel bisher nur der Molekülkomplex [BeBr 2 (SMe 2 ) 2 ] [3] beschrieben, während Komplexe mit dem Donoratom Phosphor (Phosphanliganden) unseres Wissens unbekannt sind. Wir beschreiben hier ein erstes Beispiel anhand des Komplexes [BeCl 2 (Ph 2 PCH 2 PPh 2 ) 2 ]. Andererseits sind Berylliumverbindungen mit phosphidischen Komponenten wie Be 3 P 2 [4] mit Be-P-Abständen von 211 pm, (η 5 -Pentamethyl-cyclopentadienyl)-di-tbutylphosphido-Beryllium, [(t-Bu) 2 P-Be-Cp*] [5] mit nahezu gestreckter Achse P-Be-Cp* (centroid) und einem Be-P-Abstand von 208.3(6) pm sowie der Chelatkomplex Bis(bis(Dimethylphosphanyl)(trimethylsilyl)methanid)-Beryllium, [Be{Me 3 SiC(PMe 2 ) 2 } 2 ] [6], mit Be-P-Abständen von im Mittel 213.6 pm zum Teil bereits seit längerer Zeit wohlbekannt. Eine Suspension von Berylliumchlorid in Dichlormethan reagiert mit Diphenylphosphinomethan unabhängig von dem angewandten stöchiometrischen Verhältnis der Reaktanden gemäß Gleichung (1) unter Bildung des Donor-Akzeptorkomplexes Bis(diphenylphosphino)methan-Berylliumdichlorid (1•2CH 2 Cl 2

  ein Be-Cl-und Be-P-Abstand resultiert. Die Be-P-Donor-Akzeptorbindungen sind mit Abständen von 220.6(3) pm naturgemäß deutlich länger als die vom Phosphido(1-)-Typ [(t-Bu) 2 P-Be-Cp*] [5] mit 208.3(6) pm und [Be{Me 3 SiC(PMe 2 ) 2 } 2 ] [6] mit im Mittel 213.6 pm. Den langen Be-P-Bindungen in 1 stehen kurze Be-Cl-Bindungen von 196.8(2) pm Länge gegenüber, die deutlich kürzer sind als in Komplexen [BeCl 2 (L) 2 ] mit N-Donoratomen der Liganden L [1, 2], jedoch entsprechen sie etwa den Be-Cl-Abständen in [BeCl 2 (15-Krone-5)] (197.8(2), 195.8(2) pm [9]) oder in [BeCl(12-Krone-4)] + [SbCl 4 ] -(198.5(7) und 197.4(9) pm [10]). Die relativ schwachen Be-P-Bindungen in 1 spiegeln sich in den nur marginal veränderten P-C-Bindungslängen des Phosphinoliganden gegenüber den entsprechenden P-C-Abständen im freien Liganden Ph 2 PCH 2 PPh 2 wider (siehe Tabelle 2). Etwas größer sind die Veränderungen der C-P(1)-C-Bindungswinkel durch die Koordination am Berylliumatom um +4.8°, während die C-P(2)-C-Bindungswinkel mit einer Zunahme von nur +0.8° praktisch unverändert bleiben (jeweils Mittelwerte). Eine Ausnahme macht die kräftige Aufweitung des P(1)-C(1)-P(2)-Bindungswinkels von 106.2(3)° im freien Liganden nach 115.6(1)° in Verbindung 1, die im wesentlichen durch die sterischen Verhältnisse bedingt sein dürfte. In Abbildung 2 sind die Packungsverhältnisse von Verbindung 1•2CH 2 Cl 2 wiedergegeben. Die [BeCl 2 (Ph 2 PCH 2 PPh 2 ) 2 ]-Moleküle sind entlang [010] angeordnet, wobei Kanäle entstehen, die von den Dichlormethanmolekülen fehlordnungsfrei besetzt werden. Sie sind dort durch nur sehr schwache C-Cl … H-Wasserstoffbrückenbindungen mit den Phenyl-CH-Atomen fixiert. Ähnlich schwache Kontakte C-H … Cl bestehen auch mit den am Berylliumatom gebundenen Chloridoliganden. 4 Quantenchemische Berechnungen Wir haben die Strukturen des Komplexes [BeCl 2 (Ph 2 PCH 2 PPh 2 ) 2 ] (1) sowie des freien Liganden Ph 2 PCH 2 PPh 2 mit Dichtefunktionaltheorie (DFT) auf RI-BP86/SV(P)-Niveau berechnet [15]. Die optimierte Struktur von 1 in Abbildung 1b zeigt an, daß Rechnung und Experiment sehr ähnliche Geometrien für den Komplex ergeben. In der Tabelle 2 sind die theoretischen Werte für die Bindungslängen und Winkel aufgeführt. Der Vergleich mit den experimentellen Daten zeigt eine gute Übereinstimmung zwischen Theorie und Experiment. Die geringen Abweichungen können auf Festkörpereffekte wie auch auf Fehler des quantenchemischen Näherungsverfahrens zurückzuführen sein. In Übereinstimmung mit dem Experiment werden in den Rechnungen eine relativ lange Be-P-Bindung und nur geringfügig verkürzte C(1)-P-Bindungen im Komplex 1 bezogen auf den freien Liganden gefunden. Allerdings ist die Struktur des BeCl 2 in 1 gegenüber freiem Berylliumdichlorid auf Grund der zweifachen Komplexierung deutlich verändert. Nach den Rechnungen beträgt der Winkel Cl-Be-Cl im freien BeCl 2 180 o und die Be-Cl Bindungslänge ist mit 181.7 pm wesentlich kürzer als im Komplex 1.

  ).Vergleich den bei 233 K erhaltenen Daten des Bis(diphenylphosphino)methans[7] gegenübergestellt. Die Kristallstruktur des Ligandmoleküls Ph 2 PCH 2 PPh 2 wurde später noch bei 153 K[11] und bei 293 K[12] ermittelt. Die kristallographischen Daten (ohne Cl 2 kristallisiert monoklin in der Raumgruppe C2/c mit vier Formeleinheiten pro Elementarzelle. In Abbildung 1a ist die die Molekülstruktur von 1 wiedergegeben. Das Berylliumatom besetzt die zweizählige Symmetrieachse, so daß nur je

	BeCl 2 + 2 Ph 2 PCH 2 PPh 2	  → 2 2 Cl  CH  	[BeCl 2 (Ph 2 PCH 2 PPh 2 ) 2 ]•2 CH 2 Cl 2	(1)
			1
	Bei Anwendung des Eduktverhältnisses von Gleichung (1) entsteht bereits nach kurzer Zeit Strukturfaktoren) von Verbindung 1 wurden als "supplementary publication no. CCDC-
	ohne erkennbare Wärmeentwicklung eine klare Lösung, aus der nach Einengen, 77249" beim Cambridge Crystallographic Data Centre hinterlegt. Kopien der Daten können
	Überschichten mit n-Pentan und Schockgefrieren mittels flüssigem Stickstoffs beim Auftauen kostenlos bei CCDC, 12 Union Road, Cambridge CB2 1EZ (Fax: (+44)1223-336-033; E-
	farblose Einkristalle von 1•2CH 2 Cl 2 als große Prismen kristallisieren. Im Vakuum wird das mail: deposit@ccdc.cam.ac.uk), Großbritannien, angefordert werden.
	eingelagerte Dichlormethan im Einklang mit den nur sehr schwachen intermolekularen Verbindung 1•2CH 2
	C-Cl … H-Wasserstoffbrückenkontakten (siehe unten) rasch und vollständig abgegeben.
	Das IR-Spektrum der Verbindung 1 wird im wesentlichen von den Banden des
	nichtkoordinierten Ligandenmoleküls dominiert, die zugleich im Spektrum von 1 nur wenig
	Änderungen erfahren. Eine Ausnahme beobachten wir bei den beiden P-CH 2 -P-
	Valenzschwingungen, die durch die Koordination im Spektrum von 1 deutlich kurzwellig von
	511 und 501 cm -1 nach 642 und 582 cm -1 verschoben werden und in ihren Frequenzlagen

kräftig auseinander rücken. Die Ursache hierfür ist die Aufweitung des P-C-P-Bindungswinkels von 106.2(3)° im Ph 2 PCH 2 PPh 2 -Molekül [7] nach 115.6(1)° in Verbindung 1, die mit einer Zunahme der Schwingungskopplung verbunden ist [8]. Während die Be-P-Valenzschwingungen aufgrund der langen Be-P-Abstände unterhalb von 400 cm -1 des von uns registrierten Frequenzbereichs zu erwarten sind, lassen sich die BeCl 2 -Valenzschwingungen mit antisymmetrischem und symmetrischem Charakter bei 734 und 707 cm -1 identifizieren. Dies passt gut zu den vergleichsweise [1, 2] kurzen Be-Cl-Abständen von 196.8(2) pm, wie sie beispielsweise in den Komplexen [BeCl 2 (15-Krone-5)] [9] und [BeCl(12-Krone-4)] + [SbCl 4 ] -[10] angetroffen werden, die zu Verbindung 1 ähnlichen Be-Cl-Valenzschwingungen führen. Zum vollständigen IR-Spektrum von 1 siehe experimentellen Teil. 3 Kristallstrukturanalyse von [BeCl 2 (Ph 2 PCH 2 PPh 2 ) 2 ]•2CH 2 Cl 2 (1•2CH 2 Cl 2 ) Tabelle 1 enthält die kristallographischen Daten und Angaben zu den Strukturlösungen. In Tabelle 2 sind die Bindungsparameter zusammengestellt und zum

  Demnach ist der Ph 2 PCH 2 PPh 2 -Ligand etwa so stark gebunden wie Ammoniak und der Carbenligand CF 2 . Die berechnete BDE eines NH 3 -Liganden im Komplex [BeCl 2 (NH 3 ) 2 ] beträgt auf RI-BP86/TZ2P-Niveau D e = 18.4 kcal/mol [16]. Für den Komplex [BeCl 2 (CF 2 ) 2 ] wurde auf MP2/6-31G(d)-Niveau eine BDE von D e = 18.6 kcal/mol vorhergesagt [17]. Die zweite BDE von 1 (Reaktion 3) wird auf RI-BP86/SV(P)-Niveau mit D e = 24.3 kcal/mol als stärker als die erste BDE berechnet. Sie ist aber etwas schwächer als die BDE des zweiten NH 3 -Liganden im [BeCl 2 (NH 3 ) 2 ], die auf RI-BP86/TZ2P-Niveau mit D e = 27.4 kcal/mol berechnet wird [16]. Für den Komplex [BeCl 2 (CF 2 ) 2 ] wird die zweite BDE mit D e = 19.8 kcal/mol ermittelt [17]. Die berechnete atomare Ladungsverteilung nach dem NBO-Verfahren [18] ergibt eine schwache Donierung der beiden Ph 2 PCH 2 PPh 2 -Liganden im Komplex 1 von insgesamt 0.06 e. Das Be-Atom hat im Komplex eine positive Partialladung von 1.36 e während die Chloratome eine negative Ladung von -0.71 e aufweisen. Kristallographische Daten und Angaben zur Strukturbestimmung von [BeCl 2 (Ph 2 PCH 2 PPh 2 ) 2 ]•2CH 2 Cl 2 (1•2CH 2 Cl 2 )

	Page 13 of 15	ZAAC
	H-Atome	berechnete Positionen mit gemeinsamem
		Auslenkungsparameter
	R 1	0.0386
	wR 2 (alle Daten)	0.0932
	Instrument max. Restelektronendichte/	IPDS I (Stoe) 0.429
	Strahlung 10 -6 e/pm -3	Mo-K α
	Summenformel Formelgewicht/g•mol -1 a) w = 1/[σ 2 (F o 2 )+(0.0559•P) 2 ]; P = [max(F o C 52 H 48 BeCl 6 P 4 1018.49 2 , 0)+2•F c	2 ]/3
	Kristallabmessungen/mm	0.4 × 0.36 × 0.2
	a/pm	2339.5(2)
	[BeCl 2 (Ph 2 PCH 2 PPh 2 )] Die BDE des Komplexes 1 für die Reaktion (2) beträgt auf RI-BP86/SV(P)-Niveau D e = 16.8 → BeCl 2 + Ph 2 PCH 2 PPh 2 (3) Bindungsanteil spiegelt sich auch in den langen Be-P-Abständen von 220.6(3) pm (berechnet 224.2 pm) wider, während die stark ionischen Be-Cl-Bindungen in Komplex 1 durch vergleichsweise [1, 2a, b] sehr kurze Abstände von 196.8(2) pm (berechnet 199.8 pm) auffallen. In diesen Zusammenhang passen auch die kurzen Be-P-Bindungen von 211 pm Länge des im Antifluorit-Typ kristallisierenden Be 3 P 2 mit einem Viertel der Tetraederpositionen unbesetzten Atomlagen, dessen Bindungstyp als weitgehend ionisch beschrieben wird [4]. Experimenteller Teil Vorsicht! Beryllium und seine Verbindungen sind stark toxisch (MAK-Liste A2 krebserregender Arbeitsstoffe; siehe auch die Literatur in der Übersicht [1]). Es wirkt zudem auch mutagen [19]. Der Umgang mit Berylliumverbindungen erfordert daher die Anwendung besonderer Arbeitsbedingungen. Siehe hierzu die aktuelle Übersicht aus arbeitsmedizinischer Sicht [20]. Die Versuche erfordern Ausschluß von Feuchtigkeit. Alle Handlungen wurden unter trockenem Stickstoff ausgeführt. Dichlormethan und n-Pentan (Merck, p.A.) wurden über b/pm 916.7(1) c/pm 2415.4(2) β/° 97.15(1) Zellvolumen/pm 3 5139.8(8)•10 6 Z 4 d rönt g•cm -3 1.316 Kristallsystem monoklin Raumgruppe C2/c Absorptionskorrektur numerisch µ/cm -1 4.93 Meßtemperatur/K 193(2) 2θ max /° 51.96 hkl-Werte -28 ≤ h ≤ 28, -11 ≤ k ≤ 11, -29 ≤ l ≤29 gemessene Reflexe 24584 unabhängige Reflexe 5002 R int 0.0464 Reflexe mit F o >4σ(F o ) 3329 kcal/mol. Die schwache Donierung der Phosphoratome mit dem sehr geringen ionischen Parameter 286
	Strukturlösung a)	direkte Methoden (SIR-92 [13])
	Verfeinerung gegen F 2	SHELXL-97 [14]
		Wiley-VCH

eine Säule mit Phosphorpentoxid getrocknet und mit einem Al 2 O 3 -Filter nachgereinigt.

Berylliumchlorid erhielten wir wie beschrieben

[START_REF] Neumüller | [END_REF]

durch Direktsynthese aus den Elementen. Bis(diphenylphosphino)methan war ein handelsübliches Produkt (Aldrich, 97%ig), es wurde Tabelle 1.


Dennis Kuchenbecker

Sjoerd Harder
email: sjoerd.harder@uni-due.de

Georg Jansen
email: georg.jansen@uni-due.de

Insight in Structures of Superbulky Metallocenes with the Cp BIG Ligand: Theoretical Considerations of Deca-Phenyl Metallocenes

Keywords: Metallocenes, density functional calculations, dispersion interactions Metallocenes, density functional calculations, dispersion interactions

The structures of a series of deca-phenyl metallocenes (Ph 5 Cp) 2 M, which model superbulky metallocenes, are calculated by means of density functional theory including a semi-empirical correction for dispersion interactions (DFT+D). Through a detailed investigation of the calcocene it is shown that the interactions between the phenyl substituents of the two cyclopentadienyl ligands lead to a preference of S 10 -symmetrical structures and that dispersion interactions contribute to the overall stability of superbulky metallocenes.

While the Ph substituents of the two ligands bend away from each other with standard DFT, inclusion of the dispersion correction reproduces the experimentally observed slight inclination towards each other. The experimentally observed linear correlation between the out-of-plane bending angle of the phenyl substituents and the size of the metal atom M (M = Fe, Ni, Cr, W, Ca, Yb, Sn, Sm, Sr, Ba) is also confirmed at the DFT+D level.

____________

Introduction

Although the superbulky cyclopentadienyl ligand Ph 5 Cp is synthetically readily accessible, its use in organometallic chemistry is very limited. [1] This is largely due to solubility issues. Considerable size and high rigidity and symmetry render its compounds nearly insoluble in any non-reactive organic solvent. Solubility problems can be circumvented by converting the Ph substituents into less rigid groups. [2,3] Metallocenes with the ligand (4-nBu-C 6 H 4 ) 5 Cp, which on account of its size has been abbreviated as Cp BIG , were found to be well soluble even in apolar solvents like hexane. [3] Although metallocenes with bulky Cp ligands generally show strong ligand-ligand repulsion, complexes (Cp BIG ) 2 M were found to be extraordinarily stable. Attempts to prepare the half-sandwich complex Cp BIG CaCH 2 Ph led to ligand exchange and formation of the homoleptic species (Cp BIG ) 2 Ca and (PhCH 2 ) 2 Ca (Scheme 1). [3] More remarkable is the lanthanide chemistry of this ligand: reaction of the Sm(III) complex (DMA) 3 Sm (DMA = 2-Me 2 N-benzyl) with Cp BIG H did not give the expected half-sandwich compound Cp BIG Sm(DMA) 2 but instead the metallocene (Cp BIG ) 2 Sm was isolated. [3] As the Sm(II) complex Cp* 2 Sm is even oxidized by molecular nitrogen, [4] the spontaneous reduction of a Sm(III) precursor to a Sm(II) metallocene is highly unexpected. Although these processes might be in line with sterically induced reduction (SIR), a concept recently introduced by Evans, [5] the unanticipated high stability of metallocenes with the Cp BIG ligand could also play a major role. Although one might expect repulsion between the superbulky Cp BIG ligands, there is considerable evidence for attractive Ar 5 Cp•••CpAr 5 interactions.

Please insert Scheme 1

Scheme 1. Conversion of Cp BIG H into half-sandwich complexes resulted in formation of the metallocene complexes.

(i) The metal-carbon bond distances in metallocenes with the Cp BIG ligand are shorter than expected. E.g. the Ba-C bond distances in (Cp BIG ) 2 Ba (average 2.929(2) Å) [6] are significantly shorter than those in Cp* 2 Ba (average 2.99(1) Å) [7] or in (iPr 5 Cp) 2 Ba (average 2.997(4) Å). [8] Deacon et al reported a similar contraction phenomena for (Ph 5 Cp) 2 Yb, which also shows short Cp-metal bonds. [9] (ii) As we discussed earlier, [3,6] the aryl substituents in the Cp BIG ligands are bent out of the Cp-plane (Figure 1). For smaller metals, substituents bend away from the metal and each other, defined in here with a positive bending angle. For larger metals, bending towards each other is observed, i.e. negative bending angles. In fact there is a linear correlation between the Cp-metal distance and the out-ofplane bending angle (vide infra). The aryl substituents in (Cp BIG ) 2 Ba bend towards each other with an average angle of -5.3(2) °. This contrasts sharply with generally observed repulsive interactions: e.g. the iPr groups in (iPr 5 Cp) 2 Ba bend away from each other with an average bending angle of +5.1(2)°. [8] Please insert Figure 1 Figure 1. Out-of-plane bending of the aryl groups in (Cp BIG ) 2 Ba; only the C ipso atoms of the substituents are shown. (iii) Without exception, all deca-arylmetallocene complexes crystallize with approximate S 10 -symmetry. [6] The penta-aryl Cp ligand can be regarded as a five-blade chiral propeller. Combination of propellers of equal chirality gives a D 5 -symmetric metallocene whereas opposite chiralities result in a S 10 -symmetric structure (Figure 2a). Both isomers differ by the mutual orientation of the phenyl substituents on different ligands: the S 10 -symmetric metallocene features perpendicularly interacting phenyl rings whereas the D 5 -isomer shows parallel interacting rings.

Please insert

We explained the high stability of the S 10 -symmetric metallocenes with an extended network of interligand C-H•••C(π) interactions (Figure 2b). [3] Especially for small metals, these interactions can be quite short: in (Ph 5 Cp) 2 Fe [10] an average H•••C distance of 2.41 Å has been derived. [START_REF]In crystal structures determined with X-ray diffraction, observed and refined hydrogen positions always show relatively large errors and are systematically too short. For comparison, hydrogen atoms have been placed at 1.08 Å from the C nucleus (the average C-H bond length) at idealized angles. A similar strategy has been found very useful in comparison of non-classical hydrogen bonds: S. Harder[END_REF] i.e. a H•••C contact much shorter than the sum of the van der waals radii for C and H (2.90 Å). Also for metallocenes with larger metals short C-H•••C(π) interactions have been detected. [3,6] These explain the unusually negative out-of-plane bending angles discussed in (ii).

In order to understand and quantify the unusual stability of deca-aryl metallocenes we here describe the results of a systematic theoretical investigation.

The objectives of this calculational study were the following: (i) Is it possible to reproduce the solid state structure of deca-aryl metallocenes by DFT-methods? (ii) What is the effect of the aryl substituents on structure and the overall energy of formation? (iii) What is the origin of Ar 5 Cp•••CpAr 5 attraction? (iv) Can we reproduce the linear relationship between out-of-plane bending of the aryl substituents and the Cp-metal distance, i.e. metal size?

Calculation methods

All calculations have been performed with density functional theory (DFT) methods. The PBE model [12] has been employed for the exchange-correlation (xc) functional. Since long-range dispersion interactions cannot be accounted for by a purely gradient-corrected functional such as PBE, the level of calculations has been raised to DFT+D through the semi-empirical dispersion correction proposed by Grimme. [13] Dispersion interactions between the phenyl substituents of the upper and lower Cp BIG ligands were expected to play a crucial role for association energy and molecular structure. On the other hand, the butyl substituents of the benzene rings are not expected to be of importance, they were replaced by hydrogen atoms. All calculations of the resulting (Ph 5 Cp) 2 M systems with M = Ba, Ca, Cr, Fe, Ni, Sm, Sn, Sr, W, and Yb have been carried out with the Turbomole [START_REF]a development of University of Karlsruhe and Forschungszentrum Karlsruhe GmbH[END_REF]15] quantum chemistry program package, using an orbital basis set of triple-zeta valence quality denoted as def-TZVP, an appropriate auxiliary basis set to represent Coulomb integrals in the resolution-of-the-identity (RI) approximation and effective core potentials which account for scalar relativistic effects of the heavier metal atoms (Ba, Sm, Sn, Sr, W, Yb). [16] If not mentioned otherwise, default values were used for energy and gradient convergence thresholds and the size of numerical integration grids and. Geometry optimizations of closed-shell (Ph 5 Cp) 2 M species have been carried out within the symmetry restrictions of the S 10 point group using restricted Kohn-Sham orbitals, that of open-shell cases [START_REF] Elschenbroich | Organometallchemie[END_REF] within its Abelian subgroup C i using unrestricted orbitals. Partial charges have been taken from natural population analysis (NPA). [START_REF] Reed | [END_REF]

Results and Discussion

The calcocene (Ph 5 Cp) 2 Ca has been taken as model system for closer investigation. In order to evaluate the influence of Ph susbstituents on the structure, first the simple calcocene Cp 2 Ca has been optimized. This compound is a coordination polymer with a bent structure in the solid state. [19] In agreement with previous studies we find that its calculated gas phase minimum shows a linear arrangement of Ca and the centers of the two Cp rings. [20] Its staggered (D 5h ) and the eclipsed (D 5d ) form are practically isoenergetic: using tight convergence thresholds and a refined integration their energy difference is smaller than 0.01 kJ/mol with both approaches, DFT and DFT+D. Furthermore, the Ca-C bond distances in the staggered and eclipsed forms agree within 10 -4 Å. According to calculations of the vibrational frequencies with analytical second energy derivatives both structures are minima, with lowest vibration frequencies of 21 (D 5h ) and 32 (D 5d ) wavenumbers, respectively, at the PBE+D level. These findings agree with corresponding observations for Cp 2 Mg. [20b] Table 1 shows selected geometric parameters and energies of calcocene formation, ∆E f , from the free ions Ca 2+ and Cp -, with optimized structures for the latter. Note that the dissociation energies of Ref.

[20b] refer to dissociation into neutral compounds. Surprisingly, inclusion of the dispersion correction (DFT+D) results in slight lengthening of the Ca-Cp c distance, i.e.,the distance between Ca and the center of the Cp ring, by 0.013Å. Despite this elongation, the magnitude of ∆E f increases by 22.2 kJ/mol (1 %). This apparent contradiction is likely to be a minor artefact of the damping scheme introduced by Grimme to avoid double counting of electron correlation effects: the additive dispersion correction including the damping function for a Ca-C pair of atoms starts to become smaller for distances below 3 Å, thus creating a small repulsive force. Obviously, this effect is much smaller for relatively short bond distances such as the C-C distance, where an elongation of only 0.001Å is observed (cf. Table 1). Note also that in both forms (D 5h and D 5d ) of the complex the H atoms bend away from Ca by 2.1° with DFT and by 1.9° with DFT+D, respectively, probably for the same Coulombic reasons as in CpLi. . [21] Table 1. Energies of formation from the ions and selected geometric parameters for CaCp 2 from calculations with tight convergence thresholds and refined integration grid. Energies in kJ/mol, distances in Å. Data for eclipsed and staggered structures agree within all digits shown.

The model system (Ph 5 Cp) 2 Ca was optimized within the symmetry restraints S 10 or D 5 . These correspond to the isomers shown in Figure 2a. Table 2 shows formation energies and selected geometric parameters obtained with DFT and DFT+D and, for comparison, selected geometric parameters for the crystal structure of (Cp BIG ) 2 Ca. The DFToptimized S 10 calcocene shows somewhat longer Cp-Ca bonds than the crystal structure. Whereas in Cp 2 Ca inclusion of dispersion correction led to elongation of Cp-Ca bonds, for (Ph 5 Cp) 2 Ca a contraction by 0.015 Å is observed. The DFT+D-optimized structure is in close agreement with the crystal structure. The D 5 calcocene shows somewhat longer Cp-Ca distances but also this complex is contracted when the dispersion correction is included. As both calcocenes (S 10 and D 5 ) show shortening of Cp-Ca distances upon inclusion of dispersion correction, their structures must be influenced by attractive Ph•••Ph interactions.

The S 10 -metallocene shows the typical perpendicular edge-to-face stacking, as found in the fish-bone structure of solid benzene. [22] The merry-go-round network, consisting of ten non-classical C-H•••C hydrogen bonds, can be considered as a circular form of this fish-bone structure (Figure 2b). It should be noticed that the C-H•••C bond distances in the crystal structure (average value: 2.58Å ) are reproduced well by the DFT+D model (2.53 Å). Calculations without dispersion correction gave much longer contacts (2.82 Å). On the other hand, the D 5metallocene displays face-to-face stacking of phenyl substituents, a type of interaction that plays an important role in molecular recognition. [23] Apart from the face-to-face stacking interactions within the propeller-like Ph 5 Cp ligand, there are five such interactions between the two ligands. The energies of formation are clearly in favour of the S 10metallocene (∆E = 41.1 kJ/mol with DFT+D) and explain why deca-aryl metallocenes preferably crystallize as centrosymmetric complexes with approximate S 10symmetry.

The preference for the S 10 -geometry must be related to the difference and number of Ph•••Ph interactions . According to very high level ab initio calulations (displaced) face-to-face and edge-to-face structures of the fully relaxed benzene dimer are very nearly isoenergetic (interaction energies of -11.2 and -11.1 kJ/mol for the edge-to-face and face-to-face structures, respectively). [24] In order to quantify the two different forms of stacking within the metallocenes, we calculated the interaction energies of two benzene molecules with the exact mutual orientations as found in the S 10 and D 5 structures optimized at the DFT+D level. Without inclusion of the dispersion correction all Ph•••Ph interactions were found to be endothermic. With DFT+D the strongly distorted face-to-face interactions within a single Ph 5 Cp ligand were found to be slightly exothermic (-0.67 kJ/mol for a pair of Ph substituents in the S 10 -structure and -0.16 kJ/mol in the D 5 -structure). The edge-to-face interactions between two Ph groups of the upper and lower Ph 5 Cp ligands of the S 10 -structure were found to be -8.72 kJ/mol, the corresponding face-to-face interactions in the D 5structure -8.70 kJ/mol. The sum of the ten inter-ligand and ten intra-ligand Ph•••Ph interactions gives a total interaction energy of -93.9 kJ/mol for the S 10 -structure. In the D 5structure the number of inter-ligand Ph•••Ph interactions is reduced to five. The total interaction energy for all inter-and intra-ligand Ph•••Ph interactions amounts to -45.1 kJ/mol. The difference of 48.8 kJ/mol between these numbers is in reasonable agreement with the difference of 41.1 kJ/mol in the formation energies of both structures (cf. Table 2). Since the benzene dimer is a relatively small model system we were able to check this explanation for the preference of the S 10 -structure by increasing the theoretical level considerably to coupled cluster theory at the CCSD(T) level, with an augmented correlation-consistent double-zeta valence basis set (aug-cc-pVDZ). [25] These calculations, in which the valence electrons were correlated, were made with the Molpro program package. [START_REF] Molpro | package of ab initio programs[END_REF] Employing exactly the same benzene dimer geometries as above, the counterpoisecorrected interaction energies for the strongly distorted intra-ligand face-to-face orientations were now found to be endothermic (+6.50 kJ/mol for a pair of Ph substituents in the S 10 -structure and +6.98 kJ/mol in the D 5 -structure). The inter-ligand Ph•••Ph interactions remain exothermic: we find -5.25 kJ/mol for the edge-to-face orientation in the S 10structure and -6.86 kJ/mol for the face-to-face orientation in the D 5 -structure. For the total interaction energy between all phenyl substituents one thus gets +12.5 kJ/mol in the former and +35.5 kJ/mol in the latter case, i.e. a preference of the S 10 -structure by 23 kJ/mol due to Ph•••Ph interactions at this level of theory. Note that in the limit of complete basis sets the interaction energies of both, edge-to-face and displaced face-to-face structures become more exothermic by about 1.5 kJ/mol as compared to the basis set used here, [24] suggesting the total Ph•••Ph interaction energy in the S 10structure becomes exothermic in the complete basis set limit while that in the D 5 -structure remains endothermic.

It should be noted that for the S 10 -structure of (Ph 5 Cp) 2 Ca the attractive edge-to-face interactions between the phenyl substituents of both ligands lead to an unusual negative outof-plane bending angle (cf. Table 2) of the aryl substituents, i.e. bending towards each other (Figure 1). Without inclusion of the dispersion correction out-of-plane bending is strongly positive. The origin of this bending is therefore related to mutual Ph•••Ph interaction. A corresponding reduction of the positive bending angle can also be observed for the D 5 -structure.

Although the data above provide enough evidence for attractive Ph 5 Cp•••CpPh 5 interactions, the energy of formation for S 10 -symmetric deca-phenyl calcocene (-1954 kJ/mol) is considerably smaller than that for Cp 2 Ca (-2121 kJ/mol). It is likely that formation of (Ph 5 Cp) 2 Ca from its ions (Ca 2+ and Ph 5 Cp) is less exothermic on account of delocalization of negative charge in the Ph 5 Cp ion. Although the Ph substituents are for steric reasons not completely coplanar with the Cp ring, the average dihedral angle of about 45° allows for partial delocalization of negative charge over the Ph substituents. Indeed, NPAanalysis of the Ph 5 Cp ion shows charges of -0.11 e on each Ph-substituent. This leaves a charge of -0.45 e on the C 5 ring. In contrast, the calculated NPA-charge on each of the H atoms of the Cp ion is +0.17 e and the total charge on the C 5 ring -1.85 e. Therefore, the electrostatic Cp-Ca 2+ interaction is preferred. It should be mentioned that combining the Ph 5 Cp ion with Ca 2+ leads to polarization of negative charge into the C 5 ring, which now displays an NPA-charge of -0.79 e while the Ph-substituents become nearly neutral (-0.01 e). A similar, yet somewhat weaker effect is observed for Cp in Cp 2 Ca : in the complex the charge on the C 5 ring is -2.03 e and that on each of the H atoms +0.23 e. The NPA charge on the Ca 2+ ion is very similar in both calcocenes: in Cp 2 Ca it is +1.76 e and in (Ph 5 Cp) 2 Ca +1.72 e.

Experimentally, we found a linear correlation between bending angle and Cp-M distance for a series of deca-phenyl metallocenes (vide supra). [6] In order to confirm the observed dependence between bending angle and metal size, a set of geometry optimizations was carried out for the experimentally investigated species. Results are collected in Table 3. Clearly, there is the expected strong correlation between energy of formation and charge of the metal cation. For species of the same charge, there is roughly an inverse relation between the energy of formation and the M-Cp c distance, i.e. metal size. As demonstrated by deca-phenyl stannocene and ytterbocene, however, electronic factors modify this grossly simplifying picture. Nevertheless, Figure 3 shows that there is an approximately linear relationship between the out-of-plane bending angle and the Cp-M distance. It can also bee seen that the theoretical calculations are in close agreement with the experimentally found dependence.

Please insert

Conclusions

Our detailed investigation of (Ph 5 Cp) 2 Ca via DFT calculations, including and excluding a semi-empirical correction for dispersion interactions, shows that the preference of S 10 -symmetrical structures is mainly due to inter-ligand Ph•••Ph interactions. Dispersion interactions play an important role for the relative and the overall stability of superbulky metallocenes While the phenyl substituents of the two Ph 5 Cp ligands in (Ph 5 Cp) 2 Ca bend away from each other with standard DFT, inclusion of the dispersion correction in DFT+D reproduces the experimentally observed slight inclination towards each other.

In the crystal structures of (Ph 5 Cp) 2 M one observes a linear correlation between the out-of-plane bending angle of the phenyl substituents and the size of the metal atom M along the series M = Fe, Ni, Cr, W, Ca, Yb, Sn, Sm, Sr, and Ba. This trend was confirmed at the DFT+D level. Thus dispersion interactions are the key to their quantitative and qualitative understanding.

Figure 2 .

 2 Figure 2. a) The two possible isomers for a deca-aryl metallocene complex. b) The merry-go-round C-H•••C(π) hydrogen bond network exemplary shown for (Cp BIG ) 2 Ca (partial structure).

Figure 3 .

 3 Figure 3. Correlation between the out-of-plane bending angle C ipso -C Cp ﬩Cp of the substituents and the M-Cp c distance. Filled squares denote experimental data, open squares calculated data.

Table 2 .

 2 Calculated energies of formation and selected geometrical parameters for (Ph 5 Cp) 2 Ca. Experimental data were averaged. Energies in kJ/mol, distances in Å, angles in degrees.

	Confomer Method ∆E f	Ca-Cp c Ca-C C ipso -	H•••C C-H•••C
					C Cp ﬩Cp
	S 10	Exp.		2.356	2.651 -1.21	2.58	155
		DFT	-1822.8 2.368	2.665 +3.0	2.82	162
		DFT+D -1954.1 2.352	2.650 -2.2	2.53	154
	D 5	DFT	-1803.1 2.388	2.683 +4.7
		DFT+D -1913.0 2.365	2.661 +1.1

Table 3 .

 3 Calculated (DFT+D) energies of formation and selected geometrical parameters for (Ph 5 Cp) 2 M. Experimental data (in parentheses) were averaged. Energies in kJ/mol, distances in Å , angles in degrees.

	Complex	∆E f	M-Cp c M-C	C ipso -	H•••C C-H•••C
					C Cp ﬩Cp
	[(Ph 5 C 5 ) 2 Fe]	-2652.5 1.710	2.106	+9.2	2.32	174
			(1.724) (2.12)	(+11.4)	(2.41) (173)
	[(Ph 5 C 5 ) 2 Ni] + -5741.5 1.816	2.194	+7.2	2.35	170

Wiley-VCH ZAAC

Acknowledgement

S. Harder gratefully acknowledges financial support from the DFG within the framework of SPP 1166. ____________

Supporting Information (see footnote on the first page of this article): Coordinates and energies of the optimized structures. Vibration frequencies for Cp 2 Ca.


Michael ; Veith
email: michael.veith@inm-gmbh.de

Céline Belot

Volker Huch

Laurent Guyard

Michael Knorr

Abderrahim Khatyr

Claudia Wickleder

Dr H C M Veith

Syntheses, Crystal Structure and Physico-Chemical Studies of Sodium and Potassium Alcoholates Bearing Thienyl Substituents and their Derived Luminescent Sm(III) Alkoxides

Keywords: Thienylmethoxido ligands, Hetero-cubanes with alkali metals, Samarium, Electrochemistry, Luminescence Thienylmethoxido ligands, Hetero-cubanes with alkali metals, Samarium, Electrochemistry, Luminescence

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Syntheses, Crystal Structure and Physico-Chemical Studies of Sodium and Potassium Alcoholates Bearing Thienyl Substituents and their Derived

Luminescent Sm(III) Alkoxides Michael Veith, * [a,b] Céline Belot, [a,c] Volker Huch, [a] Laurent Guyard, [c] Michael Knorr, [c] Abderrahim Khatyr [c] and Claudia Wickleder [d] Abstract. The synthesis, structural characterization, electrochemistry and luminescence properties of a series of alkali metal alcoholates and Sm(III) alkoxides with thiophene-based-OR substituents are presented. The alkali metal alcoholates 7-15 have been obtained by deprotonation of the carbinol with NaH or KH. Their molecular structures consist of tetranuclear alkali metal alcoholates with a distorted cubane-like M 4 O 4 core (X-ray structure analyses). Each alkali metal is surrounded by three carbinolate ligands and (depending on the derivative) by additional tetrahydrofuran molecules. The mononuclear samarium alkoxides {Sm[OC(C 4 H 3 S) 3 ] 3 (thf) 3 } • thf (16) and {Sm[OC(C 16 H 13 S)] 3 (thf) 3 } • thf [START_REF] Diamond | Crystal and Molecular Structure Visualization[END_REF] were synthesized by the salt metathesis reactions between {[KOC(C 4 H 3 S) 3 ] 4 (thf) 2 } • thf (7), [NaOC(C 4 H 3 S) 3 ] 4 (thf) 2 (8) or {[KOC(C 16 H 13 S)] 4 (thf) 3 } • ½ thf (11), respectively, and SmCl 3 in thf solution. The molecular structures of these air-sensitive base adducts have been determined by single-crystal X-ray crystallography and reveal an approximately octahedral coordination sphere around the samarium metal centres with three methoxido ligands and three facially arranged thf molecules. The electrochemical properties are essentially dominated by the oxidation of the thienyl units. The emission spectra of the carbinols and their derived potassium and sodium compounds display broad bands attributed to the π*→π transitions of the aromatic ligands. Luminescence studies performed on complexes 16 and 17

Introduction

Trivalent lanthanide compounds have received much attention within the last decade because of their luminescence properties and their applications in electronic materials and in biological systems [1]. The intraconfigurational 4f-4f transitions are parity forbidden and their emission and absorption spectra exhibit weak intensity upon an excitation on the lanthanide ion. However, some organic ligands can act as an "antenna", absorbing and transferring energy efficiently to the metal ion and consequently increasing their luminescence yield [2]. The choice of the ligand for complexation plays a key role in constructing efficient luminescence lanthanides complexes. Two common requirements for selecting a ligand for the coordination with lanthanide ions are the metal binding strength and ultraviolet (UV) absorption properties of ligands. Among several categories of ligands, nitrogen-and oxygen-donor groups have been used in the sensitization of lanthanide luminescence. In particular, bidendate aromatic amines, carboxylic acids and β-diketonates are known to provide energy transfer to lanthanides ions [3]. However, to date only a few examples of lanthanide complexes bearing sulphur moieties has been reported [4][5][6] probably due to the generally lower stability and the mismatch between a soft sulfur-donor ligand and a hard lanthanide metal ion. In particular, those containing thienyl rings have been barely explored, although their transition metal counterparts have been investigated in detail [7]. This interest stems from the fact that thiophene derivatives are quite attractive as organic ligands because of their electron-rich system and their electroactive character.

Complexes containing Sm(III) have been less studied than those with Eu(III) and Tb(III), since they generally exhibit lower intensity for the luminescence. But, trivalent samarium ions present an orange-red emission in the spectral region [8,9], and have been investigated in light-converting devices together with Eu(III) and Tb(III) analogues [9b, 9h]. Moreover, trivalent samarium(III) derivatives may have attractive catalytic activity: they can act as Lewis acid to activate Michael-aldol reaction [10], epoxidation of alcohols [11], Meerwein-Ponndorf-Verley-Oppenauer reaction, aldol reaction [11], Diels-Alder reaction [12] and Tischenko reaction [13]. For example, Imamoto et al. [14] have recently used the trivalent alkoxide complex Sm(III)tris (2,6-di-tert-butyl-4-methylphenoxides) to catalyze Michael-Michael-aldol-reaction of 3,3-dimethyl-2-butanone with benzalacetophenone.

In two previous papers, we have studied the synthesis and physico-chemical properties of a series of rare earth alkoxides of Y and Nd bearing thiophene moieties [5,6]. We present herein the syntheses of two novel samarium(III) alkoxides, their structural characterisation as well as electrochemical and photoluminescence properties. A strategy that we have developed recently consists of the preparation of suitable tertiary alcohols with thienyl and phenyl substituents capable of being attached on rare earth metal centres through a covalent M-O-R bond, leading to coordination compounds with singular redox and luminescence properties. Furthermore, we have investigated the deprotonation of the bulky and slightly acidic tertiary alcohol shown in Figure 1 using potassium and sodium hydride as bases. The resulting salts have been characterized crystallographically. Furthermore, they have been used for the synthesis of derivatives of samarium (III). In addition, the electrochemical and luminescence properties of all these new compounds have been explored.

Experimental Section

Materials. All reactions were performed under nitrogen atmosphere in a Schlenk apparatus.

Tetrahydrofuran and diethyl ether were distilled from sodium and kept under nitrogen.

Dichloromethane and acetonitrile were distilled from CaCl 2 and kept under nitrogen. Tris(2thienyl)methanol (1), phenylbis(2-thienyl)methanol (2), diphenyl(2-thienyl)methanol (3), phenylbis(3-thienyl)methanol (5) and diphenyl(3-thienyl)methanol (6) were prepared according to the literature [15].

HO-C(C 17 H 15 S) (4):

To a solution of 2-methylthiophene (1.57 g, 16 mmol, 1.53 mL) in diethyl ether (20 mL) was added n-butyl lithium (16 mmol, 10 mL, 1.6 M solution in hexane) at -15°C. The solution was stirred for 1 h, and then benzophenone (2.91 g, 16 mmol) in diethyl ether was added, and the mixture was allowed to reach room temperature and was stirred overnight. It was hydrolysed with an aqueous saturated sodium hydrogenocarbonate solution. The mixture was extracted with diethyl ether, and the organic layer was dried over Na 2 SO 4 and evaporated. The solid was washed in hexane. A white solid was obtained (yield 67 %, 3 g). 1 H-NMR (CDCl 3 ): δ 7.3 (m, 10H, Ph), 6.5 (m, 3 J H4-H3 = 3.4 Hz and 4 J H4-HMe = 1.03 Hz, 1H, 4-H Th), 6.4 (d, 3 J H3-H4 = 3.4 Hz, 1H, 3-H Th), 2.9 (br s, 1H, -OH), 2.4 (d, 4 J HMe-H4 = 0.7 Hz, 3H, -CH 3 ). ATR-IR: ν (OH) = 3448 cm -1 . Anal. Calcd for C 18 H 16 OS C,77.14;H 5.71;Found C,77.10;H,4.46.

General Procedure for Preparation of Potassium Alcoholates 7, 9, 11 and 12

The carbinols (1.39 g of 1; 1.37 g of 2, 1.471 g of 3; 1.431 g of 4 (5.0 mmol)) were dissolved in thf (20 mL) and slowly added to a suspension of KH (0.202 g, 5.0 mmol) in thf (5 mL). The mixture was stirred at room temperature overnight. All the KH had reacted. The solvents were evaporated, and solids were obtained from which colourless crystals can be formed in thf at 5°C. The carbinols (1.40 g of 1; 1.37 of 2; 1.42 g of 4; 1.367 g of 5; 1.338 g of 6 (5.0 mmol)) were dissolved in thf (20 mL) and slowly added to a suspension of NaH (0.121g, 5 mmol) in thf ( 5mL). The mixture was stirred at room temperature overnight.

{[KOC(C

[NaOC(C 4 H 3 S) 3 ] 4 (thf) 2 (8): All NaH had reacted. The solvent was evaporated; a solid was obtained from which colourless crystals could be obtained in thf at 5°C (yield: 15 %, 243 mg). 1 H-NMR (thf/C 6 D 6 ): δ 6.9 (dd, 3 J H5-H4 = 4.9 Hz and 4 J H5-H3 = 1.2 Hz, 12H, 5-H), 6.8

(dd, 3 J H3-H4 = 3.4 Hz and 4 J H3-H5 = 1.2 Hz, 12H, 3-H), 6.7 (dd, 3 J H4-H3 = 3.7 Hz and with polishing alumina and diamond suspension between the runs. The reference electrode was Ag/AgClO 4 (0.1 M in CH 3 CN). A platinum disk was used as an auxiliary electrode. The solvent was freshly distilled, and the solutions were prepared under nitrogen atmosphere and blanketed with N 2 before the first scan. Measurements were made at room temperature. The scan rates employed were 100 mV.s -1 . The concentration of the monomeric substrates was 10 -3 M for the carbinol and alkali metal alcoholates and approximately 3.15 ×10 -3 M for 16 and 3.32 ×10 -3 M for 17. Under these conditions, the E 1/2 of Cp 2 Fe +/0 was found to be 0.16 V (CH 2 Cl 2 ) and 0.025 V (CH 3 CN) vs. an Ag/AgClO 4 reference.

Luminescence studies. Solid-state emission and excitation spectra were recorded at room temperature on a Jobin-Yvon Fluorolog-3 spectrometer equipped with a 1000 W Xenon lamp, two double grated monochromators for emission and excitation, respectively, and a photomultiplier with a photon counting system. The emission spectra were corrected for photomultiplier sensitivity, the excitation spectra for lamp intensity and both for the transmission of the monochromators.

Crystallography. The data collection was performed on a X8 ApexII CCD diffractometer with MoKα radiation (λ = 0.71073 Å). Structures were solved by direct methods and refined by full-matrix least square methods on F 2 with SHELX-97 [16]. Drawings were made with Diamond [START_REF] Diamond | Crystal and Molecular Structure Visualization[END_REF]. All crystals of the compounds started growing up at 5°C during a period of one week. No sign of deterioration during storage under nitrogen was observed. Crystallographic data for the structure determinations are listed in Table 1, and relevant bond distances and angles are given in Tables 3456

Results and Discussion

Samarium(III) alkoxides have been prepared in the past by transesterification reactions of Sm-OiPr in the presence of an excess of other alcohols R'OH to provide Sm-OR' species [START_REF] Sankhla | [END_REF]. Mononuclear phenoxide and siloxides of type Sm(OAr) 3 (thf) 3 and Sm(OSiPh)

Synthesis of the carbinol 4

The hitherto unknown compound diphenyl(5-methyl-2-thienyl)methanol (4) was prepared by a similar method as employed for the synthesis of other carbinols [15]. This colourless solid was obtained by a classical nucleophilic addition of lithiated 2-methylthiophene on benzophenone according Scheme 1 and isolated in 67 % yield after subsequent hydrolysis and workup. The 1 H-NMR spectrum of 4, recorded in chloroform, displays three aromatic signals:

a multiplet at 7.3 ppm attributed to the protons of the phenyl groups, a multiplet at δ 6.5 and a doublet at 6.4 ppm of the 4-H and the 3-H of the thienyl unit, respectively. A broad signal at 2.9 ppm due to the alcohol function is also obtained. The latter signal, a doublet at δ 2.4, is assigned to the protons of the methyl group.

Synthesis and Characterisation of the Potassium and Sodium Thienyl-Substituted Alcoholates

We have recently prepared a series of mononuclear lanthanide carbinol complexes bearing thienyl substituents of type Ln(OR) 3 (thf) n (Ln = Nd, Er) by the above mentioned aminolysis reaction of silylamides Ln[N(SiMe 3 ) 2 ] 3 in the presence of thienyl-functionalized carbinols [5,6]. Unfortunately, we failed to isolate any Sm(III) complexes in crystalline form using this route. For this reason we have chosen the salt-elimination route to prepare the targeted samarium complexes.

The targeted potassium or sodium alcoholates 7- 13), [NaOC(C 14 H 11 S 2 )] 4 (thf) 2 ( 14) and [NaOC(C 16 H 13 S)] 4 (thf) 2 (15).

The number of thf molecules coordinated to the clusters follows from chemical analysis (see exp. section).

Table 2. 1 H-NMR chemical shifts for the alkali metal alcoholates 7-15 obtained in thf/C 6 D 6 .

Compounds Chemical Shifts 7 6.9 (dd, 3 J H5-H4 = 4.7 Hz and 4 J H5-H3 = 1.3 Hz, 12H, 5-H), 6.8 (dd, 3 J H3-H4 = 3.3 Hz and 4 J H3-H5 = 1.3 Hz, 12H, 3-H), 6.7 (dd, 3 J H4-H3 = 3.3 Hz and 3 J H4-H5 = 4.7 Hz, 12H, 4-H) 8 6.9 (dd, 3 J H5-H4 = 4.9 Hz and 4 J H5-H3 = 1.2 Hz, 12H, 5-H), 6.8 (dd, 3 J H3-H4 = 3.4 Hz and 4 J H3-H5 = 1.2 Hz, 12H, 3-H), 6.7 (dd, 3 J H4-H3 = 3.7 Hz and 3 J H4-H5 = 4.9 Hz, 12H, 4-H) 8) The molecular structures of 7, 9, 11 and 12 exhibit tetrameric units: each potassium atom is surrounded by three carbinolato ligands. In addition, two or three alkali metals are also coordinated to a tetrahydrofuran molecule (Figure 2a), 3a) and 4). Apparently, not all the potassium atoms are ligated to a solvent molecule: two atoms for 7 and 12 and one atom for 9 and 11 have no base coordination. A closer view to the surrounding of these atoms shows that the thienyl or phenyl rings are shielding the metal in a π-ligand manner preventing the possible addition of a third (7 and 12) or a fourth (9 and 11)

K(2)••••K(2) 3.754(2) K(4)••••K(4) 3.734(2) K (
tetrahydrofuran molecule (Figure 2b) and 3b) and 4). Note that the K-S distances are between 3.251(9) and 5.518( 6) Å and therefore a coordination of sulphur to potassium is very weak, if any.

We also elucidated the crystal structure of the sodium salt [NaOC(C 4 H 3 S) 3 ] 4 (thf) 2 (8). Like in the case of the potassium analogue (see above), the molecular structure of [NaOC(C 4 H 3 S) 3 ] 4 (thf) 2 ( 8) consists of a tetrameric motif with a distorted cubane-like arrangement (Figure 5). This molecular cluster is situated on a C 2 axis in the crystal. In 5). The overall molecular structure of 8 is quite comparable with those reported for [Na(µ 3 -Ombp)(DME)] 4 [23] and [Na(OC 6 H 4 Me-4)(dme)] 4 [24]. In contrast to cage compound 8, in these latter compounds each metal centre is ligated to a solvent molecule. In our case (see above), only two sodium atoms are surrounded by tetrahydrofuran. Additional intramolecular bonding as in 8 is also observed in the structures of [Na 4 (salphen) 2 (dme) 2 ] and [Na 4 (salen) 2 (dme) 2 ] [26],

where only two of the alkali metals are bonded to the Schiff base, whereas the other two complete their coordination sphere with the oxygen atom of a dme donor. The (8).

8

of the thienyl groups. The two others aromatic signals, doublet of doublets at 6.9 and 6.7 ppm (each integrating for 3H), correspond to the 4-H and 3-H of the thienyl groups, respectively.

The hydrogen atoms of tetrahydrofuran are present at 3.7 and 1.8 ppm.

Crystal Structures of the Samarium(III) Thienyl-Substituted Methoxides

Single crystal X-ray structure determinations for compounds 16 and 17, which crystallize at 5°C from tetrahydrofuran as brown-light or colourless crystals, were performed. Selected bond lengths and angles are gathered in Table 6. Unfortunately, for 17 the differentiation between the thienyl and phenyl groups is difficult due to disorder of the ligands. the crystal lattice with no interaction with the molecules (Figure 6). The overall structures of 16 and 17 is similar to that in {Nd[OC(C 4 H 3 S) 3 ] 3 (thf) 3 } • thf [5], Sm(O-2,4,6-Me 3 C 6 H 2 )(thf) 3 [20] or Sm(O-2,6-i-Pr 2 C 6 H 3 ) 3 (thf) 3 [19]. The geometry about the samarium centres is distorted octahedrally, as evidence the (C 4 H 3 S) 3) Å ( 16) and 2.552( 5) Å [START_REF] Diamond | Crystal and Molecular Structure Visualization[END_REF] and are in the range of those observed for Sm(O-2,6-i-Pr 2 C 6 H 3 ) 3 (thf) 3 [2.542(2) Å] [19].

These distances are also in accordance with those found for the compound {Nd[OC(C 4 H 3 S) 3 ] 3 (thf) 3 } • thf [5].

Electrochemical Studies

The electrochemical investigations of thiophenes and its derivatives is a classical technique to study the physico-chemical properties of thienyl compounds [28]. Since the last decade, the incorporation of transition metals or rare earths metal centres into the thiophene derivatives has emerged as interesting extensions, thus combining the intrinsic properties of metal ions with those of thienyl-based heterocycles [29][30][31]. It is well known that the most stable oxidation state of the lanthanide elements is +3 [START_REF] Cotton | Advanced Inorganic Chemistry[END_REF], but the oxidation state +2 is also wellestablished, in particular for the samarium ion [START_REF] Johnson | [END_REF]. Nevertheless the value of the Sm 3+ /Sm 2+ potential depends to the environment around the metal [34]. In this context, we investigated the electrochemical properties of the carbinols 1-6, those of their derived alkali metal alcoholates 7-15 and of the samarium alkoxides 16-17.

Carbinols and Alkali Metal Alcoholates

The values of peak potentials of carbinols 1-6 and the samarium alkoxides 16 and 17 obtained in acetonitrile are listed in Table 7.

Table 7. Values peak potentials [V, vs. Ag/AgClO 4 ] of the carbinols and their alkali metal derivatives, in acetonitrile (10 -3 M or 2 × 10 -3 for 5, 14, 6 and 15) deduced from cyclic voltammetric measurements on a platinum electrode (diameter 1 mm), scan rate 100 mV.s -1 .

E pa [V] E pc [V]

HO-C(C 4 H 3 S) 3 ( 1 (15) 1.76 -0.17

The voltammograms of 1-3 between -0.50 and +2.00 V vs. Ag/AgClO 4 on a platinum electrode at 100 mV.s -1 lead to two irreversible signals (for example see Figure 7). The first wave is assigned to the oxidation of the thienyl units [35]. The second waves correspond to the reduction of the carbocation. Indeed, during the oxidation of the thienyl units, some H + are formed and can deprotonate the carbinols leading to a stable carbocation [6,36]. The voltammograms of 5 and 6 depict only the irreversible wave due to the oxidation of the thienyl groups, at 1.62 V and 1.77 V, respectively. Note that, in comparison with 3, the oxidation peak potential of 4 is shifted towards lower values (1.55 V for 3, 1.39 V for 4): the introduction of an electron donating methyl group facilitates the oxidation process manifested by a decrease of the potential [37]. The values of the oxidation peak potentials of 5 and 6 are higher than those obtained for 2 and 3. This is probably due to the fact that, contrarily to 2 and 3, the two alpha positions of the thienyl units are unsubstituted [28h]. By repetitive cyclic voltammetry of the carbinols, no formation of polymeric films is evidenced. This failure may be explained by the high reactivity of the cation radicals generated, which can react with a molecule of solvent or undergo nucleophilic attack. These results are in good agreement with observations performed on other molecules with an unsubstituted α-position on pyrroles [38].

The voltammograms of the alkali metal alcoholates 7-15 (for example see Figure 8) show an oxidation irreversible wave due to the oxidation of the thiophene moieties. For 8-9, 11 and 13-15, a second wave is observed on the cyclic voltammogram from -0.13 to -0.27 V and corresponding to the reduction of the carbocation generated during the process (see above).

Nevertheless, for the compounds 7, 10 and 12, the lifetime of the carbocation formed during the oxidation is not long enough to be reduced. No polymeric film is formed during the oxidation process: this result matches with the findings obtained for the respective ligands. In comparison with the corresponding carbinol, the oxidation peak potentials are shifted towards lower values by 0.01-0.10 V, probably due to the inductive effect of the alkali metal which increases the electronic density of the thiophene moieties leading to an easier oxidation of this species or to the change in the interannular conjugation within the structure of the metal alcoholates [39]. Nevertheless, this observation has not been made for the sodium alcoholate 14: in this case the oxidation peak potential is shifted towards an incomprehensible higher value (1.62 V for 5 and 1.67 V for 14).

As can be seen, the number of thienyl units has no significant effect on the electrochemical properties of the compounds whereas the functionalization of these groups ( see 3 compared to 4) or their different attached positions have an influence on the oxidation values (see for example 5/6 compared to 2/3).

Samarium alkoxides

The values of peak potentials of carbinols 1 and 3 and the samarium alkoxides 16 and 17

obtained in dichloromethane are listed in Table 8 (the measurements in acetonitrile are not possible due to the insolubility of the lanthanide alkoxides). The voltammograms exhibit only one irreversible wave at 1.62 V for 16 and at 1.56 V for 17

(Figure 9) attributed to the oxidation of the thienyl moieties [35]. When potentials are cycles, no reduction of samarium(III) to samarium(II) is visible at about -0.8 V [34,40]. To explain this observation several hypotheses are possible: i) the electron-rich organic ligands make a more difficult electron transfer to the lanthanide ion shifting the reduction potential of the samarium towards high negative values [34] which are not detectable in the common electrochemical solvent, ii) the samarium metal centre is wrapped up by the electron-rich organic ligands leading to the inhibition of the reduction process and to the stabilisation of the metal centre.

Luminescence Studies

Recently, several studies have demonstrated that thiophene-derived ligand systems can be promising candidates as sensitizing chromophore in lanthanide compounds [41,42]. In these conjugated coordination compounds, the ligand acts as donor and the lanthanide ion as acceptor. But in our compounds, the conjugation is interrupted by the methoxido group and also no π-interaction between the thienyl and/or phenyl units can be assumed in the solid state (spatial distance from the aromatic groups to the metal: ~ 5 Ǻ). Therefore, it was intriguing to study, if, under these conditions, an antenna effect is still present.

The carbinols and the alkali metal alcoholates were investigated in comparison to the samarium compounds, as well to get some insight in the ligand absorptions and emissions.

Carbinols and Alkali Metal Alcoholates

The solid-state emission maxima of the tertiary alcohols 1-6 and their derived alkali metal alcoholates 7-15 are given in Table 9. All the emission spectra are very similar and consist of broad, nearly Gaussian shaped bands with nearly identical maxima which are attributed to the π*→π transitions of the aromatic units [43]. The carbinol ligands 1, 2 and 3 [6] fluoresce quite strongly in solid-state, with the peak of the emission band shifting toward lower energy with increasing number of thienyl units (Figure 10). Furthermore, it is worth pointing out that grafting a methyl group in position 5 of thienyl unit generates a red shift of ∆λ em ~ 135 nm for ligand 4 compared to ligand 3 (Figure 10), which significantly decreases the energy level of the LUMO orbital [30].

On the other hand, ligands 5 and 6 exhibit emission maxima in similar range comparing with 2 and 3, respectively.

For the alkali metal alcoholates, blue shifts of the emission maxima compared to those of the thiophenic alcohols are observed (excepted for 10). In general, this shift of the transitions compared to those of the thiophenic alcohols is due to some distortions of these units when bonded to potassium or sodium metals [85]. Note that the number of thienyl units, their attached positions or their functionalization have the same effect on the luminescence properties as those observed for their corresponding carbinols.

Samarium Alkoxides

The room temperature emission spectrum of 16 (Figure 11) upon an excitation on the organic ligand (λ ex = 270 nm, see above) displays the typical Sm 3+ bands at around 570, 604, 650 nm.

They are attributed to 4f 5 -4f respectively [9b, 9c, 9i]. Note that another samarium band at 622 nm is observed, probably also due to the 4 G 5/2 → 6 H 7/2 transition: it might be a result of splitting due to ligand field. The intense spectrum is typical for an "antenna effect", resulting in an energy transfer from the ligand to the lanthanide centre [45]. Nevertheless, in addition of the Sm 3+ emission, a broad band is assigned to the fluorescence from the organic ligand in the range from 350 to 520 nm.

The relative intensity between the broad band and the Sm 3+ emission lines suggests that the efficiency of the energy transfer ligand-to-metal process (probably a dipole-dipole energy transfer mechanism) does not seem to be maximal.

The emission spectrum of 17, when the 4 F 7/2 level (410 nm) is excited (Figure 12), is composed of a series of straight lines assigned to the Sm 3+ intra-4f glasses and glass ceramic and those for samarium complexes [8,42].

Conclusion

A series of novel potassium and sodium carbinolates containing thienyl substituents have been obtained and their crystal structures investigated. The molecular structures exhibit only distorted cubane-like M 4 O 4 cores. Each alkali metal is surrounded by three carbinolato ligands and two or three alkali ions are additionally ligated with a tetrahydrofuran molecule.

In addition, two new samarium(III) methoxides containing thienyl substituents have been synthesized and structurally characterized. Their X-ray structures reveal only mononuclear molecules with an octahedral coordination sphere around the metal centre in a facial ligand arrangement. The physico-chemical studies of the series of alkali metal alcoholates or samarium alkoxides containing thienyl substituents have shown that their electrochemical properties are only dominated by organic ligands. The emission spectra of the carbinols and potassium or sodium alcoholates depict broad bands attributed to the aromatic groups.

Nevertheless, the luminescence spectra of the Sm 3+ alkoxides exhibit an energy transfer from the ligand to the lanthanide centre.

To compare the influence of the samarium oxidation state on the crystal structure, electrochemical and luminescence properties of samarium alkoxides bearing thienyl moieties, the study of the reactivity of our alkali metal alcoholates towards SmX 2 (X = Cl, I) is in progress. Furthermore, some experiments with other rare earths such as Eu 3+ , Tb 3+ , Pr 3+ and /or with other thiophenes derivatives are underway.

Figure captions

------------------------------------------------------------------------------------------------- Bildunterschriften leider verloren gegangen.

Vielen (12). The carbon atoms of the aromatic groups are depicted as sticks.

Dank! -------------------------------------------------------------------------------------------------
The hydrogen atoms and the lattice tetrahydrofuran molecule are omitted for more clarity.

  Yield 20 % (362 mg). 1 H-NMR (thf/C 6 D 6 ): δ 6.9 (dd, 3 J H5-H4 = 4.7 Hz and 4 J H5-H3 = 1.3 Hz, 12H, 5-H), 6.8 (dd, 3 J H3-H4 = 3.3 Hz and 4 J H3-H5 = 1.3 Hz, 12H, 3-H), 6.7 (dd, 3 J H4-H3 = 3.3 Hz and

  . Most of the alkali compounds (7, 8, 9, 12) had weak reflections at higher theta values which explains the bad R-values. The structures 9 and 12 are only generally discussed without looking into the details of bonding. Under CCDC 776395 -776401 supplementary crystallographic data for the compounds are deposited. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

  m, 16H, Ph, 5-H Th), 7.0 (m, 12H, Ph),6.8 (m, 8H, 6.2 (m, 8H, 157.3 (m, 12H, Ph, 5-H Th), 7.0 (m, 24H, Ph), 6.9(d, 4H, 6.2 (s, 4H, Crystallographic Characterisation of the Thienyl-Substituted AlcoholatesAn important number of X-ray structure determinations on the alkali metal alcoholates have revealed a rich diversity of solid-state structures for these salts. Known examples show as motif dimers, trimers, cubane-like tetramers, face fused cubic tetramers and hexamers[22- 25].We succeeded in growing colourless single crystals suitable for X-ray structure determinations for compounds 7-9 and 11-12 from thf solution at 5°C. All structure determinations reveal the presence of tetrameric alkali metal alcoholates with a distorted cubane-like M 4 O 4 core (M = K or Na), whose most salient metric parameters are presented below. Some of the structures, besides their bad diffraction behaviour, suffer from disordering of the thienyl ligands.For the potassium alcoholates 7 and 11, selected bond lengths and angles are gathered in Tables3-4. The asymmetric unit of 11 contains two crystallographically independent molecules (A and B) having very close geometries (see Table4). Herein, we will only refer to the molecule A. Unfortunately, for the compounds 9 and 12, no discussion or comparison of the bond lengths and angle values is meaningful due to the poor quality of the crystals (high R-values).

  The molecular units {[KOC(C 4 H 3 S) 3 ] 4 (thf) 2 } (7) and {[KOC(C 16 H 13 S)] 4 (thf) 3 }(11) are situated on a C 2 and C 3 axis in the crystal, respectively. Tetrahydrofuran molecules are present in the crystal lattices without interaction with the central motif. The geometry in 7 and 11 around K(1), in a first approximation, is trigonal pyramidal and these for K(2) tetrahedral.These molecular structures resemble those found for [K(µ 3 -DPE)(thf)] 4 or [K(µ 3 -DPE)(py)] 4• 2 py[25]. The potassium-oxygen mean distances are found to be 2.673(4) Å (7) and 2.703(3) Å(11) and are in the range reported for [K(µ 3 -DPE)(thf)] 4 [2.641(0) and 2.720(2) Å] and [K(µ 3 -DPE)(py)] 4• 2 py [2.653(8) Å][25]. The K-O bond lengths between K(2) and the oxygen atom of the tetrahydrofuran molecule of 2.687(4) Å (7) and 2.765(4) Å (11) are in agreement with those observed for [K(µ 3 -DPE)(thf)] 4[2.720(2) Å][25]. The presence of the solvent molecules coordinated only with two (7) or three(11) potassium atoms leads to a deformation of the heterocubane core, as can be deduced from the O-K-O angles.

  contrast to {[KOC(C 4 H 3 S) 3 ] 4 (thf) 2 } • thf (7), the Na(1) atoms are surrounded by the three tris(2-thienyl)methanolato ligands and additionally ligated by a sulphur atom of the thienyl groups S(3), with a Na(1)-S(3) distance of 2.875(2) Å. The Na(2) atoms are coordinated by the three tris(2-thienyl)methanolato ligands and a tetrahydrofuran molecule. The O-Na-O angles within the Na 4 O 4 cube are in-between 88.79(8) and 95.45(8)° (Table

  Na-OC(C 4 H 5 S) 3 bond distances lie in the range found for [Na(OC 6 H 4 Me-4)(dme)] 4[2.314(0) Å][24] and [Na(µ 3 -Ombp)(DME)] 4[2.33 Å] [23], although the O-Na-O and Na-O-Na angles are different. These variations of the angles can be explained by the steric difference of the ligands and solvents ligated to the sodium atoms.

Figure 1 .

 1 Figure 1. Overview of carbinols 1-6 used as starting materials.

Figure 2 .

 2 Figure 2. a) ORTEP (30 % ellipsoid) representation of {[KOC(C 4 H 3 S) 3 ] 4 (thf) 2 } • thf (7). The carbon atoms of the heterocycles are depicted as sticks. The hydrogen atoms and the lattice thf molecule are omitted for more clarity. Two thienyl groups are found in two split positions [S(1A) and S(1B), S(2A) and S(2B)]. B) View of the distorted heterocubane core.

Figure 3 .

 3 Figure 3. a) ORTEP (30 % ellipsoid) representation of {[KOC(C 16 H 13 S)] 4 (thf) 3 } • ½ thf (11). The carbon atoms of the phenyl and thienyl groups are depicted as sticks. The hydrogen atoms and the lattice tetrahydrofuran molecule are omitted for more clarity. b) View of the distorted heterocubane core.

Figure 4 .

 4 Figure 4. ORTEP (30 % ellipsoid) representation of [KOC(C 14 H 11 S 2 )] 4 (thf) 3 (9) and [KOC(C 17 H 15 S)] 4 (thf) 2(12). The carbon atoms of the aromatic groups are depicted as sticks.

Figure 5 .

 5 Figure 5. a) ORTEP (30 % ellipsoid) representation of [NaOC(C 4 H 3 S) 3 ] 4 (thf) 2 (8). Hydrogen atoms are omitted for more clarity. b) Environment around the sodium atoms.

Figure 6 .

 6 Figure 6. ORTEP (30 % ellipsoid) representation of {Sm[OC(C 4 H 3 S) 3 ] 3 (thf) 3 } • thf (16) and {Sm[OC(C 16 H 13 S)] 3 (thf) 3 } • thf (17). The tetrahydrofuran lattice molecule and hydrogen atoms are omitted for more clarity. For 16, one type of disordered carbon atoms of the heterocycles is depicted as sticks. For 17, the thienyl and phenyl units are found in different positions [S(1) and S(2)].

Figure 7 .

 7 Figure 7. Cyclic voltammogram recorded on a platinum electrode (diameter 1 mm) in an acetonitrile solution containing HO-C(C 4 H 3 S) 3 (1) (10 -3 M) and [NBu 4 ][PF 6 ] (0.1 M), vs. Ag/AgClO 4 , at 100 mV.s -1 .

Figure 8 .

 8 Figure 8. Cyclic voltammograms recorded on a platinum electrode (diameter 1 mm) in an acetonitrile solution [NaOC(C 4 H 3 S) 3 ] 4 (thf) 2 (8) (10 -3 M) and [NBu 4 ][PF 6 ] (0.1 M), vs. Ag/AgClO 4 , scan rate 100 mV.s -1 .

Figure 9 .

 9 Figure 9. Cyclic voltammogramm recorded at a platinum electrode on a dichloromethane solution containing 17 (3.32 × 10 -3 M) and [NBu 4 ][PF 6 ] (0.1 M), vs. Ag/AgClO 4 , scan rate 100 mV.s -1 , between 0→ -1.5 → 2 and 0 V.

Figure 10 .

 10 Figure 10. Room temperature solid-state luminescence spectra. Centre: 1 (λ ex = 280 nm), dash line: 2 (λ ex = 260 nm), left: 3 (λ ex = 310 nm) and right: 4 (λ ex = 360 nm).

Figure 11 .

 11 Figure 11. Solid-state emission spectrum at room temperature for compound 16, λ ex = 270 nm.

Figure 12 .

 12 Figure 12. Solid-state emission spectrum at room temperature for compound 17, λ ex = 410 nm.

Figure 13 .Scheme 2 .Scheme 3 .

 1323 Figure 13. Solid-state excitation spectrum at room temperature for compound {Sm[OC(C 4 H 3 S) 3 ] 3 (thf) 3 } • thf (16) (solid line) and {Sm[OC(C 16 H 13 S)] 3 (thf) 3 } • thf (17) (dashed line), λ em = 651 and 650 nm, respectively.

  3

14 H 11 S 2 )] 4 (thf) 3

J H4-H5 = 4.7 Hz, 12H, 4-H). Anal. Calcd for C 64 H 60 O 7 S 12

K C, 51.81; H, 4.05; Found C, 53.02; H 3.31.

[KOC(C (9): Yield 30 % (580 mg). 1 H-NMR (thf/C 6 D 6 ): δ 7.5 (m, 8H, 5-H Th), 6.9 (m, 20H, Ph), 6.7 (m, 8H, 4-H Th), 6.5 (m, 8H, 3-H Th). Anal. Calcd for C 72 H 68 O 7 S 8 K 4 C, 59.25; H, 4.66; cannot be performed because of the sensibility. {[KOC(C 16 H 13 S)] 4 (thf) 3 } • ½ thf (11): Yield 34 % (610 mg). 1 H-NMR (thf/C 6 D 6 ): δ 7.3

(m, 12H, 5-H Th, Ph),

6.9 (m, 32H, Ph), 6.7 (m, 4H, 6.4 (m, 4H,

. Anal.

Calcd for C 82 H 80 O 7.5 S 4 K 4

C, 67.02; H, 5.40; Found C, 65.74; H, 4.60

.

[KOC(

C 17 H 15 S)] 4 (thf) 2 (12): Yield

	Ph), 7.0 (m, 24H, Ph), 6.4 (m, 4H, 4-H Th), 6.2 (m, 4H, 3-H Th), 2.2 (s, 12H, -CH 3 ). Anal.
	Calcd for C 80 H 76 O 6 S 4 K 4 C, 67.69; H, 5.35; Found C, 66.60; H, 6.60.

29 % (515 mg). 1 H-NMR (thf/C 6 D 6 ): δ 7.

3 (m, 16H,

General Procedure for Preparation of Sodium Alcoholates 8, 10, 13-15

[NaOC(C 14 H 11 S 2 )] 4 (thf) 2 (10): The

	3 J H4-H5 =
	4.9 Hz, 12H, 4-H). Anal. Calcd for C 60 H 52 O 6 S 12 Na 4 C, 53.50; H, 3.86; Found C, 52.24; H,
	3.56.
	unreacted NaH was filtered. The solvent was slowly
	evaporated, a light-brown solid precipitated, which was separated from the liquid residue.
	The isolated yield is 32 % (529 mg). 1 H-NMR (thf/C 6 D 6 ): δ 7.6 (dd, 3 J H5-H4 = 6.6 Hz and
	4 J H5-H3 = 1.3 Hz, 8H, 5-H Th), 7.0 (m, 28H, 4-H, Ph), 6.7 (dd, 3 J H4-H3 = 4.0 Hz , 8H, 3-H
	Th). Anal. Calcd for C 68 H 60 O 6 S 8 Na 4 : C, 61.81; H, 4.54; Found C, 60.61; H, 4.39.

[NaOC(C 17 H 15 S)] 4 (thf) 2 (13): The

	suspension turned into a solution. The solvent was
	slowly evaporated, a white solid precipitated, which was filtered (yield 14 %, 241 mg).
	1 H-NMR (thf/C 6 D 6 ): δ 7.3 (m, 16H, Ph), 7.0 (m, 24H, Ph), 6.4 (m, 4H, 4-H Th), 6.2 (m, 4H,
	3-H Th), 2.2 (s, 12H, -CH 3 ). Anal. Calcd for C 80 H 76 O 6 S 4 Na 4 C, 71.00; H, 5.62; Found C,
	71.00; H, 5.59.

[NaOC(C 14 H 11 S 2 )] 4 (thf) 2 (14): The unreacted

	NaH was filtered. The solvent was slowly
	evaporated; colourless crystals were obtained (yield 22 %, 362 mg). 1 H-NMR (thf/C 6 D 6 ): δ
	7.2 (m, 16H, Ph, 5-H Th), 7.0 (m, 12H, Ph), 6.8 (m, 8H, 4-H Th), 6.2 (m, 8H, 2-H Th).
	Anal. Calcd for C 68 H 60 O 6 S 8 Na 4 C, 61.81; H, 4.54; Found C, 59.54; H, 5.08.

[NaOC(C 16 H 13 S)] 4 (thf) 2 (15): The

	reaction mixture was filtered, and the solvent was
	slowly evaporated, from which a white solid precipitated (yield 31 %, 490 mg). 1 H-NMR
	(thf/C 6 D 6 ): δ 7.3 (m, 12H, Ph, 5-H Th), 7.0 (m, 24H, Ph), 6.9 (d, 4H, 4-H Th), 6.2 (s, 4H,
	2-H Th). Anal. Calcd for C 76 H 68 O 6 S 4 Na 4 C, 70.37; H, 5.24; Found C 71.03; H, 5.09.

{Sm[OC(C 4 H 3 S) 3 ] 3 (thf) 3 } • thf (16): Method 1: To a suspension of

	solution was concentrated and brown-light crystals were obtained at 5°C after a few days. The
	isolated yield is 13 % (217 mg).
	1 H-NMR (CDCl 3 ): δ 7.2 (br. s, 27H, 3-H, 4-H, 5-H), 3.6 (br. s, 8H, thf), 3.4 (br. s, 3H, thf),
	1.7 (br s, 10H, thf), 1.2 (br. s, 8H, thf), 0.9 (br s, 3H, thf). Anal. Calcd for C 55 H 59 O 7 S 9 Sm C,
	51.93; H, 4.64; Found C, 49.32; H, 4.57.
	NaH (0.104 g, 4.3 mmol) in thf (5 mL) was slowly added
	tris(2-thienyl)methanol (1.21 g, 4.3 mmol) in thf (20 mL). The mixture was stirred at room
	temperature overnight. Then, it was added to a suspension of SmCl 3 (0.373 g, 1.4 mmol) in
	thf (5 mL). The mixture was stirred at room temperature for two days. NaCl was filtered. The
	solution was concentrated and brown-light crystals were obtained at 5°C a few days later. The
	isolated yield is 24 % (430 mg).
	Method 2: To a suspension of KH (0.154 g, 3.8 mmol) in thf (5 mL) was slowly added
	Tris(2-thienyl)methanol (1.07 g, 3.8 mmol) in thf (20 mL). The mixture was stirred at room
	temperature overnight. Then, it was added to a suspension of SmCl 3 (0.328 g, 1.3 mmol) in
	thf (5 mL). The mixture was stirred at room temperature for two days. KCl was filtered. The

{Sm[OC(C 16 H 13 S)] 3 (thf) 3 } • thf (17): To

	a suspension of KH (0.193 g, 4.8 mmol) in thf
	(5 mL) was slowly added diphenyl(2-thienyl)methanol (1.28 g, 4.8 mmol) in thf (20 mL). The
	mixture was stirred at room temperature overnight. Then, it was added to a suspension of
	SmCl 3 (0.410 g, 1.6 mmol) in thf (5 mL). The mixture was stirred at room temperature for two
	days. KCl was filtered. The solution was concentrated and colourless crystals were obtained at
	5°C few days later. The isolated yield is 10 % (190 mg). 1 H-NMR (CDCl 3 ): δ 7.3 (m, 33 H,
	Ph, 5-H Th), 6.9 (dd, 3 H, 4-H Th, 3 J H4-H5 = 5.14 Hz , 3 J H4-H3 = 3.97 Hz,), 6.7 (dd, 3 H, 3-H
	Th, 3 J H3-H4 = 3.42 Hz , 3 J H3-H5 = 1.22 Hz, ,), 3.7 (m, 12 H, thf), 1.8 (m, 12 H, thf) ppm. Anal.
	Calcd for C 67 H 71 O 7 S 3 Sm C, 65.11; H 5.75; Found C, 65.18; H, 6.19.
	Instruments. The 1 H NMR spectra were recorded on a Bruker ACF-NMR (200 MHz) for 4
	and 7-15 and Bruker Avance 400 spectrometer (400 MHz, H,H-COSY) for 16-17. All
	chemical shifts (δ) and coupling constants (J) are given in ppm and Hertz, respectively.

Analytical data were measured with a LECO CHN-900 instrument. The ATR-IR spectra were performed using a Bruker Vector 22 Spectrometer equipped with Golden Gate.

Electrochemistry

. Cyclic voltammetric experiments were performed on an Autolab PGSTAT 20 Potentiostat Galvanostat (Ecochemie) equipped with a three-electrode assembly with 0.1 M [NBu 4 ][PF 6 ] (TBAF) as supporting electrolyte and CH 3 CN or CH 2 Cl 2 as solvent. The working electrode was a platinum disk of 1 mm in diameter; it was polished consecutively

Table 1 .

 1 X-ray crystallographic and refinement data for 7

-9, 11-12 and 16-17.

				ZAAC ZAAC				Page 8 of 48
	Independent reflections	9114	12917	30203	12157	14786	5629	3955
	Compounds	7 [R(int) = 0.0290]	8 [R(int) = 0.0356]	9 [R(int) = 0.0765]	11 [R(int) = 0.1092]	12 [R(int) = 0.0406]	16 [R(int) = 0.0350]	17 [R(int) = 0.0397]
	Empirical formula Completeness to theta [%]	C 64 H 60 K 4 O 7 S 12 99.9 (29.40°)	C 60 H 52 Na 4 O 6 S 12 97.5 (34.67°)	C 72 H 68 K 4 O 7 S 8 99.1 (26.49°)	C 84 H 82 K 4 O 7.5 S 3 100.0 (28.26°)	C 80 H 76 K 4 O 6 S 4 99.7 (26.44°)	C 55 H 59 O 7 S 9 Sm 99.9 (34.27)°	C 67 H 71 O 7 S 3 Sm 100.0 (26.21°)
	Formula weight Absorption correction	1482.24 None	1345.70 Multiscan	1458.14 Multiscan	1464.08 None	1418.05 Multiscan	1270.91 Multiscan	1234.77 Multiscan
	Temperature [K] Data / restraints / parameters	103(2) 9114 / 0 / 460	103(2) 12917 / 0 / 360	130(2) 30203 / 4 / 1671 12157 / 0 / 589 130(2)	130(2) 14786 / 13 / 874	130(2) 5629 / 1 / 216	130(2) 3955 / 1 / 209
	Crystal system Goodness-of-fit on F 2	Orthorhombic 2.785	Monoclinic 2.755	Monoclinic 2.076	Cubic 1.022	Monoclinic 1.228	Rhombohedral 1.433	Trigonal 1.375
	Space group Final R indices [I>2sigma(I)]	Pccn R1 = 0.0951,	C2/c R1 = 0.1052,	C2/c R1 = 0.1224,	P2(1)3 R1 = 0.0626,	C2/c R1 = 0.1107,	R3 R1 = 0.0482,	P31c R1 = 0.0490,
	a [Å] Largest diff. Peak and hole	14.246(1) wR2 = 0.2853 2.130 and -	23.19(1) wR2 = 0.2969 4.195 and -2.547 1.207 and -1.201 1.010 and -0.516 1.386 and -1.718 2.826 and 24.77(1) 24.494(1) 23.647(1) 13.940(1) wR2 = 0.3011 wR2 = 0.1497 wR2 = 0.2368 wR2 = 0.1311	wR2 = 0.1275 14.568(1) 0.916 and -0.416
	b [Å] [e•Å -3 ]	16.743(1) 1.303	13.343(1)	24.21(1)	24.4944(1)	14.219(1)	13.940(1) -1.752	14.568(1)
	c [Å]	27.71(1)	22.98(1)	49.109(3)	24.494(1)	42.900(2)	24.700(4)	15.780(1)
	α [°]	90	90	90	90	90	90	90
	β [°]	90	119.96(1)	91.55(1)	90	94.10(1)	90	90
	γ [°]	90	90	90	90	90	120	120
	Volume [Å 3 ]	6608.6(6)	6158.8(5)	29444(3)	14695.9(6)	14387(1)	4156.8(8)	2900.4(3)
	Z	4	4	16	8	8	3	2
	ρ calc [mg/m 3 ]	1.490	1.451	1.316	1.323	1.309	1.523	1.414
	µ [mm -1 ]	0.701	0.504	0.519	0.384	0.416	1.450	1.175
	F(000)	3072	2784	12160	6160	5952	1953	1278
	Crystal size [mm 3 ]	0.55x0.3x0.25	0.4x0.28x0.22	0.55x0.37x0.22	0.5x0.2x0.09	0.42x0.40x0.29	0.3x0.44x0.5	0.50x0.37x0.06
	Theta range for data collection [°] 1.47 to 29.40	1.83 to 34.67.	1.18 to 26.49	1.18 to 28.26	1.67 to 26.44	1.88 to 34.27	1.61 to 26.41
	Reflexion collected	46554	105170	123598	83983	117135	26806	16454
				Wiley-VCH Wiley-VCH

  3 (thf) 3 were also obtained by alcoholysis of the dinuclear organometallic samariumfluoride [{-(Me 3 Si) 2 C 5 H 3 } 2 SmF] 2 in the presence of slightly acidic ArOH or Ph 3 SiOH [19]. Reaction of equimolar quantities of Sm[N(SiMe 3 ) 2 ] 3 and Al(i-Bu) 3 in the presence of i-propanol or

	t-BuOH allowed the preparation of the mixed-metal alkoxide complexes
	{[(i-Pr-O)(i-Bu)Al(µ-O-i-Pr) 2 Sm(O-i-Pr)(HO-i-Pr)](µ-O-i-Pr)} 2 .	An	analogous
	reaction between Sm[N(SiMe 3 ) 2 ]

3

, Al(i-Bu) 3 and t-BuOH, followed by addition of thf,

produced the thf adduct [(thf) 2 Sm(O-t-Bu) 2 (µ-O-t-Bu) 2 Al(i-Bu) 2 ]

[20]

. But the most classical route to prepare samarium alkoxides and those of other lanthanides is the salt elimination by reaction between alkali metal alcoholates and a lanthanide halide

[21]

.

Table 2

 2

	15 have been synthesized straightforwardly

). Unfortunately, we failed to grow single crystals of 10 and 13-15. According to the 1 H-NMR spectra (Table

2

), we presume that NaH and the carbinols 2 and 5-6 react in the same manner as the other derivatives and postulate tentatively a tetrameric cage structure

Table 3 .

 3 Selected bond lengths /Å and angles /° for Compound 7.

	7

Table 4 .

 4 Selected bond lengths /Å and angles /° for {[KOC(C 16 H 13 S)] 4 (thf) 3 } • ½ thf(11) (molecules A and B).

	A

Table 5 .

 5 Selected bond lengths /Å and angles /° for [NaOC(C 4 H 3 S) 3 ] 4 (thf) 2

Table 6 .

 6 Selected bond lengths /Å and angles /° for 16 and 17.

			16		17
	Sm-O(1)		2.156(3)	2.160(4)
	Sm-O(2)		2.594(3)	2.552(5)
	O(1)-C(1)	1.391(5)	1.395(8)
	O(1)-Sm-O(1) 101.1(1)	102.3(2)
	O(1)-Sm-O(2) 92.5(1)		90.8(2)
	O(2)-Sm-O(2) 73.7(1)		76.9(2)
	C(1)-O(1)-Sm 170.53(6) 173.3(5)
	The	molecular	structures	of	{Sm[OC(C 4 H 3 S) 3 ] 3 (thf) 3 } •	thf	(16)	and
	{Sm[OC(C 16 H 13 S)] 3 (thf) 3 } • thf (17) exhibit six-coordinate mononuclear samarium alkoxides
	with three (2-thienyl)methoxido or diphenyl(2-thienyl)methoxido ligands and three
	tetrahydrofuran molecules around the samarium atoms, in a facial arrangement. Both
	molecules are situated on a threefold axis in the crystals. Additional thf molecules are filling

  These angle values are comparable with those found for Sm(O-2,6-i-Pr 2 C 6 H 3 ) 3 (thf) 3 [102.29(6)° and 79.33(6)°, respectively] [19] or Sm(O-2,4,6-Me 3 C 6 H 2 ) 3 (thf) 3

	ZAAC	Page 16 of 48
	16 or 76.9(2)° for 17]. [103.4(1) and 77.5(1)°, respectively] [20]. The Sm-O-C(C 4 H 3 S) 3 angles of 170.5(3)° and
	Sm-O-C(C 16 H 13 S) of angles of 173.3(5)° are also similar to those in
	{Nd[OC(C 4 H 3 S) 3 ] 3 (thf) 3 } • thf [169.9(1)°] [5] and in Sm(O-2,4,6-Me 3 C 6 H 2 ) 3 (thf) 3
	[170.0(3)°] [20]. The Sm-OC(C 4 H 3 S) 3 and Sm-OC(C 16 H 13 S) distances of 2.156(3) and
	2.160(4) Å are comparable to those in Sm(O-2,4,6-Me 3 C 6 H 2 ) 3 (thf) 3 [2.160(0) Å] [20],
	Sm(O-2,6-i-Pr 2 C 6 H 3 ) 3 (thf) 3 [2.158(2) Å] [19] and [Sm(OC 6 H 2 Bu t 2 -2,6-Me-4) 3 (thf)] • thf
	[2.152(7) Å] [27]. The Sm-O(thf) distances are longer with 2.594(
	Wiley-VCH

3 CO-Sm-OC(C 4 H 3 S) 3 [101.1(1)°] or (C 16 H 13 S)OC-Sm-OC(C 16 H 13 S) [102.3(2)°] and the O(thf)-Sm-O(thf) angles [73.7(1)° for

Table 8 .

 8 Values peak potentials [V, vs. Ag/AgClO 4 ] of the carbinols 1 and 3 and samarium alkoxides 16 and 17, in dichloromethane deduced from cyclic voltammetric measurements (0 → -1.5 → 1.5 → 0 V) on a platinum electrode (diameter 1 mm) at 100 mV.s -1 .

	E pa [V]

Table 9 .

 9 Solid-state emission maxima λ em[nm] of the carbinols and the alkali metal alkoxides (K, Na) with λ ex for excitation maximum.

	λ em [nm]

  5 transitions 4 G 5/2 → 6 H 5/2 (zero-zero band: forbidden transition), 4 G 5/2 → 6 H 7/2 (magnetic dipole transition), 4 G 5/2 → 6 H 9/2 (electric dipole transition),

  5 transitions: 4 G 5/2 → 6 H 5/2,7/2,9/2 . Note that, as 16, a samarium band at 622 nm is observed, probably also due to the 4 G 5/2 → 6 H 7/2 transition: it might be a result of splitting due to ligand field.The solid-state excitation spectra of 16 and 17 monitoring the 4 G 5/2 → 6 H 9/2 transition recorded at room temperature are given in Figure13. They show broad bands that cover the entire 250-300 nm region with a maximum at 270 nm for 16 and the 250-395 nm region with a maximum at 273 for 17 attributed to the π→π* transitions of the organic ligands. The spectra also present several narrow bands of the Sm 3+ ion arising from the intraconfigurational transitions from the 6 H 5/2 ground state to the following levels: 4 H 9/2 (~ 344 nm), 4 F 9/2 (~ 363 nm), 4 L 17/2 (~ 373 nm), 4 F 7/2 (~ 406 nm), ( 6 P, 4 P) 5/2 (~ 422 nm), 4 G 9/2 (~ 450 nm), 4 I 13/2 (~ 462 nm), 4 I 11/2 (~ 473 nm), 4 I 9/2 (~ 488 nm), 4 G 7/2 (~ 504 nm), 4 F 3/2 (~ 526 nm) and 4 G 5/2 (~ 568 nm). These transition values are in agreement with those found for Sm 3+ doped germinate

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Acknowledgments

We gratefully acknowledge the financial support provided by the DFG in the framework of the SPP1166 (Lanthanoidspezifische Funktionalitäten in Molekül und Material), by the Saarland University and the Fonds der Chemischen Industrie. We thank Dr. Michael Zimmer for the 1 H NMR spectra of 16 and 17. MK and LG thank the CNRS for financial support.

Synthesis of the Samarium(III) Thienyl-Substituted Methoxides

The alkaline salts of carbinols 7-15 have been used to accede to the samarium derivatives.

Three equivalents of the carbinol 1 were deprotonated in the presence of 3 equivalents NaH or KH in tetrahydrofuran at room temperature overnight. Subsequently, the in situ formed salts {[KOC(C 4 H 3 S) 3 ] 4 (thf) 2 } • thf (7) and {[NaOC(C 4 H 3 S) 3 ] 4 (thf) 2 } • thf (8), respectively were added to a suspension of 1 equivalent of SmCl 3 (Scheme 3). After stirring for further three days and work-up, brown-light single crystals of {Sm[OC(C 4 H 3 S) 3 ] 3 (thf) 3 } • thf (16) were obtained in a modest yield of 24 % and 13 %, respectively. A similar procedure allowed also the synthesis of {Sm[OC(C 16 H 13 S)] 3 (thf) 3 } • thf [START_REF] Diamond | Crystal and Molecular Structure Visualization[END_REF] by in situ deprotonation of carbinol 3 in the presence of KH (Scheme 3). Colourless crystals of have been obtained, albeit in a low yield of only 10 %.

The 1 H NMR spectrum of 16, recorded at room temperature in CDCl 3 , displays broad signals, probably due to the paramagnetic character of the Sm(III) ion. A broad aromatic signal at 7.2 ppm, which integrates for 27H, is attributed to the protons of the thienyl units. The other signals at 3.4, 1.7, 1.2 and 0.9 ppm are assigned to the different hydrogen atoms of the tetrahydrofuran molecules ligated or not to the metal centre.

The 1 H NMR spectrum of 17 exhibits five signals in CDCl 3 solution. The first, at 7.3 ppm, is a multiplet, which integrates for 33 H attributed to the protons of the phenyl groups and the 5-H