Rhone P Brocha Silalahi

Jian-Hong Liao

Yu-Fang Zeng

Tzu-Hao Chiu

Samia Kahlal

Jean-Yves Saillard

C W Liu

An Unusual Core Engineering on A Copper Hydride Nanoball

A neutral polyhydrido copper cluster, [Cu27H15{S2CN n Bu2}12] (abbreviated as [Cu27H15]), was prepared by the reaction of dithiocarbamates (dtc), Cu(I) salts and NaBH4. The isolated cluster provides insights into core engineering, demonstrating the novel ability to reversibly add or remove one copper atom from the cluster core. Single-crystal X-ray analysis reveals that the new core-shell structure exhibits a Cu24 rhombicuboctahedral outer cage and an inner Cu3 triangular kernel. The two core-shell clusters, [Cu27H15{S2CN n Bu2}12] and the previously published [Cu28H15(S2CN n Bu2)12] + (abbreviated as [Cu28H15] + ), are only differentiated by one copper atom in their inner core. Importantly, we demonstrate core engineering with the controllable reversible transition between an irregular Cu4 tetrahedron and a Cu3 triangle, whilst maintaining their outer Cu24 shell intact. The 15 hydride atoms in [Cu27H15], coordinated in three different modes, are coincident with the hydride positions in [Cu28H15] + . The degradation of [Cu27H15] in solution or the addition of one eq. Cu(I) ion leads to the conversion of [Cu27H15] into [Cu28H15] + , while the reversed transformation can be achieved by the addition of either formic acid or a reducing agent to [Cu28H15] + . A dicationic species was observed in the ESI mass spectrum, and the composition is formulated as [Cu56H30(S2CN n Bu2)24] 2+ , a dimer of [Cu27H15(S2CN n Bu2)12 + Cu + ]2 2+ . The dimeric species was further explored by DFT calculations, suggesting that the lowest energy structure consists of a [Cu28H15] + and a [Cu27H15] clusters connected through one Cu + atom bridge. As a result, [Cu27H15] is considered an intermediate species in the formation of the more stable [Cu28H15] + nanoball.

INTRODUCTION

Copper hydride nanoclusters (NCs) have historically been studied due to their potential applications in catalysis, 1 hydrogen storage, [START_REF] Dhayal | Copper hydrides clusters in energy storage and conversion[END_REF] and fascinating molecular structures. [START_REF] Dong | Cu36H10(PET)24(PPh3)6Cl2] Reveals Surface Vacancy Defects in Ligand-Stabilized Metal Nanoclusters[END_REF] A series of ligand-stabilized copper hydride clusters with various hydride coordination modes, including capping, bridging, and interstitial, have been reported. [START_REF] Dong | Cu36H10(PET)24(PPh3)6Cl2] Reveals Surface Vacancy Defects in Ligand-Stabilized Metal Nanoclusters[END_REF][START_REF] Yuan | A stable welldefined copper hydride cluster consolidated with hemilabile phosphine[END_REF] Using single-crystal neutron diffraction techniques, hydride positions of high nuclearity copper hydrides stabilized by dichalcogenolates have been reliably determined. Notable examples are Cu7H and Cu28H15 ligated by dithiocarbamate(dtc), [START_REF] Liao | Hydrido copper clusters supported by dithiocarbamates: oxidative hydride removal and neutron diffraction analysis of [Cu7(H){S2C(aza-15-crown-5)}6[END_REF][START_REF] Edwards | Chinese Puzzle Molecule: A 15 Hydride, 28 Copper Atom Nanoball[END_REF] Cu20H11, [START_REF] Dhayal | A Nanospheric Polyhydrido Copper Cluster of Elongated Triangular Orthobicupola Array: Liberation of H2 from Solar Energy[END_REF] Cu30H18. [START_REF] Barik | Polyhydrido Copper Nanoclusters with a Hollow Icosahedral Core: [Cu30H18{E2 P(OR)2 }12[END_REF] and Cu32H20 [START_REF] Dhayal | Cu32(H)20{S2P(O i Pr)2}12]: The Largest Number of Hydrides Recorded in a Molecular Nanocluster by Neutron Diffraction[END_REF] protected by dithiophosphate(dtp)/diselenophosphate(dsep), and a combination of alkynyl and dtc/dtpprotected Cu11H2, 10 Cu14PdH2, [START_REF] Chakrahari | Synthesis of Bimetallic Copper-Rich Nanoclusters Encapsulating a Linear Palladium Dihydride Unit[END_REF] Cu15H2, [START_REF] Chakrahari | Isolation and Structural of 15-Nuclear Copper Dihydride Clusters: An Intermediate in the Formation of a Two-Electron Copper Superatom[END_REF] and Cu14AgH2. [START_REF] Silalahi | Reactivities of Interstitial Hydrides in a Cu11 Template: En Route to Bimetallic Clusters[END_REF] However expanding Cu hydride NCs with novel and exciting structures is still challenging. [START_REF] Dhayal | Polyhydrido Copper Clusters: Synthetic Advances, Structural Diversity, and Nanocluster-to-Nanoparticle Conversion[END_REF] The need for convenient and simplified synthetic protocols for preparing copper hydride clusters, which are stable under ambient conditions, is in high demand. Nevertheless, some key issues, such as intrinsic instability, finite surface modifiers, and sensitivity toward the air, remain to be solved. [START_REF] Sun | Hydridocoinage-metal clusters: Rational design, synthetic protocols and structural characteristics[END_REF] Scheme 1. Core engineering at the atomic level on two copper hydrides, Cu11H2 and Cu12H2

In metal NCs, the surface protecting ligands and the kernel structures are vital to understanding their structure-properties relationship. In the past years, intensive research has established some successful methods, [START_REF] Baghdasaryan | Copper nanoclusters: designed synthesis, structural diversity, and multiplatform applications[END_REF] such as size-focusing, [START_REF] Jin | Atomically precise metal nanoclusters: stable sizes and optical properties[END_REF] fusion growth, [START_REF] Du | Fusion growth patterns in atomically precise metal nanoclusters[END_REF] atomic-precision engineerings, [START_REF] Du | Atomic-precision engineering of metal nanoclusters[END_REF] and ligand-exchange [START_REF] Nguyen | Ligand-Exchange-Induced Growth of an Atomically Precise Cu29 Nanocluster from a Smaller Cluster[END_REF] methodologies, which lead to the rational synthesis of metal NCs with high purity. However, control over the core structure of NCs is a far more challenging pursuit than over shell structure in core-shell NCs. The formation and transformation of metal NCs, usually involve the outermost metal shell and are induced by the addition of ligand and metal salts.

In contrast, the inner core engineering without altering the shell structure is hard to control mainly due to the shielding effect from the outer shell. Notable exceptions are the alloy clusters produced via the galvanic exchange method. [START_REF] Sharma | Structurally Precise Dichalcogenolate-Protected Copper and Silver Superatomic Nanoclusters and Their Alloys[END_REF] Lately the core modification of [Ag62S13(SBu t )32] 2+ (0e) can form a 2e superatom, [Ag62S12(SBu t )32] 4+ . Elimination of the central S atom in the [S@Ag14S12] core yielded a defective structure with a hollow [Ag14S12] core, which not only altered the electron count of the cluster but also quenched the photoluminescence. [START_REF] Li | Luminescent Molecular Ag-S Nanocluster[END_REF] Wang et al. established a chalcogen-induced strategy for chiral silver nanocluster synthesis and modification of the core. [START_REF] Wang | Chalcogens-Induced Ag6Z4@Ag36 (Z = S or Se) Core-Shell Nanoclusters: Enlarged Tetrahedral Core and Homochiral Crystallization[END_REF] The addition of S 2-or Se 2-ions can enlarge the inner core from tetrahedral AgS4 to Ag6Z4 (Z= S and Se). The enlargement of inner Ag clusters did not involve the truncated tetrahedral Ag36 shell. [START_REF] Wang | Chalcogens-Induced Ag6Z4@Ag36 (Z = S or Se) Core-Shell Nanoclusters: Enlarged Tetrahedral Core and Homochiral Crystallization[END_REF] The transformation of Au36 kernel of [Au48(m-MBT)26] to Au34 kernel of [Au46(m-MBT)26] can be obtained through the heating process at 80 o C; the remaining kernel is no longer symmetric but maintaining its original framework causes a significant effect on the PL intensity. [START_REF] Zhou | Traceless Removal of Two Kernel Atoms in a Gold Nanocluster and Its Impact on Photoluminescence[END_REF] In 2021, a mixed ligand technique was conducted by using both Ph2PS2 -and RC≡C -ligands to isolate paired silver NCs, Ag7S6@Ag48 and Ag6S6@Ag48, both of which display an identical Ag48 shielding shell, only differing by one single Ag atom in the core. [START_REF] Zhang | Core engineering of paired core-shell silver nanoclusters[END_REF] Recently, core engineering at the atomic level on two copper hydrides, Cu11H2 and Cu12H2, protected by dithiophosphates and alkynyl ligands, has been communicated (Scheme 1). [START_REF] Silalahi | Reactivities of Interstitial Hydrides in a Cu11 Template: En Route to Bimetallic Clusters[END_REF] The reaction is believed to occur by inserting one Cu(I) ion at the center of Cu11H2 template, which has a 3,3,4,4,4-pentacapped trigonal prismatic Cu11 cage. [START_REF] Silalahi | Copper Clusters Containing Hydrides in Trigonal Geometry[END_REF] The two hydrides inside the Cu11 are connected to the inserted copper to depict a linear CuH2 motif.

As a result, the coordination mode of two interstitial hydrides in Cu11 are modified from μ4-H trigonal pyramidal to a μ5-H trigonal bipyramidal in Cu12.

Previously we successfully synthesized an air and moisture-stable copper nanoball,

[Cu28H15{S2CNR2}12](PF6) (R= n Pr; aza-15-crown-5) (abbreviated as [Cu28H15] + ), [START_REF] Edwards | Chinese Puzzle Molecule: A 15 Hydride, 28 Copper Atom Nanoball[END_REF] where the copper hydride array consists of two types of copper atoms: an inner distorted tetrahedral core (Cu4) and those of the external rhombicuboctahedron display (Cu24 patterns. The isotope pattern of cationic [Cu28H15] + shows that the gap distance between the peaks is about 1.0 mass unit (Figure S2a). Meanwhile, for the [Cu27H15], the isotope pattern shows gap differences of the peak are about 1.0 mass unit, which corresponds to the [Cu27H15 + Cu + ] + . By close inspection between those peaks, there is an isotope pattern with a spacing difference around m/z 0.5 Da, which corresponds to the +2 dimer species (Figure S2b). Of note, The latter species has never been observed in the ESI mass spectrum of [Cu28H15(dtc)12] + . [START_REF] Edwards | Chinese Puzzle Molecule: A 15 Hydride, 28 Copper Atom Nanoball[END_REF] Unfortunately, an attempt to add Cs ions for the mass measurement to obtain the Cs adduct, such as [Cu27H15 + Cs + ] + , was unsuccessful. It could be due to the instability of [Cu27H15], resulting in the cationic [Cu28H15] + species forming during the sample preparation.

The Elemental analysis further confirms the chemical purity of [Cu27H15] with the presence of HCOOH. The carbon, hydrogen, sulfur, and nitrogen contents are 30.56%, 5.60%, 17.20% and 3.85%, respectively, which are close to the theoretical values (C: 30.96%, H: 5.55%, S: 18.19%, and N: 3.97%).

Structural analysis

The (Figure 2c), and show a slight distortion compared with the Cu24 shell in [Cu28H15] + (Figure 2d).

The inner core shows a triangle composed of three Cu atoms, disordered at eight positions (Figure S3a). The eight positions can be grouped into four sets of Cu3 triangles, each in 25% occupancy (Figure S3b). The central Cu3 triangle is located between a pair of staggered triangles of the Cu24 rhombicuboctahedron (Figure 2e (i) The assembly of Cu3H@(μ5-H)6 octahedron@ Cu24 rhombicuboctahedron@(μ3-H)8 cube@S24 truncated octahedron.

NMR spectroscopy

The 1 H NMR spectrum of [Cu27H15] displays four chemical shifts at 4.06, 1.86, 1.35, and 0.93 ppm in 2:2:2:3 integration ratios, corresponding to the protons of the n-butyl group of the dtc ligands (Figure S5). In addition, it shows three broad singlet hydride resonances at -0.57, 3.12, and 3.92 ppm, with integration ratios of 8:1:6, respectively. These values were confirmed by [START_REF] Dhayal | Copper hydrides clusters in energy storage and conversion[END_REF] The μ3-H peak at -0.55 shifted to -0.75 ppm, corresponding to the eight μ3-H in the outer Cu24 rhombicuboctahedron of [Cu28H15] + . Additionally, the shifting of the μ3-H center at 3.15 to 1.12 ppm, confirms the transition from μ3-H center in triangle shape to the μ4-H center in irregular tetrahedron shape. The -CH2 group of dtc ligand, also followed, and a shift from 4.08 ppm to 4.14 ppm, is observed. This result indicates that the [Cu27H15] possess relatively lower stability than its

[Cu28H15] + counterpart and acts as an intermediate cluster to form a more stable cationic cluster.

H2 and CO2 production

We also investigated the production of H2 and CO2 gases from the reaction of formic acid

Optical properties

The optical properties of the [Cu27H15] cluster was recorded in 2-MeTHF at ambient temperature. The UV-vis spectrum shows two well-defined absorption bands at 295, 356, and a shoulder peak at 424 nm, where the absorption bands only showed a negligible shift from the absorptions of [Cu28H15] + at 292, 353, and 425 nm (Figure S14). Thus, the core engineering process indicates no obvious changes in the optical properties of [Cu27H15] and [Cu28H15] + .

Computational results

DFT calculations at the PBE0/Def2-TZVP level (see Computational Details in the SI) were performed on the [Cu27H15] NC. For the sake of computational limitations, the [S2CN n Bu2] - ligands were replaced by the simple dtc models [S2CNH2] -. The NC energy minimum (Figure 2b) was found of nearly C3 symmetry, with the inner Cu3 triangle being parallel to a pair of opposite triangular faces of the Cu24 rhombicuboctahedron. The optimized hydride positions confirm the X-ray assumptions based on the [Cu28H15] + neutron structure. Selected computed metrical data are provided in Table 1. A good agreement with the X-ray structure is found. The natural charges of the inner Cu atoms (0.41) are lower than those of the Cu24 shell (range: 0.65-0.67). On the other hand, the inner μ3-H is more negatively charged (-0.71) than the other hydrides (range: (-0.52)-(-0.67)). The small computed Cu•••Cu Wiberg bond indices are consistent with weak Cu(I)•••Cu(I) metallophilic interactions, whereas the corresponding Cu-H values are of the same order as found in other Cu(I) polyhydrides. [START_REF] Edwards | Chinese Puzzle Molecule: A 15 Hydride, 28 Copper Atom Nanoball[END_REF][START_REF] Dhayal | A Nanospheric Polyhydrido Copper Cluster of Elongated Triangular Orthobicupola Array: Liberation of H2 from Solar Energy[END_REF][START_REF] Barik | Polyhydrido Copper Nanoclusters with a Hollow Icosahedral Core: [Cu30H18{E2 P(OR)2 }12[END_REF][START_REF] Dhayal | Cu32(H)20{S2P(O i Pr)2}12]: The Largest Number of Hydrides Recorded in a Molecular Nanocluster by Neutron Diffraction[END_REF][START_REF] Silalahi | Copper Clusters Containing Hydrides in Trigonal Geometry[END_REF][START_REF] Chakrahari | Synthesis of Bimetallic Copper-Rich Nanoclusters Encapsulating a Linear Palladium Dihydride Unit[END_REF][START_REF] Nakajima | Tetra-, hexa-and octanuclear copper hydride complexes supported by tridentate phosphine ligands[END_REF] A significant gap of 3.37 eV separates the HOMO (of 62% metal character) from a block of vacant π*(dtc) combinations. The HOMO-1 and HOMO-2 have a similar metal participation as the HOMO, whereas the orbitals situated below have a mixed sulfur (lone pairs)/3d(Cu) character, in most of them the sulfur character is (moderately) dominating. The TD-DFT-simulated UV-vis spectrum of the [Cu27H15] model is in a very good agreement with its experimental counterpart (Figure S14). The two major simulated absorption bands at 300 and 327 nm are associated with transitions from the S lone pair/3d(Cu) block to the π*(dtc) block and therefore are of mixed LLCT (major) and MLCT (minor) character. The shoulder at ~ 450 nm is also resulting from transitions of the same type, but with a slightly larger MLCT character. It is noteworthy that the HOMO is not involved in any UV-vis transition.

DFT calculations were also used to explore the question of the nature of a "dimer" of

[Cu56H30{S2CN n Bu2}24] 2+

EXPERIMENTAL SECTIONS

General materials and methods

All the reactions were carried out under an N2 atmosphere by using the standard Schlenk technique. The solvents used in this work were distilled following standard protocols before use.

All chemicals were purchased from different commercial sources available and used as received.

[Cu(CH3CN)4](PF6) [START_REF] Kubas | Tetrakis(acetonitrile)copper(I) hexafluorophosphate[END_REF] and K(S2CN n Bu2) [START_REF] Kaugars | Reaction of Hydrazidoyl Chlorides with Sodium N,N-dialkyldithiocarbamates[END_REF]

Single-Crystal X-ray Crystallography

The single crystals of [Cu27H15] were mounted on the tip of glass fiber coated with paratone oil, then frozen. Data were collected on a Bruker APEX II CCD diffractometer using graphite monochromated Mo Kα radiation (λ = 0.71073 Å) at 150K. Absorption corrections for the area detector were performed with SADABS, [START_REF] Sheldrick | version 2014-11.0, Bruker Area Detector Absorption Corrections[END_REF] and the integration of raw data frame was performed with SAINT. [START_REF] Sheldrick | v4.043[END_REF] The structure was solved by direct methods and refined by least-squares against F 2 using the SHELXL-2018/3 package, [START_REF] Sheldrick | A short history of SHELX[END_REF][START_REF] Gruene | Refinement of macromolecular structures against neutron data with SHELXL[END_REF]

  experimental and theoretical isotope distribution patterns (Figure 1: insets B and C). The spectrum of the deuterated derivative [Cu27D15] depicts an intense peak at m/z 4258.2865 (calc. m/z 4258.2693) corresponding to [Cu27D13H2+Cu + ] + . Its simulated isotopic pattern matches well with the experimental observation (Figure S1).

Figure 1 .

 1 Figure 1. Positive-mode ESI-MS of [Cu27H15] cluster. Inset: simulated (red curve) and experimental (black curve) isotope patterns of A: [Cu28H15{S2CN n Bu2}12]2 2+ and [Cu27H15{S2CN n Bu2}12 + Cu + ] + , B: [Cu27H14{S2CN n Bu2}12]2 2+ , and C: [Cu27H14{S2CN n Bu2}12 + + Cu + ] 2+ .

  molecular structure of [Cu27H15], determined by single-crystal X-ray diffraction, reveals a core-shell cluster with multiple layers. It consists of 27 Cu atoms, 15 hydrides, and 12 dtc ligands (Figure 2a), precisely one less Cu atom than [Cu28H15] + . The optimized structure of [Cu27H15] shown in Figure 2b. To our great surprise, the striking difference between structures [Cu27H15] and [Cu28H15] + lies in the number of metals situated in the inner core. Interestingly, the inner core of [Cu27H15] misses one copper atom but maintains the same outer Cu24 skeleton as [Cu28H15] + . The metal skeleton of [Cu27H15] can be divided into an outer Cu24 shell and an inner Cu3 core. The outer 24 Cu atoms, are arranged in a rhombicuboctahedral (83 + 64 + 124) array 26

  ), and each Cu atom of the Cu3 triangle points to half of the squares (64) of Cu24. Compared with [Cu28H15] + , the kernel is a Cu4 tetrahedron (Figure 2f), and each triangle faces an edge where the squares of Cu24 meet. The disordered Cu3 triangle reflects its fluxional nature within the inner metal core (Figure S4), similar to the disordered Cu4 tetrahedral core in [Cu28H15] + . Regarding the Cu24 rhombicuboctahedron, the adjacent CuRhom-CuRhom distances of [Cu27H15] lie within the range of 2.5709(17) -2.7313(18) Å, slightly shorter than those in [Cu28H15] + (2.603(1) -2.824(1) Å). The average Cucore-Cucore distance (2.531 Å) of the central Cu3 triangle in [Cu27H15] is also smaller than the average distance (2.644 Å) of the central Cu4 tetrahedron in [Cu28H15] + . It can be assumed that the lower nuclearity in the central core of [Cu27H15] results in a severely distorted outer Cu24 rhombicuboctahedron. A total of 15 hydride atoms are classified into three types: eight pyramidal μ3-H (Htri), each caps on the eight triangles (83) of Cu24 rhombicuboctahedron; six square-pyramidal μ5-H (Hsp) each connects the square (64) of Cu24 and one Cu atom from the inner core; and one pyramidal μ3-H (Hcent) above the central Cu3 triangle (Figure 2g). The hydride atoms in [Cu27H15] are co-incident with 15 hydride positions of [Cu28H15] + determined by neutron diffraction (Figure 2h), but the coordination environment of the hydrides are partially different. For example, six μ5-H in [Cu27H15] vs. two μ6-H + four μ5-H in [Cu28H15] + , and one central μ3-H in [Cu27H15] vs. one μ4-H in [Cu28H15] + , respectively. These three types of hydride/deuteride correspond to the observed three resonances in the 1 H/ 2 H NMR spectrum (vide infra.). The dtc ligands play an important role in stabilizing the whole framework.Twelve ligands cap the square faces (124) of the Cu24 rhombicuboctahedron through (μ2, μ2) fashion, with average Cu-S distance of 2.370 Å. The 24 sulfur atoms are connected to form a truncated octahedron (64 + 86) as the first (or outer) layer, followed by a (μ3-H)8 cube (64), Cu24 rhombicuboctahedron (83 + 64 + 124), (μ5-H)6 octahedron (63), one Cu3 triangle(13), and one hydride at the cluster center (Figure2i). This new onion-type structure forms a sibling of [Cu28H15] + , a "Chinese puzzle ball".[START_REF] Edwards | Chinese Puzzle Molecule: A 15 Hydride, 28 Copper Atom Nanoball[END_REF]

Figure 2 .

 2 Figure 2. (a) The molecular structure of [Cu27H15{S2CN n Bu2}12] with butyl groups omitted for clarity. (b) The optimized structure of [Cu27H15{S2CN n H2}12]. (c) Cu24 rhomboctahedron in [Cu27H15] and (d) [Cu28H15] + . (e) Cu3@Cu24 and (f) Cu4@Cu24 framework. (g) Cu27H15 and (h) Cu28H15 motifs. (i) The assembly of Cu3H@(μ5-H)6 octahedron@ Cu24

  H NMR spectroscopy of the deuteride-labelled analogue [Cu27D15] at -0.51, 3.10, and 4.02 ppm (Figure S6), signifying the existence of three types of hydrides in [Cu27H15]. The two hydride resonances relatively downfield, at δ = 3.12 and 3.92 ppm, correspond to one central μ3-H, and six μ5-H. The remaining hydrides centered at δ = -0.57 ppm are assigned to eight capping μ3-H. We found that hydride chemical shifts in both 1 H and 2 H NMR spectra are quite diagnostic in determining the species of [Cu27H15] and [Cu28H15] + . Three broad hydride peaks in [Cu28D15] + centered at -0.72, 1.31, and 4.29 ppm are shifted to -0.50, 3.14, and 4.03 ppm in [Cu27D15] in their 2 H NMR spectra (Figure 3). Interestingly, a large downfield shift of hydride resonance from 1.31 ppm to 3.12 ppm corresponds to a change in the core structure from a tetrahedral Cu4 core in [Cu28H15] + to a Cu3 triangle in [Cu27H15].

Figure 3 .Figure 4 .

 34 Figure 3. (a) 2 H NMR spectra (CHCl3, δ = 7.25 ppm) of [Cu27D15] and (b) [Cu28D15] + .

  with [Cu28H15] + (Scheme S3). Unexpectedly, besides producing H2 and CO2 gases, the reaction with formic acid also generates [Cu27H15] as a new product. The presence of [Cu27H15] was identified by NMR spectroscopy. In the 1 H NMR spectrum in CDCl3 (FigureS9), showed that the chemical shifts of the 15 hydrides belonging to [Cu28H15] + (-0.82, 1.31, and 4.16 ppm) were shifted to the chemical shifts of 15 hydrides in [Cu27H15] (-0.63, 3.34, and 4.59 ppm). Concurrently, the presence of H2 gas was identified at 4.59 ppm. Based on the[START_REF] Silalahi | Reactivities of Interstitial Hydrides in a Cu11 Template: En Route to Bimetallic Clusters[END_REF] C NMR spectrum (FigureS10), the CO2 resonance was identified at 123.9 ppm. The in-situ generated [Cu27H15] was also confirmed by the ESI mass spectrum where the peak at 4245.18 da (calc. 4246.1 da) corresponds to the adduct ion of [Cu27H15{S2CN n Bu2}12 + Cu + ] + , which is in good agreement between the experimental and simulated isotopic pattern (FigureS11). The formation of [Cu27H15] is not observable only for the n Bu alkyl group. We generate another derivative of [Cu27H15] by using the n Pr group. The 1 H and 2 H NMR spectra indicate similar hydrides position as with the n Bu group (Figure S12-S13). A similar interconversion between [Cu27H15] and [Cu28H15] + will happen with n Pr derivatives. Since the transformation only occurred at the core of the [Cu27H15] can be seen with different alkyl ligands.

Synthesis of [ Cu27D15{S2CN n

 Cu27D15{S2CN Bu2}12], [Cu27D15]. The deuterated complexes [Cu27D15] was synthesized under the same reaction conditions of [Cu27H15] using deuteride source NaBD4. Yield: 0.042 g (20.13%, based on Cu). ESI-MS: m/z 4258.2865 (calc. m/z 4258.27) for [Cu27D13H2{S2CN n Bu2}12+Cu + ] + . 2 H NMR (46.1 MHz, acetone, δ, ppm): -0.51 (bs, 8D, μ3-D), 3.11 (bs, 1D, μ3-D), 4.03 (bs, 6D, μ5-D).Synthesis of [Cu27(H)15{S2CN( n Bu)2}12] from [Cu28(H)15{S2CN( n Bu)2}12](PF6). In a flame-driedSchlenk tube, [Cu28(H)15{S2CN( n Bu)2}12](PF6) (0.05 g, 0.011 mmol) was suspended in THF (15 mL) along with LiBH4•thf (0.06 mL, 0.11 mmol) and stirred at -20 o C for 6 hours. The solvent was evaporated under a vacuum, and the residue was dissolved in ether with water (3x15 mL). After the organic separation layer, the solution was filtered and dried under a vacuum. Further, the residue was with methanol to get rid of the impurities. The residue dissolved in ether and passed through Al2O3 to get an orange powder [Cu27(H)15{S2CN( n Bu)2}12]. Yield: 0.0079 g (16.55%, based on Cu).

  Bu2}12+Cu + ] + . An exact match of the isotopic pattern of this peak is demonstrated by a simulated mass spectrum. Two minor peaks at m/z 4182.27 (B) and 2133.60 (C) were also observed which correspond to [Cu27H14{S2CN n Bu2}12]2 2+ and [Cu27H14{S2CN n Bu2}12+Cu + ] 2+ , respectively. A good agreement was observed between the

	composition of the m/z 4248.21 peak can be attributed to [Cu28H15{S2CN n Bu2}12]2 2+ (calc. m/z
	The 27 copper atoms are arranged in a two-shell configuration of Cu3@Cu24 with 12 dtc ligands 4247.91), a dimer of [Cu27H15{S2CN n
	attached to the outermost Cu24 shell. The core engineering modified an irregular Cu4 tetrahedron
	of [Cu28H15] + into a Cu3 triangle in [Cu27H15] and kept the outer Cu24 shell intact. Reversible
	transformations via a one-atom migration mechanism between [Cu28H15] + and [Cu27H15] can be
	achieved by adding either reducing agents or formic acid into the [Cu28H15] + cluster and the
	addition of Cu(I) ion to [Cu27H15], respectively.
	RESULTS AND DISCUSSION
	Synthesis
	In a typical one-pot synthesis, the new [Cu27H15] cluster was prepared with a modest yield
	of 25.54% from the reaction mixture of [Cu{CH3CN}4](PF6), dithiocarbamate ligands and LiBH4
	under N2. The reaction mixture was allowed to stir at -20 o C for 4 hours, and in the last stage, a
	small amount of MeOH was added to enhance the reactivity of [BH4] -. Alternatively, the [Cu27H15]
	cluster can be obtained from the manipulation of [Cu28H15] + . This can be achieved with two
	strategies, firstly the addition [BH4] -in a 1:10 ratio to [Cu28H15] + (16.55% yield). Secondly, the
	addition of five equivalents of formic acid to [Cu28H15] + results in [Cu27H15]. Importantly, the
	transformation is reversible and the addition of one equiv. of copper(I) salt to [Cu27H15] yields
	back [Cu28H15] + . The [Cu27H15] cluster appeared to undergo uncharacterized degradation processes
	in solution to form the [Cu28H15] + cluster. Its corresponding deuterated derivative
	[Cu27D15{S2CN n Bu2}12] (abbreviated as [Cu27D15]) was synthesized to further support the presence
	of fifteen hydride ligands confirmed through various spectroscopic studies.
	Mass spectroscopy
	To identify the molecular formula and the charge-state nature of [Cu27H15], its composition
	was obtained by analyzing its positive-ion ESI-MS spectrum. The spectrum shows an intense peak
	at m/z 4248.21, which corresponds to [Cu27H15{S2CN n Bu2}12+Cu + ] + (calc. 4247.18). Its simulated
	isotopic pattern matches well with the experimental observation (Figure 1: inset A). A close
	inspection of the main peak reveals a characteristic isotopic pattern, where adjacent peaks have a
	half-unit spacing (Figure 1, inset A), indicating a cluster charge of +2 dimer species. The

). These copper hydrides are good models of hydrogen storage materials as they evolve H2 gas upon reacting with acid or under sunlight irradiation. Herein, we isolate a new, intricate core-shell structure, a sibling of [Cu28H15] + .

Table 1 .

 1 composition that was identified by mass spectrometry. Calculations were run on the [Cu56H30{S2CNH2}24] 2+ simplified model. Because of convergence problems with the Gaussian program, we switched to the ADF2020 program with calculations at the BP86/TZP level (see Computational Details). Two types of structures were tested, one with two [Cu27H15] clusters linked by two Cu + bridges and the other one consisting of a [Cu27H15] and a [Cu28H15] +units connected via one Cu + bridge. Three different optimized geometries were found, of which the two less stable are of the first type (FigureS15). The most stable one is of the second type. In this lowest energy structure, the Cu + bridge is tetrahedrally bonded to two sulfurs of each unit. In addition, a direct Cu-S bond is formed between the two clusters. Of course, we cannot pretend that this optimized structure corresponds to the dimer of [Cu27H15{S2CN n Bu2}12+ Cu + ] + identified in the ESI-MS experiments, but our results indicate that such dimeric structures can exist. It is of note that the existence of a dimeric species of [Au25(PET)18] -, can be also observed in the mass spectrometry experiments,[START_REF] Baksi | Au25(SR)18] 2-: a noble metal cluster dimer in the gas phase[END_REF] which could be attributed to the formation of transient cluster aggregates in the gas phase. Selected DFT-computed data (averaged values) for the [Cu27H15] NC model. X-ray averaged values are provided for comparison. All distances in Å. WBI = Wiberg bond index.

	Interatomic distances	DFT [WBI]	X-ray	Natural atomic charges
	1 x Cu-(µ3-H)	1.651 [0.117]	-	Cucore	0.41
	8 x Cu-(µ3-H)	1.686 [0.162]	-	CuRhom	0.66
	6 x Cu-(µ5-H)	1.890 [0.075]	-	1 x (µ3-H), Hcent	-0.71
	Cucore-Cucore	2.578 [0.044]	2.548(5)	8 x (µ3-H), Htri	-0.66
	Cucore-CuRhom	2.621 [0.062]	2.531(4)	6 x (µ5-H), Hsp	-0.54
	CuRhom-CuRhom	2.629 [0.046]	2.6208(17)
	Cu-S	2.399 [0.151]	2.370(3)
	CONCLUSION
	In summary, a neutral copper(I) polyhydrido cluster, [Cu27H15{S2CN n Bu2}12], has been
	prepared and characterized by single-crystal X-ray diffraction, multi-nuclear NMR spectroscopy,
	ESI mass spectroscopy, and DFT calculation. The metal framework reveals a distorted Cu24
	rhombicuboctahedral shell with an encapsulated Cu3 triangular core in its center, stabilized by
	twelve dtc ligands. Both [Cu27H15] and [Cu28H15] + have a similar Cu24 shell and the same ligand
	binding motif but with different inner cores. The former cluster can be produced by adding
	reducing agents and formic acid into the parent [Cu28H15] + cluster. The reaction of [Cu27H15] and
	Cu + salt re-generating [Cu28H15] + establishes a reversible reaction. These results indicate that the
	metal addition/subtraction process has occurred through the metal exchange between the outer
	Cu24 shell and the inner core so that an unusual core engineering of copper hydride clusters has

  were prepared by following the procedure reported in the literature. NMR spectra were recorded on Bruker Avance DPX 300 MHz and Avance II 400 MHz NMR spectrometers that operates at 300 and 400 MHz while recording 1 H and 46.1 MHz for .12 (bs, 1H, μ3-H), 3.92 (bs, 6H, μ5-H), 4.06 (t, 48H, CH2CH2CH2CH3). UV-vis [λmax in nm, (ε in M -1 cm -1 )]: 295 (26000), 356 (15600).

	Synthesis of [Cu27H15{S2CN n Bu2}12], [Cu27H15]. In a flame-dried Schlenk tube, NaBH4 (0.085 g,
	0.8 mmol) was suspended in CH3CN (10 mL) along with K(S2CN n Bu2) (0.170 g, 0.27 mmol) and
	the addition THF (20 mL). The reaction mixture was stirred for 15 minutes at -20 o C and followed
	by the addition of [Cu(CH3CN)4](PF6) (0.5 g, 0.54 mmol). The resulting mixture continued stirring
	for 4 hours. The colour of the mixture gradually changed to the orange solution. The solvent was
	evaporated under a vacuum, and the residue was dissolved in ether and washed with water (3x15
	mL). After separating the organic layer, it was filtered and dried under a vacuum. Further, the
	obtained orange residue was washed with methanol and hexane to remove the byproducts
	[Cu8H{S2CN n Bu2}6](PF6) and [Cu7H{S2CN n Bu2}6]. The remaining residue dissolved in ether and
	passed through Al2O3. Finally, the solvent was evaporated to dryness under vacuum to get a pure
	orange powder of [Cu27H15{S2CN n Bu2}12].
	Yield: 0.053 g (25.54%, based on Cu). ESI-MS: m/z 4248.2140 (calc. m/z 4247.1853) for
	[Cu27H15{S2CN

2 H. Residual solvents proton have used references (δ, CDCl3, 7.26) and (δ, d6-acetone, 2.10). ESImass spectrum recorded on a Fison Quattro Bio-Q (Fisons Instruments, V.G. Biotech, U. K.). UVvisible absorption spectra were measured on a Perkin Elmer Lambda 750 spectrophotometer using quartz cells with a path length of 1 cm. n Bu2}12 + Cu + ] + . 1 H NMR (300 MHz, d6-acetone, δ, ppm): -0.57 (bs, 8H, μ3-H), 0.93 (t, 72H, CH2CH2CH2CH3), 1.35 (m, 48H, CH2CH2CH2CH3), 1.86 (m, 48H, CH2CH2CH2CH3), 3

  incorporated in SHELXTL/PC V6.14.[START_REF] Sheldrick | version 6.14 (PC version) Program Library for Structure Solution and Molecular Graphics[END_REF] All nonhydrogen atoms were refined anisotropically. Hydride atoms (H0, H1M, H2M, H3M, H4M) were located from the residual densities and refined with distance constraints. CCDC no. 2201480 contains the supplementary crystallographic data in this article. These data can be obtained free of

	charge	from	The	Cambridge	Crystallographic	Data	Centre	via	www.

ccdc.cam.ac.uk/data_request/cif.

ACKNOWLEDGMENT

This work was supported by the National Science and Technology Council (111-2123-M-259-002). France-Taiwan ANR-MOST program (project Nanoalloys, ANR-18-CE09-0037-01), and the GENCI French National Computer Resource Center (A0030807367).

Computational Details

The geometry optimizations of the [Cu27H15{S2CN n Bu2}12] model were carried out within the formalism of the density functional theory (DFT) with the Gaussian16 package, [START_REF] Gaussian ; Frisch | [END_REF] using the PBE0 functional [START_REF] Adamo | [END_REF] and the Def2-TZVP basis set from EMSL Basis Set Exchange Library. [39][40] All the optimized geometries were characterized as true minima by vibrational analysis. The natural atomic orbital (NAO) charges and Wiberg bond indices were computed with the NBO 6.0 program. 41 The UV-visible transitions were calculated on the above-mentioned optimized geometries by means of time-dependent DFT (TD-DFT) calculations at the same PBE0/Def2-TZVP level. The UV-visible spectrum was simulated from the computed TD-DFT transitions and their oscillator strengths by using the SWizard program, [START_REF] Gorelsky | SWizard program[END_REF] each transition being associated with a Gaussian function of half-height width equal to 3000 cm -1 . Geometry optimizations of the [Cu56H30{S2CNH2}24] 2+ "dimeric" structures were performed with the ADF2020 package [START_REF] Te Velde | [END_REF] using the BP86 functional [44][45] and the TZP basis set. 46 ASSOCIATED CONTENT Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org. X-ray crystallography, NMR spectroscopy, ESI mass spectrum, and DFT calculations (PDF)

AUTHOR INFORMATION

Corresponding Authors

Jean-Yves Saillard -Univ Rennes, CNRS, F-35000 Rennes, France; orcid.org/0000-0003-4469-7922; E-mail: jeanyves.saillard@univ-rennes1.fr C. W. Liu


Alicia Ayerdi Gotor
email: alicia.ayerdi-gotor@unilasalle.fr

Soukeye Gadiaga

Germination requirements to grow minor pulses in North Europe climates

Introduction

Europe lacks of local vegetal proteins and is highly dependent on imported soybean. The changes on food habits with the vegan diet or just the reduction of meat consumption is increasing the demand on veggie alternatives and if possible local. Additionally since the 50'-60' the production area of pulses has been decreasing, now representing less than 25% (Fig 1, FAOSTAT 2021). Worldwide there is a great diversity on pulses which could be suitable for temperate climate. The objective of this study is to determine the feasibility of production of tropical pulses in temperate climate by a first evaluation of the minimal temperature to germinate as a first step to evaluate the potential sowing date.

Materials and Methods

The germination of 6 minor pulses : Adzuki bean (Vigna angularis), Cowpea (Vigna unguiculata), Mung bean (Vigna radiata), Pigeon Pea (Cajanus cajan), Rice bean (Vigna umbellata), Scarlett Runner bean (Phaseolus coccineus) and chickpea (Cicer arietinum) was evaluated for 7 days in culture chambers at 5 temperatures: 5°C, 10°C, 15°C, 20°C and 25°C. Percentage of germinated seeds was done at 24, 48, 72, 96 and 192h hours after putting the seeds on watered bed. The radicle, hypocotyl and epicotyl lengths were measured in five representative plantlets at 3, 8 and 11 days after water imbibition. Final foliar area and total dry biomass was measured at the end of the experience.

Results

Pulses germination at different temperatures showed that at 5°C and 10°C there were no seed able to germinate of the considered species after 8 days. At 15°C Rice bean, Adzuki bean and Cowpea showed a slow germination capacity whereas it was the most suitable temperature for chickpea. Scarlett runner bean had germination problems more related to seed quality than for temperature problems. We can stablish that for the pulses studied the base temperature for germination is between 10 and 15°C.

The measurements on the growth of plantlets at the 3 positive temperatures showed that at 15°C the growth is really slow the first 11 days for all the species but enough to ensure the installation of the crop in the target climatic areas of the North of France and Benelux where summers are quite cold. Other experimentation undertaken showed that once emerged plantlets can support temperatures under 5°C for short periods of time without damage.

The foliar surface of 100 plantlets the 11 th day varied from 209 cm² for Adzuki at 15°C (Tab. 1) to the foliar surface Scarlett runner bean growing at 25°C reaching 2329 cm². Chicken seed did not support temperatures above 20°C as grains melt after 5 days at this temperature, where the minor pulses supported those temperatures much better.

Conclusions

According to those results, in Northern France it will be possible to sown this pulses the second decade of May as it's already the case for Soybean with an slow growth the first days. Next steps will be to evaluate the growing developing degrees necessary to reach the maturity and determine if in the regions of interest the sum could be cumulated before the rains come back in October.

This research was made thanks to the grant to the project CALEGE funded by the SFR Condorcet 2020 Main hypothesis: -Tropical pulses will germinate with temperatures over 10°C -With a high temperatures the germination will be faster -High temperatures will accelerate the growth of plantlets

Fig 1 .

 1 Fig 1. Evolution of harvested area (ha) in Europe between 1961 ad 2019 (FAOSTAT, 2021)

Tab. 1 .

 1 Foliar and dry biomass of 100 plantlets at the 11 th days of germination of 7 species of pulses Fig 4. Plantlets of 2 species (Top Left: Cowpea 25°C, Top Right: Mung bean 15°; Down Left Cowpea 15°C; Down Right: Mung bean 25°C) at their 8 th day of germination

Foliar surface 100 plantlets (cm²) at 11th day Dry biomass 100 plantlets (g) at 11th day

		15°C	20°C	25°C	15°C	20°C	25°C
	Adzuki bean	209,26	173,00	359,17	0,94	0,48	2,42
	Chickpea	322,00	232,83		3,22	15,20
	Cowpea	358,70	760,42	822,35	4,05	1,49	8,05
	Mung bean	298,53	322,75	319,24	2,01	0,47	2,56
	Pigeon pea		1282,86			11,17
	Rice bean		2329,83			24,50
	Scarlett			2384,83			28,16