domain: chim phys

text:
Maria Maniadi

Nicolas Mercier
email: nicolas.mercier@univ-angers.fr

Alla Skorokhod

Maroua Ben

Haj Salah

Pierre Bidaud

Piétrick Hudhomme

Claudio Quarti
email: claudio.quarti@umons.ac.be

Wei Li

David Beljonne

Jacky Even

Claudine Katan

Constantinos C Stoumpos

Quasi 3D electronic structures of Dion-Jacobson layered perovskites

chemical engineering of the interlayer was one of the motivations leading in 2018 to the discovery of Dion-Jacobson multilayered halide perovskites. 3 The 2D A + (n>1 perovskite prototype is based on B n X 3n+1 perovskite network incorporating small organic cations) separated by either long size monocations (A' + ) or dications (A'' 2+ ). This leads to the following formula: (A') 2 (A) n-1 B n X 3n+1 and (A'')(A) n-1 B n X 3n+1 (<100> series according to the Mitzi's classification), [4][5][6] with n measuring the number of BX 6 octahedra along the thickness of the individual 2D inorganic sheet. The size and conformation of the A' + or A" 2+ spacers directly affect the interlayer distance, which in turn impacts the interlayer transport properties. These are also influenced by the relative shift between adjacent layers (usually measured as fraction of metal-metal distance), with eclipsed (0,0) configuration guaranteeing the most effective overlap between the orbitals of apical iodides, compared to staggered (1/2, 1/2) in plane displacement, for a given interlayer separation. Except a rare case where a A' + monocation can lead to eclipsed situation with quite short I…I distance (4.27 Å in (HO(CH 2 ) 2 NH 3 ) 2 PbI 4 ), 7 the few 2D perovskites exhibiting an eclipsed situation with close I…I contacts (<4.30 Å) are based on short A" 2+ dications. 3,8,9 Such perovskites are classified as DJ (Dion-Jacobson) perovskites. 10 It has been shown that close I…I distances can lead to strong dispersion for both the valence and conduction electronic bands. Moreover, it has been demonstrated that a light-activated interlayer contraction occurs in such perovskites boosting the photovoltaic efficiency of a perovskite solar cells (PSCs) based on a phase pure 2D multi-layered perovskite active layer, from 15 % to 18%. 11 Furthermore, thick (n=3,4) 2D perovskites also feature smaller exciton binding energies and ideal valence band matching with parental 3D compounds, leading to efficient hole extraction in PSCs. 11 Overall, the search for such new layered perovskites with short interlayer separation and that sustain the formation of multi-n compounds is of great interest for technological applications. 1 Thus far, only a few dications have afforded multilayered DJ compounds. The cyclic 4AMP (4-(aminomethyl)piperidinium, Scheme 1) 3 and 4AMPY (4-(aminomethyl)pyridinium) 8 dications have four carbon atoms separating the two ammonium ends and form multi-n (n=1,4) 2D layered perovskites with eclipsed (0, 0) stacking motif and short I…I distance. Notice that four carbon alkylated + H 3 N(CH 2 ) 4 NH 3 + dication was also successfully incorporated into a 2D halide perovskite but only for the thinner n=1 A"PbI 4 structure. 12 The shortest dications stabilizing DJ phases reported to date have three carbon atoms between ammonium ends: 3AMP (3-(aminomethyl)piperidium), 3 3AMPY (3-(aminomethyl)pyridinium) 8 and mPDA (m-phenylenediammonium, 9 Scheme 1). Noteworthy, the linear diammonium dication + H 3 N(CH 2 ) 3 NH 3 + , while leading to a n=1 PbCl 4 perovskite network, does not afford Pb n I 3n+1 network based hybrid compounds. 13 In this context we have designed and synthesized a derivative dication + H 3 NCH 2 CH(I)CH 2 NH 3 + (named DicI 2+ , Scheme 1). The substitution of a hydrogen atom by an iodine atom has several advantages. The iodine atom leads to a bulkier dication than + H 3 N(CH 2 ) 3 NH 3 + , which should allow, as for mPDA or 3AMP, the formation of DJ compounds. In addition, as demonstrated recently by some of us for multilayered perovskites based on the I(CH 2 ) 2 NH 3 + monocation, weak electronic hybridization takes place between the iodine from the organic with those from the inorganic lattice, which enhances the interlayer electronic coupling although the quite long I ap ….I ap distance of 6.1 Å. 14 Herein, we report the synthesis of the 2-iodopropane-1,3-diamonium dication (DicI 2+ ), and the layered perovskites (DicI)(MA) n-1 Pb n I 3n+1 (n= 1-4, MA + = methylammonium), a rare series of DJ perovskites. In fact, due to both a suitable size of DicI 2+ cations and halogen bonding between iodine atoms of DicI 2+ and apical iodides (I (ap) ) of the perovskite layers, a perfect eclipsed situation of adjacent layers takes place, and unprecedent short I (ap) ….I (ap) distances are observed. For these compounds, density functional theory (DFT) calculations anticipate sizeable valence band dispersion along the direction perpendicular to layers, leading to small effective masses for out-of-plane motions of holes, similar to usual in-plane effective masses. Although less pronounced, a similar effect is also predicted for electrons. Hence, this multi-n series of 2D perovskites exhibits a quasi 3D like electronic band structure and these DJ compounds appear as good candidates for PSCs applications, both as active material or in 3D/2D bilayer stacks. Results and Discussion. The synthesis of the 2-iodopropane-1,3-diamonium diodide ((DicI)I 2 ) has been carried out in three steps from the commercial 1,3-aminopropan-2-ol molecule which has been recently incorporated in lead deficient 3D perovskites. 15 The amino groups of 1,3-aminopropan-2-ol are first protected using di-tert-butyl dicarbonate (Boc 2 O) leading to the di-tert-butyl (2-hydroxypropane-1,3diyl)dicarbamate compound as a white solid in quantitative yield (Scheme S1 and Fig. S1, details in SI). The introduction of the mesylate leaving group was then carried out using methane sulphonyl chloride in the presence of triethylamine in 83% yield. The obtained white solid was treated with a HI solution and heated at 75°C over night. Both deprotection of Boc amino protecting groups and nucleophilic substitution of the mesylate group by the iodide anion could occur simultaneously. Finally, the addition of ethyl acetate caused the precipitation of the expected (DicI)I 2 salt which was isolated in 86% yield. The 2-iodopropane-1,3-diammonium dication (DicI 2+ ) was characterized by 1 H and 13 C NMR spectra (Fig S1). The n= 1 compound (DicI)PbI 4 is obtained as red, plate-like crystals from a slow cooling of a HI solution containing the metal precursor (PbI 2 ) and the dication salt (DicI)I 2 in 1/1 ratio (see SI). For both n=2 and n=3 compounds, the reaction was non-stoichiometric using the spacer (DicI 2+ ) as the limiting reagent. In a first vial, the dication salt is dissolved in HI under constant heating (~130 o C) while in a second one, the metal precursor (PbO) is first added in HI giving a clear yellow solution before the slow addition of methyammonium iodide (MAI). Then the content of the first vial was added, the reaction mixture being left under reflux for 10-15 minutes. The solution was left to cool slowly to ambient temperature, using the glass cover to maintain the equilibrium conditions. A day later, scarlet, plate like crystals (n=2) and nearly black, plate like crystals (n=3), were obtained as pure phases (see details in Exp. part) as revealed by X-ray powder diffraction (XRD, Fig. S2) and optical characterizations. Interestingly, the above procedure is an efficient and conveniently used method in order to obtain the 2D perovskite members (n = 2, 3) in their pure phase, which cannot be obtained when the reaction is done using stoichiometric ratio. All the n=1-3 compounds are stable up to 215°C and no thermal accident occurs in the RT-175°C range (see TGA and DSC curves, Fig. S4).

A general view of the crystal structures of the (DicI)(MA) n-1 Pb n I 3n+1 (n = 1-4) compounds is shown in Fig. 1 (see also Fig. S3a). Detailed crystallographic data are provided in the Supporting Information (Tables S1-3). The n=1 and n=2 compounds crystallize in the centrosymmetric space group Cmce and Pbam, respectively, while the n=3 and n= 4 perovskites are described in the non-centrosymmetric space group Aea2 and Pba2, respectively. The short DicI 2+ dication involves an eclipsed configuration of consecutive adjacent layers along the stack axis, as illustrated for the n= 1 compound (Fig. 1, inset). As shown in Fig. 2a, only ammonium heads of dications are localized within the perovskite sheet. This is known to induce a tilt of PbI 6 octahedra leading to out-of-plane distortions. For (DicI)PbI 4 (n= 1), we clearly observe that, if half equatorial iodides are contained in planes defined by Pb atoms, the other half are out of these planes (Fig. 1). The distortions of a perovskite layer can be illustrated by the Pb-I(eq)-Pb bond angles (eq= equatorial). For n= 1, these angles are of 180° along b (Pb and I(eq) in planes) and 143° along c. For the multilayered compounds (n= 2-4), the outer layers as well as the inner layers (n= 3, 4) display similar out-of-plane tilt, the Pb-I (eq) -Pb bond angles being in the 145-180° range with average values of 161.5° (n=1), 158.3° (n= 2), 160.9° (n= 3) and 162.4° (n=4) (see details in Table S3). As regards to Pb-I (ax) -Pb bond angles (ax= axial, see Fig. S3b), they are close to 160° for all n= 2-4 compounds (Table S3). Octahedra belonging to the n= 1 compound and to the inner layers of the n= 3 and n= 4 compounds are quite regular (Pb-I bond distances in the 3.17-3.22 Å (n= 1), 3.10-3.20 Å (n= 3) or 3.14-3.18 Å and 3.13-3.23 Å ranges (n= 4)). In contrast, octahedra of the n= 2 compound as well as those belonging to the outer layers of the n=3 and n= 4 perovskites appear more distorted (Pb-I bond distances in the 3.07-3.27 Å (n= 2), 3.03-3.33 Å and 3.07-3.24 Å (n= 3), 3.04-3.33 Å and 3.05-3.30 Å (n= 4) ranges).

Not only the DicI 2+ dication affords the formation of these (DicI)(MA) n-1 Pb n I 3n+1 multilayered perovskites of DJ type where an eclipsed situation of adjacent layers occurs, but it leads to unprecedented short I (ap) …I (ap) distances. The figure 2a shows the I (ap) …I (ap) and I (ap) ….I (orga) interactions (I (ap) : apical iodide of perovskite layers; I (orga) : iodine of DicI 2+ ) at the organic-inorganic interface of the (DicI)(MA) 2 Pb 3 I 10 compound. Organic halogens are known to be involved in halogen bonding interactions. 16,17 The origin of this electrostatic interaction comes from the anisotropy of the electron density around the organic halogen nucleus, which can be represented by an ellipsoid elongated in the direction across the C-X bonding axis. Thus, a Lewis base (B) such as iodide could interact with the electron-deficient region of X (ideal C-X….B bond angle of 180°), while a Lewis acid (A) could interact with the electron-rich region of X (ideal C-X….A bond angle of 90°). In the structure of DicI 2+ based perovskites, as illustrated in (DicI)(MA) 2 Pb 3 I 10 , the organic iodine atom interacts with two iodides of adjacent layers, the C-I…I (ap) distances being approximately 3.90 Å which is less than twice the van der Waals radius of I (4.0 Å), and the C-I….I (ap) bond angles is 149.4° which deviates from the ideal value of 180°. 2a especially highlights all these weak interactions at the organicinorganic interface. Table 1 lists the shortest I (ap) …I (ap) and I (ap) …I (orga) distances observed in the (DicI)(MA) n-1 Pb n I 3n+1 series as well as shortest I (ap) …I (ap) distances found in some selected DJ perovskites based on short dications: 3AMP, 3 4AMP, 3 mPDA 9 and H 2 BDA. 12 It appears that the I (ap) …I (ap) observed in n= 3 and n= 4 compounds of the (DicI)(MA n)-1 Pb n I 3n+1 series are the shortest one among the set and, to the best of our knowledge, the shortest ever reported. Sizeable electronic communication in the direction perpendicular to layers is thus anticipated (vide infra). Interestingly, both I (ap) …I (ap) and I (ap) ….I (orga) distances decrease with increasing thickness of the perovskite layer, from n=1 to n= 4 (Fig. 2b). For I (ap) …I (ap) , a similar trend has been observed with 3AMP (4.187 Å to 3.999 Å from n= 1 to n= 4), 3 4AMP (4.211 Å to 4.103 Å from n= 1 to n= 4), 3 and mPDA (4.273 Å to 3.988 Å from n= 1 to n= 3). 9 More, the new Dicl-based DJ series is in a favourable situation for the formation of multilayered compounds, thanks to a small negative lattice mismatch with the 3D reference MAPbI 3 structure (see Supporting Information and Fig. S6), which limits the accumulation of strain energy for intermediate n-values. 18 This is in favour of stable higher n-values compositions, especially with methylammonium as perovskitizers, given that MAPbI 3 has no instability towards a thermodynamic d-phase.

In sight of their potential application in photovoltaics, we characterized the optical properties of these compounds, performing diffuse reflectance measurements between 185-1400 nm (UV-vis-NIR spectroscopy) and photoluminescence (PL) spectroscopy (Fig. 3). The diffuse reflectance measurements at room temperature (Fig. 3a) can't resolve the exciton absorption from the bandgap absorption. However, the compounds exhibit steep absorption edges from which the optical band-gap can be set at 2.12 eV, 1.98 eV, 1.76 eV and 1.55 eV, for n=1-3 and MAPbI 3 , respectively, as evaluated from steep absorption onset (see Fig. S5). Consistently, the 3D MAPbI 3 compound exhibits the lowest energy gap (n=∞ layers). The impact of shorter I (ap) …I (ap) distances on optical band gaps in DicI based DJ perovskites compared to other DJ perovskites is difficult to estimate because the distortions of perovskite layers, which are very different in all these materials, have also a strong impact on band gaps. The spectra of n= 1 layered perovskites based on DicI 2+ , 3AMP 2+ , 4AMP 2+ , mPDA 2+ and BA + cations are shown in Fig. 3b. Although a longer apical iodide distance, one compound, (3AMP)PbI 4 (d= 4.187 Å), exhibits a lower energy absorption band than (DicI)PbI 4 (d= 4.033 Å) which can be explained by strong out-of-plane distortions in the latter compared to the former. Photoluminescence properties of specimens obtained from all n compounds, as shown in Fig. 3c, were measured at room temperature using a confocal microscope setup with a steady-state excitation source (532 nm). The photoluminescence emission energy of the series of multilayered perovskites decreases with increasing layer thickness, hence paralleling the trend in absorption. The photoluminescence spectra consist of one single emission peak for each of the compounds corresponding to the absorption spectra. A sharp, weak PL emission was observed for all of the compounds at 550 nm, 593 nm and 630 nm, for n=1, 2 and 3, respectively. This is the signature of efficient energy relaxation processes of charge carriers through the perovskite electronic band structures and down to the emitting edge states. We further investigated the electronic properties of newly reported (DicI)(MA) n-1 Pb n I 3n+1 series, by performing periodic DFT calculations. To this aim, we considered the structural models retrieved from single-crystal XRD analysis (Fig. 1) and performed partial optimization of the organic component. This allows to preserve the structural details for the inorganic lattice evinced from the previous analyses. To ease the comparison of the band dispersion and avoid complications raising from their different Bravais lattices (see Table S1), we described all n=1,4 (DicI)(MA) n-1 Pb n I 3n+1 compounds within a conventional primitive orthorhombic lattice. In addition, we rotated the axes, with the plane stacking direction now matching the c-axis, so that the reciprocal direction associated to the plane stacking corresponds in all cases to ΓàZ. Band dispersion are calculated using the PBE exchange-correlation potential, including Spin-Orbit-Coupling (SOC). This approach is known to underestimate the single-particle band gap of 2D halide perovskites but provides consistent trends for different compounds and effective masses in reasonable agreement with the experiments, and was widely employed in the past (details about the employed software and the computational set-up can be found in the Supporting Information). halide perovskites. Dielectric profiles are shown for the full compounds (red line) and for the composing inorganic PbI 4 frame (black line) and organic spacers (DicI and BA, blue line), as obtained following the composite approach described in Ref. 24 . Horizontal dashed lines are common to the two graphs and to ease the comparison between the dielectric profiles.

Band structure for n=1 (DicI)PbI 4 compound is shown in Figure 4a, compared to that of other two n=1 reference compounds, namely, widely-studied butylammonium (BA + ), 19,21,23 and (3AMP 2+ ). 3 Most notably, while (BA) 2 PbI 4 shows flat dispersion along the Γ®Z direction associated to the plane stacking, both (3AMP)PbI 4 and (DicI)PbI 4 exhibit significant band dispersion, especially in the valence region, indicating effective interlayer communication and anticipating sizeable vertical hole transport. Band dispersion of (DicI)PbI 4 in the Γ®Z direction is very similar to that of (3AMP)PbI 4 halide perovskite, whose n=3 analogue recently demonstrated 18% efficiency performance in pure 2D PSCs. 11 Conduction band is comparably much less dispersed, as was previously explained on the basis of symmetry allowed atomic hybridization. 25 While the valence band maximum features a contribution from the p z orbitals of the apical iodines (p z being the p-orbital polarized along the plane stacking direction), the conduction band minimum features a contribution only from the p xy orbitals of the apical iodines, whose orientation does not allow for an effective mix of the Bloch states of adjacent layers. Band dispersion for n=2-4 compounds are illustrated in Fig. 4b, showing progressive reduction of the band gap with increasing the thickness of the inorganic frame, as due to corresponding reduction of the quantum confinement. 6 One may notice that increase in the inorganic layer thickness is accompanied by a progressive decreases in the valence band maximum and opposite increase in the dispersion in the conduction band minimum. Nevertheless, the comparison of the band dispersion for different compounds should be taken with care. First, because many structural details contribute to determine the band dispersion, as the tilting of the octahedra, the crystal lattice parameters and the number of the inorganic layers per unit cell (band folding for the n=1,3 compounds), the latter even influencing the interpretation of the bands themselves. Furthermore, increased band dispersion with compound thickness should not be straightly associated with enhanced interlayer mobility. It may indeed indicate the case where the electronic conjugation is enhanced within the individual inorganic Pb n I 3n+1 sheet, due to reduced quantum confinement, with interlayer interactions remaining unaffected. Band dispersion within all the first Brillouin zone are reported in the Supporting Information (Fig. S7), with thicker n= 3,4 showing Rashba induced spin-splitting of the bands, consistently with the loss of inversion symmetry. 26 Modelling charge transport in 2D halide perovskites is a very challenging task not achieved yet in the literature, as these materials likely sustain different in-and out-of-plane transport mechanisms in a very anharmonic lattice. Still, effective masses as estimated from the curvature of the frontier levels may serve as a useful descriptor to clarify vertical transport properties in these compounds, as compared to other references from the literature. 14,22,[27][28][29] For (DicI)PbI 4 , we estimated out-of-plane hole/electron effective masses of 0.25/1.54, which are much smaller than those of (BA) 2 PbI 4 and reach values surprisingly close to those reported for in-plane directions. 14,22,29 Noteworthy, a sizeable reduction by a factor of 2 of the hole effective mass is predicted by comparison with (3AMP)PbI 4 (0.25 versus 0.5). (DicI)PbI 4 vertical electron effective masses are close to those of (3AMP)PbI 4 (1.34). These small estimates for the effective masses should be first understood in terms of the short interlayer distance, with the planes passing for the apical iodides separated by 6.7 Å and 3.9 Å for (BA) 2 PbI 4 and (DicI)PbI 4 , respectively. Additionally, the advantageous eclipsed motif characteristic of the DJ prototype also contributes in maximizing the overlap between atomic orbitals. Full list of charge effective masses along the plane stacking direction are reported in the Supporting Information (Table S4).

We also estimated the dielectric function profile of (DicI)PbI 4 compound along the plane stacking direction, together with (BA) 2 PbI 4 compound, taken as reference (Fig. 4c). The procedure for the estimation of the dielectric profile is taken from Ref. 26 and is performed considering three inorganic layers and the spacers requested to preserve charge neutrality (the procedure is detailed in the Supporting Information). Interestingly, the dielectric constant of the central inorganic layer of the (DicI)PbI 4 compound is 0.5 larger than that of (BA) 2 PbI 4 . In addition, also the minima of the profile, associated with the organic spacer, increase from 2.2 to 3.7, overall indicating a reduction of the dielectric contrast. To assess the cause of this difference, we further computed the dielectric profile of the sole inorganic and organic components, as computed separately, and found that the organic profile is very close for the two materials. The reduction of the interlayer distance lies therefore at the origin of the reduced dielectric confinement in (DicI)PbI 4 . This in turn may anticipate some reduction of the exciton binding energy which may ease dissociation of excitons in this compound. On the other hand, one may wonder whether the DicI 2+ spacer does contribute to the small effective mass values. In a previous work by some of us, we showed that iodine atomic states from iodo-ethylammonium spacer are partially involved in the formation of the frontier levels of the inorganic frame and contribute to the reduced out-of-plane effective mass in those 2D compounds. 14 In that case, the iodine-containing spacer acted as mediator in the vertical charge transport, compared to the usual direct hybridization of the Bloch states from the two separated layers. To understand whether DicI 2+ has a similar role, we performed additional DFT simulations by substituting the iodine in the spacer with bromine, chlorine or hydrogen, and computed corresponding Γ®Z dispersion and effective masses. This substitution leads to some changes in the corresponding band structure (see Fig. S8), in particular in the spacing between the VBM and deeper states in the valence, at Γ. The latter may be conceptually associated with the interplanar interactions, as following the band folding due to the presence of two layers per cell. Nevertheless, the impact in terms of hole effective mass, as related to the curvature of the top valence band, is minimal (0.25, 0.24, 0.24 for Br, Cl and H, respectively) hence suggesting the spacer does not play a similar mediating role as the iodo-ethylammonium spacer. 14 This, however, should be considered in line with the exceptionally small effective masses of the DicIbased compounds, stemming from the very short interlayer distance of the present compounds (3.9 Å) compared to that found in iodine-ethylammonium based 2D halide perovskites (6.1 Å).

In other words, in the present case, the electronic coupling between adjacent layers is so effective that the contribution from the organic iodine becomes marginal. To better illustrate this concept, we performed a computational experiment, where we progressively expanded the cell in the plane stacking direction and we increased the interlayer separation (Fig. 5a). This should weaken the direct coupling from adjacent layers, so to make emerge the potential influence of the indirect interaction associated to the halide from the spacer. We hence recomputed the effective hole mass, with the spacer incorporating either a iodine, a bromine or a chlorine, finding indeed that the increase of the interlayer separation leads to heavier effective masses, as expected from less effective overlap of the atomic orbitals (Fig. 5b). Nevertheless, the decrease is faster for the chlorine than for the bromine and from the iodine, paralleling the spatial extension of the outer electronic shell of these atoms, hence highlighting the indirect role played by the halide from the spacer. Total energy differences also suggest that the halide from the spacer has a role in the thermodynamic stabilization of the 2D perovskite frame. Separation of the layers as from Fig. 5a in fact leads to a decrease of the total energy of the system which however depends on the halide from the spacer. In particular, the thermodynamic cost of introducing an interlayer separation of 0.75 Å is larger when with DicI spacer (0.76 eV/chem.u.) than for DicBr (0.73 eV/chem.u./0.75 Å) or a DicCl (0.70 eV/chem.u./0.75 Å).

Conclusion.

In this work, we report on the synthesis of the 2-iodopropane-1,3-diamonium dication (DicI 2+ ) and the synthesis and characterization of a rare series of 2D DJ layered perovskites, (DicI)(MA) n-1 Pb n I 3n+1 (n= 1-4). Due to both a suitable size of DicI 2+ cations and halogen bonding between organic iodine and apical iodides (I (ap) ) of perovskite layers, a perfect eclipsed situation of adjacent layers takes place, and unprecedent short I (ap) …I (ap) distances (<3.90 Å) are observed. The optical band-gap of the pure n= 1-3 compounds have been estimated to 2.12 eV, 1.98 eV and 1.76 eV from diffuse reflectance measurements. DFT calculations highlight significant valence band dispersion along the G®Z direction perpendicular to layers, and effective masses of out-of-plane hole/electron have been estimated at 0.25/1.54 for the prototype compound (DicI)PbI 4 . These values which are similar to usual in-plane effective masses, are much smaller than those of (BA) 2 PbI 4 and, for holes, smaller than those of other DJ perovskites (0.50 for (3AMP)PbI 4 ). This indicates these multilayered compounds feature quasi 3D electronic structure especially for hole transport, hence appearing as very good candidates for 2D materials in perovskite solar cells. The synthesis of the (DicI)I 2 salt from commercial 1,3-aminopropan-2-ol is described on Scheme S1. To a solution of di-tert-butyl dicarbonate (Boc 2 O) (5.2 g, 2.4 eq., 24 mmol) in 60 mL THF was added dropwise a solution of 1,3-aminopropan-2-ol (0.90 g, 1 eq., 10 mmol) in 80 mL of THF / H 2 O (1/1, v/v) mixture . The solution was stirred for 24 hours at room temperature. The solvent was partially concentrated under reduced pressure to remove THF and the residue was extracted with diethyl ether. The organic layer was washed with brine, then dried with anhydrous magnesium sulphate, filtered and concentrated under reduced pressure. Recrystallisation in a mixture of diethyl ether and petroleum ether afforded after filtration the white solid -(6.90 g) of di-tert-butyl (2-hydroxypropane-1,3diyl)dicarbamate in quantitative yield. To a solution of diamino diprotected molecule (0.725 g, 2.5 mmol) in 10 mL of dichloromethane (HPLC purity) was added distilled triethylamine (0.5 mL, 3.75 mmol). The solution is cooled in an ice bath, then methane sulphonyl chloride (0.23 mL, 3 mmol) is added dropwise. After stirring for 24 hours at room temperature under argon atmosphere, 0.5 mL of water was added and the mesylate compound was extracted with dichloromethane. The organic phase was washed with water, then dried with magnesium sulphate, filtered, and concentrated under reduced pressure. Crystallization using a minimum of dichloromethane and petroleum ether afforded after filtration the mesylate compound (0.76 g) in 83% yield. The mesylate compound (1g, 2.7 mmol) was introduced into a 10 mL flask and HI acid was added till it covered the compound. The system was plugged by a septum into which a needle was inserted i to create the isobar. The solution was left to stir overnight at 75℃. , Ethyl acetate was then added to the reaction mixture and left for 2 hours in order to completely precipitate the 2-iodopropane-1,3diammonium diodide [(DicI) 2+ 2I -]salt . The compound was filtered and washed with ethyl acetate. The salt was placed in the oven to dry at 70℃ for 1 hour and isolated (1.06 g) in 86% yield. 1 H and 13 C NMR spectra (Figure S1) were obtained on a 500 MHz Advance III HD spectrometer (500 MHz for 1 H and 125 MHz for 13 C). Chemical shifts were reported in ppm according to tetramethylsilane using the solvent residual signal as an internal reference (CD 3 OD : δ H = 3.31 ppm, δ C = 49.0 ppm).

A-

Synthesis

Coupling constants (J) were given in Hz. Resonance multiplicity was described as dd (doublet of doublets), tt (triplet of triplets). Carbon spectra were acquired with a complete decoupling for the proton.

A2-Synthesis of the layered perovskites (DicI)(MA) n-1 Pb n I 3n+1

PbI 2 (99.9%), PbO (99.9%), hydroiodic acid (57 wt % in H 2 O, distilled, stabilized, 99.95%), and hypo phosphorous acid solution (50 wt % in H 2 O), and MAI (>99.5%) were purchased from Sigma-Aldrich and used as received.

Synthesis of (DicI)PbI 4 (n=1). HI (3mL) and was added to a mixture of PbI 2 (50.0mg, 0.1mmol) and (DicI) 2+ 2I -(50.0mg, 0.1mmol) in a 20mL scintillation vial, resulting in a mild effervescence (CO 2 emission). The resulting mixture was magnetically stirred to 130℃, resulting in a clear yellow solution.

After 30 minutes, stirring was discontinued and the reaction was allowed to cool naturally to ambient temperature. After 30 minutes, red needle-shaped crystals precipitated at the bottom of the vial. The

Scheme 1 .

 1 Scheme 1. The targeted DicI 2+ dication and selected dications that have afforded DJ multilayered perovskites based on three (3AMP, mPDA) or four (4AMP) carbon atoms separating ammonium ends (the linear diammonium cations + H 3 N(CH 2 ) m NH 3 + -m= 3 (C3), 4 (C4)-are drawn for comparison) (the two other cations affording DJ phases, 3AMPY and 4AMPY have conjugated rings compared to 3AMP and 4AMP)

Fig. 1

 1 Fig.1General view of crystals structures of (DicI)(MA) n-1 Pb n I 3n+1 (n= 1-4) along the layers plane. For the n= 1 compound, a partial view along the a axis -perpendicular to layers-of two adjacent layers is also provided as inset revealing their eclipsed stacking and the position of DicI 2+ cations in the interlayer space.

Fig. 2 a

 2 Fig. 2 a) Partial view of the structure of (DicI)(MA) 2 Pb 3 I 10 showing the I (ap) …I (ap) and I (ap) ….I (orga) interactions (I (ap) : apical iodide of perovskite layers; I (orga) : iodine of DicI 2+ ; distances in Å) at the organicinorganic interface : ball and stick (left) and space-filling (I radius of 1.98 Å, right) representations; b) d(I (ap) …I (ap) ) and d(I (ap) ….I (orga) )= f(n) in (DicI)(MA) n-1 Pb n I 3n+1 (n= 1-4).

Fig. 3

 3 Fig. 3 (a) Optical absorption of the (DicI)(MA)n-1PbnI3n+1 perovskites (n = 1, 2, 3) and ¬MAPbI3, obtained from diffuse reflectance measurements converted using the Kubelka-Munk function (α/S = (1 -R)2 /2R). (b) Reflectance spectra of (DicI)PbI4 (n=1) 2D halide perovskite, compared to similar measurements reported in the literature for other n=1 compounds: 3AMP, 4AMP, (Reprinted with Permission from Ref. 3) mPDA (Reprinted with Permission from Ref. 9) and BA (Reprinted with Permission from Ref. 19). Copyright American Chemical Society. (c) Photoluminescence spectra of n=1-3 and ¬MAPbI3 (n = ∞) obtained from a micro-PL setup (lexc =532nm) for 0.4mW laser power and a 1µm laser beam radius.

Fig. 4

 4 Fig. 4 (a) Band dispersion for n=1, (DicI)PbI 4 2D halide perovskite, compared with corresponding band dispersion in reference (3AMP)PbI 4 and (BA) 2 PbI 4 halide perovskite; the highlighted area is associated to the dispersion in the plane stacking direction. (b) Band structure dispersion for n=2-4 (DicI)(MA) n- 1 PbI n I 3n+1 2D halide perovskites. (c) Dielectric profile computed for the (DicI)PbI 4 and (BA) 2 PbI 4 2Dhalide perovskites. Dielectric profiles are shown for the full compounds (red line) and for the composing inorganic PbI 4 frame (black line) and organic spacers (DicI and BA, blue line), as obtained following the composite approach described in Ref.24 . Horizontal dashed lines are common to the two graphs and to ease the comparison between the dielectric profiles.

Fig. 5

 5 Fig. 5 (a) DicIPbI 4 (n=1) models with increased interlayer distances; b) corresponding hole effective masses, with the halide from the cation corresponding to iodine, bromine and chlorine.

A1-Synthesis of 2

 2 Scheme S1. Synthesis of the (DicI)I2 salt from commercial 1,3-aminopropan-2-ol.

1 H

 1 Fig. S1. a) 1 H NMR of 2-iodopropane-1,3-diammonium salt in CD 3 OD and its enlargment b) 13 C NMR of 2-iodopropane-1,3-diammonium salt in CD 3 OD, c) Mass spectrum (MALDI-TOF) of 2iodopropane-1,3-diammonium salt

  resultant precipitate was isolated via suction filtration and cleaned with ethylene acetate. Yield: 46.8mg (51.09%) Synthesis of (DicI)(MA)Pb 2 I 7 (n=2). HI (5mL) and H 3 PO 2 (0.5mL) were added in a 20mL scintillation vial of PbO (334.5mg, 1.5 mmol). After 5 minutes of stirring to 130℃, MAI (159.0mg, 1mmol) was added into the dissolved solution, resulting in a clear yellow solution. In another 20mL scintillation vial (DicI) 2+ 2I -(114.0mg, 0.25mmol) are dissolved in HI (0.5mL) under heating and stirring to 200℃. After, the vial with the (DicI) becomes a clear solution we add its content into the first vial without any significant change in the color of the solution. The resulting mixture was magnetically stirred resulting in a clear yellow solution. We heat the solution at 200℃ until about half of the solvent has evaporated.After 30 minutes, stirring was discontinued and the reaction was allowed to cool naturally to ambient temperature. After 1day, scarlet parallelepiped crystals precipitated at the bottom of the vial. The resultant precipitate was isolated via suction filtration. Yield: 135.8mg (35.35%) Synthesis of (DicI)(MA) 2 Pb 3 I 10 (n=3). HI (4mL) and H 3 PO 2 (0.5mL) were added in a 20mL scintillation vial of PbO (446.0mg, 2mmol). After 5 minutes of stirring to 130℃, MAI (318.0mg, 2mmol) was added into the dissolved solution, resulting in a clear yellow solution. In another 20mL scintillation vial (DicI) 2+ 2I -(45.6mg, 0.1mmol) are dissolved in HI (0.5mL) under heating and stirring to 200℃. After, the vial with the (DicI) becomes a clear solution we add its content into the first vial without any significant change in the color of the solution. The resulting mixture was magnetically stirred resulting in a clear yellow solution. After 30 minutes, stirring was discontinued and the reaction was allowed to cool naturally to ambient temperature. After 1day, dark-red plate-like crystals precipitated at the bottom of the vial. The resultant precipitate was isolated via suction filtration. Yield: 107.5mg (49.8%) Crystals of (DicI)(MA) 3 Pb 4 I 13 (n=4). A process similar to that described for the pure phase of (DicI)(MA) 2 Pb 3 I 10 (n=3) involving different PbO/MAI ratios, as for instance 3 mmol/2 mmol, leads to a mixture of n= 3 and n= 4 crystals. A selection of a n=4 single crystal allowed solving its crystal structure from SCXRD data.

Table 1 .

 1 I (ap) …I (ap) and I (ap) ….I (orga) distances in (DicI)(MA) n-1 Pb n I 3n+1 (n= 1-4) and in selected DJ perovskites.As a result of the short size of DicI 2+ dication as well as C-I….I (ap) interactions, a very short I (ap) …I (ap) distance of 3.882 Å is encountered in (DicI)(MA) 2 Pb 3 I 10 . The space filling representation of the figure

	Dication	Layered perovskite	I(ap)…I(ap)	I(ap)…I(orga)
						distance (Å)	distance (Å)
	DicI	2+				(DicI)PbI4	4.033	3.972
						(Dic)(MA)Pb2I7	3.916	3.910
						(Dic)(MA)2Pb3I10	3.882	3.898
						(Dic)(MA)3Pb4I13	3.880	3.886
	3AMP	2+	(3AMP)(MA)2Pb3I10	4.021	-
	4AMP	2+	(4AMP)(MA)2Pb3I10	4.105	-
	mPDA	2+	(mPDA)(MA)2Pb3I10	3.988	-
	H2BDA	2+	(H2BDA)PbI4	4.285	-

Acknowledgements. The work at ISCR and MOLTECH-Anjou was mainly supported by the Agence Nationale pour la Recherche (MORELESS project). C. K. and J. E. acknowledge funding from the European Union's Horizon 2020 program, through an Innovation Action under Grant Agreement No. 861985 (PeroCUBE). The present research benefited from computational resources made available on Lucia, the Tier-1 supercomputer of the Walloon Region, infrastructure funded by the Walloon Region under the grant agreement n°1910247. W.L. acknowledges financial support of Wallonie-Bruxelles International (WBI) Excellence scholarship. D. B is FNRS research director. C.Q. is FNRS research associate. This work received financial support under the EUR LUMOMAT project and the Investments for the Future program ANR-18-EURE-0012 for P.B. as Master LUMOMAT student. CCS acknowledges support from the Special Account for Research Funding of the University of Crete under grant KA10652.

Notes and references

Author Contributions. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Conflicts of interest.

There are no conflicts to declare

B-X-ray diffraction characterization B1-Powder X-ray Diffraction (PXRD)

The Bruker D8 ADVANCE was used to analyze the powder patterns of the synthesized compounds. It is mounted in the Bragg-Brentano geometry in θ-2θ measurement. The X-rays are formed by a copper anti-cathode of wavelength 1.5406 Å allowing us to obtain a diffractogram of I=f(2θ). The detection angles that measured with this XRD model started from 5⁰ up to 40⁰. The data collected and analyzed using EVA and OriginPro software, respectively. All experimental XRD patterns seem well fit with the calculated ones obtained from single crystal X-ray data meaning that the n=1, n= 2 and n= 3 compounds are obtained as pure phases (Figure S2). Comparing the powder patterns for n = 1-3, we observe that all patterns exhibit peaks in different angles. For the n=1, a small characteristic peak shows up right before 2θ = 10°, corresponding to the (200) plane, while there is an intense double peak right before 2θ = 16°, corresponding to the (020) and (002) planes, respectively. For n=2, some peaks including the first one (right after 2θ = 5°, corresponding to (001) crystallographic plane), are not observed in the experimental pattern due to their low signal to noise ratio. An intense peak shows up right after 2θ = 10°, corresponding to the (002). We also observe an intense double peak right before 2θ = 15°, corresponding to the (020) and (200) planes. For n=3, we observe a characteristic slightly weak diffraction right before 2θ = 10°, and an intense peak right above the same angle, corresponding to the (004) and (113) planes, respectively. A characteristic double peak is observed at the PXRD of n=3 as well, right before 2θ = 15°, corresponding to the (020) and (115) planes, respectively.

B2-Single crystal X-ray Diffraction (SCXRD)

X-ray diffraction data were collected on a Rigaku Oxford Diffraction SuperNova diffractometer equipped with Atlas CCD detector and micro-focus Cu-K α radiation (λ = 1.54184 Å). Data were collected at 293 K. Intensities were corrected for Lorentz-polarization effects, as well as for absorption effect (gaussian method using CrysAlisPro program -CrysAlisPro, Rigaku Oxford Diffraction, V1.171.41.118a, 2021). Crystal structures were solved by charge flipping and refined (full-matrix leastsquares on F 2 ) using the Jana2006 package. CCDC numbers are : 2283257 (n= 1), 2283259 (n= 2),

-a--b-

C-

Thermal and optical characterization C1-Thermal characterization

Thermogravimetric analysis (TGA). A full set of data were adopted via Diamond TGA set up, which was purchased from Perkin Elmer Company. The TGA device consists of an electronic high accuracy weight scale, which is connected with a high temperature oven surrounding the supplement area. Data At temperatures around 400℃, all diagrams display a significant mass loss of PbI 2 . For n=1 (52.27%) this corresponds to ~1 PbI 2 , per formula unit, while for n=2 (51.44%) and n=3 (60.01%), that corresponds to ~2 PbI 2 and ~3 PbI 2 per formula unit, respectively.

Differential Scanning Calorimetry (DSC).

A full set of data were collected via DSC-250 for all n=1-3 compounds. Approximately 2.3 mg of each sample were placed in aluminum pans which were then hermetically closed. They were placed in the calorimeter along with an empty reference pan. The samples were first maintained in a 2 min isothermal state and then heated from 30 ℃ up to 170 ℃ with a rate of 10 ℃/𝑚𝑚𝑚𝑚𝑎𝑎. The samples then maintained in a 2 min isothermal state and then cooled from 170

℃ down to 30 ℃ with a rate of 10 ℃/𝑚𝑚𝑚𝑚𝑎𝑎. The process was repeated twice, with the first cycle discarded as it was performed only to erase the samples thermal history.

The DSC diagrams for the 3 compounds are provided Figure S4. No endothermic nor exothermic peaks were observed in the 30℃-170℃ range meaning in particular that no phase transition takes place in the studied temperature range. Photoluminescence Spectroscopy (PL). Photoluminescence spectra were collected on oriented crystals of the (Dic)(MA) n-1 Pb n I 3n+1 perovskites (n = 1-3) using Horiba LabRam Evolution high resolution confocal Raman microscope spectrometer (600 g/mm diffraction grating) equipped with a diode CW laser (532 nm, 35 mW) and a Synapse CCD camera. The incident laser beam was parallel to the (010) direction of the crystals and focused at ∼1 μm spot size. Unless stated otherwise, the maximum power output of the laser source was filtered to 0.01% of the maximum power output.

D-Theoretical analyses and simulations

Lattice mismatch analysis. In the framework of the lattice mismatch model for multilayered 2D perovskites 5 , the possible accumulation of strain within the perovskite lattice for intermediate n values is evaluated from the relative difference between the in-plane lattice parameters of the n=1 compound of the series and the lattice parameter of the 3D perovskite reference (here MAPbI 3 ). The evolution of the in-plane lattice parameter as a function of n, is characteristic of the strain relaxation in the lattice.

Very large mismatches prevent systems from forming materials with high n values, as the accumulation of strain energy scales as the square of the lattice mismatch 5 . This situation is encountered in the PEA series, which exhibits a larger (negative) mismatch than the BA series (Figure S6). We may notice that the DJ 3AMP series presents a positive mismatch on the same order as the one of the BA series, leading also to the observation of multilayered compounds up to n=4. The new Dicl-based DJ series reported in the present work is in a favorable situation, with a limited negative lattice mismatch, explaining the possible formation of multilayered compounds up to n=4. Band structure calculations. Periodic DFT calculations have been performed within the planewave/pseudopotential formalism, as implemented in the Quantum-Espresso suite 9,10 . As reported in the main text, these are based on standard GGA method for the description of the exchange and correlation potential, as proposed by Perdue et al., 11 and performed within the non-collinear spin description, with inclusion of spin-orbit-coupling. Energy cutoff for the planewave expansion of the single particle states and electronic density was set to 25 Ry and 200 Ry, respectively, along with ultrasoft pseudopotentials 12 . The present computational set-up was shown to provide good trade-off between accuracy and computational cost 13 . Periodic models from single-crystal XRD were used as reference for calculations. Van der Waals interactions were included using the DFT-D2 method 14 , for the optimization of the atomic positions of the organic component. Due to similar in-plane lattice parameters for the various, we used same 3x3 automatic sampling of the Brillouin zone 15 , for the reciprocal directions associated to the inorganic plane. Out of plane sampling instead reflected the length of the direct lattice parameter associated with the plane-stacking (final samplings corresponding to 3x3x2, for n=1,2,4 and n=3x3x1 for n=3).

Dielectric profile calculations. Dielectric profiles were calculated following the procedure in Ref. 16 .

It consists in performing electronic structure calculations of periodic slabs of 2D halide perovskites and evaluating the variation of the electronic density following application of electric field (0.01 V/Å) along the plane stacking direction. Periodic DFT calculations are performed using atomic-centered, periodic DFT calculations, as implemented in the SIESTA code 17 . Core electrons are described with Troullier-Martins pseudopotentials 18 , while the valence wavefunction is developed over a double-zeta polarized basis set of finite-range numerical pseudoatomic orbitals. All compounds discussed within primitive orthorhombic frame, with plane stacking axis oriented along z. This ease the comparison between different compounds. The highlighted region is associated to interlayer band dispersion. Table S4. Effective masses along the plane stacking direction for 2D A m MA n Pb n I 3n+1 halide perovskites containing different spacers (BA, m=2 -3AMP, m=1 -DicI, m=1). For DicI spacer, we consider hypothetical compounds where the iodine from the spacer is substituted by a hydrogen, a chlorine and a iodine


Alfred Lemierre
email: alfred.lemierre@outlook.com

Damien Gendry
email: damien.gendry@univ-14rennes.fr

Marie-Margaux Poirier
email: mariemargaux.poirier@orange.fr

Valentin Gillet
email: valentin.gillet.37@gmail.com

Romain Vullo
email: romain.vullo@univ-rennes.fr

Hans-Dieter Sues

The oldest articulated ranid from Europe: A Pelophylax specimen from the earliest Oligocene of Chartres-de -Bretagne (NW France) 4 5

Ranids represent an important part of the extant anuran diversity of Europe.

28

One of the best-known genera is Pelophylax (green-water frog). This genus is considered to 29 have arrived in Europe during the Eocene/Oligocene transition, with numerous occurrences of 30 the genus throughout European Oligocene sites. Unfortunately, most of the specimens are 31 isolated bones, hampering our understanding of the diversity and evolution of the genus during 32 this time. We here present the description of an incomplete but articulated anuran skeleton 33 from the earliest Oligocene of Chartres-de-Bretagne (Western France). This specimen, missing 34 its head, preserves almost all postcranial bones articulated and skin impressions. The 35 osteological description allows to assign this specimen to Pelophylax kl. esculentus, making it 36 one of the oldest known occurrences of the genus. We also suggest that specimens assigned to 37 the late Oligocene "Rana" aquensis should be referred to the genus Pelophylax. The presence 38 of a Pelophylax in Western Europe during the early Oligocene indicates that the genus had 39 already spread throughout Europe, no later than 5 Ma after its emergence in the eastern part of 40 the continent. It suggests that Pelophylax benefitted from the extinction of ranoids during the 41 "Grande Coupure.

Soft Tissues 174

The soft tissues surround most of the bones, except for the skull and part of the 175 tibiofibula on both M1 and M2 (Fig. 2A,C). Although it is not well defined in most region, the preservation around the hands, femora, and cloacal region allows interpretation of this feature out, with only faint traces of centra and transverse processes preserved. Where bone is still 194 present, the vertebrae are exposed in dorsal view, but the neural region has been crushed or 195 eroded on all vertebrae, leaving the centrum exposed (Fig. 4). Presacral and sacral vertebrae 196 are only preserved on M1. A single sacral vertebra is identified, while five presacral vertebrae 197 are preserved. The atlas, second and third vertebrae are not preserved, due to a missing piece 198 on M1 (Fig. 2A). IGR 144547 likely possessed eight presacral vertebrae.

199 Vertebra IV-The centrum and transverse processes of the fourth vertebra are 200 preserved as crushed bone in dorsal view. The centrum is broken anteriorly. It connects 201 posteriorly with the fifth vertebra and on its right lateral side with the sternum (Fig. 4A,B). 254 expect near the glenoid fossa. The pars acromialis is wide (3.3 mm), and part of this processus 255 is preserved as bone exposed in dorsal view in the glenoid region (see Fig. 5B). The glenoid 256 region is poorly preserved, with undefined crushed bony elements visible (Fig. 5B). As the 257 specimen is exposed dorsally, it suggests that most of the bony elements form the base of the 258 pars glenoidalis, distinct from the crushed pars acromialis (Fig. 5B). Thus, it is not possible to 259 assess the size of the pars glenoidalis and if the latter and the pars acromialis were separated by 5B). It slightly extends anteriorly, but does not seem to form an anterior hook (as seen in 277 Thaumastosaurus; Laloy et al., 2013;Lemierre et al., 2021).

278

Both coracoids were likely in contact medially when accounting for the connecting 279 cartilage of the coracoids (Ecker, 1889). This is characteristic of the firmsternal condition for 280 the pectoral girdle (sensu Cope, 1864;Boulenger, 1886).

281

Sternum-The sternum is preserved as a crushed bone (exposed in dorsal view) within 282 the space left by the vertebral column on M1 (Fig. 5B). The reconstruction shows that the bone 283 is fully ossified (Fig. 5C). The bone is elongated anteroposteriorly (4.5 mm) and hourglass-284 shaped. Both anterior and posterior regions are wider than the shaft and the anterior region is 285 wider than the posterior.

286

Omosternum?-A small, poorly preserved element is preserved anterior to the 287 preserved medial region of the right clavicle on M1. It is very small (2.24 mm length) and 288 crescentic (Fig. 5A,B). It likely represents around half of a bony element. A putative 289 reconstruction indicates the element had an inverted Y-shape (Fig. 5C). The posterior end 290 seems connected to the extremitas medialis of the clavicle. The remaining part of the bone is a 291 slender stylet (Fig. 5B). The position and shape of this element is incompatible with a vertebral 292 element. Thus, we tentatively interpreted this element as an incomplete omosternum. As for the 293 non-overlapping coracoids, the presence of an ossified omosternum is diagnostic for a 294 firmsternal pectoral girdle (sensu Boulanger, 1886). and shaft of the ilia as flattened bones, exposed in medial view (Fig. 2A). Both distal ends are 299 in contact with the posterior region of the sacral apophyses. The acetabular region is only 300 preserved as an imprint exposed in lateral view of the left ilium on M1 (Fig. 2A). On M2, the 301 left ilium is preserved in its acetabular region with most of the bone intact and exposed in 302 lateral view (Fig. 2B,6B). The right ilium has been broken in two. Its distal region on M1 is it could have been the result of damage during the splitting of M1 and M2 by the collector. The 305 acetabular region is displaced and covers part of the right femur and the dorsal acetabular 306 expansion of the right ilium on M2 (Fig. 2C). This part of the right ilium is preserved as a bone 307 exposed in medial view. The distal region of both ilia is preserved on M2 as imprints exposed 308 in medial view. The ilium is around 19.5 mm long. It is slightly longer than the urostyle. The 309 iliac shaft is slightly compressed laterally. The shaft bears a high dorsal crest (same height as 310 the iliac shaft) on its whole length (Fig. 2A), as seen on M1. The dorsal protuberance ('tuber 311 superior' in Bailon, 1999) is a large pyriform structure protruding laterally posterior to the 312 dorsal crest (Fig. 6B,C). The supracetabular fossa is well-developed (Fig. 6B,C). The dorsal 313 acetabular expansion is not fully preserved but seems short and oriented posteriorly (Fig. 6C).

314

The ventral acetabular expansion has a large ventral vector (Fig; 6B,C). Its preacetabular angle 315 is clearly acute (Fig. 6C). In medial view, there is no interiliac tubercle. ,7D). The proximal region of the left humerus is preserved mostly as 323 crushed bone (exposed in dorsal view) but its outline is difficult to determine (Fig. 7A,B). No 324 crista ventralis is preserved. If present, the crista did not extend past the mid-diaphysis (region 325 preserved as a ventral imprint; Fig. 7C). The distal region of the right humerus is preserved as 326 an imprint exposed ventrally. The fossa cubitalis is shallow and slightly triangular shaped (Fig.

327

7C, D). The fossa does not extend on the diaphysis. The eminentia capitata (humeral ball in transversely (Fig. 8B). It articulates with the ulnare part of the articular surface of the 357 radioulna, the radiale, and the distal ulnare (Fig. 8B). Three distinct articular facets are present 358 on the ulnare. The posteromedial region of this element is slight protruding towards the radiale 359 (Fig. 8B). This protrusion is interpreted as the fused intermedium (following Fabrezi and 360 Alberch, 1996).

361

The radiale is the largest (both in width and length) of the proximal carpals. Its shape is 362 difficult to discern but seems circular (Fig. 8). It articulates with the radial part of the articular 363 surface of the radioulna, the ulnare, the distal radial element, and the distal carpalia III and IV 364 (Fig. 8B). All four articular facets are concave (Fig. 8B).

365

The distal radial element is free. It articulates with the radiale, the distal carpale II, and 366 the prepollex (Fig. 8B). The distal radial element is crescent-shaped, and its lateral margin is 367 concave (Fig. 8B). Its proximal margin seems close to the radial (Fig. 8B). This is likely an 368 artefact of preservation, as this region is difficult to visualize (Fig. 8A).

369

The distal row has three bones preserved: the distal carpal element (fused distal carpalia 370 III, IV and ulnare element), the distal carpal II, and the prepollex (Fig. 8A). Distal carpalia III,

371

IV and ulnare element (distal carpale V of Fabrezi & Alberch, 1996) are all fused into a single 372 large bone (Fig. 8B). It contacts the ulnare, radiale, metacarpals III-V and the distal carpale II 373 (Fig. 8B). The anterior margin bears two distinct articular surfaces for the ulnare and radiale 374 (Fig. 8B). There is no indication that distinct articular facets are present on the posterior margin 375 (Fig. 8B). The bone is crescentic, with a convex posterior margin (Fig. 8B).

376

Distal carpale II is a small circular element (Fig. 8B). It contacts the distal radial 377 element, the prepollex, the distal carpal element, and the metacarpal II (Fig. 8B).

378

The prepollex is barely evident. Most, if not all, neobatrachians possess a prepollex 379 composed of two distinct bones (Fabrezi & Barg, 2001). Unfortunately, only a single imprint is 380 visible on the left hand of IGR 144547 (Fig. 8A). On its right hand this region is not preserved 381 (Fig. 2B). As the two bones of the prepollex are often in contact (see Roček et al., 2022:fig. 382 2L) it is possible that they left a single imprint. The prepollex is small and triangular (Fig. 8B).

383

It contacts the distal radial element, the distal carpale II, and the metacarpal II (Fig. 8B). are poorly preserved and poorly defined (Fig. 2A). Metacarpal II contacts the distal carpale II, 387 and prepollex proximally and the phalanx I of II distally (Fig. 8B). It is one of the longest 388 metacarpals (4,7 mm). Its proximal head is wider than its distal head. Both proximal and distal 389 articular facet seems flat and straight (Fig. 8B). The bone is elongated, with a rather narrow 390 diaphysis (Fig. 8B). Metacarpal III is shorter (4.5 mm) than metacarpal II. It contacts the distal 391 carpale III proximally and the phalanx I of digit III distally. It is preserved with bone, with both 392 proximal and distal heads are broken, while the diaphysis seems complete (Fig. 8A). As for 393 metacarpal II, the diaphysis is elongated and narrow. The proximal head is wider than the distal 394 head (Fig. 8B). The proximal and distal articular facets are flat and straight (Fig. 8B).

395

Metacarpal IV is as long as metacarpal III (4.5 mm). It contacts the distal carpale IV 396 proximally and the phalanx I of digit IV distally. As for metacarpal III, its distal and proximal 397 heads are broken, and most of the diaphysis is broken as well (Fig. 8A). The proximal end 398 bears a flat articular surface (Fig. 8B). The distal head is too damaged to assess the shape of its 399 articular facet (Fig. 8B).

400

Metacarpal V is as long as metacarpal II (4.8 mm). It contacts the distal ulnare element 401 proximally and the phalanx I of digit V distally. It is complete (Fig. 8B) . Its proximal head is 402 wider than its distal head. The articular facet of the proximal head is concave (Fig. 8B). The 403 articular facet of the distal head is flat.

404

Phalanges-Phalanges are only preserved on the left hand, on both M1 and M2.

405

Phalanx I is preserved on all digits (Fig. 8A). It is preserved as an imprint on digits II and V, 406 and as a complete bone on digits III and IV. On digits II and IV, the phalanx is elongate (3.3 408 IV, the preservation shows that the proximal head is wider than its distal head (Fig. 8B). Both 409 articular facets are flat. On digits III and V, phalanx I is shorter (2.8 and 2.4 mm), and the 410 proximal and distal heads are of the same width (Fig. 8B).

411

Phalanx II is also preserved on all digits. It is preserved as an imprint on digits II and V, 412 and as a complete bone on digits III and IV. For digits II and III, it is the terminal phalanx. It is 413 very short (1.5 mm). The phalanx narrows distally, before ending into a knob (Fig. 8B). On 414 digits IV and V, the phalanx II is connected distally to the phalanx III (Fig. 9B). It is shorter 415 than the phalanx I (2.6 and 2.2 respectively mm). Both proximal and distal heads are not 416 distinct from the diaphysis.

417

Phalanx III is preserved on digit IV only as an imprint (Fig. 8A). It is the terminal 418 phalanx for digits IV and V (missing on IGR 144547). It is identical to the terminal phalanx of 419 digits II and III. It is short (1.5 mm) and bears a knob on its distal end (Fig. 8B). head of the femur is badly preserved and mostly crushed near the acetabulum (Fig. 9B). No 426 crest nor flange is visible on its lateral and medial margines (Fig. 9B). The femur is slightly 427 sigmoid (S-shaped). No crest is visible on the femur shaft.

428 Tibiofibulae-Only the left tibiofibula is incompletely preserved on both M1 and M2.

429

The proximal region is preserved as an uncrushed bone, while the diaphysis is mostly 430 preserved as an imprint (exposed in ventral view). The distal region is not preserved (Fig. 9A, 431 B). The proximal head bears a shallow groove mid-width. This groove marks the separation 432 between the fused tibia and fibula (Fig. 9A,B). The tibiofibula is long (14 mm in length) and 433 straight. Slightly more than half of the tibiofibula appears to be preserved. Thus, the complete 434 tibiofibula is probably slightly longer than the femur. (Frost et al., 2006). Within Ranoidea, only natatanuran taxa are known in 442 Europe in the Cenozoic (Roček, 2013). Furthermore, an ossified omosternum, if present, is 443 considered a natatanuran synapomorphy (Frost et al., 2006;Lemierre et al., 2021). Within this 444 clade, only Ranidae are known in Europe from the Oligocene (Sanchíz, 1998;Roček, 2013;445 Rage, 2016;Vasilyan, 2018). IGR144547 is similar to Ranidae in the following features: 446 slender rod-like sacral apophyses, the eminentia capitata of the humerus is not shifted from the 447 central axis of the humeral diaphysis and there is no crest on the femur. European ranid and their Cenozoic counterpart are sometimes hard to find (Sanchíz, 1998). In 456 addition, most of the European Pelophylax are grouped into the Pelophylax kl. esculentus, as 457 hybridization is possible between species included into this complex (Lymberakis et al., 2007), 458 and few (if any) osteological differences exists (Crochet et al., 1995). Thus, most of the taxa suggests a rapid dispersal of Pelophylax throughout western Europe during the Oligocene. This 538 opportunistic frog genus likely benefited from unoccupied ecological niches and the decrease 539 in anuran diversity following the "Grande Coupure". 182x190mm (300 x 300 DPI)

  are only preserved on M1. The clavicle articulates with the 262 scapula and humerus (forming a part of the glenoid fossa). The right clavicle is partially 263 preserved as an imprint (exposed in ventral view; Fig. 5A), while the left clavicle is not 264 preserved. The extremitas medialis is not preserved. Thus, it is not possible to assess if the 265 latter articulated with the medial margin of the coracoid. The clavicle is slender and moderately 266 developed (5.89 mm preserved). Its shaft slightly arched. The glenoid region is partially 267 obscured by fragments of unidentified bone (Fig. 5A, B). 268 Coracoids-Both coracoids are preserved on M1 as imprints exposed in ventral view 269 (Fig. 2A). The right coracoid is almost complete. It forms part of the glenoid fossa laterally, 270 thus articulating with the clavicle and humerus. It also articulates medially with the left 271 coracoid. The coracoid is shorter (6.64 mm) than the scapula. The processus glenoidalis widens 272 laterally. It bears two distinct articular facets on its proximal surface. The anterior facet 273 articulates with the clavicle and the posterior facet received the humerus. The shaft is elongated 274 transversely and narrow. The processus epicoracoidalis is anteroposteriorly elongated. It is the 275 widest region of the coracoid (5.3 mm). The processus is flat and bears a convex medial margin 276 (Fig.

  ilia are preserved on M1 and M2. M1 preserves most of the distal region

  298

  humeri are preserved only on M1. The proximal regions of both humeri 319 are preserved as both crushed bone and imprint, while the remaining of the diaphysis and distal 320 region is preserved only as an imprint exposed in ventral view. The right humerus is around 11 321 mm long. The proximal head of the right humerus is hard to identify, as the glenoid region is 322 poorly preserved (Figs. 5

  femora are preserved on M1 and M2. The left femur is incomplete on 423 M2. Both femora are preserved as a well-delimited imprints (exposed in ventral view) with 424 remnants of bone (Figs. 2A, C; 11A). Femora are long (22.1 mm) and slender. The proximal 425

  European Anurans-The presence of a bicondylar sacro-440 urostylar articulation, a firmsternal pectoral girdle and a diplasiocoelous vertebral column are 441 diagnostic for ranoid

448

  Cenozoic and extant ranids from Western Europe have been only referred to two 449 genera, Rana and Pelophylax(Duellman & Trueb, 1994; Sanchíz, 1998; Roček, 2013; Rage, 450 2016). During the twentieth and early twenty-first centuries, most authors considered the two 451 genera synonymous (with Pelophylax sometimes considered a subgenus of Rana; Frost et al., 452 2006). In consequence, almost all known Cenozoic ranid from Europe were described as 453 "Rana" (Sanchíz, 1998), regardless of their affinity towards the green water frogs (Pelophylax 454 spp.) or brown water frogs (Rana spp.). In addition, osteological differences between extant 455

FIGURE 1 . 718 FIGURE 2 .

 17182 FIGURE CAPTIONS

FIGURE 4 .

 4 FIGURE 4. Vertebral elements of IGR 144547. A, close-up on the vertebral region of IGR

Gómez & Turazzini, 2021) is wide and large (Fig.7C, D). This structure is partially preserved

Metacarpals-Metacarpals II-V are all preserved on both hands on M1 (Fig.2A, C).

ACKNOWLEDGEMENTS 542 543

We wanted to thank O. Béthoux (CR2P, MNHN) for the access and loan of the portable

Society of Vertebrate Paleontology Journal of Vertebrate Paleontology: For Review Only Society of Vertebrate Paleontology Journal of Vertebrate Paleontology: For Review Only Society of Vertebrate Paleontology Journal of Vertebrate Paleontology: For Review Only Society of Vertebrate Paleontology Journal of Vertebrate Paleontology: For Review Only Society of Vertebrate Paleontology Journal of Vertebrate Paleontology: For Review Only Society of Vertebrate Paleontology Journal of Vertebrate Paleontology: For Review Only Society of Vertebrate Paleontology Journal of Vertebrate Paleontology: For Review Only Society of Vertebrate Paleontology Journal of Vertebrate Paleontology: For Review Only Society of Vertebrate Paleontology Journal of Vertebrate Paleontology: For Review Only Society of Vertebrate Paleontology Journal of Vertebrate Paleontology: For Review Only Society of Vertebrate Paleontology Journal of Vertebrate Paleontology: For Review Only Society of Vertebrate Paleontology Journal of Vertebrate Paleontology: For Review Only Society of Vertebrate Paleontology Journal of Vertebrate Paleontology: For Review Only Society of Vertebrate Paleontology Journal of Vertebrate Paleontology: For Review Only Society of Vertebrate Paleontology Journal of Vertebrate Paleontology: For Review Only Society of Vertebrate Paleontology Journal of Vertebrate Paleontology: For Review Only Society of Vertebrate Paleontology Journal of Vertebrate Paleontology: For Review Only

light dome and formation on the use of the RTI softwares, V. Buffa (CR2P, MNHN) for the 545 formation on the use of the light dome, D. Germain (CR2P, MNHN) for access to the MNHN 546 specimens of Pelophylax aquensis. We also thank H.-D. Sues for his editorial work and two 547 anonymous reviewers for their constructive reviews of the manuscript.