Noncovalent Chalcogen Bonds and Disulfide Conformational Change in the Cystamine-Based Hybrid II Perovskite [H3N(CH2)2SS(CH2)2NH3]Pb I4

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DOI:10.1002/ejic.201301017

Nicolas Louvain,*[a][‡] Gilles Frison,[b] Jens Dittmer,[c] Christophe Legein,[c] and Nicolas Mercier*[a]

Keywords: Halogenometallates / Perovskite phases / Noncovalent interactions / Chalcogens

The cystamine-based hybrid perovskite, α-[NH3(CH2)2S–S- scopic measurements show a significant broadening of the (CH2)2NH3]PbI4 (1a), can be transformed into its polymorph, NMR spectroscopic line associated with two disordered car- β-[NH3(CH2)2S–S(CH2)2NH3]PbI4 (1b), by heat activation (T bon atoms when cooling 1b from 160 to 50 °C, thereby re- = 150 °C). The crystal structures have been characterised by vealing the presence of exchange between these related single-crystal X-ray diffraction, whereas the phase transition atoms, and this favours a molecular dynamical disorder. Di- was followed by both solid-state 1H,13C cross-polarisation sulfide bridges of cystamine molecules are engaged in weak magic-angle spinning (CPMAS) NMR spectroscopy and ther- interactions with neighbours, either another cystamine mole- modiffractometry techniques. At 150 °C, compound 1a is cule in 1a (SS···SS interactions), or iodine atoms in 1b (SS···I transformed into 1b, and, remarkably, the β phase (1b) can interactions). To evaluate the donating and accepting abili- be nearly retained down to room temperature, which means ties of the disulfide bridge, and their impact on such weak that both polymorphs 1a and 1b can coexist over a large tem- interactions, a detailed partition of the interaction energy of perature range. The structure of 1b has been solved, and it ten dimer models has been calculated and revealed that the was found that cystamine molecules are disordered over two main contribution to the intermolecular bonding comes from positions: the two related components with opposite helical the dispersion forces. conformations. Solid-state 1H,13C CPMAS NMR spectro-

Introduction Y–S or Z–S bonds (Y–S···X or Z–S···X ≈ 90°; type I), whereas nucleophiles would interact with sulfur atoms pref- Noncovalent intermolecular interactions that involve erentially along the extension of one of those covalent chalcogen atoms are well known in that they can be respon- bonds (Y–S···X or Z–S···X ≈ 180°; type II; Figure 1, sible for controlling the conformation of large molecules a).[1,3,6,10–14] These geometrical features have been interpre- from biological to synthetic architectures.[1–9] In particular, ted in terms of donating or withdrawing ability of the in- they play noninnocent roles in determining protein struc- volved sulfur atom as an orbital-type np–σ* formalism, in tures and their folding pathways.[1] Different studies have which a donating lone pair interacts with an accepting anti- underlined experimental features specific to S···X (X being bonding σ* orbital (Figure 1, b).[15] Disulfide S–S func- any chalcogen or a pnictogen) nonbonded interactions: tional groups are post-translational modifications that con- electrophiles tend to approach Y–S–Z (Y, Z being any atom trol the ternary and quaternary structures of proteins, such except hydrogen) groups along a direction perpendicular to as human insulin protein.[16,17] Organic molecules with di- Ј [a] Institut des Sciences et Technologies Moléculaires d’Angers, sulfide functional groups (R–S–S–R ) are inclined to adopt MOLTECH ANJOU, CNRS UMR 6200, Université d’Angers, two different screwed structures in solution as well as in 2 Bd. Lavoisier, 49045 Angers, France crystalline states to form a pair of chiral enantiomers, which E-mail: [email protected] [18–22] http://moltech-anjou.univ-angers.fr are described as P- and M-helical forms. The racemi- [b] Laboratoire des Mécanismes Réactionnels, Department of sation is fairly rapid in solution on account of the relatively Chemistry, Ecole Polytechnique and CNRS, low barrier of rotation of S–S bonds in the case of nonbulky 91128 Palaiseau CEDEX, France [23,24] [c] LUNAM Université du Maine, CNRS UMR 6283, Institut des R and RЈ organic groups. In materials science, organic Molécules et des Matériaux du Mans, disulfides can be used as moderate donors towards soft Avenue Olivier Messiaen, 72085 Le Mans CEDEX 9, France [‡] Current address: Institut Charles Gerhardt UMR CNRS 5253 metal ions, as well as flexible ligands in the fields of coordi- (AIME), Université Montpellier 2, CC1502, Place E. Bataillon, nation polymers or supramolecular chemistry.[25–32] Experi- 34095 Montpellier CEDEX 5, France mental studies devoted to the interactions of the disulfide E-mail: [email protected] Supporting information for this article is available on the bridge with its environment, either in organic and inorganic WWW under http://dx.doi.org/10.1002/ejic.201301017. crystals[1,6,10] or in protein structures,[11,33] show geometri-

Eur. J. Inorg. Chem. 2014, 364–376 364 © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.eurjic.org FULL PAPER cal trends that could be explained by the donating–ac- interactions between the disulfide bridge and its neighbour- cepting formalism previously exposed, and similar conclu- ing environment. The most interesting feature concerns the sions on the basis of experimental evidence have been speci- helical conformational change of disulfide components in fically made with regard to S–S···S–S, thereby placing the the solid state that can be observed for the n = 1 and n =2 emphasis on the dispersion forces as well as on a np–σ* compounds, the latter of which results in an exceptional orbital character to explain their propensity to inter- solid-state conglomerate α-(H2cys)PbI5·H3O to true race- [10,11,34] [44] act. mate β-(H2cys)PbI5·H3O reversible transition. The structural transformation of the room-temperature acentric α phase to centric β phase is reversible and was followed by variable-temperature second-harmonic-generation (SHG) measurements, as only the acentric salt is optically active. As a hysteresis was observed in the SHG = f(T) curve, both phases can coexist at a given temperature, thereby making such materials good candidates for SHG switches. Never- theless, the temperature range of phase coexistence is small,

that is, a range of 20 °C for (H2cys)PbI5·H3O. One strategy that was envisaged as a plausible way to increase the temperature range of coexistence was to rigidify the inorganic scaffold and thus obtain a 2D hybrid perovskite (the “n = ϱ ” member of the “H2cys series”), in which the rotation of Figure 1. (a) Geometrical features of S···X interactions and (b) np– H cys cations would be restrained (Scheme 1). σ* interactions between chalcogen centres (X being any chalcogen 2 or pnictogen).

The diprotonated cystamine (cys) molecule [H3N–(CH2)2– 2+ SS–(CH2)2–NH3] , here denoted by H2cys, is an organic disulfide with two ethylammonium functions at both ends. Until recently, this molecule was not often incorporated as a counterion in ionic-like compounds, even though it a priori fulfils the requirements (i.e., nonbulkiness and the presence of primary ammonium groups) for the self-assembly of layered hybrid perovskites.[35] Such hybrids can be considered multifunctional materials that combine properties of both organic and inorganic components.[36–39] For in- Scheme 1. Schematic representations of the (a) n = 2 and (b) n = ϱ stance, as organic compounds, they can be easily made into members of the H2cys series showing the potential directions of ϱ crystalline thin films,[40] whereas their interesting electronic expansion of each system with green arrows; for the n = member [37–42] (b), the expansion is restrained in the direction parallel to the inor- properties often come from the inorganic framework. ganic layers owing to the rigidity of the polymeric anions. In the course of our investigations on perovskite-like compounds, we recently focused on the synthesis of halogen- Herein we report the synthesis, solid-state NMR spectra, ometallates of BiIII and PbII hybrid materials that contain X-ray structural characterisation and quantum chemical ϱ the H2cys dication. The diprotonated cystamine could af- studies of the hybrid perovskite α-(H2cys)PbI4 (1a, n = ), ford an unprecedented series of iodoplumbate salts based which undergoes a reversible structural transformation in (2n + 2)– on PbnI4n +2 ribbons, namely, the “H2cys series” the solid state to form the polymorph β-(H2cys)PbI4 (1b, n + + ϱ {(H2cys)[(2n +2–u)/2]PbnI4n +2·(uC , vG); with C and G = ) at 150 °C. In the first part, the centric crystal struc- being any monocation and neutral guest molecule, respec- tures of 1a and 1b are described. We will show that great tively, incorporated in the structure}. structural changes occur through the transition. In particu-

Up to now, the “H2cys series” was composed of lar, the disulfide bridges of cystamine molecules are ordered (H2cys)2PbI6·2H3O(n = 1, being composed of isolated PbI6 and interact together through SS···SS noncovalent contacts [43] octahedra), (H2cys)2Pb2I10·2H3O[n = 2, the formula be- in 1a, whereas in 1b they are disordered over two positions [44] ing reduced to (H2cys)PbI5·H3O], (H2cys)4Pb3I14·I2 (n = and are approximately turned perpendicular to the inor- [45] 3) and (H2cys)6Pb5I22·4H2O(n = 5). All inorganic anions ganic layers, thus interacting with iodine atoms. In the sec- for each member of the series can be regarded as a dimen- ond part, we report on the variable-temperature measure- sional reduction of 2D hybrid perovskite layers, thus the ments of the X-ray powder diffraction (XRPD) and solid- 13 dual nature of the H2cys cation is highlighted: on the one state C NMR spectroscopic experiments, which show that hand, it is able to stabilise networks of corner-sharing PbI6 1b is retained down to 40 °C. This indicates that both poly- octahedra as is expected for nonbulky primary ammonium morphs of 1a and 1b can coexist over a large temperature cations, and on the other hand, it might prevent the forma- range (40–150 °C). Moreover, the results of the 13C NMR tion of hybrid perovskite layers owing to the strong capa- spectroscopic study converge to assign a dynamical mode bility of trapping guest molecules by means of noncovalent to the molecular disorder observed in 1b. Finally, in the

third part, we give the results of our theoretical investi- I atoms and two crystallographic independent H2cys cat- gations of SS···SS and SS···I interactions, which are system- ions (Figure 2). Compound 1a is a hybrid perovskite that 2– atically observed in cystamine-based iodometallates, includ- consists of PbI4 perovskite layers that are separated by ing the title hybrid compounds, and are suspected of play- organic cations (Figure 3, a). In the organic layers, both ening a non-innocent role in the helical conformational mo- antiomeric P and M forms of disulfide molecules are en- lecular change and/or in the molecular disorder phenomena countered in the same layer, related to each other by the n + in the solid state. glide plane. The –CH2–NH3 fragments of cystamine are located at the boundary of the inorganic sheets, thanks to intramolecular hydrogen bonds established between the + Results and Discussion –NH3 group and the neighbouring sulfur atom of each cystamine (Figure 2), thus reducing the typical hydrogen Foreword on the Synthetic Conditions bonding between the ammonium of the organic layers and the iodide of the perovskite sheets. This particular feature As mentioned previously, the n = ϱ member of the H cys 2 of ammonium cations bearing an acceptor of hydrogen series was, until recently,[46] unreported because of the syn- bonds in the β position [X–(CH ) –NH +, X = Cl, Br, OH] thetic difficulty to prevent the incorporation of guest mole- 2 2 3 limits the tilt of the PbI octahedra related to the mean cules through nonbonded interactions with the disulfide 6 plane of the layers, that is to say, the lead and equatorial bridge of the H cys cation. We speculated that this phenom- 2 iodide atoms approximately lie in the a,b plane, as already enon disturbs the self-assembly of the organic cations in emphasised for similar compounds.[47,48] Last but not least, solution during the nucleation process by keeping them the main attribute of 1a is the nonbonded interactions of from forming a suitable array of positive charges that would the cystamine cations through the sulfur atoms of their di- allow the formation of anionic 2D hybrid perovskite layers, sulfide bonds: d[S(2)···S(3)] = 3.53 Å and d[S(4)···S(4)] = and it mainly leads to 0D and 1D hybrid iodometallates. To achieve a higher inorganic dimensionality by using

H2cys, it is necessary to be able to control the interactions Table 1. Crystallographic data for 1a and 1b. of the disulfide bridge in solution prior to the crystallisa- α-(H2cys)PbI4 β-(H2cys)PbI4 tion. In the “H2cys series”, it is interesting to note that all (1a)(1b) compounds have been crystallised using acetonitrile as a Crystal system monoclinic monoclinic solvent, and all compounds, from n =1ton = 5, incorpo- Space group P21/nP21/a + [43–45] rate guest molecules (H3O ,H2O or even I2). We sup- a [Å] 17.7855(10) 9.1524(10) posed that treating PbI2 with H2cys and HI in a mixture of b [Å] 8.5500(4) 8.2510(10) acetonitrile and a polar protic solvent should give interest- c [Å] 23.270(2) 11.686(2) α [°] 90 90 ing results owing to the fact that the created ionic species β [°] 98.780(10) 104.870(10) + such as H3O should be more strongly attracted by the pro- γ [°] 90 90 tic solvent (i.e., solvated) than by the sulfur atoms of the V [Å3] 3497.2(4) 852.9(2) ρ [mgm–3] 3.301 3.384 disulfide group of H2cys dications. Indeed, the preparation calcd. of 1a, the hybrid perovskite α-(H cys)PbI , was achieved by 2θ max. 25.92 30.05 2 4 T [K] 293(2) 313(2) heating at 85 °C equimolar amounts of PbI2 and H2cys in Reflections collected 26470 (6756) 17320 (2493) an acidified 1:1 acetonitrile/ethanol solution. The resulting (unique) compound is guest-free, thus corroborating our first as- Data (parameters) 6756 (235) 2493 (80) Ͼ sumptions. Interestingly, this compound has been recently R1[I 2σ(I)] [wR2(all data)] 0.0477 (0.1270) 0.0559 (0.1692) reported, serendipitously obtained from a mixture of PbI2 + and the monocation HS–(CH2)2–NH3 in a highly concen- trated acidic solution that was expected to give the [HS– [46] (CH2)2–NH3]2PbI4 hybrid perovskite. The in situ formation of the H2cys dication by the oxidation of the thiol group of the thioethylammonium probably occurred after the self-assembly of the organic monocations in solution, therefore leading to the preformation of the 2D hybrid layers. Interestingly, the authors stated that their crystals of 1a are always obtained with another phase, the latter being a 1D-based hybrid material, which nicely emphasises the advantage of our rational synthetic approach. Figure 2. The conformations of the cystamine cations in (a) 1a and (b) 1b. The dashed bonds emphasise the intramolecular NH3···S short contacts [1a, d(S1···H1B) = 2.9283(4) Å, d(S2···H2B) = 2.7233(4) Å, d(S3···H3B) = 2.7810(4) Å, d(S4···H4B) = 2.7941(4) Å; Crystal Structures of 1a and 1b 1b, d(S1B···H0B) = 2.9899(9) Å]; some atoms are disordered over two positions (see the Exp. Section). Torsion angles: 1a, C2–S1– The asymmetric unit of 1a, which crystallises in the S2–C3 76.7(7)°, C6–S3–S4–C7 –74.6(8)°; 1b, C2A–S1A–S1B–C2B P21/n space group (Table 1), consists of two Pb atoms, eight 82(2)°.

3.71 Å [Figure 3; these values are inferior, or reasonably followed in operando on the same single crystal. As shown close, to twice the van der Waals radius of a sulfur atom; by powder thermodiffractometry (see below), the structure [49] 2·rvdw(S) = 3.66 Å]. This leads to define supramolecular of the high-temperature phase (1b) is retained down to tetramers, whereas we also observe that all disulfide bridges 40 °C. This allowed us to collect data at T = 313 K of a of cystamine are approximately parallel to the inorganic single crystal of 1b. The structure of 1b crystallises in the layers (Figure 3, a). These contacts, far from being well P21/a space group, and its unit cell is four times smaller ≈ ≈ ≈ understood, are not unusual (see below). than that of 1a (aβ aα/2, bβ bα, cβ cα/2). The asymmetric unit consists of one Pb, two I atoms and one-half of the

H2cys cations, which is disordered over two positions, thus describing both M- and P-helical conformations for one organic moiety (Figure 2). This also unambiguously proves that a helical conformational change has occurred during the transformation from 1a to 1b. The overall structure underwent major structural changes through the transition and the most spectacular ones concern the cystamine cations. Firstly, in contrast with + 1a, the –CH2–NH3 fragments in 1b are almost perpendicular to the inorganic layer, with only the ammonium heads being located in the cavities of the perovskite sheets (Fig- ure 3, b). Indeed, whereas the torsion angle S1B–C2B–C1– N is equal to 55.1(4)°, the torsion angle of the other disordered component of the cystamine cation, S1A–C2A–C1– N, is equal to –178.5(2)°, thereby preventing the presence of the intramolecular hydrogen bond between the sulfur atom S1A and the ammonium group and increasing the interactions between the latter and the perovskite layers. This effectively influences the geometry of the inorganic

sheets by tilting the PbI6 octahedra out of the a,b plane. Secondly, whereas disulfide bridges are connected together through the a priori weak SS···SS interactions and lie in a plane parallel to the inorganic layers in 1a, they are roughly perpendicular to the perovskite layers in 1b (viewed along the b axis, Figure 3, b) and interact unusually with apical iodides of the inorganic part: d(S···I) = 3.31 and 3.53 Å (the sum of van der Waals radii of S and I atoms is 3.83 Å).[49] Figure 3. Quite different molecular positions in both polymorphs Finally, the inorganic framework also undergoes a remark- (a) 1a and (b) 1b viewed along the b axis. able change from 1a to 1b, as can be seen in Figure 4. The

layout of PbI6 polyhedra that belong to a single layer is similar in both structures (the Pb–I–Pb angles in both 1a and 1b are close to 160°) but the relative positions of two Upon heating at 150 °C, compound 1a is transformed consecutive perovskite layers differ from each other. That into its polymorph 1b through a reversible solid-state reac- means a concerted rotation of polyhedra that belong to the tion. During the 1a to 1b transformation, most crystals are same layer (motion of equatorial iodides) occurred through broken into tiny fragments, and the transition could not be the transition.

Figure 4. The layout of perovskite layers in structures of (a) 1a and (b) 1b viewed along the c axis (only one component of the disordered molecule is shown in 1b).

Thermodiffractometry and Solid-State NMR Spectroscopic 164 °C on the way up (Figure 6, spectra a–f) as well as on Studies the way down (Figure 6, spectra f–l). The spectrum of 1a at 27 °C shows one broad and low resolved peak (Figure 6). The phase transformation from 1a to 1b has been fol- This spectrum was reconstructed with six contributions lowed by XRPD techniques (Figure 5). A slight shift of the with relative intensities (two of them with larger line widths (002) diffraction peak to lower angle is observed along with and double intensities) that are in agreement with the exis- an increase in temperature (20 to 130 °C), which reveals tence of two crystallographic independent cystamine dicat- that the gap between perovskite layers is increasing. Then, ions (i.e., eight different C atoms with the same multiplicity) as shown by the clear shift to low angle of the (002) reflec- for 1a (see Figure S5a and Table S5a in the Supporting In- tion at 150 °C, the supplementary space between two inor- formation). According to the expected 13C isotropic chemi- ganic layers might be provided to allow organic ligands to cal shift (δ ) values of the C(S) and C(NH ) atoms of the adjust their conformation to form 1b. Finally, it seems that iso 3 cystamine dication [estimated as δ C(S) = 32.6 ppm and the structure of 1a breathes before yielding 1b. Above iso δ C(NH ) = 41.1 ppm], the three lower δ values may be 160 °C and up to 190 °C, an unknown γ phase is obtained, iso 3 iso assigned to C(S) (i.e., C2, C3, C6 and C7) and the three and upon cooling, the β phase is recovered rapidly (T = higher δ values to C(NH ) (i.e., C1, C4, C5 and C8). 130 °C). When the temperature reaches 190 °C, the β phase iso 3 When the temperature increases from 27 to 107 °C, the sig- (1b) is transformed into an unknown γ phase, the XRPD nal of 1a does not evolve significantly (Figure 6, spectra a– pattern of which could be roughly indexed by the mono- c). In contrast, it collapses at 122 °C, with the emergence of clinic unit cell: a = 11.703 Å, b = 8.756 Å, c = 9.023 Å, γ γ γ two new lines (Figure 6, spectrum d), whereas it completely β = 101.2°, V = 907.3 Å3 (please refer to the Supporting γ γ disappears above 137 °C (Figure 6, spectra e and f). The Information). The main noticeable change concerns the cell two emerging lines are probably the signatures of the β parameters that lie in the perovskite layers, which are of phase, which indicates that both α and β phases would co- 8.251 and 9.152 Å for the β phase (T =40°C,1b) and 8.756 exist between 122 and 137 °C, whereas beyond, only the β and 9.023 Å for the γ phase (T = 190 °C). phase would be present. At this stage, we could note a slight discrepancy with the XRPD study, as the α phase was observed at 137 °C in the NMR spectra, and both α and β phases were still detected at 150 °C by diffractometry (Fig- ure 5). Taking into consideration that these techniques are sensitive to different physical variations within the solid state, dissimilarities might be due to both inherent temperature errors and temperature gradient of samples, especially for the thermodiffractometry technique (see the Exp. Sec- tion). Another plausible hypothesis might be a change of molecular behaviour within the α phase before the structural transformation from the α to β phase occurs. In other words, one might postulate that NMR spectroscopy detects a modification in the cystamine conformation at a temperature at which XRPD only identifies an increasing layer-to- layer distance [shifting to lower angles of the (002) diffrac- Figure 5. Thermodiffractometry study of 1a. Details of the pro- tion peak] in the α phase (Figure 5). The spectrum recorded cedure: Different XRPD patterns of an initial sample of 1a have at 164 °C that can be unambiguously assigned to 1b (Fig- been collected between room temperature and 190 °C, then cooled ure 6, spectrum f) was reconstructed with two contributions to 40 °C. Compound 1a (α) is transformed into 1b (β) at 150 °C, at δiso = 36.0 ppm and δiso = 42.5 ppm (Figure S5b and which becomes the γ phase at 190 °C; the upper β (40) pattern was Table S5b in the Supporting Information). 13C δ estima- collected after the sample had been kept at 40 °C for two weeks. iso tions and the similar intensities of these two lines allow the On the contrary, the α-phase 1a is recovered below 40 °C, assignment of the first one to C2A and C2B and the second which is much lower than the temperature of the initial to C1. Thus, C2A and C2B either have the same δiso value phase transformation (T = 150 °C). Moreover, the β phase or are in the fast intermediate exchange regime (i.e., they 1b is stable (at least) for two weeks at 50 °C after being exchange their positions with a rate constant larger than heated at 160 °C, and no α phase is detected during this half the magnitude of the chemical-shift difference fre- period (Figure 5). The results indicate that both poly- quency).[50] A decrease in the temperature from 164 to morphs can then coexist over the broad temperature range 50 °C (Figure 6, spectra f–k) leads to a gradual broadening of 50–140 °C. of the two NMR spectroscopic lines of 1b, especially those 1H,13C cross-polarisation magic-angle spinning assigned to C2A and C2B, as shown by the reconstruction (CPMAS) solid-state NMR spectroscopic experiments un- (Figure S5c in the Supporting Information). From 164 to der variable temperature were carried out on 1a to study 50 °C, the width of the line assigned to C1 increases by a the phase transition that leads to 1b. Figure 6 compares the factor of 2.6 and the width of the line assigned to C2A and spectra of (H2cys)PbI4 between room temperature and C2B increases by a factor of 3.9 (Table S5c in the Support-

Eur. J. Inorg. Chem. 2014, 364–376368 © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.eurjic.org FULL PAPER ing Information). Whereas one expects broadening due to Structural and Theoretical Investigations of SS···SS and lower mobility, the strong increase of the width of the line SS···I Noncovalent Interactions assigned to C2A and C2B indicates the presence of exchange (or dynamical disorder from a crystallographic An exhaustive review of the Cambridge Structural Data- point of view) between these two atoms. As the exchange base (CSD)[51] confirmed the findings previously high- rate decreases along with the temperature, the line broad- lighted. Indeed, among the 637 structures that contain a ens, and at 50 °C it is already close to the coalescence point. C(sp3)–S–S–C(sp3) fragment, 91 showed SS···SS intermolecular contacts shorter than 3.7 Å, approximately twice the van der Waals radius of sulfur.[49] The presence of these close contacts suggests that these might be due to true intermolecular interactions rather than artefacts of crystal pack-

ing. As can be seen from Figure 7, the S–S···S angles (ω3 and ω4; see their definition on Figure 8) can be roughly be separated into two groups that correspond to either type I (S–S···S ≈ 90°) or type II (S–S···S ≈ 180°) interactions.[3,6] In the case of 1a, let us notice again that SS···SS contacts are of 3.533(7) Å (S2···S3) and 3.715(7) Å (S4···S4; Fig- ure 9), whereas the SS···S angles are in the range 131–168° [S1–S2···S3, 168.6(4)°; S4–S3···S2, 142.0(1)°; S3–S4···S4, 131.3(1)°]; these results fall into the trend of the distribution of the experimental values derived from the CSD. Similar results can also be extracted for the S–S···I interactions (please refer to the Supporting Information).

Figure 6. 1H,13C CPMAS NMR spectra of 1a and 1b; the spectra were acquired in the order a-l.

Whereas upon an increase in temperature the phase transition takes place at 122 °C, upon a decrease in temperature, the recovery of 1a takes place below 50 °C. This is consistent with the hysteresis revealed by the temperature-controlled XRPD study. Moreover, the evolution of the cystamine conformation in the solid state as studied by NMR spectroscopy is highly compatible with the results of the single-crystal analysis, and therefore the presence of short Figure 8. Definition of the five important geometrical parameters, nonbonded SS···SS contacts in the α phase and SS···I con- the distance r(X1–X3), and the orientation angles ω1(y,[X1X3]), tacts in the β phase might play a role in the establishment ω2(z,[X3X4]), ω3([X1X3],[X3X4]), ω4([X2X1],[X1X3]) and of such a large hysteresis. ω5([Y1X1],[X1X3]).

Figure 7. (a) Polar scattergram plotting the SS···S interaction angles (ω3 and ω4; see Figure 8 for their definition) against the SS···S interaction distance. (b) Histogram showing the SS···S interaction angles over the compounds of the CSD.

the R–S–S–R group, whereas models G and H were built to closely characterise the SS···SS interaction in the solid state.

Figure 9. The intermolecular SS···SS and SS···I interactions at the organic–inorganic interface in the structure of 1a.

These geometrical features can be interpreted in terms of the donating or withdrawing ability of the disulfide bridge. As already emphasised, this interpretation arises from experimental investigations on chalcogen compounds.[3,10,34,52–56] Thus, when the S–S···S angle ap- proaches 180°, the disulfide entity could be an acceptor of electronic density through the σ*S–S orbital of the S–S covalent bond. In the other situation, in which the S–S···S angle equals 90°, two different cases should be considered: on the one hand, if C–S···S ≈ 0°, the disulfide bridge can behave as an accepting unit through its C–S bond (i.e., its σ*C–S antibonding orbital), and on the other hand, if C–S···S ≈ 90°, it could donate electronic density thanks to one of its lone pairs. To shed light on the origin of those interactions, their nature and their role in the conformation change, a quantum chemistry study was undertaken. We based our meth- odology on the work of Gleiter et al. in which chalcogen– chalcogen interactions between homo- and heteronuclear 1 2 1 2 species (CH3)2E ···CH3E Z(E,E =O,S,Se,Te;Z=CH3, C2H, CN) have been investigated by quantum chemistry methods.[8,9] Their strategy was to study the influence of the inductive ability of substituents attached to the chalcogen atom on the force of the interaction. The contact between two molecules in the solid state was modelled by a supramolecular dimer, with one monomer being considered an 2 electron-accepting unit (CH3E Z) and the other one being 1 an electron-donating unit [(CH3)2E ], as defined by the or- Figure 10. (a) Model systems A–H. (b) Details of the model H, bital-type np–σ* formalism (Figure 1). By varying the Z H1–2 and H2–3. 2 substituent of the CH3E Z monomer from Z = CH3 (methyl, electron-donating) through Z = C2H (alkynyl, intermediate) to Z = CN (nitrile, electron-withdrawing), it was possible to enhance the chalcogen–chalcogen interac- All the model systems, excluding G and H, were sub- tion. The electron- withdrawing effect of the nitrile group jected to full geometry optimisation at the MP2 level of amplifies the electrophilicity of the E2 atom and therefore theory as described in the Exp. Section. The main resulting increases the force of the E1···E2 np–σ* contact while short- parameters are summarised in Table 2. The equilibrium dis- ening the E1···E2 distances (shorter than the sum of the van tances of the optimised dimers are in relatively good ac- der Waals radii of E1 and E2 species). A similar methodol- cordance with twice the van der Waals radius of sulfur as ogy has therefore been followed to investigate the disulfide– demonstrated by Gleiter et al. with the MP2 method.[8,9] disulfide contacts encountered in 1a and the disulfide–iod- On the other hand, DFT[57]/B3LYP[58–61] optimisations led ide contacts of 1b, and the model dimers A–H (Figure 10) to inconsistent geometries with sulfur–sulfur intermolecular were designed for that purpose. Models A–F were con- distances between 3.8 and 7 Å (see the Supporting Infor- structed to unravel the donating and/or accepting ability of mation).

–1 Table 2. Calculated interaction energy Eint [kcalmol ], intermo- [a] lecular equilibrium distance r [Å] and orientation angles ω1–5 [°].

Models Eint r ω1 ω2 ω3 ω4 ω5 A –2.792 4.03 113.9 19.7 175.8 74.7 74.7 B –3.853 3.49 97.3 12.6 174.7 85.3 85.3 C –3.123 3.69 104.5 25.7 166.9 81.5 79.7 D –2.893 4.63 124.4 75.2 – 76.7 60.4 Figure 11. Equilibrium geometry for the model systems C, D, E E –3.702 3.57 99.3 21.6 167.8 85.4 82.7 and F (from left to right). Black dashes: S···S interactions, light F –3.179 3.89 109.3 60.6 135.8 77.6 78.4 grey: CH···S hydrogen bonds. G[a] –2.351 3.53 46.8 62.7 168.6 142.0 89.5 H1–2[a] –2.264 3.53 46.8 62.7 168.6 142.0 89.5 H2–3[a] –0.534 3.71 43.7 90.0 131.3 131.3 102.2 (as shown in Figure 1; see the Exp. Section). This result [a] For nonoptimised model systems, the geometrical features are supports the analysis of the geometries optimised at the given as the experimental ones. MP2 level: the more accepting one monomer is, the more important the contribution from the S···S interaction relative to hydrogen bonding. If we consider A, B and C, the Within the donor–acceptor hypothesis, the ideal geome- nature of the accepting monomer has a direct influence on try to obtain a maximal np–σ* interaction would be the origin of the interaction. For A, the optimised geometry ≈ ≈ reached for ω1 90° and ω2 0°. Examination of our re- is governed by hydrogen bonding, whereas in B the S···S sults (Table 2) indicates it is rather reasonable to rationalise interaction is the main term. Results for C show the inter- the present disulfide–disulfide interactions in terms of an mediate nature of the disulfide bridge as an accepting unit. np–σ* perturbative interaction, except for D (Figure 1). In- This statement is in good accordance with the conclusions deed, the ω1 angle is approximately equal to 90° for all the from Gleiter et al. about sulfide–sulfide interactions; sulfur optimised models (i.e., A–F), and it decreases when the elec- is a pivotal element in the chalcogen group.[8,9] Indeed, oxy- tron-withdrawing effect of the X4 substituent becomes more important (going from A to B,orfromD to E). When considering the A, B and C models, one can notice from the interaction distances and energies listed in Table 2 that the Me–S–S–Me entity is a moderate accepting unit with an intermediate S···S distance relative to Me–S–Me and Me– S–CN (3.69 versus 4.03 and 3.49 Å, respectively). The calculations on D, E and F are based on the Me–S–S–Me as a donating unit. Firstly, the S···S intermolecular distances are greater than those of A, B and C, which indicates that the interactions are weaker and that the Me–S–S–Me monomer is a poor donating unit. With a weak accepting unit (i.e., in the D model), the geometry of the supramolecular assembly cannot be described in terms of the np–σ* orbital interaction because the geometry does not show significant S···S interactions and mainly reveals hydrogen bonds between sulfur atoms and methyl groups (Figure 11). Models E and F, with Me–S–CN and Me–S–S–Me as accepting units, deviate from the ideal geometry of an orbital- type interaction because of the presence of the second sulfur atom on the donating monomer (Figure 11). This is indicated by an increasing ω2 angle from E to F (21.6 to 60.6°). Finally, it is clear that the alignment of disulfide bridges, seen as a fingerprint of the SS···SS interaction in the solid state, does not remain still during the optimisation because of the moderate electron-accepting and poor electron-donating nature of the Me–S–S–Me moiety. Therefore, other forces also influence the structure. The diagram in Figure 12a depicts the main results that come from the natural bond orbital (NBO) calculations, achieved to give us a qualitative representation of the rela- Figure 12. (a) Relative contribution of the S···S and hydrogen tive strength of sulfide–sulfide noncovalent interaction ver- bonding obtained from the NBO analysis for models A–H.(b) Contribution of the electrostatic (E ), induction (E ), dispersion sus hydrogen bonding. This was done by interpreting the elst ind (Edisp) and exchange-correlation (Eexch) energies to the interaction sums of the second-order interactions terms of the NBO energy Eint,SAPT as derived from the SAPT analysis (see the Exp. program in terms of hydrogen and sulfide–sulfide bonding Section).

Eur. J. Inorg. Chem. 2014, 364–376371 © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.eurjic.org FULL PAPER gen–oxygen interactions are mainly of an electrostatic na- the weak accepting nature of Me–S–S–Me. For D, E and F, ture, whereas selenium–selenium or even tellurium–tel- changing the accepting group has a different effect. Interest- lurium interactions are dominated by the np–σ* per- ingly, the Edisp absolute value for model F is the highest turbative interaction. Therefore, the sulfide–sulfide interac- among our systems, along with a smaller Eind value. Those tions represent a transition between the two previous de- findings highlight that the intermolecular interaction is scriptions, with the main contribution depending on the strong although not primarily being of orbital origin, al- force of the accepting unit. The results are somehow similar though a longer interaction distance is obtained relative to for D, E and F, and the contribution of the sulfide–sulfide C (3.89 versus 3.69 Å) and this might be due to the presence interaction increases with the force of the accepting unit. of hydrogen bonds on the donating monomer (Figure 11).

Nevertheless, the ES–X term is strictly nil for the D model, Finally, the G model has been calculated from the experi- and very small for F, thus emphasising the poor electron- mental geometry. The results show small Eind and Edisp, donating ability of the disulfide entity. On the contrary, the which could be explained if we state that the polarisability sulfide–sulfide interaction is preponderant for the experi- of the sulfur atom in the experimental system is weaker mental geometries G, H1–2 and H2–3. From the symmetry- than expected. adapted perturbation theory (SAPT) analysis, it is emphasised that the dispersion forces are the main bonding contribution to the intermolecular interaction in every model di- Conclusion mer studied (Table 3; Figure 12, b). The SAPT formalism The cystamine ligand is of interest considering its disul- has been shown to allow for a fine decomposition of non- fide bridge as well as its preferential chiral conformations. covalent interaction energies into “chemically understand- It is remarkable that five halogenoplumbate salts based on able” values such as electrostatic, induction and dispersion it were achieved, and that all the compounds define an un- (2n + 2)– forces, plus a term that comes from the electron exchange, precedented series of structures based on PbnI4n +2 [62] namely, Eelst, Eind, Edisp and Eexch. As a reminder, electro- networks. However, the main interesting features, which oc- static forces describe the ionic character of an interaction, cur in the n =1,n = 2 and n = ϱ salts, are the solid-state the induction forces represent the distortion of the electron phase transformations that involve a helical conformational cloud of a neutral specie by the permanent dipolar moment change of disulfide components on one hand, and the coex- of an adjacent specie, dispersion forces (instantaneous di- istence of the two related phases over a temperature range pole-induced dipole interactions) are commonly called van on the other hand. Although this temperature range was der Waals forces and the exchange term comes from the restricted to about 20 °C in n = 1 and 2, it is quite fortunate antisymmetrisation of the wave function to take into ac- that the coexistence temperature range in (H2cys)PbI4 (1a/ count the Pauli principle.[63] 1b, n = ϱ) is 100 °C. The coexistence of both polymorphs might be of great interest if each compound can be associ- –1 Table 3. Partition of the energies [kcalmol ] derived from SAPT ated with a different response to an external stimulus as in calculations in electrostatic (E ), inductive (E ), dispersive elst ind n = 1 and 2, the α phases (room temperature) of which are (Edisp), and exchange (Eexch) energies for model systems A–G as defined by Equation (4) to Equation (8) in the Exp. Section.[a] optically active (SHG), whereas their β phases (high temperature) are not. The most likely reason for such a large Model E E E E E 6-311G** elst ind disp exch int,SAPT temperature range of coexistence is that the 2D inorganic A 0.606 –0.334 –2.304 0.377 –1.951 frameworks are more rigid than the low-dimensional ones, B 1.038 –0.543 –2.740 0.633 –2.217 C 1.004 –0.356 –2.721 0.544 –1.931 which makes it more difficult for the organic cations to ad- D 0.904 –0.314 –2.639 0.492 –1.906 just their conformations in the solid state, especially when E 1.130 –0.407 –2.839 0.710 –1.852 the sample is cooled to low temperature. F 1.209 –0.238 –3.317 0.720 –1.932 The results of our theoretical calculations show that the G 0.928 –0.248 –2.021 0.339 –1.283 SS···SS and SS···I interactions are weak, with the dispersion [a] The last column collects the sum of the four contributions plus forces being the main bonding contribution to the intermo- δHF. For details, see the Supporting Information. lecular interaction, which most certainly indicates that such interactions have a minor role in the reversible 1a-to-1b phase transition. Calculations also show that the short ex- Along with the dispersion forces, the induction forces are perimental S···I distance (3.31 Å) that is present for both also bonding but on a smaller scale. The absolute values components of the disordered cystamine in the β phase (1b) of these forces (Eind and Edisp) increase with the electron- corresponds to a positive interaction energy. This could ex- accepting nature of the monomer, from A to B or from D plain the disorder phenomenon as a result of an oscillation to E, which is consistent with the polarisability of the sulfur of cystamine molecules between two unfavourable posi- atom. The electrostatic forces are repulsive in all systems, tions. This hypothesis of a dynamic disorder is also sup- which is as expected due to the nature of sulfur atoms. For ported by the study of 1H,13C CPMAS NMR spectroscopy instance, in analogous oxygen-containing models, the elec- versus temperature. It will be valuable in the future to see trostatic forces were found to be bonding. When consider- if the application of an electric field is able to induce a pref- ing A, B and C, dispersion and induction forces increase erential helical chiral conformation of cystamine molecules from A to B and are intermediate for C, which emphasises in motion, thus leading to polar and SHG active materials.

Experimental Section using CuKα radiation, equipped with a linear Vantec Super Speed detector and a TTK-450 temperature chamber. A set of 15 min Synthesis and Characterisation: (H2cys)PbI4 (1a) was prepared un- patterns in the 6–40° 2θ range were collected at different tempera- ® der solvothermal conditions in a 25 mL Teflon -lined PARR auto- tures. Each pattern was collected 10 min after the expected tem- clave. Hydriodic acid (1 mL, Mr = 80.92, d = 1.49, 48%) was added perature was reached, whereas the heating rate of the sample was to an acetonitrile/ethanol solution in a 1:1 ratio (8 mL) that con- 2°Cmin–1 to prevent any potential overshooting. Because the sam- tained PbI2 (146.30 mg, 0.317 mmol) and H2N–(CH2)2–SS– ple is heated mainly from below by a copper sample holder, with (CH2)2–NH2·2HCl (71.41 mg, 0.317 mmol). After the heating/cool- the thermocouple being placed with heat-conducting grease within ing steps (2 h from room temperature to 80 °C, 3 h at 80 °C and the holder a few millimetres below the sample, the temperature of 50 h from 80 °C to room temperature), nice orange block crystals the sample is subject to gradient and the temperature reading of of 1a were obtained. Crystals were filtered, then washed with cold the XRPD might suffer from it. Several pre-studies were carried ethyl acetate and dried at 40 °C to result in a yield of 49.7% out to refine both the heating rate and stabilisation time to obtain (137 mg based on PbI2). The XRPD pattern of the sample showed coherent temperature-controlled diffractograms. that all reflections could be indexed in the monoclinic cell of the hybrid perovskite of 1a. Depending on the experiments, a small Solid-State NMR Spectroscopy: NMR spectroscopic experiments amount of yellow crystals of (H2cys)3Pb5I16 could be crystallised have been performed with a Bruker Avance III spectrometer with as impurities. This compound can be obtained as a pure phase in nominal 300 MHz proton frequency, equipped with a double-reso- ethanol under the same conditions.[64] Differential scanning calo- nance WVT-type magic-angle spinning (MAS) probe head for rimetry (DSC) and thermogravimetry (TG) measurements were 4 mm rotors. The temperature was calibrated by means of 207Pb performed with DSC-2010 and TGA-2050 TA Instruments systems spectra of PbNO3 spun at 5 kHz, the same spinning frequency as in the temperature range of 20–350 °C and 20–900 °C, respectively in the main 13C experiments. In addition, the temperature gradient (given in the Supporting Information). The first endothermic peak over the dimension of the rotor was assessed by these experiments, at 125 °C in the DSC curve corresponds well to the phase transfor- which ranged from about 1 °C at 27 °C over 3 °C at 77 °C up to mation from 1a to 1b, whereas another endothermic peak at T = 5 °C at 164 °C. The temperatures given are therefore average tem- 169 °C is assigned to another solid-state reaction that leads to an peratures with the above variation. The main experiments were unidentified phase (see above). The resulting phase was then stable 1H,13C cross-polarisation (CP) experiments with a contact time of up to 250 °C and then decomposed in two steps up to 600 °C. 1 ms. For the temperature series, the spectra were acquired in the order 27, 77, 107, 122, 137, 164, 137, 122, 107, 77, 50, 27 °C. The X-ray Crystallography: X-ray diffraction data of selected single sample was kept at each temperature for 50 min for the accumu- crystals were collected with a Bruker-Nonius KAPPA-CCD dif- lation of 1024 transients, followed by temperature change and sta- fractometer equipped with a graphite-monochromated Mo-K ra- α bilisation for about 30 min. Stabilisation was verified by short test diation (λ = 0.71073 Å) at room temperature for 1a and at 40 °C spectra. The number of transients for the spectrum of 1a shown in for 1b. A summary of crystallographic data and refinement results Figure 6 was 2048. The spectra were referenced to TMS. NMR for 1a and 1b is listed in Table 1. Structures were solved using Sir92 spectra were handled and reconstructed using the DMFIT soft- program[65] and refined using the SHELXL97 package[66] im- ware.[69] plemented in the WinGX software suite.[67,68] Heavy atoms (Pb, I, S) were first located using direct methods, with C and N atoms Analysis of the Cambridge Structural Database: The Cambridge being then localised from the analysis of the Fourier-difference Structural Database (CSD) is the well-known database provided by maps. Positions and agitation parameters were refined by full-ma- the Cambridge Crystallographic Data Centre (CCDC).[51] In Octo- trix least-square routines against F2. All hydrogen atoms were ber 2010, it contained no fewer than 525093 structures. We per- treated with a riding model in each structure. There are two lead formed a statistical analysis on version 5.31 (November 2009 and atoms and iodine atoms in the asymmetric unit of 1a, which are August 2010 updates) of the CSD by using the search program [70] balanced by two crystallographic independent H2cys cations; how- ConQuest (version 1.12), the visualisation program Mer- ever, there are one lead and two iodine atoms in the asymmetric cury[70–73] and the analysing program VISTA.[74] The search was 3 3 unit of 1b, which are balanced by half of a disordered H2cys cation. carried out by defining two fragments as C(sp )–S–S–C(sp ) for the In fact, the C–S fragment is disordered over two positions (C2A/ SS···SS search; one of these fragments was replaced by one iodine C2B and S1A/S1B) in such a way that only one kind of cation that atom for the SS···I search. We requested a sulfur–sulfur interaction comprises both components is then defined with the site-occupa- distance smaller than the sum of the van der Waals radius of sulfur [49] tion factor of each component equal to 0.5 (Figure 2). Two C–C [rvdw(S) = 1.83 Å] plus 0.04 Å and a sulfur–iodine distance bond lengths that involve C1 are longer or shorter than the ex- smaller than sum of the van der Waals radius of sulfur and the – [75] pected values (1.50 Å), which correlates well with the quite high effective ionic radius of iodide anion [rionic(I ) = 2.20 Å] plus ϫ –3 2 anisotropic agitation parameters of C1 (Uiso = 0.090 10 Å ). Fi- 0.04 Å. To broaden our findings, another series of searches was nally, refinements of positions and anisotropic displacements pa- carried out by scrutinising the nonbonded contacts for the SS···SS rameters of all non-hydrogen atoms lead to R1 = 0.048 (1a) and and SS···I systems by defining the fragments as R–S–S–R (with R R1 = 0.055 (1b). A complete list of crystallographic data, along being any atom except hydrogen) in close contact with a single with the atomic coordinates, the anisotropic displacement param- sulfur or iodine atom (see the Supporting Information). Additional eters and bond lengths and angles for each compound are provided structural manipulations, and exhaustive checking of the results in the Supporting Information. provided by VISTA, have been achieved by using the software Dia- [76] CCDC-724583 (for 1a), -724584 (for 1b) and -724585 (for 2) con- mond (Crystal Impact, version 3.2f). tain the supplementary crystallographic data for this paper. These Theoretical Calculations: The methods and basis sets used to study data can be obtained free of charge from The Cambridge Crystallo- the model dimers (Figure 9) were chosen according to a previous graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. study.[8,9] The basis sets were obtained by means of the Basis Set Powder Thermodiffractometry: X-ray powder diffraction measure- Exchange (BSE) software and the EMSL Basis Set Library.[77] All ments were carried out on a D8 Advance Bruker diffractometer MP2 calculations were performed with the Gaussian 03 package

(revision D.02).[78] Pople’s 6-311G* basis set was used for carbon, Supporting Information (see footnote on the first page of this arti- hydrogen and nitrogen atoms,[79–82] whereas Dunning’s correlation cle): Structural data about 1a and 1b, XRD, TG, NMR analyses, consistent cc-pVTZ basis set was employed to describe sulfur[83,84] complementary details about theoretical calculations. and iodine[85] atoms. For the latter, the Stuttgart–Dresden–Bonn relativistic effective core potential description has been added.[85] Geometry optimisations were performed using the counterpoise Acknowledgments protocol[86] to obtain BSSE-corrected (basis sets superposition ef- Financial support from French Ministry of Education and Re- fects)[87–89] supramolecular geometries by recalculating the force search to N. L. this work was granted access to the HPC resources constants every 10 to 30 steps and setting the convergence criteria of CINES under the allocation 2009-x2009086123 made by to tight to locate the minima as precisely as possible. Natural bond GENCI (Grand Equipement National de Calcul Intensif) and to orbital (NBO, version 3.1 implemented in Gaussian 03)[15,90–95] the HPC resources of CCIPL Centre régional de Calcul Intensif analyses have been carried out at the HF level of theory on the des Pays de la Loire with help from F. Boucher. We would like to optimised geometries of the dimer (except where the experimental thank K. Szalewicz for the SAPT2006 licence and helpful dis- geometry was needed) using the aug-cc-pVTZ basis set for car- cussions about SAPT calculations. We acknowledge Dr. Mio bon,[96,97] nitrogen,[96,97] sulfur[84] and hydrogen,[96] and the SDB- Kondo for our fruitful discussions. aug-cc-pVTZ basis set for iodine atoms.[85] In the NBO algorithm, first the natural atomic orbitals (NAOs) are computed. Then, some natural atomic orbitals (NAOs) were linearly combined to obtain [1] M. Iwaoka, S. Takemoto, S. Tomoda, J. Am. Chem. Soc. 2002, natural bond orbitals. These NBOs can be grouped into four dis- 124, 10613–10620. tinct categories depending on the number of atoms on which their [2] C. Réthoré, A. Madalan, M. Fourmigué, E. Canadell, E. New J. Chem. constituting NAOs are centred (in our case, either 1 or 2) and their Lopes, M. Almeida, R. Clérac, N. Avarvari, 2007, 31, 1468–1483. electron occupation number ρ (ρՅ2). Bond NBOs are two-centred, [3] R. E. J. Rosenfield, R. Parthasarathy, J. D. Dunitz, J. Am. whereas core, lone-pair and Rydberg NBOs are centred on one Chem. Soc. 1977, 99, 4860–4862. atom only. The NBO program also provides the stabilising interac- [4] A. Lari, C. Bleiholder, F. Rominger, R. Gleiter, Eur. J. Org. tion energies between pairs of NBOs (always one bonding and one Chem. 2009, 2765–2774. antibonding) as computed by second-order perturbation theory. By [5] J. P. Glusker, Directional Aspects of Intermolecular Interactions, summing up all the energies according to Equations (1)–(3), we can Design of Organic Solids, 1998. approximate the strength of the interaction that takes place be- [6] T. Guru Row, R. Parthasarathy, J. Am. Chem. Soc. 1981, 103, tween different centres. Even though the actual value of the quanti- 477–479. Phosphorus Sulfur Silicon ties E or E have no direct meaning, they provide an elegant [7] N. Ramasubbu, R. Parthasarathy, S–X Hbond Relat. Elem. 1987, 31, 221–229. means of comparison of the relative strength of sulfide–sulfide ver- [8] C. Bleiholder, D. B. Werz, H. Köppel, R. Gleiter, J. Am. Chem. sus hydrogen bonding. Soc. 2006, 128, 2666–2674. [9] C. Bleiholder, R. Gleiter, D. B. Werz, H. Köppel, Inorg. Chem. 2007, 46, 2249–2260. [10] S. Dahaoui, V. Pichon-Pesme, J. A. K. Howard, C. Lecomte, J. Phys. Chem. A 1999, 103, 6240–6250. [11] M. Iwaoka, S. Takemoto, M. Okada, S. Tomoda, Bull. Chem. Soc. Jpn. 2002, 75, 1611–1625. [12] F. H. Allen, C. M. Bird, R. S. Rowland, P. R. Raithby, Acta Crystallogr., Sect. B: Struct. Sci. 1997, 53, 696–701. [13] P. Pyykkö, Chem. Rev. 1997, 97, 597–636. [14] M. E. Brezgunova, J. Lieffrig, E. Aubert, S. Dahaoui, P. Fertey, The fine decomposition of the interaction energies Eint were com- S. Lebègue, J. G. Angyan, M. Fourmigué, E. Espinosa, Cryst. puted using the SAPT2006 package.[62,98] Atmol1024 was used as Growth Des. 2013, 130701114127000. the necessary SCF front end.[99] These calculations were performed [15] A. E. Reed, L. A. Curtiss, F. Weinhold, Chem. Rev. 1988, 88, on the optimised geometries of the dimer (except where the experi- 899–926. mental geometry was needed) in the dimer centre basis set (DCBS) [16] W. J. Wedemeyer, E. Welker, M. Narayan, H. A. Scheraga, Bio- formalism using the counterpoise procedure. The 6-311G** basis chemistry 2000, 39, 4207–4216. sets were used for all the atoms (carbon, hydrogen, nitrogen, [17] J. Massague, M. P. Czech, J. Biol. Chem. 1982, 257, 6729–6738. [18] G. Gottarelli, B. Samori, The Chemistry of Ethers, Crown sulfur)[81,82] and were manually prepared to fit ATMOL1024 for- Ethers, Hydroxyl Groups, and Their Sulfur Analogues, Wiley, mat. The energy corrections calculated by the SAPT program have New York, 1980. been summed up to give the electrostatic (Eelst), induction (Eind), [19] R. Steudel, Angew. Chem. 1975, 87, 683–720. dispersion (Edisp) as well as the exchange-correlation (Eexch) contri- [20] R. Steudel, Angew. Chem. 1975, 87, 683; Angew. Chem. Int. Ed. butions according to Equations (4)–(8) below (the results are de- Engl. 1975, 14, 655–664. tailed in Table S9 of the Supporting Information). Details on this [21] R. Steudel, Y. Drozdova, K. Miaskiewicz, R. H. Hertwig, W. partitioning are given in the article by C. Bleiholder and its corre- Koch, J. Am. Chem. Soc. 1997, 119, 1990–1996. sponding Supporting Information.[8] [22] J. Webb, R. W. Stickland, F. S. Richardson, J. Am. Chem. Soc. 1973, 95, 4775–4783. [23] I. Bediako-Amoa, T. C. Sutherland, C.-H. Li, R. Silerova, H.- B. Kraatz, J. Phys. Chem. B 2004, 108, 704–714. [24] L. A. Neubert, M. Carmack, J. Am. Chem. Soc. 1974, 96, 943– 945. [25] S. Itoh, M. Nagagawa, S. Fukuzumi, J. Am. Chem. Soc. 2009, 123, 4087–4088. [26] T. Osako, Y. Ueno, Y. Tachi, S. Itoh, Inorg. Chem. 2003, 42, 8087–8097.

[27] Y. Ueno, Y.Tachi, S. Itoh, J. Am. Chem. Soc. 2002, 124, 12428– [65] A. Altomare, G. Cascarano, C. Giacovazzo, A. Gualardi, J. 12429. Appl. Crystallogr. 1993, 26, 343–350. [28] N. Louvain, N. Mercier, M. Kurmoo, Eur. J. Inorg. Chem. [66] G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 1654–1660. 2008, 64, 112–122. [29] T. Ottersen, L. G. Warner, K. Seff, Inorg. Chem. 2001, 40, [67] L. J. Farrugia, WinGX, v. 1.80.05, An Integrated System of 1904–1911. Windows Programs for the Solution, Refinement and Analysis [30] L. G. Warner, T. Ottersen, K. Seff, Inorg. Chem. 2001, 40, of Single Crystal X-ray Diffraction Data, Dept. of Chemistry, 2819–2826. University of Glasgow, 1997–2009. [31] M. C. Aragoni, M. Arca, M. Crespo, F. A. Devillanova, M. B. [68] L. J. Farrugia, J. Appl. Crystallogr. 1999, 32, 837–838. Hursthouse, S. L. Huth, F. Isaia, V. Lippolis, G. Verani, Crys- [69] D. Massiot, F. Fayon, M. Capron, I. King, S. Le Calvé, B. tEngComm 2007, 9, 873–878. Alonso, J. O. Durand, B. Bujoli, Z. Gan, G. Hoatson, Magn. [32] F. M. Tabellion, S. R. Seidel, A. M. Arif, P. J. Stang, J. Am. Reson. Chem. 2002, 40, 70–76. Chem. Soc. 2001, 123, 7740–7741. [70] I. J. Bruno, J. C. Cole, P. R. Edgington, M. Kessler, C. F. Mac- [33] M. Iwaoka, S. Takemoto, M. Okada, S. Tomoda, Chem. Lett. rae, P. McCabe, J. Pearson, R. Taylor, Acta Crystallogr., Sect. 2001, 132–133. B: Struct. Sci. 2002, 58, 389–397. [34] S. A. Moggach, D. R. Allan, S. Parsons, L. Sawyer, J. E. War- [71] C. F. Macrae, I. J. Bruno, J. A. Chisholm, P. R. Edgington, P. ren, J. Synchrotron Radiat. 2005, 12, 598–607. McCabe, E. Pidcock, L. Rodriguez-Monge, R. Taylor, J. [35] D. B. Mitzi, Prog. Inorg. Chem. 1999, 48, 1–121. van de Streek, P. A. Wood, J. Appl. Crystallogr. 2008, 41, 466– [36] A. Bonamartini-Corradi, A. M. Ferrari, L. Righi, P. Sgara- 470. botto, Inorg. Chem. 2001, 40, 218–223. [72] C. F. Macrae, P. R. Edgington, P. McCabe, E. Pidcock, G. P. [37] C. Kagan, D. B. Mitzi, C. Dimitrakopoulos, Science 1999, 286, Shields, R. Taylor, M. Towler, J. van der Streek, J. Appl. Crys- 945–947. tallogr. 2006, 39, 453–457. [38] D. B. Mitzi, K. Chondroudis, C. Kagan, IBM J. Res. Dev. 2001, [73] R. Taylor, C. F. Macrae, Acta Crystallogr., Sect. B: Struct. Sci. 45, 29–45. 2001, 57, 1–13. [39] D. B. Mitzi, C. Dimitrakopoulos, J. Rosner, D. Medeiros, Z. [74] CCDC, VISTA - A Program for the Analysis and Display of Xu, C. Noyan, Adv. Mater. 2002, 14, 1772–1776. Data Retrieved from the CSD, Cambridge Crystallographic [40] D. B. Mitzi, J. Mater. Chem. 2004, 14, 2355–2365. Data Centre, 12 Union Road, Cambridge, England, 1994. [41] S. Sourisseau, N. Louvain, W. Bi, N. Mercier, D. Rondeau, F. [75] R. D. Shannon, Acta Crystallogr., Sect. A: Found. Crystallogr. Boucher, J.-Y. Buzaré, C. Legein, Chem. Mater. 2007, 19, 600– 1976, 32, 751–767. 607. [76] W. T. Pennington, J. Appl. Crystallogr. 1999, 32, 1028–1029. [42] Y. Takahashi, R. Obara, K. Nakagawa, M. Nakano, J.-Y. Tok- [77] D. Feller, J. Comput. Chem. 1996, 17, 1571–1586. ita, T. Inabe, Chem. Mater. 2007, 19, 6312–6316. [78] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, [43] N. Louvain, N. Mercier, J. Luc, B. Sahraoui, Eur. J. Inorg. M. A. Robb, J. R. Cheeseman, J. A. J. Montgomery, T. Vreven, Chem. 2008, 23, 3592–3596. K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tom- [44] N. Mercier, A. L. Barrès, M. Giffard, I. Rau, F. Kajzar, B. Sah- asi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, raoui, Angew. Chem. 2006, 118, 2154; Angew. Chem. Int. Ed. G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, 2006, 45, 2100–2103. R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, [45] N. Louvain, W. Bi, N. Mercier, J.-Y. Buzaré, C. Legein, G. Cor- O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratch- bel, Dalton Trans. 2007, 965–970. ian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gom- [46] A. Lemmerer, D. Billing, CrystEngComm 2010, 12, 1290–1301. perts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. [47] N. Mercier, S. Poiroux, A. Riou, P. Batail, Inorg. Chem. 2004, Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. 43, 8361–8366. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dap- [48] S. Sourisseau, N. Louvain, W. Bi, N. Mercier, D. Rondeau, J.- prich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, Y. Buzaré, C. Legein, Inorg. Chem. 2007, 46, 6148–6154. A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. [49] A. Bondi, J. Phys. Chem. 1964, 68, 441–451. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, [50] M. H. Levitt, Spin Dynamics: Basics of Nuclear Magnetic Reso- G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, nance, Wiley, 2008. D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayak- [51] F. H. Allen, Acta Crystallogr., Sect. B: Struct. Sci. 2002, 58, kara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, 380–388. M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian 03,Re- [52] S. Wu, A. Greer, J. Org. Chem. 2000, 65, 4883–4887. vision D.02, Gaussian, Inc., Wallingford, CT, 2004. [53] A. Kucsman, I. Kapovits, Organic Sulfur Chemistry: Theoreti- [79] T. Clark, J. Chandrasekhar, G. W. Spitznagel, P. v. R. Schleyer, cal and Experimental Advances, Elsevier Scientific Publishing J. Comput. Chem. 1983, 4. Co., Amsterdam, 1985. [80] L. A. Curtiss, M. P. McGrath, J. P. Blaudeau, N. E. Davis, [54] A. F. Cozzolino, I. Vargas-Baca, S. Mansour, A. H. Mahmoud- R. C. J. Binning, L. Radom, J. Chem. Phys. 1995, 103, 6104– khani, J. Am. Chem. Soc. 2005, 127, 3184–3190. 6113. [55] W. Nakanishi, S. Hayashi, N. Itoh, Chem. Commun. 2003, 124– [81] R. Krishnan, J. S. Binkley, R. Seeger, J. A. Pople, J. Chem. 125. Phys. 1980, 72, 650–654. [56] W. Nakanishi, S. Hayashi, N. Itoh, J. Org. Chem. 2004, 69, [82] A. D. McLean, G. S. Chandler, J. Chem. Phys. 1980, 72, 5639– 1676–1684. 5648. [57] P. Hohenberg, W. Kohn, Phys. Rev. 1964, 136, B864–B871. [83] K. A. Peterson, T. H. J. Dunning, J. Chem. Phys. 2002, 117, [58] A. D. Becke, J. Chem. Phys. 1993, 98, 5648–5652. 10548–10560. [59] C. Lee, W. Yang, R. G. Parr, Phys.Rev.B1988, 37, 785–789. [84] D. E. Woom, T. H. J. Dunning, J. Chem. Phys. 1993, 98, 1358– [60] B. Miehlich, A. Savin, H. Stoll, H. Preuss, Chem. Phys. Lett. 1371. 1989, 157, 200–206. [85] J. M. L. Martin, A. Sundermann, J. Chem. Phys. 2001, 114, [61] S. H. Vosko, L. Wilk, M. Nusair, Can. J. Phys. 1980, 58, 1200– 3408–3420. 1211. [86] P. Sanz, M. Yáñez, O. Mó, J. Phys. Chem. A 2002, 106, 4661– [62] B. Jeziorski, R. Moszynski, K. Szalewicz, Chem. Rev. 1994, 94, 4668. 1887–1930. [87] B. Paizs, S. Suhai, J. Comput. Chem. 1998, 19, 575–584. [63] W. P a u l i J r, Z. Phys. 1927, 43, 601–623. [88] P. Salvador, B. Paizs, M. Duran, S. Suhai, J. Comput. Chem. [64] N. Louvain, N. Mercier, Solid State Sci. 2008, 10, 1269–1275. 2001, 22, 765–786.

[89] F. B. van Duijneveldt, J. G. C. M. van Duijneveldt- [97] R. A. Kendall, T. H. J. Dunning, R. J. Harrison, J. Chem. Phys. van de Rijdt, J. H. van Lenthe, Chem. Rev. 1994, 94, 1873– 1992, 96, 6796–6806. 1885. [98] R. Bukowski, W. Cencek, P. Jankowski, B. Jeziorski, M. Jezior- [90] J. E. Carpenter, 1987. ska, S. A. Kucharski, V. F. Lotrich, A. J. Misquitta, R. Moszynski, K. Patkowski, R. Podeszwa, S. Rybak, K. Szalew- [91] J. Mol. Struct. 169 J. E. Carpenter, F. Weinhold, 1988, , 41–62. icz, H. L. Williams, R. J. Wheatley, P. E. S. Wormer, P. S. [92] J. P. Foster, F. Weinhold, J. Am. Chem. Soc. 1980, 102, 7211– Zuchowski, SAPT2006: An ab initio Program for Many-Body 7218. Symmetry-Adapted Perturbation Theory Calculations of Inter- [93] A. E. Reed, F. Weinhold, J. Chem. Phys. 1983, 78, 4066–4073. molecular Interaction Energies. [94] A. E. Reed, F. Weinhold, J. Chem. Phys. 1985, 83, 1736–1740. [99] V. R. Saunders, M. F. Guest, ATMOL program package, SERC [95] A. E. Reed, R. B. Weinstock, F. Weinhold, J. Chem. Phys. 1985, Daresbury Laboratory, Daresbury, UK. 83, 735–746. Received: August 6, 2013 [96] T. H. J. Dunning, J. Chem. Phys. 1989, 90, 1007–1023. Published Online: December 2, 2013