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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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Noncovalent Chalcogen Bonds and Disulfide Conformational Change in the Cystamine-Based Hybrid II Perovskite [H3N(CH2)2SS(CH2)2NH3]Pb I4 FULL PAPER DOI:10.1002/ejic.201301017 Noncovalent Chalcogen Bonds and Disulfide Conformational Change in the Cystamine-Based Hybrid II Perovskite [H3N(CH2)2SS(CH2)2NH3]Pb I4 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 struc- tural 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 tem- perature 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 pri- ori fulfils the requirements (i.e., nonbulkiness and the pres- ence of primary ammonium groups) for the self-assembly of layered hybrid perovskites.[35] Such hybrids can be con- sidered 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 com- pounds, 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.
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