Abstract
Two new organic–inorganic salts of perhalidometallates with protonated organic amine cations have been synthesized and characterized by X-ray diffraction and thermal analysis. (CHBMAH2)ZnBr4·3/2H2O 1 and (CHBMAH2)ZnCl4 4 [(CHBMAH2)2+: 1,3-cyclohexanebis(methylammonium)] were obtained in single-crystal form. The crystal packing in all of the obtained compounds is governed by the formation of various non-covalent intermolecular forces between tetrahalidometallate anions and organic cations, assisted by water molecules in the hydrates. Hirshfeld surface analysis denotes that the most important contributions to the crystal packing are X···H/H···X (X: Cl, Br, I) and H···H interactions. Interestingly, the compound 1,3-cyclohexanebis(methylammonium)tetrachloridozincate (II) dihydrate, (CHBMAH2)ZnCl4·2H2O 2, undergoes thermally-triggered single-crystal-to-single-crystal (SCSC) transformation upon dehydration to produce a supramolecular solid compound, 1,3-cyclohexanebis(methylammonium) tetrachloridozincate (II), (CHBMAH2)ZnCl4 4. The SCSC transformation causes changes in the lattice parameters and a structural rearrangement. Furthermore, the catalytic properties of (CHBMAH2)ZnCl4·2H2O 2 and (CHBMAH2)CdI4·2H2O 3 have been explored in the acetalization process using various uncommon alcohols, beyond methanol or ethanol, for the first time in the literature, with outstanding results, and opening the door to the formation of alternative acetals.
Highlights
The possibility of producing novel functional materials with important properties gives a strong stimulus for the research of organic–inorganic hybrid compounds
SCSC transformation is accompanied by a rearrangement of the network of intermolecular contacts that stabilizes the crystal packing, which frequently results in noticeable changes in the global structural network
The new compound (CHBMAH2)ZnBr4·3/2H2O 1 crystallizes in the orthorhombic system with a non-centrosymmetric space group P21212 and a Flack parameter of 0.014(6), indicating that the absolute structure given by the structure refinement is correct
Summary
The possibility of producing novel functional materials with important properties gives a strong stimulus for the research of organic–inorganic hybrid compounds. Within the organic–inorganic hybrid materials, perhalidometallates of protonated amines constitute a large family of materials, showing in some cases non-centrosymmetric structures, which are expected to have interesting properties, such as piezoelectricity, ferroelectricity, ferroelasticity, pyroelectricity [13,14,15,16,17], and even uses as catalysts [18,19]. In this case, various non-covalent weak bonds, such as hydrogen bonding and Coulombic and van der Waals interactions, govern the crystal packing of these materials. Kinzhybalo and co-workers (2018) have reported a compound tetra-n-butylammonium hypodiphosphate hydrate [24] in which water is removed from the crystal upon heating, accompanied by a reorganization of the ions present in the crystal
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