The Comparative Study of Four Hexachloroplatinate, Tetrachloroaurate, Tetrachlorocuprate, and Tetrabromocuprate Benzyltrimethylammonium Salts: Synthesis, Single-Crystal X-Ray Structures, Non-Classical Synthon Preference, Hirshfeld Surface Analysis, and Quantum Chemical Study

Abstract

Four benzyltrimethylammonium(BTMA) salts were successfully prepared: bis(benzyltrimethy lammonium) hexachloroplatinate (1), benzyltrimethylammoniumtetrachloroaurate (2), bis(benz yltrimethylammonium) tetrachlorocuprate (3), and bis(benzyltrimethylammonium) tetrabromocuprate (4) frombenzyltrimethylammoniumhydroxide (Triton B). Their crystal structures were determined by single-crystal X-ray diffraction, and the supramolecular architectures were characterized hierarchically. Extended Hirshfeld surface analysis, including enrichment ratio calculations, was performed to evaluate intermolecular interactions. Nonclassical hydrogen bonds, such as C–H. . .Cl(Br), involving the anions, contribute to the formation of self-assembled architectures. Additional stabilization arises fromπ. . .π and Cu–Br. . .π interactions, particularly in crystals 2 and 4, respectively. Hirshfeld surface analysis showed that H. . .H and C. . .H/H. . .C interactions are the dominant contributors in all crystals. According to enrichment ratio calculations, C. . .H/H. . .C interactions in 1, 3, and 4; Cl. . .H/H. . .Cl in 1 and 3; Cu. . .H/H. . .Cu in 3 and 4; and Br. . .H/H. . .Br and Br. . .C/C. . .Br in 4 are statistically favored in the crystal packing. Halogen bonding Cl. . .Cl was observed in 1 but does not significantly influence packing. Energy framework calculations indicated that dispersive interactions are favorable in the analyzed crystals. A library of H-bonding supramolecular patterns, including interchangeable synthons, is provided andmay guide the rational design of new derivatives with controllable features. Finally, the topology of intermolecular connections and the electronic structure of the benzyltrimethylammonium cation, investigated by quantum-chemical calculations, provide insights into its reactivity.