Synthesis, crystal structure, vibrational study, optical properties and Hirshfeld surface analysis of bis(2,6-diaminopyridinium) tetrachloridocobaltate(II) monohydrate

Abstract

The title organic–inorganic hybrid compound, (C5H8N3)2 [CoCl4]·H2O, was synthesized by slow evaporation at room temperature. Single-crystal X-ray diffraction analysis indicates that the asymmetric unit in this compound consists of one tetrahedral geometry [CoCl4]2-, two protonated organic cations (C5H8N3)+ and one water molecule of crystallization, all of which lie in general positions. In the crystal structure, the inorganic layers are built from tetrachloridocobaltate anions [CoCl4]2- and free water molecules, linked together by OH⋯Cl hydrogen bonds. The organic cations are intercalated between the inorganic layers via NH⋯Cl hydrogen bonds and form chains through aromatic donor–acceptor interactions. Crystal cohesion is achieved through NH⋯Cl, OH⋯Cl, NH⋯O and CH⋯Cl hydrogen bonds between organic cations, inorganic anions and the water molecules building up a three-dimensional network. The functional groups present in the crystal were studied by FTIR spectroscopy. Investigation of the optical properties of the compound confirmed its semiconducting properties by revealing a direct optical band gap at 1.67 eV. Photoluminescence proprieties were also reported. The three-dimensional Hirshfeld surface (3D-HS) analysis and the two-dimensional fingerprint plots (2D-FP) reveal that the structure is dominated by H⋯Cl/Cl⋯H and H⋯H contacts.