Synthesis, characterization, and Hirshfeld surface analysis of coordination compounds composed of two different aminopyridines, isothiocyanate ligand molecules, and two different transition metal atoms

In this article, we describe the successful synthesis of three coordination compounds formed by the ligands 3-aminopyridine, 4-aminopyridine, and isothiocyanate ion with copper atoms and 4-aminopyridine and isothiocyanate ion with cadmium atoms, and their structural characterizations. The crystal structures of the compounds were determined by single crystal X-ray diffraction. According to that technique, the open formulae of these compounds are [Cu(3-aminopyridine)₂(NCS)₂] (<b>1</b>), [Cu(4-aminopyridine)₃(NCS)₂] (<b>2</b>), and [Cd(4-aminopyridine)₂(NCS)Cl] (<b>3</b>). In addition, the suitability of the structures of the compounds was characterized by elemental analysis, thermal analysis, and Fourier transform infrared spectroscopy. The single crystal X-ray diffraction analyses of these coordination compounds showed that the first of these coordination compounds had a 1D crystal structure and the other two had a 3D crystal structure. N-H⋯S, N-H⋯N, N-H⋯Cl, N-H⋯π, and C-H⋯π bonds and their combinations were effective in the formation of the crystal structures of the said coordination compounds. The metal atoms [Cu(II), Cu(II), and Cd(II)] in these coordination compounds were surrounded by various ligand molecules in a square planar, square pyramidal, and octahedral arrangement, respectively. In order to investigate some chemical and structural properties of these coordination compounds, theoretical calculations were performed with the software package Gaussian 03. The highest occupied molecular orbital (HOMO), lowest occupied molecular orbital (LUMO), and natural bond orbital (NBO) values of the coordination compounds were used in these calculations. When the energy gap value between the HOMO and LUMO states of the compounds was examined, it was predicted that compound <b>3</b> may have lower kinetic stability, higher chemical activity, and lower semiconductor properties than all the other compounds. According to the Hirshfeld surface analysis of the compounds, C⋯H, S⋯H, H⋯H, and N⋯H interactions are generally seen in the crystal structures of all compounds. In addition, Cd⋯Cl, Cd⋯S, H⋯Cl, and Cl⋯Cl interactions also occur in compound <b>3</b>.