Impact of cyanide co-ligand to convert crystal structure of pyrazole-based copper coordination compounds from a dinuclear to a polymeric structure and DFT calculations of [Cu2(tpmp)X2] (X = Cl and I)

Abstract

Two coordination copper (I) compounds containing pyrazole-based ligand of N, N, N′, N′-tetra-[3,5-dimethyl-1-pyrazolyl) methyl] –paraphenylenediamine (tpmp) namely [Cu2(tpmp)Cl2] (1) and [Cu3(tpmp)Cl CN2]n (2) were designed and synthesized. Reaction of tpmp ligand with Cu(I) in 1:2 ratio gives a discrete homodinuclear complex of 1, while addition of cyanide co-ligand leads to the formation of polymer 2. The considered compounds have been characterized by single-crystal X-ray diffraction, infrared spectroscopy and elemental analysis (CHN). The Cu(I) center in 1 is three-coordinated with a distorted trigonal geometry while in 2, cyanide functions as a bridging co-ligand to form a polymer with three types of coordination geometries around the copper atoms including, distorted linear, trigonal planar and trigonal pyramidal with coordination numbers of 2, 3 and 4, respectively. In the structure of 1, neighboring dinuclear units were linked by the CH…Cl intermolecular hydrogen bonds along the three crystallographic axes. In polymer 2, connection between the adjacent chains by the CH…N hydrogen bonds forms a centipede-like skeleton which further extended by the CH…Cl non-covalent intermolecular interactions along the ab and ac planes. DFT calculations on the optimized unit cells of [Cu2(tpmp)X2] (X = Cl and I) which have the same chemical formula in the gas phase, indicate that the observed transitions in the UV–Vis spectra could be mainly assigned to the halogen to ligand charge transfer (XLCT). Topology analysis, Density of States (DOS) spectra, Natural Population Analysis (NPA) as well as second order perturbation theory calculations were also performed on these compounds. Apart from slightly difference between the obtained properties from the DFT calculations which can be attributed to the difference between the electronegativity of the halogen atoms, they have the same electronic properties. This can be assigned to the identical structure of these compounds in the gas phase.