Synthesis, crystal structure and reactivity of copper(II) complexes of tetradentate N2S2 donor ligands

Two new hexa-coordinated mononuclear copper(II) complexes of two ligands L1 and L2 containing NSSN donor sets formulated as [Cu(L)(H2O)2](NO3)2 [1a, L = 1,2-bis(2-pyridylmethylthio)ethane (L1), 1b L = 1,3-bis(2-pyridyl-methylthio)propane (L2)] were synthesized and characterized by physico-chemical and spectroscopic methods. In 1a the single crystal X-ray crystallography analysis showed a distorted octahedral geometry about copper(II) ion. The crystal packing evidences pairs of complexes arranged about a center of symmetry and connected through a H-bond occurring between aquo ligands and nitrate anions. On reaction with chloride and pseudohalides (N3− and SCN−), in acetonitrile at ambient temperature, complexes 1 changed to monocationic penta-coordinated mononuclear copper(II) species formulated as [Cu(L)(Cl)]NO3 (2), [Cu(L)(N3)]NO3 (3), and [Cu(L)(SCN)]NO3 (4). These copper(II) complexes have been isolated in pure form from the reaction mixtures and characterized by physico-chemical and spectroscopic tools. The solid-state structure of 2a, established by X-ray crystallography, shows a trigonal bipyramidal geometry about the metal ion with a trigonality index (τ) of 0.561.