Three copper(II) complexes constructed from 4-(2-pyridyl)- 1H -1,2,3-triazole ligands: syntheses, structures, optical, and electrochemical properties

Three Cu(II) complexes constructed from 4-(2-pyridyl)-1H-1,2,3-triazole (L), namely, [CuL2Cl2]·H2O, [CuL2(CH3OH)(NO3)]NO3 and [CuL2(H2O)]SO4, have been synthesized and characterized. X-ray crystal structure analyses revealed that [CuL2Cl2]·H2O and [CuL2(CH3OH)(NO3)]NO3 have octahedral geometries, whilst [CuL2(H2O)]SO4 adopts a square-pyramidal coordination geometry. In all three complexes, the Cu(II) atoms are chelated by two L ligands in the basal plane, whilst the apical positions are occupied by Cl−, NO3−, CH3OH or H2O. The bandgaps between the HOMO and LUMO were estimated by cyclic voltammetry (CV) and diffuse reflectance spectroscopy (DRS) to be 3.43, 3.12, and 3.74 eV, respectively. Theoretical calculations on each structure gave similar results to the experiments. Frontier molecular orbital analyses showed that the higher electron density on the apical ligand, the lower the bandgap.