Co(II), Ni(II) and Cu(II) complexes of azo-aminopyrazole ligand: Spectroscopic, crystal structure and quantum chemical calculations

Reaction of 5-Methyl-4-(2-nitro-phenylazo)-2-phenyl-2H-pyrazol-3-ylamine (H₂L) with Co(II), Ni(II) and Cu(II) salts affords complexes of the type [M(HL)₂], which were characterized by elemental analysis, FT IR, UV-Vis, magnetic susceptibility, conductance measurements and single crystal X-ray diffraction. H₂L crystallizes in a monoclinic space group C2/c, while the Cu(II) complex crystallizes in the triclinic P1¯(2) space group. H₂L behaves as a mono-negatively bidentate ligand via NN and NH^-. Comparison between the crystal and the optimized data at DFT/B3LYP/6-31G(d) level of theory was discussed. Time-dependent DFT calculations were performed to assign the electronic spectra. The natural charge of Ni^II is more reduced than Co^II and Cu^II, which suggests the higher complexation ability of H₂L toward the former ion.