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

•Synthesis of pyrazoles metal complexes containing azo group.•Crystal structures of azo ligand and CuII complex were investigated.•Structural properties were studied both experimentally and theoretically.•Electronic transitions were assigned by the aid of TD-DFT 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 NiII is more reduced than CoII and CuII, which suggests the higher complexation ability of H2L toward the former ion.

Graphical abstractReaction 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].Figure optionsDownload full-size imageDownload as PowerPoint slide