Crystal Structure and DFT Computations of a Solid-State Solution of Mixed Mononuclear Cu(II)/Co(II) Complex

Abstract

A novel mixed molecular Cu (II) and Co (II) complexes [Cu L₂]_0.82 and [CoL₂]_0.18 (1) where HL = (4-salicylaldaimine antipyrine) derived from            4-aminoantipyrine and 2-hydroxybenzaldehyde, was isolated as a green solid and characterized by Fourier Transform Infrared Spectroscopy (FTIR), Ultra-Violet Visible spectroscopy (UV-Vis) and Single-crystal x-ray diffraction. Compound 1 is a solid-state solution that contains a statistical mixture of two different molecular complexes: 82% of a 17-electron Cu (II) complex and 18% of a 15-electron Co (II) complex. By looking at the structure, it seems that the two metal ions occupy the same metal site, which is not true; at least a small distance between them exists, verified using the Density functional theory (DFT). A divalent metal cation binds four coordination sites in each molecular complex from two corresponding bidentate Schiff base ligands. Each metal atom is coordinated with two nitrogen and two oxygen atoms of the Schiff base ligand in a geometry much closer to pseudo-tetrahedral than planar. DFT calculations were used to validate the trends observed in bond lengths and angles in this structure. By using the DFT methods, it is seen that there are no significant differences in the experimental values obtained by single-crystal X-ray diffraction. It should be noted that the experimental results belong to the solid phase, while the theoretical calculations belong to the gas phase.