Design, synthesis and physico-chemical studies of a Co(II)/Co(III) mixed-valence complex: An experimental and DFT approach

Abstract

The bidentate amine, 2-picolylamine [2-(aminomethyl) pyridine: AMP], and concentrated hydrobromic acid have been used to synthesize a CoII/CoIII mixed-valence complex. Single crystals of the new compound were grown by the slow evaporation solution process at room temperature. The title compound crystallizes in the monoclinic system, space group P21/n, with a = 14.624 (5) Å, b = 10.302 (5) Å, c = 23.743(5) Å , β = 95.280(5)° and Z = 4. The crystal structure consists of three crystallographically independent bromide ions, one diprotonated AMP, one half water molecule and two crystallographically independent Cobalt(II) and Cobalt(III) ions: one has an octahedral geometry while the other is tetrahedrally coordinated. The crystal packing diagram reveals interesting non-covalent interactions involving NH···Br, OH···O and OH···Br hydrogen bonds, leading to the generation of 3D supramolecular architecture. The structural data, the BVS (Bond Valence Sum) calculations, the magnetic and the spectroscopic measurements are in agreement with a six-coordinate Cobalt(III) and four-coordinate Cobalt(II) mixed-valence complex. In this work, the experimental and theoretical study on molecular structure and vibrational spectral analysis of the new product has been reported. Theoretical calculations were performed by using density functional theory (DFT) at the B3LYP/LAN2DZ basis set levels. The electronic parameters such as frontier molecular orbitals, electrostatic potential and HOMO-LUMO energy were calculated. NLO and thermodynamic properties were studied. The theoretical values show good agreement with experimental values. Finally, thermal analysis and temperature dependent magnetic susceptibility measurements have been performed.