Synthesis, structures, electronic properties and DFT calculations of cobalt(II) complexes with a redox non-innocent naphthoquinone ligand

The present work reports the syntheses of two cobalt(II) complexes, 1 and 2, with a naturally occurring redox non-innocent 2-hydroxy-1,4-naphthoquinone ligand in the presence of two substituted pyridines as ancillary ligands, one with an electron withdrawing group and the other with an electron donor group. Both compounds have been characterized in the solid state by IR spectroscopy and in solution by UV-Vis spectroscopy and cyclic voltammetry. Their molecular structures were determined by the single crystal X-ray diffraction study. The structures of both complexes are similar as in both cases the pyridyl ligands are cis coordinated and the naphthoquinone moiety plays a crucial role in the crystal packing by participation through pi center dot center dot center dot pi, C-H center dot center dot center dot pi and hydrogen bonding interactions. DFT calculations are consistent with the UV-Vis spectral assignment and the geometrical preferences of the complexes. Electrochemical studies clearly demonstrate that the redox properties of the lawsonate ligand can be tuned significantly by the introduction of substitution in the ancillary pyridine ligands. (C) 2016 Elsevier Ltd. All rights reserved