Synthesis, characterization, and single crystal X-ray structures of [CoIII((BA)2en)(thiobenzamide)2]PF6 and [CoIII(acacen)(thiobenzamide)2]ClO4 and their solvatochromic properties

Abstract

New cobalt(III) complexes of two tetradentate Schiff base ligands, acacen = bis(acetylacetone)ethylenediimine dianion and (BA)2en = bis(benzoylacetone)-ethylenediimine dianion, with two axial thiobenzamide (tb) ligands have been synthesized by solid state methods and characterized by elemental analyses, IR, UV–Vis, and 1H-NMR spectroscopy. Both complexes show solvatochromism in a variety of solvents. The crystal and molecular structures of (1) and (2) were determined by X-ray crystallography. The structure (1) contains two independent [CoIII((BA)2en)(tb)2]+ complexes, two independent PF6 anions, and one well ordered ethyl acetate solvent molecule per asymmetric unit. In contrast, the structure (2) contains two independent [CoIII(acacen)(tb)2]+ complexes of C2 symmetry, a disordered ClO4 group and disordered toluene molecules. The octahedral coordination of Co(III) is distorted and the Schiff base ligands (ONNO donors) coordinate the cobalt ion in four equatorial positions, and the two axial positions are occupied by S-bonded thiobenzamide molecules. Intramolecular N–H···O hydrogen bonds donated by the thiobenzamide molecules add to the stability of the complexes in the solid state. The IR, UV–Vis, and 1H-NMR spectra of the two complexes and their solvatochromic properties are also discussed. The compounds exhibit LLCT mediated by the metal center.