Cobalt(III) complexes with thiosemicarbazones as co-ordinating agents. Spontaneous resolution by crystallization and absolute configuration

Abstract

Two new cobalt(III) complexes with pyridoxal [3-hydroxy-5-(hydroxymethyl)-2-methylpyridine-4-carbaldehyde] and pyruvic acid thiosemicarbazones (H₂L and H₂pt)[Co(HL)₂]Cl·EtOH 1 and [Co(Hpt)(pt)]2 respectively, have been synthesized and characterized using single-crystal X-ray diffraction and IR and CD spectroscopic methods. The structure of 2-thio-6-azathymine [6-methyl-3-thioxo-1,2,4-triazin-5-(2H,4H)-one] obtained upon cyclization of methyl pyruvate thiosemicarbazone in the course of its complexation reaction with cobalt(II) salts is also described. The structure of 1 consists of discrete [Co(HL)₂]⁺ cations, Cl^– anions and ethanol solvate molecules, that of 2 consists of neutral monomers and the two ligands are not equivalent. In both complexes the co-ordination geometry about cobalt is distorted octahedral and the two ligands are in the mer configuration (S and O atoms cis to each other and the N atoms trans). Complex 1, an example of optical resolution by preferential crystallization, is chiral.