Thiosemicarbazones as co-ordinating agents. Part 5. Zinc complexes derived from methyl pyruvate- and pyridoxal-thiosemicarbazone

Abstract

Reaction of zinc chloride or acetate with two ligands, methyl pyruvate thiosemicarbazone (Hmpt) and pyridoxal thiosemicarbazone (H₂L), lead to the formation of five novel complexes which have been characterized by spectroscopic methods. The crystal structure of three compounds: [Zn(Hpt)₂]1, [Zn(Hept)Cl₂]2 and [{Zn(HL)Cl}₂]·2H₂O 3(H₂pt = pyruvic acid thiosemicarbazone, Hept = ethyl pyruvate thiosemicarbazone) have been determined by X-ray methods from diffractometer data and refined by least squares to R 0.054 (1), 0.034 (2) and 0.029 (3) for 1205, 1590 and 2134 observed reflections respectively. All the zinc complexes seem to be influenced significantly by the nature of the solvent and, consequently by the resulting pH. The transesterificated (Hept) and hydrolysed (H₂pt) forms of the original ligand (Hmpt) have been selectively isolated depending on the experimental conditions. In 1 the co-ordination geometry about zinc is distorted octahedral while in 2 and 3 the metal is five-co-ordinated, the geometry about zinc being better described as intermediate between an ideal square pyramid and trigonal bipyramid.