Thiosemicarbazones as co-ordinating agents. Part 4. Synthesis, spectroscopic characterization and X-ray structure of two cobalt(III) complexes with pyridoxal thiosemicarbazone

Abstract

Two pyridoxal (3-hydroxy-5-hydroxymethyl-2-methylpyridine-4-carbaldehyde) thiosemicarbazone (H₂L) complexes of cobalt have been synthesised and structurally characterized by spectroscopic and X-ray diffraction methods. Crystallographic parameters: [Co(H_0.5L)₂]·3.5H₂O 1 space group C2/c, a= 10.335(1), b= 29.026(3), c= 16.564(2)Å, β= 94.85(3)°, Z= 8, R= 0.053, R′= 0.057; [Co(HL)L]·4.5H₂O 2, space group Pa= 11.195(1), b= 12.138(2), c= 11.128(1)Å, α= 103.23(3), β= 99.42(2), γ= 115.49(2)°, Z= 2, R= 0.058. In both compounds the cobalt atom is co-ordinated in a rather distorted octahedron to two molecules of pyridoxal thiosemicarbazone which are not equivalent. They are cobalt(III) complexes although the starting material was a cobalt(II) salt, differing in the H-atom positions of the pyridine nitrogen atoms. In 1 both the pyridine nitrogen atoms are ‘semiprotonated’: this is responsible for a loss of regularity in the arrangement of the water molecules. In 2 only one pyridine nitrogen atom is protonated. A. strong symmetric N ⋯ H ⋯ N hydrogen bond [2.685(9)Å] is present in complex 1.