Complexes with sulphur and selenium donor ligands. Part 8. Some 4-phenylthiosemicarbazone complexes of cobalt(II) and the crystal structure of bis(acetone 4-phenylthiosemicarbazone)cobalt(II) bromide (green form)

Abstract

Some thiosemicarbazone complexes of Co^II of general formula CoL₂X₂ and Co(L – H)₂(L = NHPh·CS·NH·N:CR¹R²; X = Cl, Br, or I) have been prepared and characterised by spectroscopic methods in the solid state and in some non-aqueous solutions. When R¹ and/or R² is an aryl group the ligand is unidentate and tetrahedral complexes are obtained. When R¹ and R² are alkyl groups the ligand is bidentate and trigonal-bipyramidal complexes [CoL₂X]X are obtained. Phenyl substitution at position 4 of the thiosemicarbazone thus seems to exert little effect on the stereochemistry adopted, and the complexes are similar to those of the unsubstituted ligand analogues. The crystal structure of the green form of [Co(NHPh·CS·NH·N:CMe₂)Br]Br has been determined. Crystals are orthorhombic, space group Fddd, with unit-cell dimensions a= 17.039(3), b= 24.184(8), c= 24.852(7)Å, and Z= 16. The structure has been solved by Patterson and Fourier methods from automatic diffractometer data and refined by least-squares techniques to R 0.077 from 612 independent non-zero reflections. The ligands are bidentate, the co-ordination about Co^II being trigonal bipyramidal of chromophore [CoS₂N₂Br], with two sulphur atoms and the bromine atom lying in the trigonal plane. Possible structures for these complexes in solution and for some corresponding thiocyanates containing unsubstituted thiosemicarbazones are briefly discussed.