Preparation, spectroscopic characterization and X-ray crystal and molecular structures of nickel(II), copper(II) and zinc(II) complexes of the Schiff base formed from isatin and S-methyldithiocarbazate (Hisa-sme)

Complexes of general formula, [M(isa-sme)(2)]center dot n(solvate) [M = Ni2+,Cu2+, Zn2+, Cd2+; isa-sme = monoanionic form of the Schiff base formed by condensation of isatin with S-methyldithiocarbazate; n = 1 or 1.5; solvate = MeCN, DMSO, MeOH or H2O] have been synthesized and characterized by a variety of physicochemical techniques. An X-ray crystallographic structure determination of the [Ni(isa-sme)(2)] center dot MeCN complex reveals a six-coordinate, distorted octahedral geometry. The two uninegatively charged, tridentate, Schiff base ligands are coordinated to the nickel(II) ion meridionally via the amide O-atoms, the azomethine N-atoms and the thiolate S-atoms. By contrast, the crystal structure of [Zn(isa-sme)(2)] center dot MeOH shows a four-coordinate distorted tetrahedral geometry. The two dithiocarbazate ligands are coordinated as N,S bidentate chelates with the amide O-atom not coordinated. The structure of the copper(II) complex [Cu(isa-sme)(2)] center dot DMSO is complicated and comprises two different complexes in the asymmetric unit, one four- and the other five-coordinate. The four-coordinate copper(II) has a distorted (flattened) tetrahedral geometry as seen in the Zn(II) analogue whereas the five-coordinate copper(II) has a distorted square-pyramidal geometry with one ligand coordinated to the copper(II) ion as a tridentate (N, S, 0) ligand and the other coordinated as a bidentate N, S chelate. EPR spectroscopy indicates that in solution only one form is present, that being a distorted tetrahedral complex. (C) 2007 Elsevier Ltd. All rights reserved.