Preparation and structural characterization of nickel(II), cobalt(II), zinc(II) and tin(IV) complexes of the isatin Schiff bases of S-methyl and S-benzyldithiocarbazates

The molecular structures of the isatin Schiff bases of S-methyldithiocarbazate (Hisasme) and S-benzyldithiocarbazate (Hisasbz) have been determined by X-ray diffraction and their complexes of general formula [ML2]center dot n(solvate) [M = Co2+, Ni2+, Zn2+; L = anionic forms of Hisasme or Hisasbz: solvate = DMF, DMSO; n =1, 2] and [Sn(L)Ph2CL]center dot nMeOH (n = 0, 1) have been synthesized and characterized by a variety of physicochemical techniques and X-ray diffraction. The bis-ligand complexes, [Ni(isa-sbz)(2)]center dot 2DMSO and [Co(isasme)(2)]center dot DMF have a six-coordinate, distorted octahedral geometry with the two uninegatively charged tridentate ONS ligands coordinated to the metal ions meridionally via the amide O-atoms, the azomethine nitrogen atoms and the thiolate sulfur atoms. By contrast, the crystal structure of [Zn(isasbz)(2)].2DMF shows a four-coordinate distorted tetrahedral geometry with the two Schiff bases coordinated as NS bidentate ligands via the azomethine nitrogen atoms and the thiolate sulfur atoms. Steric constraints of the rigid tridentate ligands lead to unusual 'pseudo-coordination' of the O-donors which occupy sites close to the metal but too distant to be considered as true coordinate bonds. The crystal structures of the tin(IV) complexes [SnLPh2CL]center dot nMeOH (L = isasme and isasbz: n = 0, 1) also show that the Schiff bases act as monoanionic bidentate NS chelating agents coordinating the tin(IV) ion via the azomethine nitrogen atoms and the thiolate sulfur atoms, the tin atom in each complex is five-coordinate with a highly distorted geometry intermediate of square pyramidal and trigonal bipyramidal. Again Sn center dot center dot center dot O contacts are weak and do not qualify as coordinate bonds. (C) 2010 Elsevier Ltd. All rights reserved.