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]·n(solvate) [M = Co2+, Ni2+, Zn2+; L = anionic forms of Hisasme or Hisasbz; solvate = DMF, DMSO; n = 1, 2] and [Sn(L)Ph2Cl]·nMeOH (n = 0, 1) have been synthesized and characterized by a variety of physicochemical techniques and X-ray diffraction. The bis-ligand complexes, [Ni(isasbz)2]·2DMSO and [Co(isasme)2]·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]·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⋯O contacts are weak and do not qualify as coordinate bonds.

Graphical abstractX-ray crystallographic structure determination shows that the complexes, [Ni(isa-sbz)2]·2DMSO and [Co(isasme)2]·DMF, where isasme and isasbz are the deprotonated forms of the isatin Schiff bases of S-methyl and S-benzyldithiocarbazates, respectively, have a distorted octahedral geometry. By contrast, [Zn(isasbz)2]·2DMF is tetrahedral. The organotoin(IV) complexes [Sn(isasme)Ph2Cl]·MeOH and [Sn(isasbz)Ph2 Cl] have a distorted square-pyramidal geometry.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Two forms of the isatin Schiff base of S-benzyldithiocarbazate(Hisasbz) have been isolated and structurally characterized by X-ray diffraction. ► A rare high-spin six-coordinate bis-chelated cobalt(II) complex of the isatin Schiff base of S-methyldithiocarbazate(Hisasme) has been structurally characterized. ► A bis-ligand zinc(II) complex of Hisasbz, in which the Schiff base acts as an NS bidentate chelating agent, has been prepared and characterized. ► Five-coordinate organotin(IV) complexes of general formula [Sn(NS)Ph2Cl] (NS = deprotonated form of the isatin Schiff bases acting as bidentate NS donor ligands) have been structurally characterized.