Dimeric nickel(II) and copper(II) complexes of the pentadentate N3S2 chelating agents derived from S-alkyl/aryl esters of dithiocarbazic acid

Abstract

The helical dimeric copper(II) complex, [Cu(dapsbz)] (dapsbz = doubly deprotonated form of the 2,6-diacetylpyridine Schiff base of S-benzyldithiocarbazate) has been synthesized and structurally characterized. Each Schiff base in the dimer acts as a doubly negatively charged N S pentadentate chelating agent, providing three donor atoms, viz. the pyridine nitrogen atom, the azomethine nitrogen atom and the thiolate sulfur atom, to one copper ion and the azomethine nitrogen atom and thiolate sulfur atom to the second copper(II) ion. The stereochemistry adopted by each copper(II) ion in the dimer is five-coordinate, approximately square-pyramidal, with a CuNS coordination core. In the dimeric nickel(II) complex, [Ni(dapsme)] (dapsme = doubly deprotonated form of the 2,6-diacetylpyridine Schiff base of S-methyldithiocarbazate), the Schiff base also coordinates with the two nickel(II) ions as pentadentate NS chelating agent, but here the pyridine nitrogen atom of each ligand acts as a bridging donor atom. The azomethine nitrogen and thiolate sulfur atoms of one arm of a ligand coordinate with one nickel ion whereas the azomethine nitrogen and thiolate sulfur atoms of the other arm of the same ligand coordinate with a second nickel atom, the stereochemistry adopted by each nickel atom in the dimer being distorted octahedral with a NiNS coordination sphere