Mixed-ligand ternary complexes of potentially pentadentate but functionally tridentate Schiff base chelates

Abstract

The potentially pentadentate chelate 2,6-diacetylpyridine-bis(N-methyl-S-methyldithiocarbazate) (Nmedapsme) has been synthesized and structurally characterized by X-ray diffraction. Its reactions with nickel(II) salts did not lead to pentadentate coordinated ligand complexes but ternary complexes of general formula, [Ni(Nmedapsme)(nmesme)L]X·H 2O (L = Br −, I −; X = I −, BF 4 −) where Nmedapsme binds as a tridentate and nmesme = N-methyl-S-methyldithiocarbazate. The related ternary nickel(II) complexes of formula, Ni(Nmedapsme)(nmetsc)Br 2 has also been prepared and characterized. X-ray crystal structures of [Ni(Nmedapsme)(nmesme)I]I·H 2O and [Ni(Nmedapsme)(nmesme)Br]BF 4·H 2O revealed that, in these complexes, the Nmedapsme ligand acts as a tridentate NNN donor while the distal S-donors are not coordinated. The bidentate ( NS) ligand, nmesme coordinates to the nickel(II) ion via the amino nitrogen and the thione sulfur atoms, the sixth coordination site is occupied by an anion. In both complexes, the nickel(II) ion adopts a distorted octahedral configuration. The complex [Cu(nmesme) 2(ONO 2)]NO 3 was obtained from an unsuccessful attempt to complex copper(II) with Nmedapsme. Hydrolysis of the parent Schiff base Nmedapsme occurred during complexation. An X-ray crystallographic structure analysis shows that the complex, [Cu(nmesme) 2(ONO 2)]NO 3 has an approximately square–pyramidal geometry with the two nmesme ligands coordinated to the copper(II) ion as NS bidentate chelating agents via the amino nitrogen and thione sulfur atoms and the fifth coordination position of copper(II) is occupied by a monodentate nitrate ligand.