Synthesis and spectroscopic studies on transition-metal nitrates and thiocyanates of a chelating imidazole-thioether ligand. The crystal structures of diaquabis[5-methyl-4-(ethyl-mercaptomethyl)imidazole]nickel(II) dinitrate, diaquabis[5-methyl-4-(ethyl-mercaptomethyl)imidazole] copper(II) dinitrate and bis[5-methyl-4-(ethyl-mercaptomethyl)imidazole] bis(thiocyanato- N)cobalt(II)

Abstract

The synthesis and characterization of some monomeric transition-metal coordination compounds with the novel bidentate ligand 5-methyl-4-(ethyl- mercaptomethyl)imidazole (abbreviated memi) are described, viz. [M(memi) 2(H 2O) 2](NO 3) 2 and M(memi) 2(NCS) 2 with M = Co, Ni, Cu. Single crystals of [Ni(memi) 2(H 2O) 2](NO 3) 2 ( A), [Cu(memi) 2(H 2O) 2](NO 3) 2 ( B) and Co(memi) 2(NCS) 2 ( C) were used in structure determinations. The three compounds all crystallize in the monoclinic space group P2 1/ n with Z = 2. The cell dimensions for compound A are a = 10.402(2), b = 13.589(4), c = 8.476(3) Å, β = 108.35(2)°, V = 1137.21 Å 3 and D x = 1.551 g cm −3. The cell dimensions of compound B are a = 10.451(3), b = 13.430(5), c = 8.757(4) Å, β = 109.24(3)°, V = 1160.35 Å 3 and D x = 1.53 g cm −3. The cell dimensions for compound C are a = 12.147(7), b = 9.096(4), c = 10.363(4) Å, β = 102.14(4)°, V = 1119.27 Å 3, and D x = 1.447 g cm −3. The structures were solved by heavy-atom techniques and refined by least-squares methods to residual R w values of 0.032 ( A), 0.033 ( B) and 0.046 ( C). The coordination geometry of the metal ion in all compounds is distorted octahedral. In compounds A and B the metal ion is lying on a centre of symmetry and is surrounded by two thioether sulfur atoms, two imidazole nitrogen atoms and two oxygen atoms from water molecules. In contrast to the nickel ion in structure A the copper ion in compound B has a significantly elongated octahedral geometry in the direction of the oxygen molecules. The compound with the much stronger coordinating anion, NCS (compound C) resembles the structures of A and B in having the same coordination geometry with the thiocyanate anions coordinating instead of the water molecules.