Structural trends in a series of divalent transition metal triazole complexes

Abstract

A series of bis bidentate complexes of 4-amino-3-methyl-1,2,4-triazole-5-thione, SN 4C 3H 6 (amt), with the divalent ions Mn, Fe, Co, Cu, and Zn have been crystallized by direct combination of the ligand and metal nitrate or perchlorate hydrate salt in ethanol. The structures were determined by single crystal X-ray diffraction techniques. In all cases, the triazole coordinates through the amine and thione substituents on the five-membered ring. The isostructural compounds [Mn(amt) 2(H 2O) 2](ClO 4) 2 ( 1) and [Fe(amt) 2(H 2O) 2](ClO 4) 2 ( 2) have the triazole and water ligands in a trans arrangement. The octahedral coordination shows a tetragonal distortion as the MN bonds are 0.15 Å longer than the MO bonds. The nitrate salts [Mn(amt) 2(H 2O) 2](NO 3) 2 ( 3), [Co(amt) 2(H 2O) 2](NO 3) 2 ( 4), and [Zn(amt) 2(H 2O) 2](NO 3) 2 ( 5), are also isostructural, but have the water molecules cis to each other and the triazoles arranged so that the amine groups are cis while the thiones are trans. The nitrate salt of the copper(II) complex, [Cu(amt) 2(H 2O) 2](NO 3) 2 ( 6), is similar in structure to 1 and 2; however, it is the water molecules which are more distant in the Jahn–Teller distorted coordination sphere. When sulfate is used in place of nitrate, a square pyramidal complex [Cu(amt) 2(SO 4)]·2H 2O ( 7) is obtained in which two pseudo-inverted triazole ligands form the base while the apex is a monodentate sulfato ligand. Neither water molecule is coordinated to the metal in this compound. These results are discussed in terms of the coordination behavior of the triazole ligand in these and similar systems.