Coordination geometries of bis(4-amino-3-ethyl-1,2,4-triazole-5-thione) complexes of Mn, Fe, Co, Ni, Cu and Zn: relationship to the 3-methyl analogs

Abstract

A series of bis bidentate complexes of 4-amino-3-ethyl-1,2,4-triazole-5-thione, SN4C4H8 (aet, 1), of the divalent ions Mn, Fe, Co, Ni, 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 the complexes, the triazole bonds to the metal ion through the amine and thione substituents on the five-membered ring. [Mn(aet)2(H2O)2](NO3)2 (2) has the water molecules cis to each other and the triazoles arranged so that the amine groups are cis while the thiones are trans. The Mn-N distances (2.381(2) Å) are elongated relative to the Mn-O bond lengths (2.157(2) Å). [Fe(aet)2(H2O)2](ClO4)2·2H2O (3) has all like-ligands trans to one another and extra water molecules in the lattice hydrogen-bonded to the coordinated water. The compounds [Co(aet)2(H2O)2](NO3)2 (4), [Ni(aet)2(H2O)2](NO3)2 (5), and [Zn(aet)2(H2O)2](NO3)2 (6) are isostructural and display trans geometries similar to 3. The anhydrous compound [Cu(aet)2(NO3)2] (7) has the triazole ligands in a distorted square plane with like-donor atoms cis to each other. The Jahn–Teller distorted sixfold coordination is completed by O atoms of the nitrate anions at distances of 2.476(3) and 2.690(3) Å. These structures are compared with those of a recently reported series of 4-amino-3-methyl-1,2,4-triazole-5-thione complexes in order to gauge the effect of the alkyl group on the coordination behavior of the triazole ligand towards the divalent first row transition metals.