Coordination geometries of bis(4-amino-3-alkyl-1,2,4-triazole-5-thione) complexes of first-row transition metals: crystal structures of complexes with propyl and hydrogen in the 3-position. Relationship to the 3-methyl and 3-ethyl analogs

A series of bis bidentate complexes of 4-amino-3-propyl-1,2,4-triazole-5-thione, SN4C5H10 (apt, 1) of the divalent ions Fe, Co, Ni, and Zn has 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. [Fe(apt)2(H2O)2](ClO4)2 (2) has the like-ligands trans to each other. The FeN distances (2.259(5) Å) are elongated relative to the FeO bond lengths (2.092(5) Å). The compounds [Co(apt)2(H2O)2](NO3)2·2H2O (3), [Ni(apt)2(H2O)2](NO3)2·2H2O (4), and [Zn(apt)2(H2O)2](NO3)2·2H2O (5) are isostructural, with the water molecules cis to each other and the triazole ligands positioned with the amine groups cis and S atoms trans. A series of complexes of 4-amino-1,2,4-triazole-5-thione (aht, 6) of divalent Mn, Co, and Zn has also been crystallized by similar means and structurally characterized. [Mn(aht)2(H2O)2](ClO4)2 (7) has the ligands arranged as in 3, though with a non-centrosymmetric packing (space group C2). The cis MnN distances are significantly longer (2.377(2) Å) than the MnO distances (2.160(2) Å). [Co(aht)2(H2O)2](ClO4)2 (8) possesses the trans geometry found in 2, though with comparable CoN and CoO bond lengths (2.175(3) and 2.082(3) Å). [Zn(aht)2(H2O)2](ClO4)2 (9) is isostructural with 7. These structures are compared with those of two recently reported series of 4-amino-3-alkyl-1,2,4-triazole-5-thione complexes (alkyl=methyl and ethyl) 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.