Synthesis, reactivity, structural studies and magnetic properties of 4-amino-1,4-dihydro-3-methyl-1,2,4-triazole-5-thione copper complexes

Abstract

By reaction of CuCl2 with 4-amino-1,4-dihydro-3-methyl-1,2,4-triazole-5-thione (HL) in a 4 : 1 molar ratio and in a 12 mol dm–3 HCl medium, at room temperature, the complex [CuCl2(HL)]·H2O 1 was isolated in an orthorhombic form. With an excess of CuCl2 a polymeric complex [{Cu2Cl4(HL)}n]·nH2O 2 was isolated, while introduction of a bar of metallic copper gave a polymeric mixed-valence CuI–CuII(1 : 2) complex [{Cu3Cl5(OH2)(HL)2}n]·2nH2O 3. Crystals of 1 are orthorhombic, space group Pbca, a= 16.256(1), b= 15.611(2), c= 7.327(1)A and Z= 8. Crystals of 2 are orthorhombic, space group Pbca, a= 12.900(3), b= 12.965(5), c= 14.250(5)A and Z= 8. Crystals of 3 are monoclinic, space group P21/a, a= 34.099(8), b= 8.704(3), c= 7.163(3)A, β= 96.14(2)° and Z= 4. The structures have been solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least squares to R= 0.0393, 0.0582 and 0.0467 for 1132, 1346 and 3177 observed reflections respectively. In 1 the triazole acts as a chelating ligand through the sulfur and the aminic nitrogen atoms and the co-ordination of CuII is fundamentally square planar. In 2 the ligand acts in a tridentate manner, chelating and bridging through the iminic nitrogen atom. The [Cu2Cl4(HL)] units can be considered as inner salts and are joined in a head-to-tail fashion forming zigzag polymeric chains. In 3 the two independent ligands present different behaviours; one chelates a CuII atom as in 1, while the other acts as a µ3 ligand chelating another CuII atom and bridging through the iminic nitrogen and the sulfur atoms two CuI atoms. The magnetic properties were investigated by measurements of electron paramagnetic resonance microwave absorption. For all compounds S=½ spectra were observed with spectroscopic g constants in the range ca. 2.05–2.20. The resulting single-ion g tensors are typical of a tetragonal elongated copper(II) ion where covalency plays a relevant role due to the presence of the SCNN chelating structure. The magnetic local axes deduced on this basis are strictly related to the copper co-ordination planes (obtained from the structural data) confirming the oxidation state II for all the copper atoms except for the tetrahedral CuI in 3.