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 Cu^I–Cu^II(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)Å and Z= 8. Crystals of 2 are orthorhombic, space group Pbca, a= 12.900(3), b= 12.965(5), c= 14.250(5)Å and Z= 8. Crystals of 3 are monoclinic, space group P2₁/a, a= 34.099(8), b= 8.704(3), c= 7.163(3)Å, 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 Cu^II 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 Cu^II atom as in 1, while the other acts as a µ₃ ligand chelating another Cu^II atom and bridging through the iminic nitrogen and the sulfur atoms two Cu^I 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 Cu^I in 3.