Dimetallic complexes derived from a novel dinucleating chelating symmetric triazole ligand; crystal structure, magnetic properties and ESR study of bis[μ-3,5-diacetylamino-1,2,4-triazolato-O ′,N 1,N 2,O ″]bis[(nitrato)(aqua)copper(II)] ‡

Reaction of 3,5-diacetylamino-1,2,4-triazole (Hdaat) with copper(II), nickel(II) and cobalt(II) salts yields dinuclear co-ordination compounds, which were spectroscopically characterized. The crystal and molecular structure of one of the compounds, bis[µ-3,5-diacetylamino-1,2,4-triazolato-O′,N 1,N 2,O″]bis[(nitrato)(aqua)copper(II)] 1, was determined by single-crystal X-ray diffraction. Complex 1 consists of dinuclear units with an inversion center at the midpoint of the Cu–Cu vector. The most remarkable feature of this structure is that the daat ligand forms a six-membered chelate ring [Cu–N3–C3–N1–C2–O1; Cua–N4–C4–N5–C5–O2], in contrast with the five-membered chelate rings always found in comparable triazole derived dimers. This structural feature is studied in the context of the geometry of the bridging system. Variable-temperature ESR spectral and magnetic susceptibility data indicate antiferromagnetic behaviour. The magnetic susceptibility data (4–290 K) are interpreted using the spin Hamiltonian Ĥ = –2J(ŜCu1·ŜCu2), and yielded J = –36 cm–1 and g = 2.13. The magnitude of the exchange interaction is compared with previously reported magnetostructural data for related double 1,2,4-triazole-N1,N2 bridged dinuclear copper(II) compounds. A correlation between the exchange parameter J and the N–Cu–N angle is described. Variable-temperature magnetic susceptibility measurements (2–300 K) for the Ni(II) and Co(II) analogous compounds confirmed the dimeric nature of these compounds and showed the presence of antiferromagnetic exchange; the corresponding J values are rationalized on the basis of the structural features of the isostructural Cu(II) compound 1.