Dimetallic complexes derived from a novel dinucleating chelating symmetrictriazole ligand; crystal structure, magnetic properties and ESR study of bis[mu-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), nicke l(II) and cobalt(II) salts yields dinuclear co-ordination compounds, which were spectroscopically characterized. The crystal and molecular structure o f one of the compounds, bis[mu-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-r ay diffraction. Complex 1 consists of dinuclear units with an inversion cen ter at the midpoint of the Cu-Cu vector. The most remarkable feature of thi s structure is that the daat ligand forms a six-membered chelate ring [Cu-N 3-C3-N1-C2-O1; Cua-N4-C4-N5-C5-O2], in contrast with the five-membered chel ate rings always found in comparable triazole derived dimers. This structur al feature is studied in the context of the geometry of the bridging system . Variable-temperature ESR spectral and magnetic susceptibility data indica te antiferromagnetic behaviour. The magnetic susceptibility data (4-290 K) are interpreted using the spin Hamiltonian (H) over cap=-2J((S) over cap(Cu 1).(S) over cap(Cu2)), and yielded J=-36 cm(-1) and g=2.13. The magnitude o f the exchange interaction is compared with previously reported magnetostru ctural data for related double 1,2,4-triazole-N1,N2 bridged dinuclear coppe r(II) compounds. A correlation between the exchange parameter J and the N-C u-N angle is described. Variable-temperature magnetic susceptibility measur ements (2-300 K) for the Ni(II) and Co(II) analogous compounds confirmed th e dimeric nature of these compounds and showed the presence of antiferromag netic exchange; the corresponding J values are rationalized on the basis of the structural features of the isostructural Cu(II) compound 1.