Synthesis, structural characterization and magnetic behaviour of two new (μ1,3-N3)2 dinuclear nickel compounds:: study of the magnetic transition at 235 K for the cis-(μ1,3-N3)2[Ni(dl-cth)]2(ClO4)2 compound

The dinuclear compounds cis-(mu(1,3)-N-3)(2)[Ni(dl-cth)](2)(ClO4)(2) (1a) and cis-(mu(1,3)-N-3)(2)[Ni(dl-cth)](2)(PF6)(2) . (CH3)(2)NCHO (2), in which dl-cth is the dl isomer of 5,5,7,12,12,14-hexamethyltetraazacyclotetradecane, were synthesized by reaction of the [Ni(dl-cth)](2+) cation with azido ligand in aqueous medium. Compound 1a crystallizes in the orthorhombic system, group Pbca, a = 14.784(2), b = 15.371(2), c = 19.954(3) Angstrom, V = 4534.4(1) Angstrom(3), Z = 4, R = 0.039 and shows a magnetic and structural transition centred at 235 K, giving an amorphous compound 1b. Complex 2 crystallizes in the monoclinic system, group P21/c, a = 12.215(4), b = 9.675(2), c = 24.221(4) Angstrom, beta = 99.46(2)degrees, V = 2823.5(1) Angstrom(3), Z = 4, R = 0.054, Magnetic measurements show very strong antiferromagnetic coupling for 1a (J = -113 cm(-1)) and moderate coupling for 1b and 2 (J = -64.5 and -75.1 cm(-1)). The magnetic data are discussed on the basis of the structural parameters, which suggest a distortion from a planar, eight-membered Ni-2(mu(1,3)-N-3)(2) ring for 1a to a chair conformation for 1b. (C) 1998 Elsevier Science S.A. All rights reserved.