CRYSTAL-STRUCTURE AND SPECTROSCOPIC AND MAGNETIC-PROPERTIES OF 2 CIS-AZIDO CATENAS OF NICKEL(II) - CIS-CATENA-MU-N3)[NI(BIPY)2](X) (X=CLO4, PF6)

The compounds cis-catena-(mu-N3)[Ni(bipy)2](ClO4) (1) and cis-catena-(mu-N3)[Ni(bipy)2](PF6) (2) (where bipy = 2,2'-bipyridine) have been synthesized and characterized. Both crystallize in the monoclinic P2(1)/c space group. For 1, a = 20.830(3) angstrom, b = 15.497(4) angstrom, c = 13.90(1) angstrom, beta = 101.72(3)-degrees, V = 4393(3) angstrom3, Z = 4, R = 0.065, and R(w) = 0.070. In the case of compound 2, a = 21.173(3) angstrom, b = 15.781(2) angstrom, c = 13.930(4) angstrom, beta = 100.04(2)-degrees, V = 4583(2) angstrom3, Z = 4, R = 0.071, and R(w) = 0.075. The nickel(II) ions are octahedral with the two bipy ligands and end-to-end azido bridges in a cis-arrangement. This configuration of the azido bridges has not been reported so far. Magnetic measurements of both compounds show strong antiferromagnetic couplings between the nickel cations through the azido ions. The obtained exchange parameters are J = -33.0 cm-1 for the perchlorate compound 1 and J = -22.4 cm-1 for the hexafluorophosphate complex 2, with a gyromagnetic tensor value of g = 2.15 in both cases. The magnetic behavior has been compared with that of the trans-azido chains known in the literature and analyzed by extended Huckel MO calculations.