CRYSTAL-STRUCTURE AND SPECTROSCOPIC AND MAGNETIC-PROPERTIES OF 2 NOVEL MONO(MU-HALO) COPPER(II) CHAINS WITH AN UNUSUAL ZIGZAG ARRANGEMENT - [CU(C13H13N3)X]PF6 (X=CL,BR)

Three new compounds [Cu(C13H13N3)Cl)(PF6).nH(2)O [n = 1 (1); n = 0 (2)] and [Cu(C13H13N3)Br](PF6) (3), where C13H13N3 = pepci = N-(2-pyridylethyl)pyridine-2-carbaldimine, have been synthesized and the crystal structures of 2 and 3 determined at room temperature. Both compounds crystallize in the orthorhombic system, space group Pc2(1)b and Z = 16, with cell parameters of a = 7.804(2) Angstrom, b = 24.686(4) Angstrom, c = 34.376(9) Angstrom, and V = 6623(3) Angstrom(3) for compound 2 and a = 7.904(3) Angstrom, b = 24.816(3) Angstrom, c = 34.289(4) Angstrom, and V = 6726(3) Angstrom(3) for compound 3. The structure of 2 was refined to an R value of 0.068 (R(w) = 0.055), while the structure of 3 was refined to R = 0.071 (R(w) = 0.067). Both structures consist of [Cu(pepci)X](+) (X = Cl, Br) cations which stack along the a axes and PF6- anions sited in the interchain space. In the stack, two successive copper complexes ate in an alternating orientation, to give a novel zigzag mono(mu-halide) chain structure. There are four independent [Cu(pepci)X](PF6) molecules in the unit cell, which are repeated four times. The chloro compounds 1 and 2 are not isostructural phases, compound 1 being characterized as a dimer. Magnetic properties of the compounds have been investigated down to 4 K. The chloro complexes exhibit weak antiferromagnetic interactions, while the bromo one is ferromagetic. The magnetic susceptibility data for both chains (2 and 3) have been fitted by using a linear chain model. The obtained parameters are J/k = -2.0 K (1.39 cm(-1)) (2) and J/k = +1 K (0.70 cm(-1)) (3). However, the data corresponding to complex 1 have been fitted to a dimer system, with an exchange coupling constant of -3.0 K (2.09 cm(-1)). Magneto-structural correlations in the chloro-bridged chains have been analyzed by using extended Huckel molecular orbital calculations.