Synthesis, structural characterisation and magnetic behaviour of two new 1-D trans-(mu(1,3)-N-3)nickel(II) compounds. Observation of magnetic transition at 288 and 137 K and determination of the Haldane gap for the trans-{(mu(1,3)-N-3)[Ni(meso-cth)}(

摘要

The compounds trans-{(mu(1,3)-N-3)[Ni(meso-cth)]}(n)(ClO4)(n) (1) and trans-{(mu(1,3)-N-3)[Ni(meso-cth)]}(n)(PF6)(n) (2), in which meso-cth is the meso isomer of 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, have been synthesised by reaction of the corresponding [Ni(meso-cth)](ClO4)(2) with azido ligand in aqueous medium. Crystal structures of I and 2 have been solved. Compound 1 crystallises in the orthorhombic system, group Pnab, a = 12.134(3) Angstrom, b = 16.107(4) Angstrom, c = 34.527(7) Angstrom, V = 6748 (3) Angstrom(3), Z = 12, R = 0.058. In the unit cell of I there are two different chains A and B in ratio 2:1. Compound I shows two structural transitions centred at 288 and 137 K, giving the compounds 1b and 1c with small differences in crystallographic parameters. Complex 2 crystallises in the orthorhombic system, group Pcnb, a = 11.756(3) Angstrom, b = 12.292(4) Angstrom, c = 16.381(3) Angstrom, V = 2367.1(11) Angstrom(3), Z = 4, R = 0.046. Magnetic measurements have been performed for the two compounds, showing strong antiferromagnetic coupling in I and moderate coupling in 2. The J parameters found from the best fit of the experimental data for I are J(A) = -43.9 cm(-1) and J(B) = -39.7 cm(-1) in the range 300-137 K and J(A) = -39.9 cm(-1) and J(B) = -40.0 cm(-1) in the range 137-170 K and J = -21.1 cm(-1) for 2. Magnetic results, which are well-correlated to the structural parameters (mainly bonds and torsion angles), show good agreement with the model previously reported by the authors. The Haldane gap has been calculated for compound 1. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 59]