One-dimensional oxalato-bridged metal(II) complexes with 4-amino-1,2,4-triazole as apical ligand

The synthesis, chemical characterization, thermal behavior and magnetic properties of six new one-dimensional oxalato-bridged metal(II) complexes of formula [M(mu-ox)(4atr)(2)](n) [M-II = Cu (1), Ni (2), Co (3), Zn (4), Fe(5)] and [Cd(mu-ox)(4atr)(2)-(H2O)](n) (6) (ox = oxalato dianion, 4atr = 4 -amino- 1, 2,4 -triazole) are reported. The crystal structures of 1 and 6 have been solved by single-crystal X-ray diffraction, whereas the remaining compounds have been studied by means of X-ray powder diffraction methods. Compounds 1-5 are isomorphous and crystallize in the triclinic space group P1 with unit cell parameters for 1 of a 5.538(1) angstrom, b = 7.663(1) angstrom, c = 7.711(2) angstrom, alpha = 62.2 1 (1)degrees, beta = 73.91 (1)degrees, gamma = 86.11 (1)degrees, and Z = 1. The crystal structures are comprised of one-dimensional linear chains in which the trans-[M(4atr)(2)](2+) units are sequentially bridged by bis(bidentate) oxalato ligands, resulting in an octahedral O4N2 donor set. Cryomagnetic susceptibility measurements show the occurrence of antiferromagnetic intrachain interactions for 2, 3, and 5, whereas compound 1 exhibits a weak ferromagnetic coupling in agreement with the out-of-plane exchange pathway involved. The magnetic behavior of 1 and 2 is analyzed and discussed in the light of the available magneto-structural data for analogous systems. Cd-II complex crystallizes in the monoclinic space group C2/c with unit cell parameters of a = 16.128(2) angstrom, b = 6.757(1) angstrom, c = 11.580(2) angstrom, beta = 104.46(1)degrees, and Z = 4. Its crystal structure contains one-dimensional chains in which metal centers are heptacoodinated to four oxygen atoms from two symmetry-related bis(bidentate) oxalato bridges, two endocyclic nitrogen atoms of trans-coordinated triazole ligands and one water molecule, to give a CdO4OwN2 pentagonal-bipyramidal geometry. Thermoanalytical and variable-temperature X-ray powder diffraction analyzes show that compound 6 undergoes a reversible dehydration-hydration process in which the anhydrous residue crystallizes with a different crystal lattice retaining the dimensionality of the oxalato-metal framework. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).