Synthesis, crystal structure and magnetic properties of bis[μ-bis(3-(pyridin-2-yl)-1,2,4-triazole-N′,N1,N2)] bis[triaqua nickel(II)] tetranitrate

A new dinuclear nickel(II) coordination compound of formula [Ni-2(Hpt)(2)(H2O)(6)](NO3)(4) (Hpt = 3-(pyridin-2-yl)-1,2,4-triazole) was synthesized. The structure was solved at 298 K by single-crystal X-ray analysis. Bis[mu-bis(3-(pyridin-2-yl)-1,2,4-triazole-N',N1,N2)] bis[triaqua nickel(II)] tetranitrate (C14H24N12O18Ni2) crystallizes in the triclinic space group P-1, a = 7.2266(1), b = 9.9144(1), c = 11.2647(1) Angstrom, alpha = 66.854(1)degrees, beta = 74.000(1)degrees, gamma=86.400(2)degrees, V=712.42(1) Angstrom(3), Z = 1 (dinuclear units), 2823 reflections (I> 2 sigma(I)), R1 = 0.0442, wR2 = 0.1197. The Ni(II) ions are bridged by two neutral Hpt ligands coordinating via N1 and N2 in the equatorial plane, Ni(1)-Ni(1)' = 4.098(1) Angstrom. The Hpt bridging mode is asymmetric (Ni(1)-N(1)' = 2.074(2) Angstrom, Ni(1)-N(2)=2.052(2) Angstrom, N(1)-N(2)-Ni(1) = 138.8(1)degrees, N(2)-N(1)-Ni(1)' = 124.3(1)degrees). The octahedral environment around nickel(II) is completed by the coordinating pyridyl group (Ni(1)-N(31) = 2.123(2) Angstrom) and three coordinating water molecules (Ni(1)-O(1) = 2.083(2) Angstrom, Ni(1)-O(2) = 2.053(2) Angstrom, Ni(1)-O(3) = 2.049(2) Angstrom). The Ni(II) pairs are antiferromagnetically coupled, with J= -4.65 cm(-1) (based on the spin Hamiltonian: H= -2J[S-Ni1. S-Ni2]). The J value was rationalized on the basis of the geometry around Ni(II). The superexchange pathway involves the sigma orbitals of the N1,N2-diazine moiety of the bridging 1,2,4-triazole network. The nature and the magnitude of the antiferromagnetic exchange is discussed on the basis of the structural features. (C) 1998 Elsevier Science S.A. All rights reserved.