Linear trinuclear coordination compounds with 4-ethyl-1,2,4-triazole. Structure and magnetic properties

Abstract

The synthesis and characterisation of a series of linear trinuclear coordination compounds containing 4-ethyl-1,2,4-triazole (Ettrz) are presented. The crystal structure of the first linear trinuclear Mn(II) compound [Mn 3(Ettrz) 6(H 2O 6](CF 3SO 3) 6 was determined at room temperature. The compound crystallizes in the space group P 3 1 c, with lattice constants a = b = 14.545(2) Å and c = 20.072(3) Å. In the linear trimer the metal ions are linked by three 1,2-bidentate coordinating triazole ligands. The manganese ions are coordinated octahedrally. For the terminal metal ions the octahedral coordination is completed by H 2O molecules. The coordination distances are: MnN 2.24 Å and MnO 2.19 Å. The Co(II), Ni(II) and Zn(II) compounds are X-ray isomorphous with the Mn(II) compound. The magnetic exchange in the Mn, Co and Ni compounds is antiferromagnetic with J values of −0.6 cm −1, −14.7 cm −1 (Ising approximation) and −9.4 cm −1, respectively. An expression for the magnetisation and magnetic susceptibility of a linear Mn(II) trimer is presented. The Cu(II) and Cd(II) compounds, with composition [M 3(Ettrz) 9(H 2O) 3](CF 3SO 3) 6(H 2O) x, are also likely to be trinuclear. The terminal coordination sites in these compounds appear to be occupied by three monodentate coordinating triazole ligands and three water molecules. Surprisingly, the magnetic exchange in the Cu compound appears to be ferromagnetic.