SYNTHESIS, STRUCTURAL, SPECTROSCOPIC AND MAGNETIC STUDIES OF 2 AZIDO AND THIOCYANATO NICKEL(II) DINUCLEAR COMPLEXES WITH FERROMAGNETIC INTERACTIONS

From a newly synthesised tridentate ligand [pepci = N'-(2-pyridin-2-ylethyl)pyridine-2-carbaldimine] two new octahedrally co-ordinated nickel(II) dimers, [{Ni(pepci)(N3)2}2] 1 and [{Ni(pepci)(NCS)2}2] 2, have been prepared. The crystal structure 1 has been solved. It crystallizes in space group P2(1)/c with four formula weights in a cell measuring a = 9.198(3), b = 17.382(6), c = 19.356(7) angstrom, and beta = 99.57(1)-degrees. The structure consists of isolated dimeric units in which the nickel ions are linked by two azide bridging groups in an end-on fashion. Two pepci ligands and two terminal azide groups complete the co-ordination spheres. Inside the dimer, each Ni(pepci)(N3)2 entity is crystallographically non-equivalent. There are two different bridging angles Ni(A)-N(4A)-Ni(B) 102.2(2) and Ni(B)-N(4B)-Ni(A) 101.0(2)-degrees. The co-ordination geometry at each nickel atom is approximately octahedral. The Ni(A) ... Ni(B) distance is 3.297(1) angstrom. For complex 2 a dimeric structure involving end-to-end thiocyanate bridging groups is proposed. Magnetic susceptibility data, measured from 4 to 300 K, were fitted to the Ginsberg equation, giving the parameters (cm-1): J = +36.3, D = -18.8, z'J' = 0.0 (N3); and J = +4.9, D = -9.8, z'J' = +0.33 (NCS). The magnetic behaviour of these and related complexes is discussed and some magnetostructural trends are given.