Spectroscopic and magnetic properties of two ferromagnetically coupled nickel( II ) dimers [{Ni(terpy)(NCX) ₂ } ₂ ](terpy = 2,2′ :6′,2″-terpyridine, X = S or Se). Crystal structure of the thiocyanate

Two new binuclear nickel(II) complexes [{Ni(terpy)(NCX)2}2](X = S or Se) have been prepared from 2,2′ :6′,2″-terpyridine (terpy) ligand. The crystal structure of [{Ni(terpy)(NCS)2}2]1 was solved by direct methods and refined by least-squares analysis to a discrepancy factor of 0.050. The crystals are triclinic, space group P, with lattice constants a= 8.822(2), b= 9.569(1), c= 10.906(1)Å, and α= 74.35(1), β= 85.19(2), γ= 78.75(2)°. The dimer, whose halves are related by a crystallographic inversion centre, consists of two nickel atoms co-ordinated to two terpy ligands, two terminal NCS ligands and two end-to-end NCS bridging ligands. Each NiII has a distorted-octahedral environment. The Ni ⋯ Ni distance is 5.633(3)Å and the bridging angles are 100.0(8) and 159(2)°. The complex [{Ni(terpy)(NCSe)2}2]2 was found to be isomorphous [a= 8.867(3), b= 9.592(4), c= 11.047(3)Å, α= 73.64(3), β= 83.44(3) and γ= 76.67(2)°]. Magnetic susceptibility data, measured from 2 to 300 K, were fitted to the Ginsberg equation, giving the parameters J=+4.9 cm–1, D=–4.3 cm–1 and z′ J′=+0.02 cm–1(NCS) and J=+10.1 cm–1, D=–10.0 cm–1 and z′ J′=+0.01 cm–1(NCSe). The magnetic behaviour of these and related complexes is discussed and some magnetostructural trends are given.