Nickel(II) complexes of the isomeric tetraazamacrocyclic ligands 1,11-and 1,8-bis(2-pyridylmethyl)-cyclam and of a structurally constrained N4,N8-methylene bridged analogue

The nickel(II) complexes of 1,8-bis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane (L-1) and of the isomeric ligand 1,11-bis(2'-pyridylmethyl)-1,3,8,1 1-tetraazacyclotetradecane (L-2) have been isolated. The X-ray. crystal structure of a mixed acetate/chloride salt of [NiL1](2+) revealed an octahedral Ni coordination by two N atoms of the pyridine groups (in c is-related positions) and four of the macrocycle, which is folded along the 1,8-direction and bound in the Lis-V configuration. The results of UV-Visible absorption spectroscopy and cyclic voltammetry in solution and the effective magnetic moments in the solid state are also consistent with octahedral N-6-coordination of high-spill nickel(II). The intermediate in the synthesis of ligand L a bis-(2-pyridylmethyl) substituted formamidinium cation (L-3)(+) reacted with nickel(II) perchlorate to form a [Ni(H2L3)Cl](2+) complex incorporating a methylene bridge between the non-pyridylmethylated N atoms (N-4 and N-8) of the macrocycle, which was characterised by X-ray crystallography. The Ni atom has a fac-octahedral coordination by the two pyridine and three macrocyclic nitrogens (the Fourth one, N-4, qs protonated) and one Cl atom. (C) 2001 Elsevier Science Ltd. All rights reserved.