Nickel(II) complexes of the isomeric tetraazamacrocycic ligands 1,11-and 1,8-bis(2-pyridylmethyl)-cyclam and of a structurally constrained N~4, N~8-methylene bridged analogue

摘要

The nickel(Il) complexes of 1,8-bis(2'-pyridylmethyl)-1,4,8.II-tetraazacyclotetradecane (ll) and of the isomeric ligand 1,11- bis(2'-pyridylmethyl)-1,4,8,II-tetraazacyclotetradecane (l2) have been isolated. The X-ray crystal structure of a mixed acetate, chloride salt of [Nil 1]~(2+) revealed an octahedral Ni coordination by two N atoms of the pyridine groups (in cis-related positions) and Jour of the macrocycle, which is folded along the 1,8-direction and bound in the cis- 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-spin nickel(II). The intermediate in the synthesis of ligand l2, a bis-(2-pyridylmethyl) sOOstituted formamidinium cation (l3)+, reacted with nickel(Il) perchlorate to form a [Ni(H_2l_3)Cl]~(2+) complex incorporating a methylene bridge between the non-pyridylmethylated N atoms (N4 and N8) of the macrocycle, which was characterised by X-ray crystallography. The Ni atom has afac-octahedral coordination by the two pyridine and three macrocyclic nitrogens (the fourth one, N_4, is protonated) and one Cl atom.