Synthesis and structural characterization of nickel(II), copper(II) and zinc(II) complexes with the hexadentate ligand 2,13-bis(2-pyridylmethyl)-3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,01.18,07.12]docosane

The complexes [Ni(L-2)]Cl-2. 10H(2)O (1), [Cu(L-2)](ClO4)(2). 3H(2)O (2), [Cu-2(L-2)(H2O)(2)Cl-2]Cl-2 (3) and [Zn(L-2)]Cl-2. 10H(2)O (4) (L-2=2,13-bis(2-pyridylmethyl)-3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0(1.18),0(7.12)]docosane) have been synthesized and characterized by X-ray crystallography, electronic absorption, C-13 NMR and magnetic susceptibility as well as cyclic voltammetry. The crystal structures of 1 and 4 show that the metal ion has a slightly distorted octahedral geometry with two nitrogen atoms of the pendant arms at the axial positions. However, 2 exhibits a square-planar geometry, coordinated by secondary and tertiary nitrogen donors of the macrocycle. Furthermore, 3 reveals a binuclear structure and a center of symmetry in which the each copper ion is coordinated by a distorted square-pyramidal geometry with an N3Cl basal plane and a water molecule in the apical position. The magnetic behavior for 3 shows that a ferromagnetic interaction between the copper(II) ions is predominant at intermediate temperature and then a weaker antiferromagnetic coupling is involved at lower temperature. Cyclic voltammetric studies for 1-3 indicate that 1 undergoes quasireversible one-electron oxidation to the Ni(III) and reversible one-electron reduction to the Ni(I), 2 undergoes a irreversible one-electron reduction to the Cu(I) state, while 3 undergoes an overall quasi-reversible two-electron reduction to the binuclear Cu(I) complex. (C) 1999 Elsevier Science Ltd. All rights reserved.