Solution properties of the nickel(II,III) and copper(II,III) complexes of trans-dioxocyclam (trans-dioxocyclam=5,12-dioxo-1,4, 8,11-tetraazacyclotetradecane) and the X-ray crystal structure of the N-rac-isomer of the nickel(II) complex

The crystal and molecular structures of the N-rac-isomer of the nickel(II) complex of 14-membered amide-containing macrocycle [NiL1].4H(2)O (H2L1=5,12-dioxo-1,4,8,11-tetraazacyclotetradecane) have been determined. Two deprotonated amide and two amine donors co-ordinate to the nickel(II) in nearly square planar manner with Ni-N-amine bonds longer than Ni-N-amide ones (1.930 vs. 1.898 Angstrom). Water molecules do not co-ordinate and form hydrogen bond bridges between macrocyclic units in the crystal lattice. The analysis of H-1 NMR data confirmed that the solid-state conformation of the macrocycle in N-rac[NiL1] is retained in aqueous solution though equilibrated with some amount of N-meso isomer. The comparison of the spectroscopic characteristics of the M(II) and M(III) complexes and the redox potentials of M(III/II) couples (M=Ni and Cu) for ML1 with those for ML2-(H2L2-=5,7dioxo-1,4,8,11-tetraazacyclotetradecane) revealed a rather small influence of the trans- vs. cis-arrangement of amide donors in coordination spheres of the metal ions. (C) 2003 Elsevier B.V. All rights reserved.