Synthesis and characterization of nickel(II) complexes of hexaazamacrotetracyclic ligand containing organic ligands

Abstract

The complexes [Ni(H 2L)Cl 2]Cl 2·2H 2O ( 2), [Ni 2(L) 2(N 3) 4]·5H 2O ( 3) and [Ni(L)(tp)]·2H 2O ( 4) (L=1,3,10,12,15,18-hexaazatetracyclo[16,2,1,1 12.15,0 4.9]docosane; tp=terephthalate) have been synthesized and structurally characterized by X-ray crystallography, spectroscopic and cyclic voltammetry. The crystal structure of 2 has a distorted octahedral geometry with two secondary and two tertiary amines of the macrocycle and two chloride ions. In 3, the coordination geometry around the nickel atom is a distorted octahedral with four nitrogen atoms of the macrocycle and two nitrogen atoms of the azide groups. The nickel(II) ions in the complex 4 are bridged by the terephthalate anions to form infinite one-dimensional chain, which shows an elongated octahedral trans arrangement about each nickel(II) ion. The magnetic behavior of 4 exhibits a weak antiferromagnetic interaction with J value of −1.18(3) cm −1. Cyclic voltammetry of the complexes gives two one-electron waves corresponding to Ni(II)/Ni(III) and Ni(II)/Ni(I) processes. The electronic spectra and redox potentials of the complexes also reveal a high-spin six-coordinated geometry, which is reflected by the nature of the organic ligands.