Synthesis, structural, spectral, electrochemical and spin equilibrium studies of hexaaza macrotricyclic complexes

Nickel(II) and copper(II) complexes of 14-membered hexaaza macrocyclic ligand (CBA) with C-methyl substituent have been synthesized and characterized by spectral, electrochemical and X-ray crystallographic techniques. The crystal structure of [Ni(CBA)](ClO4)(2) indicates a square-planar geometry with two secondary and two tertiary amines of the macrocycle. The copper(II) complex [Cu(CBA)(ClO4)(2)] shows a distorted octahedral geometry and the two perchlorate ions are weakly coordinated to the metal ion in the axial position. The [Ni(CBA)](ClO4)(2) complex exhibit solvent dependant high-spin/low-spin equilibrium between the triplet and singlet d(8) electronic ground states. The equilibrium viz., [Ni(CBA)](2+) +2H(2)O (sic) [Ni(CBA)(H2O)(2)](2+) studies in aqueous solution over a temperature range of 283-313 K indicates Delta H degrees = -23.98 +/- 0.05 KJ mol(-1) and Delta S degrees = -78.63 +/- 0.1 K-1 mol(-1). (C) 2009 Elsevier Ltd. All rights reserved.