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

摘要

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 d8 electronic ground states. The equilibrium viz.,[NiCBA22H2ONiCBAH2O22 studies in aqueous solution over a temperature range of 283–313 K indicates DH = 23.98 ± 0.05 KJ mol1 and DS = 78.63 ± 0.1 K1 mol1.