Abstract
A new bifunctionalized tetraaza macrocycle, 1,8-bis(2-hydroxyethyl)-C-rac-5,5,7,12,14,14-hexamethyl-1,4,8,11-tetraaza-cyclotetradecane, H2Lb2OH has been synthesized by the reaction of ethylene oxide and C-rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane. The crystal structure of [CuLb2OH](ClO4)2 shows the metal ion in tetragonally elongated octahedral geometry, coordinated by the oxygen atoms of the pendant arms in the trans-axial position. Cu(II) complexes of macrocyclic ligands 1,8-bis(2-cyanoethyl)-C-rac-5,5,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, (Lb2CN), 1,8-bis(3-aminopropyl)-C-rac-5,5,7,12,14,14-hexamethyl-1,4,8,11-tetraaza-cyclotetradecane, (Lb2NH2), C-rac-5,5,7,12,14,14-hexamethyl-1,4,8,11-tetraaza-cyclotetradecane-1-ethanoic acid, (HLb1) and C-rac-5,5,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-1,8-diethanoic acid, (H2Lb2) were also synthesized and characterized. The molecular structure of [CuLb2CN](ClO4)2 and [CuLb1](ClO4) shows the macrocycle in trans-I configuration with square planar and distorted square pyramidal geometries respectively at the metal centers. The cyclic voltammetric studies of the complexes reveal that Cu(I) oxidation state is highly stabilized by the ligand Lb2CN. The pH dependent coordination geometry changes of complexes [CuLb1](ClO4) and [CuLb2] based on the changes in their electronic spectra are discussed. The kinetics of acid promoted dissociation reactions of complex [CuLb2CN](ClO4)2 has been studied in HCl-NaCl solutions (I = 5.0 M). The possible mechanisms of the reactions, the factors influencing the rate and the relative importance of the solvent separation and protonation pathway are discussed.