Abstract
A series of Cu(II) complexes of C-meso-1,5,8,12-tetramethyl-1,4,8,11-tetraazacyclotetradecane, (LmMe4) have been synthesized and characterized. The crystal structure of [Cu(LmMe4)(ClO4)](ClO4)(blue) showed the macrocycle in unstable trans-II stereochemistry, while structures of complexes [Cu(LmMe4)(N3)2] and [Cu(LmMe4)(OH2)2]Y2 (Y = NO2, Cl, Br, I) showed macrocylic ligand in stable trans-III stereochemistry. The metal ion is in tetragonally elongated octahedral geometry in all the complexes. The electronic spectral and redox properties of the complexes are discussed. The kinetics of acid dissociation of complex, [Cu(LmMe4)(ClO4)](ClO4)(blue), has been studied in aqueous HNO3-NaNO3 solutions (m = 5.0 M). Kinetic results indicate rate = kobs [Cu(LmMe4)2+] =(kH [H+] + kd) [Cu(LmMe4)2+] with kH = 2.66’10-5 dm-3 mol-1 s-1 and kd = 5.54’10-5 s-1 at 25.0°C. The mechanism of the reaction is discussed. The new N-functionalized tetraaza macrocycle, 1,8-bis(2-acetic acid)-C-meso-4,7,11,14-tetramethyl-1,4,8,11-tetraazacyclotetradecane,(LmMe4-2COOH) has been synthesized. The crystal structure of [Cu(LmMe4-2COOH)](ClO4)2 showed the macrocyclic ligand in trans-III stereochemistry. Interestingly the two pendant N-acetic acid groups remain protonated and coordinate the metal ion through the carbonyl oxygen atoms in trans-octahedral geometry. Cu(II) complexes of 1,8-bis(2-cyanoethyl)-C-meso-4,7,11,14-tetramethyl-1,4,8,11-tetraazacyclo-tetradecane, (LmMe4-2CN) and 1,8-bis(2-cyanoethyl)-C-meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclo-tetradecane, (teta-2CN) have also been synthesized and characterized. The redox properties of these complexes revealed that Cu(I) oxidation state is highly stabilized by these macrocycles. The kinetics of acid dissociation of these complexes have been studied in HCl-NaCl solutions (m = 5.0 M). Kinetic results indicate rate = kobs [Cu(LmMe4-2CN)2+] =(kH [H+] + kd) [Cu(LmMe4-2CN)2+] with kH = 1.47’10-6 dm-3 mol-1 s-1 and kd = 2.36’10-6 s-1 at 25.0°C. Kinetic results indicate rate = kobs [Cu(teta-2CN)2+] = 1.15’10-6 [H+]2 + 1.81’10-6 [H+] + 4.49’10-6 at 25.0°C. The mechanisms of the reactions are discussed.