Thermodynamic and kinetic study of copper(II) complexes with N-methylene(phenylphosphinic acid) derivatives of cyclen and cyclam

Equilibria in the Cu2+-H4L1 and Cu2+-H4L2 systems, where H4L1 is 1,4,7,10-t etraaza-cyclododecane-1,4,7,10-tetrayl-tramethylene-tetrakis(phenylphosphin ic acid) and H4L2 is 1,4,8,11-tetraaza-cyclotetradecane-1,4,8,11-tetrayl-te tramethylene-tetrakis(phenylphosphinic acid), were investigated by glass el ectrode potentiometry at 25 degreesC (I = 0.1 mol dm(-3) KNO3). A simple ch emical model with the metal:ligand molar ratio 1:1 was found in the systems . The presence of main species, [CuL1](2-)(log beta = 20.37(4)) and [CuL2]( 2-) (log beta = 17.19(2)), was also confirmed by MALDI-TOF/MS. The dissocia tion kinetics of the complexes was followed by spectrophotometry and a mech anism of the dissociation was proposed. Activation parameters (activation e nthalpy and entropy) of the dissociation were estimated. For the Cu2+ -H4L1 system, the complex dissociation starts after protonation of the phosphini c pendant arms and its mechanism is similar to the decomplexation of [Cu(cy clen)](2+). The Cu2+ complex with H4L2 is kinetically much less stable. The proton transfer from the phosphinic pendant arm to the azacycle plays a si gnificant role in the reaction mechanism of both the complexes. (C) 2001 El sevier Science B.V. All rights reserved.