Add time:09/09/2019         Source:sciencedirect.com

Equilibria in the Cu2+–H4L1 and Cu2+–H4L2 systems, where H4L1 is 1,4,7,10-tetraaza-cyclododecane-1,4,7,10-tetrayl-tetramethylene-tetrakis(phenylphosphinic acid) and H4L2 is 1,4,8,11-tetraaza-cyclotetradecane-1,4,8,11-tetrayl-tetramethylene-tetrakis(phenylphosphinic acid), were investigated by glass electrode potentiometry at 25°C (I=0.1 mol dm−3 KNO3). A simple chemical model with the metal:ligand molar ratio 1:1 was found in the systems. The presence of main species, [CuL1]2− (log β=20.37(4)) and [CuL2]2− (log β=17.19(2)), was also confirmed by MALDI-TOF/MS. The dissociation kinetics of the complexes was followed by spectrophotometry and a mechanism of the dissociation was proposed. Activation parameters (activation enthalpy and entropy) of the dissociation were estimated. For the Cu2+–H4L1 system, the complex dissociation starts after protonation of the phosphinic pendant arms and its mechanism is similar to the decomplexation of [Cu(cyclen)]2+. The Cu2+ complex with H4L2 is kinetically much less stable. The proton transfer from the phosphinic pendant arm to the azacycle plays a significant role in the reaction mechanism of both the complexes.

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