Thermodynamic and kinetic study of copper(II) complexes with N-methylene(phenylphosphinic acid) derivatives of cyclen and cyclam
| Authors | |
|---|---|
| Year of publication | 2001 |
| Type | Article in Periodical |
| Magazine / Source | Polyhedron |
| MU Faculty or unit | |
| Citation | |
| Field | Analytic chemistry |
| Keywords | Polyazamacrocycles; phosphinic acids; cyclen and cyclam derivatives; copper(II) complexes; potenciometry; kinetics; stability constants |
| Description | Equilibria in the Cu2+-H4L1 and Cu2+-H4L2 systems, where H4L1 is 1,4,7,10-tetraaza-cyclododecane-1,4,7,10-tetrayl-tramethylene-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 degreesC (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 beta = 20.37(4)) and [CuL2](2-) (log beta = 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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