| Author |
Hermann, P. Santos, I. Michalicová, R. Sevcík, R. Santos, I. C. Campello, M. P. C. Vanek, J. Lubal, P. |
| Description |
Author Affiliation: Sevcík R ( Department of Chemistry, Faculty of Science, Masaryk University, Kotlárská 2, 611 37 Brno, Czech Republic. lubal@chemi.muni.cz.); Vanek J ( Department of Chemistry, Faculty of Science, Masaryk University, Kotlárská 2, 611 37 Brno, Czech Republic. lubal@chemi.muni.cz and Central European Institute of Technology (CEITEC), Masaryk University, Kamenice 5, 625 00 Brno, Czech Republic.); Michalicová R ( Department of Chemistry, Faculty of Science, Masaryk University, Kotlárská 2, 611 37 Brno, Czech Republic. lubal@chemi.muni.cz.); Lubal P ( Department of Chemistry, Faculty of Science, Masaryk University, Kotlárská 2, 611 37 Brno, Czech Republic. lubal@chemi.muni.cz and Central European Institute of Technology (CEITEC), Masaryk University, Kamenice 5, 625 00 Brno, Czech Republic.); Hermann P ( Department of Inorganic Chemistry, Faculty of Science, Universita Karlova (Charles University), Hlavova 2030, 128 40 Prague 2, Czech Republic.); Santos IC ( Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10, 2695-066 Bobadela LRS, Portugal. pcampelo@ctn.tecnico.ulisboa.pt.); Santos I ( Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10, 2695-066 Bobadela LRS, Portugal. pcampelo@ctn.tecnico.ulisboa.pt.); Campello MP ( Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10, 2695-066 Bobadela LRS, Portugal. pcampelo@ctn.tecnico.ulisboa.pt.) |
| Abstract |
The kinetic properties of Cu(II) complexes of $H_{4}dota$ and its analogues with one $(H_{5}do3ap),$ two in the 1,7-position $(trans-H_{6}do2a2p),$ three $(H_{7}doa3p)$ and four $(H_{8}dotp)$ phosphonic acid pendant arms were investigated. The formation of a Cu(II) complex with $H_{4}dota,$ $trans-H_{6}do2a2p$ and $H_{8}dotp$ at a slightly acidic pH is faster for the phosphonic acid derivatives than for $H_{4}dota,$ but with no simple dependence on the number of $–CH_{2}PO_{3}H_{2}$ substituents $(trans-H_{6}do2a2p$ > $H_{8}dotp$ > $H_{4}dota;$ pH 4–6). Relative differences in the reactivity among the differently protonated species $(H_{n}L^{x−})$ of the same ligand are successively decreased with the more phosphonic acid groups in the ligand. The faster complexation is probably caused by the higher ability of phosphonates to bind the metal ion and/or to assist in the transfer of protons from the ring amine groups to the bulk water. The acid-assisted decomplexation kinetics of the complexes was followed in highly acidic solutions $([H^{+}]$ = 0.01–5 M) and at different temperatures (15–70 °C) to determine the activation parameters of the reaction. The kinetic inertness of the Cu(II) complexes follows the order: $H_{4}dota$ > $H_{5}do3ap$ > $trans-H_{6}do2a2p$ > $H_{7}doa3p$ > $H_{8}dotp.$ To obtain information on the influence of additional pendant arms, analogous data were obtained for $trans-H_{2}do2a.$ The ligand is less reactive than $H_{4}dota,$ but the kinetic inertness of its Cu(II) complex is similar to that of the $H_{4}dota$ complex. As it was considered that the published thermodynamics data on the $Cu(II)–H_{8}dotp$ system are probably incorrect, the system was re-investigated. It showed a very high stability for the $[Cu(dotp)]^{6−}$ species and the easy formation of several $Cu_{2}L$ species in the presence of an excess of the metal ion. Also, the structure of the $(H_{6}doa3p)^{−}$ anion in the solid state was determined. These experimental data demonstrate that the substitution of acetic acid pendant arms by methylphosphonic acid ones in $H_{4}dota-like$ ligands increases the rate of complexation but significantly decreases the kinetic inertness of the Cu(II) complexes. |
