Tris(phosphonomethyl)cyclen Derivatives: Thermodynamic Stability, Kinetics, Solution Structure, and Relaxivity of Ln(3+) Complexes

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Authors

LIMA Luis M.P. DELGADO Rita HERMANN Petr ŠEVČÍK Radek LUBAL Přemysl CARVALHO Henrique F. MARTINS André F. TÓTH Éva GERALDES Carlos F.G.C.

Year of publication 2012
Type Article in Periodical
Magazine / Source Eur. J. Inorg. Chem.
MU Faculty or unit

Central European Institute of Technology

Citation
Web http://onlinelibrary.wiley.com/doi/10.1002/ejic.201101335/abstract
Doi http://dx.doi.org/10.1002/ejic.201101335
Field Inorganic chemistry
Keywords macrocyclic ligands; lanthanide complexes; thermodynamics; kinetics; relaxivity
Description The lanthanide (Ln3+) complexes of three cyclen-based ligands containing three methylphosphonate pendant arms were studied, the ligands being 1,4,7,10-tetraazacyclododecane-1,4,7-triyltris(methylphosphonic acid) (H6do3p), 3-[4,7,10-tris(phosphonomethyl)-1,4,7,10-tetraazacyclododec-1-yl]propanoic acid (H7do3p1pr), and 10-(3-hydroxypropyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyltris(methylphosphonic acid) (H6do3p1ol). The three macrocyclic ligands form complexes of very high thermodynamic stability with all studied Ln3+ ions. Kinetic studies showed that the acid-assisted dissociation of Ce3+ complexes of these ligands is much faster than for the complex of the related ligand H8dotp [1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayltetrakis(methylphosphonic acid)]. The number of water molecules coordinated to the Eu3+ and Gd3+ complexes was estimated to be < 1 for the do3p1ol ligand but ca. 1 for the other two ligands, as obtained by time-resolved luminescence spectroscopy and by 1H and 17O relaxometric measurements. The NMR spectroscopic data indicate the existence of a considerable contribution from second-sphere water molecules to the relaxivity of all the Gd3+ complexes studied. The 1H and 31P NMR spectra of the Eu3+, Yb3+ and Lu3+ complexes showed that the propionate arm in the [Ln(do3p1pr)]4 complexes and the propanol arm in the [Ln(do3p1ol)]3 complexes are not bound to the Ln3+ ion. The [Ln(do3p)]3 and [Ln(do3p1pr)]4 complexes have a clear preference for the TSAP (twisted square antiprismatic) isomer, while both SAP (square antiprismatic) and TSAP isomers are present in solutions of the [Ln(do3p1ol)]3 complexes.
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