Publication details
Tris(phosphonomethyl)cyclen Derivatives: Thermodynamic Stability, Kinetics, Solution Structure, and Relaxivity of Ln(3+) Complexes
| Authors | |
|---|---|
| Year of publication | 2012 |
| Type | Article in Periodical |
| Magazine / Source | Eur. J. Inorg. Chem. |
| MU Faculty or unit | |
| 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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