Lanthanide(III) Complexes of 4,10‐Bis(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecane‐1,7‐diacetic acid (trans‐H6do2a2p) in Solution and in the Solid State: Structural Studies Along the Series |
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Authors: | M Paula?C Campello Dr Sara Lacerda Dr Isabel?C Santos Dr Giovannia?A Pereira Dr Carlos F?G?C Geraldes Prof?Dr Jan Kotek Dr Petr Hermann Dr Jakub Vaněk P?emysl Lubal Vojtěch Kubí?ek? Dr Éva Tóth Isabel Santos Dr |
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Institution: | 1. Departamento de Química, Instituto Tecnológico e Nuclear, Estrada Nacional 10, 2686‐953 Sacavém (Portugal), Fax: (+351)?21‐9946185;2. Department of Life Sciences and Center of Neurosciences and Cell Biology, Faculty of Science and Technology, University of Coimbra, P.O. Box 3046, 3001‐401 Coimbra (Portugal), Fax: (+351)?239853607;3. Department of Chemistry, University of Aveiro, CICECO, 3810‐193, Aveiro (Portugal);4. Department of Inorganic Chemistry, Universita Karlova v Praze (Charles University in Prague), Hlavova 2030, 12840 Prague 2 (Czech Republic), Fax: (+420)?22195‐1253;5. Department of Chemistry, Faculty of Science, Masaryk University, Kotlá?ská 2, 61137 Brno (Czech Republic), Fax: (+420)?54949‐2494;6. Centre de Biophysique Moléculaire, CNRS, Rue Charles Sadron 45071 Orléans Cedex 2 (France), Fax: (+332)?38‐63‐15‐17‐94 |
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Abstract: | Complexes of 4,10‐bis(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecane‐1,7‐diacetic acid (trans‐H6do2a2p, H6 L ) with transition metal and lanthanide(III) ions were investigated. The stability constant values of the divalent and trivalent metal‐ion complexes are between the corresponding values of H4dota and H8dotp complexes, as a consequence of the ligand basicity. The solid‐state structures of the ligand and of nine lanthanide(III) complexes were determined by X‐ray diffraction. All the complexes are present as twisted‐square‐antiprismatic isomers and their structures can be divided into two series. The first one involves nona‐coordinated complexes of the large lanthanide(III) ions (Ce, Nd, Sm) with a coordinated water molecule. In the series of Sm, Eu, Tb, Dy, Er, Yb, the complexes are octa‐coordinated only by the ligand donor atoms and their coordination cages are more irregular. The formation kinetics and the acid‐assisted dissociation of several LnIII–H6 L complexes were investigated at different temperatures and compared with analogous data for complexes of other dota‐like ligands. The Ce( L )(H2O)]3? complex is the most kinetically inert among complexes of the investigated lanthanide(III) ions (Ce, Eu, Gd, Yb). Among mixed phosphonate–acetate dota analogues, kinetic inertness of the cerium(III) complexes is increased with a higher number of phosphonate arms in the ligand, whereas the opposite is true for europium(III) complexes. According to the 1H NMR spectroscopic pseudo‐contact shifts for the Ce–Eu and Tb–Yb series, the solution structures of the complexes reflect the structures of the Ce(H L )(H2O)]2? and Yb(H L )]2? anions, respectively, found in the solid state. However, these solution NMR spectroscopic studies showed that there is no unambiguous relation between 31P/1H lanthanide‐induced shift (LIS) values and coordination of water in the complexes; the values rather express a relative position of the central ions between the N4 and O4 planes. |
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Keywords: | crystal structures kinetics lanthanides MRI contrast agents structure elucidation |
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