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Technical University of Crete
Technical University of Crete
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| URI: | http://purl.tuc.gr/dl/dias/C5B50531-D7FA-474D-A458-63EFA4081B4F | ||
| Year | 1997 | ||
| Type of Item | Peer-Reviewed Journal Publication | ||
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| Bibliographic Citation | P.L Jones, A. J Amoroso, J. C. Jeffery, J. A McCleverty, E.Psillakis, L. H Rees, M. D Ward , "Lanthanide complexes of the hexadentate n-nonor Podand tris[3-(2-pyridyl)pyrazolyl]hydroborate: Solid-state and solution properties ", In. chem. ,vol. 36, no. 1 , pp.10-18,1997.doi:10.1021/ic960621m https://doi.org/10.1021/ic960621m | ||
| Appears in Collections |
The hexadentate N6-donor podand tris[3-(2-pyridyl)pyrazolyl]hydroborate (TpPy) contains 2-pyridyl fragments attached to the pyrazolyl C3-positions such that each arm is a bidentate chelate. Three series of lanthanide(III) complexes were prepared: [M(TpPy)(MeOH)2F][PF6] (series A), [M(TpPy)(NO3)2] (series B), and [M(TpPy)2][BPh4] (series C). Crystallographic studies showed that series A and B have a 1:1 metal:TpPy ratio, with the metal ion lying within the podand cavity and the remaining coordination sites occupied by solvent molecules and/or counterions to give 9-coordination (A, with one fluoride and two methanol ligands) or 10-coordination (B, with two bidentate nitrate ligands). The C complexes were prepared in the absence of any coordinating anions and have a 1:2 metal:TpPy ratio with an unusual icosahedral geometry arising from coordination of the 12 nitrogen donors from two interleaved podands. Conductivity studies on the B complexes show that in water the nitrates dissociate to give [M(TpPy)(H2O)q](NO3)2; the relaxivity of [Gd(TpPy)(NO3)2] in water is 4.4 s-1 mM-1, a value comparable to those of clinically useful MRI contrast enhancement agents. Comparison of emission lifetimes of [M(TpPy)(NO3)2] (M = Eu, Tb) in H2O/D2O and CH3OH/CD3OD give values for q, the number of coordinated solvent molecules, of 3.6 (water) and 2.6 (methanol). The C complex [Tb(TpPy)2][BPh4] also has q = 2.6 in methanol, suggesting that partial ligand dissociation allows access of solvent molecules to the metal coordination sphere.
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