Lanthanide complexes of the hexadentate N-donor podand tris[3-(2-pyridyl)pyrazolyl]hydroborate: Solid-state and solution properties
- Univ. of Bristol (United Kingdom); and others
The hexadentate N{sub 6}-donor podand tris[3-(2-pyridyl)pyrazolyl]hydroborate (Tp{sup Py}) contains 2-pyridyl fragments attached to the pyrazolyl C{sup 3}-positions such that each arm is a bidentate chelate. Three series of lanthanide(III) complexes were prepared: [M(Tp{sup Py})(MeOH){sub 2}F][PF{sub 6}] (series A), [M(Tp{sup Py})(NO{sub 3}){sub 2}] (series B), and [M(Tp{sup Py}){sub 2}]-[BPh{sub 4}] (series C). Crystallographic studies showed that series A and B have a 1:1 metal:Tp{sup Py} 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:Tp{sup Py} 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(Tp{sup Py})(H{sub 2}O){sub q}](NO{sub 3}){sub 2}; the relaxivity of [Gd(Tp{sup Py}(NO{sub 3}){sub 2}] in water is 4.4 s{sup -1} mM{sup -1}, a value comparable to those of clinically useful MRI contrast enhancement agents. Comparison of emission lifetimes of [M(Tp{sup Py})(NO{sub 3}){sub 2}] M = Eu, Tb) in H{sub 2}O/d{sub 2}O and CH{sub 3}OH/Cd{sub 3}OD give values for q, the number of coordinated solvent molecules, of 3.6 (water) and 2.6 (methanol). The C complex [Tb(Tp{sup Py}){sub 2}][BPh{sub 4}] also has q = 2.6 in methanol, suggesting that partial ligand dissociation allows access of solvent molecules to the metal coordination sphere.
- OSTI ID:
- 518389
- Journal Information:
- Inorganic Chemistry, Vol. 36, Issue 1; Other Information: PBD: 1 Jan 1997
- Country of Publication:
- United States
- Language:
- English
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