ic960621m_si_002.pdf (1.47 MB)
Lanthanide Complexes of the Hexadentate N-Donor Podand Tris[3-(2-pyridyl)pyrazolyl]hydroborate: Solid-State and Solution Properties
journal contribution
posted on 1997-01-01, 00:00 authored by Peter L. Jones, Angelo J. Amoroso, John C. Jeffery, Jon A. McCleverty, Elefteria Psillakis, Leigh H. Rees, Michael D. WardThe 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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Lanthanide ComplexesCHcoordination sitesemission lifetimesbidentate nitrate ligandsOHODligand dissociationSolution Propertiesmetal coordination spherepyrazolyl C 3metal ioninterleaved podandsbidentate chelateC complexeshexadentate N 612 nitrogen donorspodand cavityseries CTp PyB complexes showMRI contrast enhancement agentsConductivity studiesicosahedral geometryCrystallographic studiesmethanol ligands
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