%0 Journal Article
%A L. Jones, Peter
%A Amoroso, Angelo J.
%A Jeffery, John C.
%A McCleverty, Jon A.
%A Psillakis, Elefteria
%A Rees, Leigh H.
%A Ward, Michael D.
%D 1997
%T Lanthanide Complexes of the Hexadentate N-Donor Podand
Tris[3-(2-pyridyl)pyrazolyl]hydroborate: Solid-State and Solution Properties
%U https://acs.figshare.com/articles/journal_contribution/Lanthanide_Complexes_of_the_Hexadentate_N-Donor_Podand_Tris_3-_2-pyridyl_pyrazolyl_hydroborate_Solid-State_and_Solution_Properties/3616527
%R 10.1021/ic960621m.s002
%2 https://acs.figshare.com/ndownloader/files/5705115
%K Lanthanide Complexes
%K CH
%K coordination sites
%K emission lifetimes
%K bidentate nitrate ligands
%K OH
%K OD
%K ligand dissociation
%K Solution Properties
%K metal coordination sphere
%K pyrazolyl C 3
%K metal ion
%K interleaved podands
%K bidentate chelate
%K C complexes
%K hexadentate N 6
%K 12 nitrogen donors
%K podand cavity
%K series C
%K Tp Py
%K B complexes show
%K MRI contrast enhancement agents
%K Conductivity studies
%K icosahedral geometry
%K Crystallographic studies
%K methanol ligands
%X 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.
%I ACS Publications