%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