Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Isostructural series of nine-coordinate chiral lanthanide complexes based on triazacyclononane
AU - Walton, James W.
AU - Carr, Rachel
AU - Evans, Nicholas H.
AU - Funk, Alexander M.
AU - Kenwright, Alan M.
AU - Parker, David
AU - Yufit, Dmitry S.
AU - Botta, Mauro
AU - De Pinto, Sara
AU - Wong, Ka-Leung
PY - 2012/8/6
Y1 - 2012/8/6
N2 - Nonadentate ligands based on triazacyclononane incorporating pyridyl-2-phosphinate groups form an isostructural series of complexes with Ln ions in the solid state and in solution. The Ln ion is effectively shielded from the solvent environment. Crystal structures reveal a rigid C-3-symmetric tricapped trigonal-prismatic coordination geometry that is maintained in solution for the methyl and phenylphosphinate series, as shown by multinuclear NMR analysis. Variable-temperature measurements of the field dependence of the water proton relaxivity in gadolinium complexes indicate that these systems exclude solvent from the primary coordination environment and minimize the second sphere of solvation. The electronic relaxation time for the gadolinium methylphosphinate complex has been estimated to be 550 (+/-150) ps by EPR and NMR methods, compared to values of around 0.30-0.05 ps for the terbium-ytterbium series, deduced by analyzing the field dependence (4.7-16.5 T) of the P-31 NMR longitudinal relaxation times. Values are compared with analogous azacarboxylate ligand complexes, supporting a key role for donor atom polarizability in determining the electronic relaxation. Spectral emission behavior in solution of samarium, europium, terbium, and dysprosium complexes is compared, and the resolved RRR-Zeta and SSS-Delta complexes show strong circularly polarized luminescence. The molecular quadratic hyperpolarizability has been measured in solution using hyper-Raleigh light-scattering methods, for the whole series of lanthanide complexes of one ligand. The values of reach a maximum around the center of the series and are not simply dependent on the number of f electrons, suggesting a dominant contribution from the octupolar rather than the dipolar term.
AB - Nonadentate ligands based on triazacyclononane incorporating pyridyl-2-phosphinate groups form an isostructural series of complexes with Ln ions in the solid state and in solution. The Ln ion is effectively shielded from the solvent environment. Crystal structures reveal a rigid C-3-symmetric tricapped trigonal-prismatic coordination geometry that is maintained in solution for the methyl and phenylphosphinate series, as shown by multinuclear NMR analysis. Variable-temperature measurements of the field dependence of the water proton relaxivity in gadolinium complexes indicate that these systems exclude solvent from the primary coordination environment and minimize the second sphere of solvation. The electronic relaxation time for the gadolinium methylphosphinate complex has been estimated to be 550 (+/-150) ps by EPR and NMR methods, compared to values of around 0.30-0.05 ps for the terbium-ytterbium series, deduced by analyzing the field dependence (4.7-16.5 T) of the P-31 NMR longitudinal relaxation times. Values are compared with analogous azacarboxylate ligand complexes, supporting a key role for donor atom polarizability in determining the electronic relaxation. Spectral emission behavior in solution of samarium, europium, terbium, and dysprosium complexes is compared, and the resolved RRR-Zeta and SSS-Delta complexes show strong circularly polarized luminescence. The molecular quadratic hyperpolarizability has been measured in solution using hyper-Raleigh light-scattering methods, for the whole series of lanthanide complexes of one ligand. The values of reach a maximum around the center of the series and are not simply dependent on the number of f electrons, suggesting a dominant contribution from the octupolar rather than the dipolar term.
KW - NUCLEAR-MAGNETIC-RESONANCE
KW - NONLINEAR-OPTICAL CHROMOPHORES
KW - PARAMAGNETIC METAL-COMPLEXES
KW - ELECTRON SPIN RELAXATION
KW - MRI CONTRAST AGENTS
KW - F-ELECTRONS
KW - PROTON RELAXATION
KW - SOLID-STATE
KW - QUADRATIC HYPERPOLARIZABILITY
KW - TRANSLATIONAL DIFFUSION
U2 - 10.1021/ic300147p
DO - 10.1021/ic300147p
M3 - Journal article
VL - 51
SP - 8042
EP - 8056
JO - Inorganic Chemistry
JF - Inorganic Chemistry
SN - 0020-1669
IS - 15
ER -