A novel extended covalent tripod for assembling nine-coordinate lanthanide(III) podates: A delicate balance between flexibility and rigidity

被引:33
作者
Koeller, S
Bernardinelli, G
Bocquet, B
Piguet, C
机构
[1] Univ Geneva, Dept Inorgan Analyt & Appl Chem, CH-1211 Geneva 4, Switzerland
[2] Univ Geneva, Lab Xray Crystallog, CH-1211 Geneva 4, Switzerland
关键词
chelates; helical structures; lanthanides; N ligands;
D O I
10.1002/chem.200390099
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
The introduction of long semirigid spacers between the capping carbon atom of the tripod and the unsymmetrical tridentate binding units provides the novel, extended covalent podand tris-{2-[2-(6-diethylcarbamoylpyridin-2-yl)-1-ethyl-1H-benzoimidazol- 5-yl-methoxy]ethyl]methane (L-15). Reaction of L-15 with lanthanide(iii) in acetonitrile. produces stable podates [Ln(L-15)](3+) (Ln=La-Lu) in which three tridentate binding units are facially organized. These wrap around the nine-coordinate pseudo-tricapped trigonal-prismatic metal ions. The crystal structure of [La(L-15)](ClO4)(3) (18, LaC67H82N12O18Cl3, trigonal, R3c, Z = 6) reveals the formation of a C-3- symmetrical triple-helical podate. Two slightly different arrangements of the flexible ethylenoxy parts of the spacer are observed in the solid state in agreement with the formation of two conformational isomers (M:m) in a 4:1 ratio. A qualitative analysis of the aromatic diamagnetic anisotropies affecting the NMR signals of [Ln(L-15)](3+) (Ln = La, Y, Lu) in solution, combined with the quantitative determination of electron-induced relaxation in the paramagnetic complex [Nd(L-15)](3+), demonstrate that the solid state structure is maintained in solution. This leads to a mixture of two triple-helical conformers of similar stabilities and that do not interconvert on the NMR timescale between 243 and 343 K. Particular attention has been given to the structural programming of extended covalent tripods for facially organizing unsymmetrical tridentate binding units around Ln(III). Photophysical measurements show. that L-15 efficiently protects the metallic coordination spheres and sensitizes Eu-III and Tb-III. upon UV irradiation.
引用
收藏
页码:1062 / 1074
页数:13
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