Tripodal nonadentate

Gateau, C., Mazzanti, M., Pecaut, J., Dunand, F.A., and Helm, L. Solid-state and solution properties of the lanthanide complexes of a new nonadentate tripodal ligand derived from 1,4,7-triazacyclononane, Dalton Trans. (2003), 2428-2433. 

In order to limit flexibility, three tridentate binding units similar to L3 have been connected to a covalent tri(2-aminoethyl)amine (TREN) tripod to give the nonadentate podand L4. Upon reaction with /J(III) (R = La-Eu, Yb, Lu, Y) in acetonitrile/nitromethane (1 1), the NMR spectra confirm the formation of the expected C3-symmetrical complexes [/ (L4)]3+ (Re-naud et al., 1999). The methylene protons are systematically diastereotopic at 298 K. For the diamagnetic cations R = Y, Lu, no coalescence is observed in the accessible temperature range (233-343 K), but the rate of helical interconversion increases with increasing ionic radii and [La(L4)]3+ shows coalescence at 323 K, thus pointing to a fast /J- Ea(L4)]3+ = M-... 

Rigault S., C. Piguet, G. BemardineUi, G. Hopfgartner, Lanthanide-Assisted Self-Assembly of an Inert, Metal-Containing Nonadentate Tripodal Receptor. Angew. Chem. Int. Ed. 37, 169—172... 

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