Chirality Induction in Crystalline Solids Containing Sandwich-type [Ln(alpha(2)-P2W17O61)(2)](17-) Polyoxotungstates and Proline

摘要

Chiral crystalline compounds of the series of [Ln(alpha(2)-P2W17O61)(2)](17-) polyanions embracing nearly all the lanthanide (Ln) ions were successfully isolated using Pro (proline) as a chiral director. In each compound, the polyanion and Pro were associated through a stereoselective interaction involving N(H)center dot center dot center dot O hydrogen bonding. P-31 NMR and circular dichroism studies revealed the induction of chirality by Pro in the racemic aqueous systems of the [Ln(alpha(2)-P2W17O61)(2)](17-) polyanions, i.e., the Pfeiffer effect. Mechanistically, this racemization was regulated by competitive enantiomeric interactions between the L-/D-Pro and L-/D-polyanions, with only one racemization route (the on-site rotation of the [Ln (alpha(2)-P2W17O61)(2)](17-) unit) observed, independent of the nature of Ln.