On chirality induction in the crystalline solid-containing sandwich-type [Ln(α-PW11O39)2]11− polyoxotungstate and proline

Abstract

A series of lanthanide (Ln) ion-containing enantiomeric crystalline compounds of [Ln(α-PW₁₁O₃₉)₂]¹¹⁻ polyanions was successfully isolated by using proline (Pro) as a chiral inducer. In the crystals of the obtained compounds, Pro and the polyanions were associated with a stereoselective interaction through N⋯O hydrogen bonds. The ³¹P-NMR and circular dichroism spectroscopies showed the Pfeiffer effect for Pro in racemic aqueous solutions of the L- and D-polyanion in the presence of L- or D-Pro, respectively. The racemisation was found to be controlled by the competitive enantiomeric interaction between L-Pro/D-Pro and L-/D-polyanion, indicating two different racemisation routes depending on the Ln element in the polyanions.