Structural characterization of Keggin sandwich-type [LnIII(α-PW11O39)2]11− (Ln = La and Ce) anion containing a pseudo-cubic LnIIIO8 center

We successfully obtained [Ln(α-XW11O39)2]11− (Ln = La and Ce) anions with an approximate cubic LnIIIO8 geometry for the first time in [Me4N]10H[La(α-PW11O39)2]·21H2O (1) and [Me4N]10H[Ce(α-PW11O39)2]·19H2O (2) ([Me4N]+ = tetramethylammonium). The anion is spherically surrounded by [Me4N]+ cations in highly symmetric arrangement. The resulting approximate C2h symmetry of the anion is more stable than C2v, which is explained in terms of lower steric hindrance between the two [PW11O39]7− moieties. 31P NMR spectroscopy of 1 and 2 revealed that [Ln(α-XW11O39)2]11− anions in aqueous solutions partially dissociate into [Ln(H2O)n(PW11O39)]4− and [PW11O39]7− species.