Influence of the pH on the Condensation of Tetravalent Cerium Cations in Association with [α‐SiW9O34]10– Leading to the Formation of a Ce6O4(OH)4 Core

Abstract

The reaction of Na10[α‐SiW9O34] with 4f tetravalent cerium cations in aqueous solution in the presence of sodium acetate at different pH values leads to the stabilization of three cerium‐based polyanionic molecular clusters [Ce3(µ2‐OH)3(µ3‐O)(SiW9O34)2]13– (1), [Ce3(µ2‐O)3(SiW9O34)2]14– (2), and {[Ce6(µ3‐O)4(µ3‐OH)4]2(W8O32)(SiW9O34)4}32– (3). The condensation behavior of cerium in this kind of association with trivacant polyoxometalates (POMs) when a pH variation occurs is relatively unknown and needed to be explored. Compounds 1 and 2 consist of a trinuclear cerium cluster fragment stabilized by two POM moieties with a variation of the central cerium cluster from [Ce3(µ2‐OH)3(µ3‐O)] to [Ce3(µ2‐O)3]. Compound 3 appears much more condensed with two hexanuclear [Ce6(µ3‐O)4(µ3‐OH)4] groups that are stabilized by the SiW9O34 moieties and a W8O32 tungsten ring. This evolution in cluster size and composition reflects the pH variation applied during their synthesis. The molecules have been characterized by single‐crystal X‐ray diffraction, 183W and 29Si NMR spectroscopy, IR spectroscopy, thermogravimetric analysis (TGA), and SEM/energy‐dispersive X‐ray (EDX) microscopy. The three compounds obtained here exemplify the influence of pH on the condensation of tetravalent cations and open a new route toward the stabilization of polynuclear tetravalent clusters by nucleophilic O‐donating POM species.