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

The reaction of Na 10 [α‐SiW 9 O 34 ] 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 [Ce 3 (µ 2 ‐OH) 3 (µ 3 ‐O)(SiW 9 O 34 ) 2 ] 13– ( 1 ), [Ce 3 (µ 2 ‐O) 3 (SiW 9 O 34 ) 2 ] 14– ( 2 ), and {[Ce 6 (µ 3 ‐O) 4 (µ 3 ‐OH) 4 ] 2 (W 8 O 32 )(SiW 9 O 34 ) 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 [Ce 3 (µ 2 ‐OH) 3 (µ 3 ‐O)] to [Ce 3 (µ 2 ‐O) 3 ]. Compound 3 appears much more condensed with two hexanuclear [Ce 6 (µ 3 ‐O) 4 (µ 3 ‐OH) 4 ] groups that are stabilized by the SiW 9 O 34 moieties and a W 8 O 32 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, 183 W and 29 Si 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.