Synthesis and crystal structure of hexacerium(IV) cluster-containing Keggin polyoxometalate trimer

Abstract A novel hexacerium(IV) cluster-containing polyoxometalate (POM), K 18 [{Ce 6 (μ 3 -O) 4 (μ 3 -OH) 4 (OAc) 2 }(A-α-SiW 9 O 34 ) 2 (α-SiW 11 O 39 )]·37H 2 O ( K 18 Ce 6 - POM ), was unexpectedly obtained by a reaction of the potassium salt of open-Dawson POM, K 13 [{K(H 2 O) 3 } 2 {K(H 2 O) 2 }α,α-Si 2 W 18 O 66 ]·19H 2 O ( K - open POM ), with (NH 4 ) 2 [Ce(NO 3 ) 6 ], in a 0.5 M KOAc/HOAc buffer solution (pH 4.8) at 80 °C, and unequivocally characterized by X-ray crystallography, 1 H, 13 C, and 29 Si NMR spectroscopy, FTIR spectroscopy, complete elemental analysis, and TG/DTA. X-ray crystallography revealed that the monolacunary Keggin unit, [α-SiW 11 O 39 ] 8 − , and the two trilacunary Keggin units, [A-α-SiW 9 O 34 ] 10 − , are connected by a central Ce 6 -oxo/hydroxide cluster moiety, [Ce 6 (μ 3 -O) 4 (μ 3 -OH) 4 (OAc) 2 ] 10 + , to form a trimeric Keggin polyanion, [{Ce 6 (μ 3 -O) 4 (μ 3 -OH) 4 (OAc) 2 }(A-α-SiW 9 O 34 ) 2 (α-SiW 11 O 39 )] 18 − ( Ce 6 - POM ). 1 H, 13 C, and 29 Si NMR spectra in D 2 O suggested that the Ce 6 -POM was obtained as a single species and its molecular structure was maintained in solution.