Synthesis and structural investigation of sandwich polyoxotungstates containing cerium (III/IV) and mono-lacunary Keggin tungstophosphate units

Abstract

The two isostructural anions, [Ce III(α-PW 11O 39) 2] 11− and [Ce IV(α-PW 11O 39) 2] 10−, both composed of Ce III/IV sandwiched by two mono-lacunary Keggin units [α-PW 11O 39] 7−, were isolated as dimethylammonium salts and structurally characterized by single-crystal X-ray diffraction analysis. The structures of the [Ce III/IV(α-PW 11O 39) 2] 11−/10− anions exhibit two enantiomers d- and l-forms due to C 2 (2) symmetry from the square-antiprismatic coordination of the central Ce III/IVO 8 polyhedron. The Ce III compound crystallizes in achiral space group P2 1/ n, while the Ce IV analog in chiral space group P2 1 shows spontaneous resolution without any chiral auxiliaries. The correlation between the ionic radius of the central metal (M) and twist angle of the two mono-lacunary units was studied for a series of [M(α-PW 11O 39) 2] n − (M = Ce III/IV, Eu III, Zr IV, Hf IV) anions and explained in terms of steric repulsion between the O atoms in the mono-lacunary units.