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

摘要

The two isostructural anions, [Ce-III(alpha-PW11O39)(2)](11) and [Ce-IV(alpha-PW11O39)(2)](10), both composed of Ce-III/IV sandwiched by two mono-lacunary Keggin units [alpha-PW11O39](7) , were isolated as dimethylammonium salts and structurally characterized by single-crystal X-ray diffraction analysis. The structures of the [Ce-III/IV(alpha-PW11O39)(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 (CeO8)-O-III/IV polyhedron. The Ce-III compound crystallizes in achiral space group P2(1), 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(alpha-PW11O39)(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.