Synthesis, crystal structure and properties of the bichromium(III)-substituted tungstosilicate: [N(CH3)4]4[A-β(1,2)-SiW10Cr2O36(OH)2(H2O)2]·5H2O

A bichromium(III)-substituted pseudo-Keggin-type tungstosilicate, [N(CH3)4]4[A-β(1,2)-SiW10Cr2O36(HO)2(H2O)2]·5H2O (1), was synthesized with the conventional method from A-β-SiW9 and characterized by elemental analysis, IR spectroscopy and electronic spectroscopy, thermal gravimetric analysis. Its crystal structure was determined by single-crystal X-ray diffraction analysis. In 1, two CrO4(OH)(H2O) octahedra are corner-linked and fill in two vacancies of the A-β-SiW9O3410−. The other vacancy is occupied by a WO6 unit, leading to a A-β-pseudo Keggin anion, [A-β(1,2)-SiW10Cr2O36(HO)2(H2O)2]4−. Variable temperature magnetic susceptibilities indicate that there exists a weak antiferromagnetic interaction between Cr atoms. Photoluminescent emission peaks of 1 are observed at 410–500 nm which is attributed to the 4A2g → 4T1g transition of Cr3+ ion confirmed by theoretical calculation.