On The Existence of Highly Condensed Sulfatotungstates and Sulfatomolybdates

The first alkaline earth sulfatotungstate Ca[WO(SO 4 ) 3 ] is also the first one featuring a condensed anionic host structure. A solvothermal approach by using tungstic acid, CaSO 4 and oleum led to Ca[WO(SO 4 ) 3 ] comprising corrugated two‐dimensional (2D) layers in the a ‐ b plane. It crystallises in a new structure type in space group Pnma (no. 62). Blue α‐K 2 [MoO 2 (SO 4 ) 2 ] marks the first highly condensed structure for sulfatomolybdates, synthesized via melting MoO 3 and K 2 S 2 O 7 . It crystallises in a new structure type in the non‐centrosymmetric space group Cc (no. 9), yielding a doubled SHG response compared with potassium dihydrogen phosphate. Electron spin resonance spectroscopy proves the presence of Mo 5+ ions causing the blue color. High condensation of the sulfate, tungstate and molybdate moieties seems to be remarkable considering the highly charged centres S 6+ , W 6+ , and Mo 6+ . Moreover, the electrostatic, optical, and thermal properties of the title compounds are elucidated. UV–vis measurements show a pronounced ligand‐to‐metal‐charge–transfer of the tungstate and molybdate moieties dominating the absorption edge. Thermal gravimetric analysis reveals a rather high thermal stability for both compounds.