Three sandglass-type molybdophosphates obtained via a new route: Synthesis and characterization of X7[PMo8O30] (X=Na+, K+, NH4+)

Three new polyoxometalates X7[PMo8O30] (X=Na+, 1; K+, 2; NH4+, 3) have been synthesized with the classical Keggin and/or Dawson heteropolymolybdophosphates and PCl5 in acetonitrile-water solutions via hydrothermal treatment. The three compounds were characterized by different analyses including IR, 31P NMR spectroscopy, elemental analysis, electrochemistry, thermogravimetric analysis (TGA) and powder X-ray diffraction (XRD). Single crystal X-ray analyses were carried out on Na7[PMo8O30] (1) and (NH4)7[PMo8O30] (3). Compound 1 and 3 crystallize in the orthorhombic system. The structure of compound 2 was confirmed by the IR spectra and powder XRD. All the three compounds contain the same octamolybdophosphate polyoxoanion [PMo8O30]7−, which consists of two Mo4O15 moieties linked by one central PO4 tetrahedron, leading to a remarkable sandglass-like structure.