Crystal structure and disorder in a Tetrakis (tetraphenyl phosphonium) dodecamolybdate phosphate [(PPh4)4 Mo12O40P. 3DMF]

Department of Solid State Physics, Indian Association for the Cultivation of Science
â—‹Krishna Chowdhury Monika Mukherjee

The polyoxomolybdates with alpha-Keggin structure form an important class of compounds, which can accommodate several guest moieties in the anionic cavity, and the use of different counter cations makes these system capable of forming supramolecular assembly. The molecular structure of the title complex consisting of [Mo12O40P]4- anions, tetraphenyl phosphomium (PPh4)+ cations and solvent DMF molecules has been determined from single crystal X-ray analysis data. The structure was solved by the direct methods and refined to an R value of 0.0702. The polyoxoanion shows the disordered alpha-Keggin structure. The PO4 group was orientationally disordered over two positions related by an inversion center. The anionic structure of the complex has a central P atom surrounded by a cube of eight oxygen atoms and the Mo atoms are situated at the corners of a regular cubooctadedron. The polyoxoanion [Mo12O40P]4-, thus consists of a central PO4 tetrahedron surrounded by four corner-sharing Mo3O13 units; the three edge-sharing MoO6 octahedra form as almost spherical unit with an approximate diameter 7.07 . The packing arrangements in the complex can be visualized as systems of polyoxometalate units forming channels along the y-direction into which infinite columns of (PPh4)+ cations and solvent DMF molecules are placed.