Synthesis, Characterization and Crystal Structure of the Charge Transfer Compound [CH_3NH_2CH_3]_2[CH_3-NHCH_3]_4H_4[P_2W_(18)O_(62)]·H_2O with Dawson-type Polyoxometalate Subunit

The charge transfer compound [CH_3NH_2CH_3]_2 [CH_3 NHCH_3]_4H_4[P_2W_(18)O_(62)]·H_2 O with polyoxometalate subunit has been synthesized from octadecatungstodiphosphoric acid and dimethylamine in acetonitrile aqueous solution, and characterized by IR, UV spectral techniques. X-ray single crystal structural analysis indicates the title compound crystallizes in the monoclinic space group P2_1/n, with lattice parameters a=2.306 2(5) nm, b=1.383 1(3) nm, c=2.468 8(5) nm, β=113.95(3)°, V=7.197(2)nm~3, Z=4, R_1=0.052 3. The title compound consists of two protonated dimethylamine molecules, four dimethylamine molecules, one water molecule, four protons and a heteropolyanion of[P_2W_(18)O_(62)]~(6-). The results of IR spectra and X-ray single crystal diffraction reveal that there is comparatively stronger interaction between organic groups and heteropolyanions in the solid state. The curve of TG-DTA elucidates that the process of mass loss of the title compound is carried out in three stages. The study of temperature-changing IR spectra reveals that the framework of the heteropolyanion decomposes at ca. 500℃.