Dawson结构多金属氧酸电荷转移化合物[CH_3NH_2CH_3]_2[CH_3NHCH_3]_4H_4[P_2W_(18)O_(62)]·H_2O的合成、表征及晶体结构

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

以α-18-钨磷酸和二甲胺为原料在乙腈的水溶液中合成了分子组成为[CH_3NH_2CH_3],[CH_3-NHCH_3]_4H_4[P_2W_(18)O_(62)]·H_2O的电荷转移化合物,并用IR、UV光谱等手段进行了表征。结构测定结果表明,化合物的晶体属于单斜晶系,P2_1/n空间群,α=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。结构分析表明,标题化合物的分子由2个质子化的二甲胺分子、4个二甲胺分子、4个质子、1个水分子和1个杂多阴离子[P_2W_(18)O_(62)]^(6-)组成。IR光谱和X射线单晶衍射结果表明,在固态下,有机给体与杂多阴离子之间存在相互作用;TG-DTA曲线表明,化合物的失重分3步进行;变温红外光谱结果表明,杂多阴离子骨架在500℃左右分解。

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℃.