The single crystal of heteropoly blue, H8SiMo12O40.12H2O, the electrochem. reduced product of molybdenum-silicon heteropoly acid (H4SiMo12O40), was prepared by electrochem. reduction and evaporation in a nitrogen atomsphere The crystal structure of the product was determine The heteropoly blue H8SiMo12O40.12H2O, is tudenic, space group P1 with a 1.3769(3), b 1.4346(4), c 1.4134(4) nm, a 120.47(2), b 110.70(2), g 66.11(2)? Z = 2 R = 0.0608. The heteropoly blue anion was determine to have Keggin structure and a-isomer and it remained the structure of the unreduced heteropoly acid anion. But the distortion of the structure and the changes of bond length and bond angle take place obviously. The 4 Mo5+ Positions were determine in the structure.

Key words: CRYSTAL STRUCTURE DETERMINATION, X-RAY DIFFRACTION ANALYSIS