Synthesis and Characterization of 18-Molybdopyrophosphate Complex

The existence of a heteropoly 18-molybdopyrophosphate was ascertained in both solid and solution states. The yellow complex was formed in solutions of 0.05 M (M=mol dm−3) Mo(VI)/5×10−3 M pyrophosphate/0.1–0.7 M HCl/60% (v/v) CH3CN at ambient temperatures, being isolated as tetraalkylammonium (R4N+) salts where R=n-C4H9 and C2H5. The presence of organic solvents was essential for the preparation of the complex. The 18-molybdopyrophosphate complex underwent a four-step reduction in 95% (v/v) CH3CN–water containing 0.1 M HClO4, yielding mixed-valence blue species by the electrochemical reduction at the respective steps of a reversible two-electron transfer. The heteropoly skeleton is retained in the blue complexes. The UV-visible and IR spectroscopic characteristics, and the formation conditions of the 18-molybdopyrophosphate complex were also elucidated.