OXYGEN-TRANSFER FROM PEROXOMETALATES AS A NEW AND GENERAL-ROUTE TO THE SYNTHESIS OF OXOPOLYMETALATES - RATIONAL SYNTHESIS OF MO2O7(2-), MO6O19(2-) AND MO7O24(6-) - EVIDENCE OF A M2O7(2-) WITH LINEAR M-O-M AXIS

The oxopolymolybdates, [Mo2O7]2-, [Mo6O19]2- and [Mo7O24]6- have been obtained via oxygen transfer reaction from a peroxomolybdate [Mo2O2(mu-2-O)(O2)4(H2O)2]2-, obtained by the treatment of HOOH on MoO3. In the case of dimolybdate, the oxygen acceptor is Ph3P, while Ph3GeCl functions as an oxygen receptor for the generation of higher polymolybdates. Three dimensional X-ray structure analysis indicates that (PPN)2[Mo2O7] contains a linear Mo-O-Mo axis and MoO3 oxygens in each fragment are staggered with respect to those of the other. The structural identity of the PPh4 and PPN salts of hexamolybdate and the PPh4 salt of heptamolybdate has been established by their superimposable X-ray powder diffractogram with those of the respective authentic samples prepared. This work presents further evidences in favour of our recent contention that peroxometalates serve as a useful precursor intermediate for the synthesis of oxopolymetalates.