Antimony-substituted Keggin-type polyoxomolybdates: Polar crystals and catalytic oxidative dehydrogenation of alcohols

An antimony-substituted polyoxomolybdate, [PSbIII(H2O)Mo11O39](4-), Of the alpha -Keggin structure, has been synthesized. Although the molecular struc ture is typical, we have found from the analysis of the X-ray diffraction d ata that the crystal is anisotropic with alignment of the molecular units s o that the substituted antimony atoms are all directed along the polar c ax is and on the same side of the molecular unit. UV/Vis, ESR and magnetic sus ceptibility data support a formulation of [PSbIII(H2O)Mo11O39](4-) whereby there is partial electron delocalization with some formation (10-20%) of Mo V. Oxidation of [PSbIII(H2O)Mo11O39](4-) with ozone or bromine yields the o xidized species [PSbV(O)Mo11O39](4-) and [PSbV(Br)Mo11O39](3-). In the anae robic oxydehydrogenation of alcohols, [PSbV(O)Mo11O39](4-) is more active t han [PSbV(Br)Mo11O39](3-). Catalytic aerobic oxidation of benzylic alcohols to aldehydes was also possible with no over-oxidation and formation of car boxylic acids.