Mechanistic Polyoxoanion Chemistry: Intramolecular Rearrengements of the α-Mo8O26(4-), C6H5AsMo7O25(4-), and (C6H5As)2Mo6O24(4-) Anions

Article abstract of DOI:10.1021/ja00310a033

The dynamic behavior of the α-Mo8O26(4-), C6H5AsMo7O25(4-), and (C6H5As)2Mo6O24(4-) anions as (n-C4H9)4N(1+) salts in CH3CN has been studied by using variable-temperature (17)O NMR line-shape analysis, (17)O spin saturation transfer techniques, and (17)O label crossover experiments.The C6H5AsMo7O25(4-) anions shows two distinct types of fluxional behavior that can be related to the anion's structure, a puckered Mo6O18 ring capped on opposite sides by tridentate tetrahedral MoO4(2-) and C6H5AsO3(2-) units.The low-temperature process involves Mo6O18 ring inversion accompained by twisting of the C6H5AsO3(2-) subunit and twisting or flipping of the MoO4(2-) subunit.Only weak (> 2.2 Angstroem) molybdenum-oxygen bonds are broken and reformed.The higher temperature process, although mechanistically undefined, involves cleavage of stronger (1.7-2.0 Angstroem) molybdenum-oxygen bonds.Evidence is presented for related processes in the α-Mo8O26(4-) and (C6H5As)2Mo6O24(4-) anions.Possibilities for observing related ring inversions and reorientations of tetrahedral subunits in other early transition-metal polyoxoanions are also discussed.