Oxygen exchange and protonation of polyanions: a multinuclear magnetic resonance study of tetradecavanadophosphate(9–) and decavanadate(6–)

摘要: Unlike decavanadate(6–), tetradecavanadophosphate(9–) shows pH-dependent differential rates of exchange oxygen with solvent water. If the anion's structure is described as a Keggin-type ‘sphere’ polar ‘caps,’ then at pH > 5 caps are kinetically stabilised respect to ‘equator,’ whereas < 1 destabilised and only four half-hemisphere three-octahedron units resist exchange. These observations related bulk distortions heteropolyanion which can be deduced from variations 17O, 51V, 31P chemical shifts pH. The values pKa1= 4.7 pKa2= 1.3 have been determined for heteropolyanion. Decavanadate(6–) distorts similarly. singly bridging shown increase bond angle decreases.