Multicomponent Polyanions. 46. Characterization of the Isomeric Keggin Decamolybdodivanadophosphate Ions In Aqueous Solution by 31P and 51V NMR

The Keggin decamolybdodivanadophosphate ions have been studied in aqueous 0.6 M Na(Cl) medium by potentiometry and 31 P (202.5 MHz) and 51 V (131.55 MHz) NMR spectrometry. An assignment of all detected resonances of decamolybdodivanadophosphate species to individual Keggin isomers is proposed. The five positional isomers of α-[Mo 10 V 2 PO 40 ] 5- were identified and characterized. Two minor [Mo 10 V 2 PO 40 ] 5- species, probably β-Keggin isomers, were also observed. The pK a values of the conjugate monoprotonated species, [HM 10 V 2 PO 40 ] 4- , have been precisely determined from the 31 P and 51 V chemical shift vs pH behavior, using α-[Mo 10 V 2 PO 40 ] 4- as internal standard