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A Potentiometric and ( 31 P, 51 V) NMR Study of the Aqueous Molybdovanadophosphate System
Author(s) -
Selling Anna,
Andersson Ingegärd,
Grate John H.,
Pettersson Lage
Publication year - 2000
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200007)2000:7<1509::aid-ejic1509>3.0.co;2-7
Subject(s) - chemistry , potentiometric titration , aqueous solution , resonance (particle physics) , nuclear magnetic resonance spectroscopy , ion , chemical shift , equilibrium constant , inorganic chemistry , stability constants of complexes , analytical chemistry (journal) , stereochemistry , organic chemistry , physics , particle physics
The equilibrium speciation of the quaternary system H + /MoO 4 2− /HVO 4 2− /HPO 4 2− in aqueous 0.600 M Na(Cl) at 25 °C and 90 °C was studied by pH potentiometry and 31 P (202.5 MHz) and 51 V (131.6 MHz) NMR spectrometry. The study focused on solutions containing the oxoanion components in the ratios (Mo + V)/P = 12:1 and Mo/V ⩾ 3.8, in the pH range 0−5, wherein Keggin anions of the formula [H z Mo 12− x V x PO 40 ] (3+ x − z )− with x = 1−3 are the predominant species. Formation constants (log β) and p K a values for Keggin anions with x = 1−3 were determined from 31 P and 51 V resonance chemical shift data, 31 P resonance intensity data, and pH potentiometric data with the multidata least squares calculation program LAKE. The [Mo 11 VPO 40 ] 4− anion does not protonate, [Mo 10 V 2 PO 40 ] 5− anions can be monoprotonated, and [Mo 9 V 3 PO 40 ] 6− anions can be triprotonated. The six most intense 31 P NMR resonances of [H z Mo 9 V 3 PO 40 ] (6 − z )− could be followed over the pH range studied. It was also possible to assign some 31 P resonances to a specific isomer of [Mo 9 V 3 PO 40 ] 6− .