Equilibria and dynamics of some aqueous peroxomolybdophosphate catalysts: A potentiometric and31P NMR spectroscopic study

Fabian Taube, Ingegärd Andersson, Sarah Angus-Dunne, Andrea Bodor, Imre Tóth, Lage Pettersson

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

The equilibrium spcciation in the pH+ + q/MoO4 2- + rH2O2 + sH2PO4 - + tSO42- ⇌ (H+) p(MoO42-)q(H2O 2)r-(H2PO4-) s(SO42-)tp-2q-s-2t system in 0.300 M Na2(SO4) medium at 25 °C and [H 2O2]tot/[Mo]tot > 2 has been determined from potentiometric data and 31P NMR integral and chemical shift data in the range 1.0 ≤ pH ≤ 9.0, 2.0 ≤ [MoO 42-]tot/mM ≤ 293, 32 ≤ [H 2O2]tot/mM ≤ 640, 2 ≤ [H 2PO4-]tot/mM ≤ 60 and 200 ≤ [SO42-]tot/mM ≤ 380. Species with the following compositions were obtained: MoX2P3- (0,1,2,1,0), MoX2P2- (1,1,2,1,0), MoX2P- (2,1,2,1,0), Mo2X4P3- (2,2,4,1,0), Mo 2X4P2- (3,2,4,1,0), Mo3X 6P3- (4,3,6,1,0), Mo3X6P 2- (5,3,6,1,0) and Mo4X8P3- (6,4,8,1,0). The numbers and charges of molybdenum (Mo), peroxide (X), phosphate (P) and sulfate (S) in each species are given in the abbreviated formula MoqXrPsSt p-2q-s-2t. The numbers in parentheses refer to the values of p, q, r, s and t in the formula above. The following formation constants with 3σ were obtained; log β0,1,2,1,0 = 5.16 ± 0.09, log β1,1,2,1,0 = 12.73 ± 0.02 (pKa = 7.63), log β2,1,2,1,0 = 16.14 ± 0.03 (pKa = 3.42), log β2,2,4,1,0 = 25.03 (± 0.04), log β 3,2,4,1,0 = 29.54 ± 0.02 (pKa = 4.51), log β4,3,6,1,0 = 42.30 ± 0.03, log β 5,3,6,1,0 = 44.06 ± 0.08 (pKa = 1.76), log β6,4,8,1,0 = 57.30 ± 0.07. pKa values for H3PO4 and H2PO4- were determined to 2.00 and 6.48, respectively. Chemical exchange processes were detected by 31P NMR 2D EXSY and selective magnetisation transfer experiments between the complexes. An averaged lifetime, τ(X 2Mo-OP) ∼ 30 ms, can be estimated for the MoX2P and Mo2X4P species at pH = 5.5 and 5 °C.

Original languageEnglish
Pages (from-to)2512-2518
Number of pages7
JournalDalton Transactions
Issue number12
DOIs
Publication statusPublished - Jun 21 2003

ASJC Scopus subject areas

  • Inorganic Chemistry

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