A 31P-NMR study of the H+-MoO42--(HP)O32--HPO42--(C6H5P)O32--(CH3P)O32- system at low Motot/Ptot ratio - Formation of mixed-hetero X2M5-type polyanions
2009 (English)In: Dalton Transactions, no 17, 3321-3327 p.Article in journal (Refereed) Published
Formation of X2M5-type heteropolyanions in the aqueous mixed-hetero H+-MoO42--(HP)O32--HPO42--(C6H5P)O32--(CH3P)O32- system has been studied by 31P-NMR at [Mo]tot/[Pall]tot = 1.5 at 298(1) K in 0.600 M Na(Cl) ionic medium. The -log[H+] range 1.4-6.2 has been covered. The pKa values of methylphosphonate were determined from 31P-NMR chemical shift data in the range of 0 < -log[H+] < 13.2 as H(CH3P)O3- 7.30 and H2(CH3P)O3 2.05. All four-component H+-MoO42--P1-P2 subsystems (P1 and P2 are two of the four phosphorus-containing components), except H+-MoO42--(HP)O32--HPO42-, which has been studied previously, were examined instead of the full six-component system in order to simplify the evaluation of the NMR spectra. The concentrations were adjusted to [Mo]tot = 60 mM and [P1]tot = [P2]tot = 20 mM in the measurements. All conceivable P2M5 and (P1)(P2)M5 heteropolyanions were identified. The following novel X2M5-type polyanions were found and their formation constants are given in logarithmic values with 3 in parentheses: (CH3P)2Mo5O214- 69.68(7), (HP)(C6H5P)Mo5O214- 67.09(4), (C6H5P)PMo5O225- 63.23(5), H(C6H5P)PMo5O224- 68.11(4), (HP)(CH3P)Mo5O214- 67.85(4), (CH3P)PMo5O225- 64.14(7), H(CH3P)PMo5O224- 68.89(4) and (C6H5P)(CH3P)Mo5O214- 69.18(4). The equilibrium conditions are illustrated in distribution diagrams. Phosphite proved to bind more weakly in X2M5-type polyoxometallates than phosphate or phosphonates, which are almost equally favoured in complexation.
Place, publisher, year, edition, pages
The Royal Society of Chemistry , 2009. no 17, 3321-3327 p.
IdentifiersURN: urn:nbn:se:umu:diva-21855DOI: 10.1039/b818530aOAI: oai:DiVA.org:umu-21855DiVA: diva2:212055