Dimeric cations of molybdenum(VI)

Cruywagen, J. J.; Heyns, J. B. B.; Rohwer, E.F.C.H.

doi:10.1016/0022-1902(78)80306-6

Cited by 58 publications

(23 citation statements)

References 6 publications

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“…However, molybdic acid will begin to protonate and dimerise when Z > 2 (Eqs. (7)e(9)) [8,11,16,17,24,25], which is undesirable for 12-MPA formation.…”

Section: Mo(vi) Speciation and 12-mpa Formationmentioning

confidence: 98%

The molybdenum blue reaction for the determination of orthophosphate revisited: Opening the black box

Nagul

McKelvie

Worsfold

et al. 2015

Analytica Chimica Acta

325

247

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The molybdenum blue reaction, used predominantly for the determination of orthophosphate in environmental waters, has been perpetually modified and re-optimised over the years, but this important reaction in analytical chemistry is usually treated as something of a 'black box' in the analytical literature. A large number of papers describe a wide variety of reaction conditions and apparently different products (as determined by UV-visible spectroscopy) but a discussion of the chemistry underlying this behaviour is often addressed superficially or not at all. This review aims to rationalise the findings of the many 'optimised' molybdenum blue methods in the literature, mainly for environmental waters, in terms of the underlying polyoxometallate chemistry and offers suggestions for the further enhancement of this time-honoured analytical reaction.

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“…However, molybdic acid will begin to protonate and dimerise when Z > 2 (Eqs. (7)e(9)) [8,11,16,17,24,25], which is undesirable for 12-MPA formation.…”

Section: Mo(vi) Speciation and 12-mpa Formationmentioning

confidence: 98%

The molybdenum blue reaction for the determination of orthophosphate revisited: Opening the black box

Nagul

McKelvie

Worsfold

et al. 2015

Analytica Chimica Acta

325

247

View full text Add to dashboard Cite

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“… 14 Previous spectroscopic and calorimetric investigations of Mo(VI) revealed the presence of three oxocation dimers, HMo 2 O 6 + , Mo 2 O 5 2+ , and HMo 2 O 5 3+ , which begin to form just above 0.1 mM Mo. 12 − 15 The dimerization reaction was shown to be enthalpy-driven (Δ H = −30 kJ/mol), which is derived from the formation of a free water molecule to form Mo 2 O 5 2+ coupled with an unfavorable entropy change due to an increase in molecular order. 16 Dimerization of two singly charged monomers ( eq 3 ) results in the doubly charged dimer Mo 2 O 5 2+ and the following equilibria are considered …”

Section: Introductionmentioning

confidence: 99%

Speciation of Molybdenum(VI) in Chloride Media at Elevated Mo Concentrations

2020

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Speciation of Mo(VI) in chloride media (0.5–11 M HCl) at elevated Mo concentrations (0.1–300 mM Mo) was investigated using UV spectroscopy. In addition to five major monomeric species, H 2 MoO 4 , H 3 MoO 4 + , H 3 MoO 4 Cl, MoO 2 Cl 2 , and MoO 2 Cl 3 – , chemometric analysis of UV spectra suggests the presence of three cationic dinuclear species that predominate in solutions of 1–4.5 M HCl at >20 mM Mo concentrations. Thermodynamic values and molar absorptivity spectra were calculated from UV spectrophotometric data using refined numerical methods. The stability constants determined for three Mo dimers are log β = 3.53 ± 0.05 (H 2 Mo 2 O 5 2+ ), log β = 3.60 ± 0.04 (H 3 Mo 2 O 5 3+ ), and log β = 2.91 ± 0.03 (H 3 Mo 2 O 6 Cl 2+ ).

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“…The cationic molybdenum species in highly acidic solutions absorb at ca. 240 nm (dimer) and below 220 nm (monomeric form) [22]. Both of these values lie beyond the spectral range we investigated.…”

Section: Solution Compositionmentioning

confidence: 87%