Anomalous Peak Intensities in the EXAFS of Polynuclear Molybdenum Compounds

Miyanaga, Takafumi; Fujikawa, Takashi; Matsubayashi, Nobuyuki; Fukumoto, Takao; Yokoi, Kunihiko; Watanabe, Ichiro; Ikeda, Shigerô

doi:10.1246/bcsj.62.1791

Cited by 23 publications

(9 citation statements)

References 15 publications

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“…Particularly, studies on Keggin- [17] Previous studies in this area have been performed by Watanabe and coworkers. [18] Zhang heteropolyanions. [19] EXAFS was used to determine the local structure of tetrahedral Co III in [CoW 12 O 40 ] 5-.…”

Section: M(h 2 O)o 39 ]mentioning

confidence: 99%

Structural Studies of Keggin‐Type Polyoxotungstates by Extended X‐ray Absorption Fine Structure Spectroscopy

et al. 2007

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Extended X-ray absorption fine structure spectroscopy (EXAFS) was used to characterize several Keggin- n-, X = P, Si, B (transition-metal-substituted anions). The role of multiple-scattering contributions was evaluated for [PW 12 O 40 ] 3-for which an accurate structure determination was available. The results from the multiple-scattering analyses were compared with the singlescattering method. The average W-shell inter-atomic distances were determined in relation to a selected tungsten atom (W c ) by W L III edge transmission analysis. Several shells of up to 3.8-4.0 Å were identified. For the anion [PW 12 O 40 ] 3-, the obtained inter-atomic distances in the solid sample and in acetonitrile were identical but for the lacunary anion the

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Section: M(h 2 O)o 39 ]mentioning

confidence: 99%

Structural Studies of Keggin‐Type Polyoxotungstates by Extended X‐ray Absorption Fine Structure Spectroscopy

et al. 2007

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“…Spectroscopic techniques, including NMR, MS, and UV-vis, have been widely applied to identify many of these polymers . However, except for a few studies on mononuclear M(VI) species in aqueous solution ,− and some solid standards, ,− XAS spectroscopies have been less frequently used to identify polymeric aqueous M(VI) species. To determine the suitability of XAS spectra for characterizing such species, it is necessary to first investigate the spectral behavior of materials with well-defined structures.…”

Section: Results and Discussionmentioning

confidence: 99%

Spectroscopic Study of the Behavior of Mo(VI) and W(VI) Polyanions in Sulfuric–Phosphoric Acid Mixtures

Zhang

et al. 2021

Inorg. Chem.

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The solution chemistry of Mo(VI) and W(VI) in mixtures of sulfuric and phosphoric acids is relevant to the development of practicable hydrometallurgical processes for the recovery and separation of these two elements from low-grade scheelite ores. The behavior of Mo(VI) and W(VI) in such mixtures has been studied using X-ray absorption near-edge structure (XANES) and extended Xray absorption fine structure (EXAFS), nuclear magnetic resonance (NMR), and small-angle X-ray scattering (SAXS) spectroscopies, along with electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS). Where applicable, these techniques have produced a selfconsistent picture of the similarities and differences between the chemical speciation of Mo(VI) and W(VI) as functions of solution composition, mostly at a constant phosphorous/metal (P/M; M = Mo(VI) or W(VI)) ratio of ∼1. In dilute acidic media (0.02 mol•kg −1 H + , without H 2 SO 4 ), Mo(VI) exists mostly (∼60%) as P 2 Mo 5 O 23 6− with the remaining ∼40% as β-Mo 8 O 26 4− . Under the same conditions, W(VI) is largely present as NaPW 11 O 39 6− (∼80%) and P 2 W 5 O 23 6− (∼10%), with the remainder probably occurring as isopolytungstates such as W 12 O 42 12− and some tungstophosphate dimers such as P 2 W 18 O 62 6− . At higher acid concentrations (≲5 mol•kg −1 H 2 SO 4 ), polymeric Mo(VI) anions are broken down to form the oxocations MoO 2 2+ and Mo 2 O 5 2+and their protonated forms, with the dimers becoming increasingly dominant at higher acidities (∼80% in 5 mol•kg −1 H 2 SO 4 ). In stark contrast, W(VI) polyanions do not decompose at higher acidities but instead form (∼70% in 0.6 mol•kg −1 H 2 SO 4 ) a Keggin ion, PW 12 O 40 3− . Further acidification with H 2 SO 4 results in the agglomeration of this Keggin ion, forming clusters of about 50 and 100 Å in diameter that ultimately produce crystalline precipitates, which could be identified in part by their X-ray diffraction patterns. Possible application of these findings to the hydrometallurgical separation of Mo and W using acidic solutions is briefly discussed, based on a limited number of batch solvent extractions.

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“…Mo and W produce the same type of polyanions, such as M 6 O 19 2− (see Figure 6a), and show interesting catalytic properties. These Mo and W polyanion hexamers are highly symmetric structures, and their EXAFS shows interesting behavior [28,29]. Figure 6b shows the EXAFS Fourier transform for M 6 O 19 2− (M=Mo and W).…”

Section: Structural Disorder In Polyanion Of Mo and Wmentioning

confidence: 99%

Local Structure and Dynamics of Functional Materials Studied by X-ray Absorption Fine Structure

Miyanaga

2021

Symmetry

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X-ray absorption fine structure (XAFS) is a powerful technique used to analyze a local electronic structure, local atomic structure, and structural dynamics. In this review, I present examples of XAFS that apply to the local structure and dynamics of functional materials: (1) structure phase transition in perovskite PbTiO3 and magnetic FeRhPd alloys; (2) nano-scaled fluctuations related to their magnetic properties in Ni–Mn alloys and Fe/Cr thin films; and (3) the Debye–Waller factors related to the chemical reactivity for catalysis in polyanions and ligand exchange reaction. This study shows that the local structure and dynamics are related to the characteristic function of the materials.

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Anomalous Peak Intensities in the EXAFS of Polynuclear Molybdenum Compounds

Cited by 23 publications

References 15 publications

Structural Studies of Keggin‐Type Polyoxotungstates by Extended X‐ray Absorption Fine Structure Spectroscopy

Structural Studies of Keggin‐Type Polyoxotungstates by Extended X‐ray Absorption Fine Structure Spectroscopy

Spectroscopic Study of the Behavior of Mo(VI) and W(VI) Polyanions in Sulfuric–Phosphoric Acid Mixtures

Local Structure and Dynamics of Functional Materials Studied by X-ray Absorption Fine Structure

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