Mixed-Valence Minerals of Iron and Titanium: Correlations of Structural, Mössbauer and Electronic Spectral Data

Burns, Roger G.; Nolet, D. A.; Parkin, K. M.; McCammon, Catherine; Schwartz, K.

doi:10.1007/978-94-009-9076-0_10

Cited by 16 publications

(4 citation statements)

References 55 publications

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“…A related recent example of an unsupported molecular μ-oxo bridged TiOCr 3+ heterobimetallic complex yields similar results with a Ti - Cr bond distance of 3.13 Å and an MMCT absorption maximum at 288 nm (∼7000 M –1 cm –1 , Δν 1/2 ≈ 4000 cm –1 ), and although the absorption band is significantly narrower than what we have observed for our TiOMn binuclear unit anchored on silica, the oscillator strengths are of similar magnitude . Overall, these results agree with those observed for a wide range of mineral oxide based MMCT chromophores as discussed by Blasse and others, − as well as synthetic materials such as Prussian Blue and analogous complexes ,− which typically exhibit oscillator strengths of ∼10 –2 –10 –1 . Thus, the coupling constant, which also has a dependence on the molar extinction coefficient and full width at half-maximum, is similar for the TiOMn unit calculated here compared to other MMCT chromophores.…”

Section: Discussionsupporting

confidence: 88%

“…The large electronic coupling constant, H ABopt , value of 4200 cm –1 estimated from the optical absorption of the Ti 4+ –O-Mn 2+ → Ti 3+ –O-Mn 3+ MMCT absorption spectrum (Figure ) is consistent with values expected based on the spectral parameters for solid mixed metal oxides − and cyano-bridged Prussian blue analogues ,− reported in the literature. From a structural and spectroscopic standpoint, the mixed metal oxides provide the closest analogy to all-inorganic heterobinuclear units on silica surfaces.…”

Section: Discussionsupporting

confidence: 87%

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Excited State Electron Transfer of All-Inorganic Heterobinuclear TiOMn²⁺ Chromophore Anchored on Silica Nanoparticle Surface

McClure

Frei

2014

J. Phys. Chem. C

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The oxo-bridged heterobinuclear chromophore TiOMn 2+ has been covalently anchored onto a silica nanoparticle surface, allowing for the preparation of optically transparent solid state samples. Optical spectra of the material yield a broad metal-to-metal charge-transfer (MMCT) transition in the UV with a tail extending to 550 nm. Fitting the absorption band to a Gaussian curve gives a maximum at 44 610 (±230) cm −1 (587 (±20) M −1 cm −1 ) with a full width at half-maximum of 17 320 (±160) cm −1 , and yields an electronic coupling constant, H ABopt , of 4200 cm −1 by Hush analysis. Transient absorption measurements of transparent pressed pellets in vacuum yield a 2.43 (±0.20) μs lifetime at room temperature. The temperature dependence of the lifetime in the range of 10−40 °C gives an activation energy of 1.67 (±0.36) kcal/mol and pre-exponential factor A of 7.3 (±4.4) × 10 6 s −1 . This temperature dependence results in an electronic coupling constant H ABkin of less than 1 cm −1 . The disparity between the large electronic coupling indicated by fitting the absorption band and the very small coupling based on temperature dependent kinetic measurements suggests that the observed microsecond back electron transfer is from an electronic state that is distinct from the initially excited MMCT state. It is proposed that the initially excited high spin state (S = 5/2) branches on the ultrafast time scale between back electron transfer to the ground state (S = 5/2) and intersystem crossing to a low spin MMCT state (S = 3/2 or 1/2). With intersystem crossing to a lower spin state available as a competitive pathway, these robust chromophores are promising for driving multielectron catalysis in an integrated artificial photosynthesis system.

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Section: Discussionsupporting

confidence: 88%

Section: Discussionsupporting

confidence: 87%

Excited State Electron Transfer of All-Inorganic Heterobinuclear TiOMn²⁺ Chromophore Anchored on Silica Nanoparticle Surface

McClure

Frei

2014

J. Phys. Chem. C

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“…3a and Table S3 in the Supplementary Materials ). We note that this Fe 2.8+ component is an average because of the above-mentioned rapid charge exchange between Fe 2+ and Fe 3+ ions at the octahedral sites, similarly to Fe 3 O 4 33 . This finding is in excellent agreement with the above BVS oxidation states of the Fe ions obtained from the single crystal XRD data.…”

Section: Resultsmentioning

confidence: 79%

Discovery of Fe7O9: a new iron oxide with a complex monoclinic structure

Sinmyo

Bykova

Ovsyannikov

et al. 2016

Sci Rep

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Iron oxides are fundamentally important compounds for basic and applied sciences as well as in numerous industrial applications. In this work we report the synthesis and investigation of a new binary iron oxide with the hitherto unknown stoichiometry of Fe7O9. This new oxide was synthesized at high-pressure high-temperature (HP-HT) conditions, and its black single crystals were successfully recovered at ambient conditions. By means of single crystal X-ray diffraction we determined that Fe7O9 adopts a monoclinic C2/m lattice with the most distorted crystal structure among the binary iron oxides known to date. The synthesis of Fe7O9 opens a new portal to exotic iron-rich (M,Fe)7O9 oxides with unusual stoichiometry and distorted crystal structures. Moreover, the crystal structure and phase relations of such new iron oxide groups may provide new insight into the cycling of volatiles in the Earth’s interior.

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“…Cronstedtite is a 1:1 layer silicate belonging to the small group of mixed-valence iron minerals which have Fe 2 + and Fe 3+ on crystallographically equivalent octahedral sites (Burns et al 1980). As a result of Fe 2+ ---~Fe 3+ electron transfer, these materials are relatively good electrical conductors; they are black in colour with metallic lustre.…”

Section: Introductionmentioning

confidence: 99%

Electrical and magnetic properties of cronstedtite

et al. 1989

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Abstract. Two samples of cronstedtite, a mixed valence serpentine with ideal formula ~Fe 2 + Fe 3 + t [Si,Fe 3 +]Os (OH)4,have been examined by X-ray and neutron diffraction, thermopiezic analysis, magnetization and susceptibility measurements and M6ssbauer spectroscopy. The conductivity is thermally activated, with activation energies of 0.25 eV in the basal plane and 0.37 eV in the perpendicular direction. The shape of paramagnetic M6ssbauer spectra above 200 K is influenced by charge fluctuations in octahedral sites and fits of spectra at temperatures up to 410 K with a stochastic relaxation model give an activation energy of 0.19 eV. Static charge ordering sets in progressively below about 100 K. Cronstedtite orders antiferromagnetically below 12 K in a structure with antiferromagnetic octahedral sheets and moments perpendicular to the a-axis. Magnetic and charge-ordered structures are proposed for the ideal composition.

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Mixed-Valence Minerals of Iron and Titanium: Correlations of Structural, Mössbauer and Electronic Spectral Data

Cited by 16 publications

References 55 publications

Excited State Electron Transfer of All-Inorganic Heterobinuclear TiOMn²⁺ Chromophore Anchored on Silica Nanoparticle Surface

Excited State Electron Transfer of All-Inorganic Heterobinuclear TiOMn²⁺ Chromophore Anchored on Silica Nanoparticle Surface

Discovery of Fe7O9: a new iron oxide with a complex monoclinic structure

Electrical and magnetic properties of cronstedtite

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Mixed-Valence Minerals of Iron and Titanium: Correlations of Structural, Mössbauer and Electronic Spectral Data

Cited by 16 publications

References 55 publications

Excited State Electron Transfer of All-Inorganic Heterobinuclear TiOMn2+ Chromophore Anchored on Silica Nanoparticle Surface

Excited State Electron Transfer of All-Inorganic Heterobinuclear TiOMn2+ Chromophore Anchored on Silica Nanoparticle Surface

Discovery of Fe7O9: a new iron oxide with a complex monoclinic structure

Electrical and magnetic properties of cronstedtite

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Product

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Excited State Electron Transfer of All-Inorganic Heterobinuclear TiOMn²⁺ Chromophore Anchored on Silica Nanoparticle Surface

Excited State Electron Transfer of All-Inorganic Heterobinuclear TiOMn²⁺ Chromophore Anchored on Silica Nanoparticle Surface