Resolving Mn framework sites in large cage aluminophosphate zeotypes by high field EPR and ENDOR spectroscopy

Arieli, D.; Prisner, Thomas F.; Hertel, M.; Goldfarb, Daniella

doi:10.1039/b310800g

Cited by 23 publications

(25 citation statements)

References 36 publications

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“…This results in a more gradual release of the Co 2+ ions in the crystallization mixture when synthesis proceeds. In addition, the use of alcohols as solvents prevents the formation of Co(OH) 2 (H 2 O) 4 or other hydroxylated Co compounds, which are easily made in aqueous solutions when the pH gradually increases during the synthesis of microporous aluminophosphates. Similar effects hold for ethylene glycol and to a lesser extent for ethanol, although at present we do not have any explanation why different CoAPO materials require different solvent molecules in order to increase the amount of framework Co 2+ .…”

Section: Discussionmentioning

confidence: 99%

“…One of the most fascinating researches on microporous AlPO 4 -n materials is the process of isomorphous substitution, in which framework Al 3+ and/or P 5+ ions are replaced by e.g. transition metal ions, such as Mn 2+ [3][4][5][6], Fe 3+ [7,8], V 4+ [9][10][11][12][13], Ti 4+ [14,15], Zn 2+ [16,17], Nb 5+ [18], Cr 3+ [19][20][21] and Co 2+ [22][23][24][25][26]. This process can generate Brö nsted acid and redox sites, leading to intriguing shape-selective catalytic performances.…”

Section: Introductionmentioning

confidence: 99%

“…AlPO 4 -n molecular sieves consist of alternating aluminum oxygen and phosphorus oxygen tetrahedra building up an open and neutral framework structure with microporous channels and/or pores [1,2]. One of the most fascinating researches on microporous AlPO 4 -n materials is the process of isomorphous substitution, in which framework Al 3+ and/or P 5+ ions are replaced by e.g.…”

Section: Introductionmentioning

confidence: 99%

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Solvent effects in the synthesis of CoAPO-5, -11 and -34 molecular sieves

Fan

Dou

et al. 2005

Microporous and Mesoporous Materials

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Series of CoAPO-5, CoAPO-11 and CoAPO-34 molecular sieves have been synthesized starting from a synthesis gel varying in its amount of Co 2+ and type of solvent molecule. Four protonic solvents have been investigated: water, ethanol, ethylene glycol and glycerol. The obtained crystalline materials were characterized with X-ray diffraction; diffuse reflectance UV-Vis-NIR spectroscopy; infrared spectroscopy; elemental analysis; electron microscopy microprobe analysis and thermo-gravimetrical analysis. It was found that the type of solvent has a strong influence on the crystallization behavior and the substitution degree of Co 2+ for Al 3+ in the framework of microporous aluminophosphates. Ethanol, ethylene glycol and glycerol seem to be the best solvents for the synthesis of single-phase and highly crystalline Co-rich CoAPO-34, CoAPO-11 and CoAPO-5 molecular sieves, respectively. By varying the type of solvent molecule, Co content and template amount in the synthesis gel it was possible to increase the substitution degree of framework Co 2+ in microporous aluminophosphates. In this manner, around 10%, 25% and 36% of Al 3+ could be replaced by Co 2+ in the framework of CoAPO-11, CoAPO-5 and CoAPO-34, respectively. These substitution degrees are substantially higher than those for CoAPO materials synthesized in the presence of water.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Solvent effects in the synthesis of CoAPO-5, -11 and -34 molecular sieves

Fan

Dou

et al. 2005

Microporous and Mesoporous Materials

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“…2b). In a recent study we have determined experimentally the sign of a iso to be negative, 25 which has been further confirmed by 275 GHz ENDOR measurements 26 and therefore the lines corresponding to specific M S and m I values can be assigned, as noted on The 55 Mn ENDOR spectra recorded at each of the m I components is given in Figure 8a and the ENDOR frequencies are listed in Table 4. The spectra corresponding to the M S D transitions produce only one line while for the others, two resolved line are present, 20 the splitting of which is given to first order by 2P (see Eqn 5).…”

Section: Cmentioning

confidence: 90%

“…Recently, we have characterized the Mn(II) coordination environment in a number of MnAlPO n materials by W-band 55 Mn ENDOR. 25 There, several Mn(II) types were distinguished by their different hyperfine couplings, but the quadrupole interaction was not resolved. The measurements, however, were carried out on polycrystalline samples exhibiting very broad lines.…”

Section: Mn Endor Measurementsmentioning

confidence: 98%

Dynamics and structure in the Mn2+ site of concanavalin A as determined by high-field EPR and ENDOR spectroscopy

2005

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The properties of the Mn2+ site in the protein concanavalin A were investigated by single crystal W-band EPR/ENDOR (electron-nuclear double resonance) measurements. Initially, room temperature EPR measurements were carried out, one type of Mn2+ was identified and its zero-field splitting (ZFS) tensor was determined. In contrast, low temperature EPR measurements showed that two chemically inequivalent Mn2+ are present, Mn(A)2+ and Mn(B)2+, differing in their ZFS tensors. Variable temperature measurements revealed a two-site exchange between the two types. Although the dynamic process has been characterized by its rate and activation energy, just from the EPR measurements it was not possible to assign it to a specific residue. 1H ENDOR measurements of the water and imidazole protons, which are the main contributors to the ENDOR spectra, showed only one type of signals, namely, they were not sensitive to the differences between Mn(A)2+ and Mn(B)2+. 55Mn ENDOR spectra, which are dominated by the 55Mn isotropic hyperfine, a(iso), and the nuclear quadrupole interaction did sense the differences. Analysis of the spectra recorded with the magnetic field along the crystallographic axes showed that the two have the same a(iso) but different quadrupole tensors.

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Electron Paramagnetic Resonance Applications to Catalytic and Porous Materials

Goldfarb

2008

Electron Paramagnetic Resonance

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Resolving Mn framework sites in large cage aluminophosphate zeotypes by high field EPR and ENDOR spectroscopy

Cited by 23 publications

References 36 publications

Solvent effects in the synthesis of CoAPO-5, -11 and -34 molecular sieves

Solvent effects in the synthesis of CoAPO-5, -11 and -34 molecular sieves

Dynamics and structure in the Mn2+ site of concanavalin A as determined by high-field EPR and ENDOR spectroscopy

Electron Paramagnetic Resonance Applications to Catalytic and Porous Materials

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