Localization of Hydrogen and Content of Oxonium Cations in Alunite via Neutron Diffraction

Schukow, H.; Breitinger, Dietrich K.; Zeiske, Th.; Kubanek, F.; Mohr, J.; Schwab, R.

doi:10.1002/(sici)1521-3749(199906)625:6<1047::aid-zaac1047>3.0.co;2-f

Cited by 16 publications

(13 citation statements)

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“…The monovalent ions are coordinated by 12 O atoms or hydroxyl groups. There are weak hydrogen bonds between the Al 2 -OH groups and the O atoms in the sulfate tetrahedron that point towards the cavity (Wang et al 1965;Schukow et al 1999;Lager et al 2001).…”

Section: Introductionsupporting

confidence: 89%

“…The structure also contains a single A (A = Na + , K + , H 3 O + ) site (Wang et al 1965;Schukow et al 1999;Lager et al 2001). Thus, the 27 Al, 23 Na, and 39 K NMR spectra of a stoichiometric alunite will each consist of a single NMR resonance.…”

Section: Introductionmentioning

confidence: 78%

“…Specifi cally, the Al-O distances are typically longer for Al-OH 2 (ca. 1.9 Å) compared to bridging Al 2 -OH (1.86 Å) (Schukow et al 1999). Substitution of terminal OH 2 ligands for bridging hydroxyls results in a smaller quadrupole coupling and a non-axially symmetric local 27 Al-bonding environment, as observed for Al D ( Table 2).…”

Section: Discussionmentioning

confidence: 99%

“…Although no satisfactory structural model is available for a pure D 3 O + alunite, a direct comparison with alunite [KAl 3 (SO 4 ) 2 (OH) 6 ] is possible since these structures have similar unit-cell parameters. An O-H···O distance of 2.91 Å (Schukow et al 1999) was obtained for an alunite sample with nominally 12% H 3 O, which is in excellent agreement with our measurement.…”

Section: Hydronium Alunite (H 3 O-alu)mentioning

confidence: 99%

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Characterization of defects and the local structure in natural and synthetic alunite (K, Na, H3O)Al3(SO4)2(OH)6 by multi-nuclear solid-state NMR spectroscopy

Nielsen

Majzlan

Phillips

et al. 2007

American Mineralogist

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The local structural environments in a series of natural and synthetic alunite samples [ideally AAl 3 (SO 4 ) 2 (OH) 6 , A = H 3 O + , D 3 O + , Na + , and K + ] have been probed by solid-state 1 H, 2 H, 23 Na, 27 Al, and 39 K NMR spectroscopy. The natural alunite [KAl 3 (SO 4 ) 2 (OH) 6 ] and synthetic hydronium alunite samples contain few structural defects, whereas the synthetic natroalunite and alunite samples have ca. 10% Al vacancies based on 27 Al NMR. A new 27 Al local environment (Al D ) was observed and assigned to Al with one Al vacancy in the fi rst cation sphere. Three different proton environments, Al 2 -OH, Al-OH 2 , and H 3 O + are detected by 1 H and 2 H MAS NMR. The hydronium ion (H 3 O + ) is only observed in hydronium alunite, and is associated with the stoichiometric regions of the sample. It was not detected in 1 H and 2 H NMR spectra of alunite and natroalunite despite K (Na) occupancies of signifi cantly less than 100%, as determined from elemental analysis. Thus, our NMR results suggest that the common assumption, namely that an A vacancy and an Al 3+ vacancy are compensated by adding an H 3 O + and 3 H + (creating 3 Al-OH 2 groups), respectively, is too simplistic. Instead, a signifi cant fraction of the Al 3+ vacancies are compensated for by 4 H + ions, resulting in 4 Al-OH 2 groups per vacancy. This substitution is accompanied by the simultaneous deprotonation of a H 3 O + ion present on the A site. The resultant H 2 O molecule is unnecessary for charge balance, accounting for the A-site defi ciency often observed. The presence of Al 3+ and A + vacancies appears closely correlated based on NMR.

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Section: Introductionsupporting

confidence: 89%

Section: Introductionmentioning

confidence: 78%

Section: Discussionmentioning

confidence: 99%

Section: Hydronium Alunite (H 3 O-alu)mentioning

confidence: 99%

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Characterization of defects and the local structure in natural and synthetic alunite (K, Na, H3O)Al3(SO4)2(OH)6 by multi-nuclear solid-state NMR spectroscopy

Nielsen

Majzlan

Phillips

et al. 2007

American Mineralogist

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“…All subsequent work (e.g. Menchetti and Sabelli, 1976;Schukow et al, 1999;Stoffregen et al, 2000;Majzlan et al, 2006) has shown this to be correct.…”

mentioning

confidence: 99%

Thermal expansion of alunite up to dehydroxylation and collapse of the crystal structure

et al. 2012

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The high-temperature (HT) behaviour of a sample of natural alunite was investigated by means of in situ HT single-crystal X-ray diffraction from room temperature up to the dehydroxylation temperature and consequent collapse of the crystal structure. In the temperature range 25À500ºC, alunite expands anisotropically, with most of the contribution to volume dilatation being produced by expansion in the c direction. The thermal expansion coefficients determined over the temperature range investigated are: a a = 0.61(2)610 À5 K À1 (R 2 = 0.988), a c = 4.20(7)610 À5 K À1 (R 2 = 0.996), a c /a a = 6.89, a V = 5.45(7)610 À5 K À1 (R 2 = 0.998). At~275À300ºC, a minor discontinuity in the variation of unit-cell parameters with temperature is observed and interpreted on the basis of loss of H 3 O + that partially substitutes for K + at the monovalent A site in the alunite structure. Increasing temperature causes the Al(O,OH) 6 sheets, which remain almost unaltered along the basal plane, to move further apart, and this results in an expansion of the coordination polyhedron around the intercalated potassium cation. Sulfate tetrahedra act as nearly rigid units, they contract a little in the lower temperature range to accommodate the elongation of the Al octahedra.

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ChemInform Abstract: Localization of Hydrogen and Content of Oxonium Cations in Alunite via Neutron Diffraction.

et al. 1999

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Dedicated to Professor H. D. Lutz, Siegen, on the Occasion of his 65 th Birthday.Abstract. Polycrystalline alunite-d 6 KAl 3 (OD) 6 (SO 4 ) 2 , prepared by hydrothermal reaction of Al 2 (SO 4 ) 3 , K 2 SO 4 and D 2 SO 4 , was studied by neutron powder diffraction performed on the diffractometer E2 (HMI-BENSC, Berlin). Rietveld refinement of the data set for T = 2 K yielded the crystallographic data: space group R3m, Z = 3, trigonal setting, a = 694.

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Localization of Hydrogen and Content of Oxonium Cations in Alunite via Neutron Diffraction

Cited by 16 publications

References 0 publications

Characterization of defects and the local structure in natural and synthetic alunite (K, Na, H3O)Al3(SO4)2(OH)6 by multi-nuclear solid-state NMR spectroscopy

Characterization of defects and the local structure in natural and synthetic alunite (K, Na, H3O)Al3(SO4)2(OH)6 by multi-nuclear solid-state NMR spectroscopy

Thermal expansion of alunite up to dehydroxylation and collapse of the crystal structure

ChemInform Abstract: Localization of Hydrogen and Content of Oxonium Cations in Alunite via Neutron Diffraction.

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