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H-bonding scheme in allactite; a combined single-crystal X-ray and neutron diffraction, optical absorption spectroscopy, FTIR and EPMA-WDS study

G. Diego Gatta, Ferdinando Bosi, Maria Teresa Fernandez Diaz and Ulf Halenius
H-bonding scheme in allactite; a combined single-crystal X-ray and neutron diffraction, optical absorption spectroscopy, FTIR and EPMA-WDS study
Mineralogical Magazine (August 2016) 80 (5): 719-732

Abstract

The crystal chemistry of allactite from Langban, Varmland (Sweden) was investigated by single-crystal X-ray and neutron diffraction, optical absorption spectroscopy, Fourier-transform infra-red spectroscopy (FTIR) and electron microprobe analysis by wavelength-dispersive spectroscopy (EPMA-WDS). The optical spectra indicate the presence of Mn in valence state 2+ only. Assuming 16 O atoms per formula unit, arsenic as As (super 5+) and the (OH) content calculated by charge balance, the resulting formula based on the EPMA-WDS data is (Mn (sub 6.73) (super 2+) Ca (sub 0.13) Mg (sub 0.12) Zn (sub 0.02) ) (sub Sigma 7.00) (As (super 5+) ) (sub 2.00) O (sub 16) H (sub 8) , very close to the ideal composition Mn (sub 7) (AsO (sub 4) ) (sub 2) (OH) (sub 8) In the unpolarized FTIR spectrum of allactite, fundamental (OH)-stretching bands are observed at 3236, 3288, 3387, 3446, 3484, 3562 and 3570 cm (super -1) , suggesting that a number of OH environments, with different hydrogen bond strengths, occur in the structure. The neutron structure refinement shows that four independent H sites occur in allactite with full site occupancy, all as members of hydroxyl groups. The complex hydrogen-bonding scheme in the allactite structure is now well defined, with at least nine hydrogen bonds energetically favorable with mono-, bi- and trifurcated configurations.


ISSN: 0026-461X
EISSN: 1471-8022
Coden: MNLMBB
Serial Title: Mineralogical Magazine
Serial Volume: 80
Serial Issue: 5
Title: H-bonding scheme in allactite; a combined single-crystal X-ray and neutron diffraction, optical absorption spectroscopy, FTIR and EPMA-WDS study
Affiliation: Universita degli Studi di Milano, Dipartimento di Scienze della Terra, Milan, Italy
Pages: 719-732
Published: 201608
Text Language: English
Publisher: Mineralogical Society, London, United Kingdom
References: 26
Accession Number: 2016-072879
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 5 tables
N58°52'60" - N61°02'60", E01°42'00" - E14°30'00"
Secondary Affiliation: Sapienza Universita di Roma, ITA, ItalyInstitut Laue-Langevin, FRA, FranceSwedish Museum of Natural History, SWE, Sweden
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201635
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