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Complex weblike hydrogen bonding in large "drain pipe" channels of wightmanite revealed by new X-ray and spectroscopic measurements

Bernard W. Liebich, Anthony R. Kampf, Edwin Gnos and Cedric Schnyder
Complex weblike hydrogen bonding in large "drain pipe" channels of wightmanite revealed by new X-ray and spectroscopic measurements
The Canadian Mineralogist (June 2021) 59 (2): 321-336

Abstract

The wallpaper-type crystal structure of wightmanite, Mg (sub 5) (BO (sub 3) )O(OH) (sub 5) .1-2H (sub 2) O, has been reanalyzed in order to better understand the position and bonding of hydrogen atoms. Single-crystal structure refinement yielded the monoclinic I2/m unit cell a=13.5165(18), b=3.0981(3), c=18.170(3) Aa, beta =91.441(6) degrees , and V=760.65(17) Aa (super 3) , Z=4. Hydrogen atoms of OH groups pointing to the inside of the elliptical channels oriented parallel to [010] are arranged in the form of two overlying, a-c parallel planar pentagons. The two pentagons point in opposite directions. Hydrogen-bond analysis shows that the hydroxyl groups are linked by complex polyfurcated, intra-molecular hydrogen bonds forming a web-like network coating the walls of the channels. The longest distance between hydrogens (7.226 Aa) is observed in the pentagonal planes of the channel. The anisotropically refined oxygen atoms of the zeolitic water show their strongest vibration parallel to the b axis and in the direction of the largest diameter of the elliptical channel and similarly form a complex inter-molecular hydrogen-bond system to the hydroxyl groups coating the channel walls. This complex bonding is expressed in the Raman spectrum by a broad band between 3100 and 3300 cm (super -1) that is assigned to the OH/H (sub 2) O stretching mode and one strong band at 3661 cm-1 attributable to an OH-stretching mode. Infrared spectra also show a pronounced broad band between 3200 and 3700 cm (super -1) attributed to H (sub 2) O and OH-stretching modes. The weak bands around 1600 cm (super -1) observed in the Raman and IR spectra are probably due to relatively weakly bound water in the channels.


ISSN: 0008-4476
EISSN: 1499-1276
Coden: CAMIA6
Serial Title: The Canadian Mineralogist
Serial Volume: 59
Serial Issue: 2
Title: Complex weblike hydrogen bonding in large "drain pipe" channels of wightmanite revealed by new X-ray and spectroscopic measurements
Affiliation: Via Saleggi 9, Ascona, Switzerland
Pages: 321-336
Published: 20210614
Text Language: English
Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada
References: 30
Accession Number: 2021-045177
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 7 tables
N35°55'00" - N37°30'00", W120°49'60" - W118°19'60"
Secondary Affiliation: Natural History Museum of Los Angeles County, USA, United StatesNatural History Museum of Geneva, CHE, Switzerland
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2021, American Geosciences Institute. Abstract, copyright, Mineralogical Association of Canada. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202131
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