Solid-state MAS NMR study of pentameric aluminosilicate groups with 180 degrees intertetrahedral Al-O-Si angles in zunyite and harkerite

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Other| February 01, 1995 Solid-state MAS NMR study of pentameric aluminosilicate groups with 180° intertetrahedral Al-O-Si angles in zunyite and harkerite Peter J. Dirken; Peter J. Dirken University of Kent at Canterbury, Physics Laboratory, Canterbury, United Kingdom Search for other works by this author on: GSW Google Scholar Arno P. M. Kentgens; Arno P. M. Kentgens Search for other works by this author on: GSW Google Scholar Gerda H. Nachtegaal; Gerda H. Nachtegaal Search for other works by this author on: GSW Google Scholar Ad M. J. van der Eerden; Ad M. J. van der Eerden Search for other works by this author on: GSW Google Scholar J. Ben H. Jansen J. Ben H. Jansen Search for other works by this author on: GSW Google Scholar American Mineralogist (1995) 80 (1-2): 39–45. https://doi.org/10.2138/am-1995-1-205 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Peter J. Dirken, Arno P. M. Kentgens, Gerda H. Nachtegaal, Ad M. J. van der Eerden, J. Ben H. Jansen; Solid-state MAS NMR study of pentameric aluminosilicate groups with 180° intertetrahedral Al-O-Si angles in zunyite and harkerite. American Mineralogist 1995;; 80 (1-2): 39–45. doi: https://doi.org/10.2138/am-1995-1-205 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract The minerals zunyite, Al13Si5O20(OH,F)18Cl, and harkerite, Ca24Mg8[AlSi4(O,OH)16]2(CO3)8(BO3)8(H2O,Cl), have been studied by means of solid-state27Al MAS NMR. Zunyite contains Si5O16 pentamers and harkerite contains AlSi4(O,OH)16 pentamers. These pentameric groups are unique because their T-O-Si angles are almost 180°. Chemical analysis of the zunyite sample shows that it has excess Al: the Al-Si ratio is 2.9, compared with the ideal of 2.6.High-speed spinning 27Al MAS NMR spectra (11–13 kHz) showed two more signals than the spectra obtained by Kunwar et al. (1984). The signal with δiso = 46.8 ± 0.5 ppm represents the excess Al, which enters the central Si1 site of the Si5O16 pentamer. This assumption is confirmed by the fact that δiso of Al in the AlSi4(O,OH)16 pentamer in harkerite is 44 ± 1 ppm. Additional proof comes from comparing the electrostatic energy and the quadrupole interaction of Al in either a Si1 or Si2 configuration.The Al site in the pentamers of zunyite and harkerite can be considered as a q4(4Si) site. In this case, Al-O-Si angles are correlated with the 27Al chemical shift (Lippmaa et al., 1986). This correlation holds well for the27Al data for harkerite. The value for zunyite indicates that the structure adapts to the incorporation of Al in the Si1 site by a narrowing of the Al-O-Si angle to 171 ± 2.5°. The lower limit of the chemical shift range for Al in framework aluminosilicates is decreased by 12 ppm, from 55.8 ppm for mordenite to 44 ppm for harkerite. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.