Mineralogical Journal
Online ISSN : 1881-4174
Print ISSN : 0544-2540
ISSN-L : 0544-2540
 
Ab initio calculation of 29Si NMR chemical shifts for the clusters of Si (OH)4, Si (OH)5 and Si(OH)6−2
Masami KANZAKI
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1996 Volume 18 Issue 1 Pages 1-8

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Abstract

In order to identify five-coordinated Si(Siv) species in crystalline and amorphous silicates by NMR spectroscopy, 29Si NMR chemical shifts for the clusters of Si(CH3)4 (TMS), Si(OH)4, Si(OH)5 and Si(OH)6−2 were calculated using ab initio molecular orbital theory. The calculated shifts relative to TMS cluster were −71.7 and −179.0 ppm for Si(OH)4 and Si(OH)6−2, respectively, and are in good agreement with observed shifts. The calculated shift for Si(OH)5 was −127.4 ppm, falls just between the shifts of Si(OH)4 and Si(OH)6−2. The chemical shift for Siv species in polymerized silicates is expected to appear at about −150 ppm, if the effect of polymerization is considered. Present calculation thus supports the assignment of −150 ppm peak as Siv species, which has been found in the alkali-silicate glasses quenched from high pressures.

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© 1996 Japan Association of Mineralogical Sciences
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