29Si and 1H NMR spectroscopy of high-pressure hydrous magnesium silicates

B. L. Phillips, P. C. Burnley, K. Worminghaus, A. Navrotsky

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49 Scopus citations

Abstract

We present NMR spectroscopic data, obtained by 1H MAS, 1H static spin-echo, and 29Si{1H} CP-MAS techniques, for a series of hydrous magnesium silicate samples synthesized at high pressure. This series includes chondrodite, β-Mg2SiO4, and phases A, B, superhydrous B, and E. Phases B and superhydrous B give very narrow 29Si NMR peaks and display the most deshielded SiVI chemical shifts yet reported: -170.4 ppm for B and -166.6 for superhydrous B. The 1H NMR spectra of B and superhydrous B confirm the presence of paired hydroxyls, as determined from refinement of the H positions from X-ray diffraction data. The 1H MAS NMR spectra of phase B contain peaks for the two distinct hydrogen positions, with chemical shifts of +4.7 and +3.3 ppm. The static 1H spectrum contains a powder pattern characteristic of a strongly coupled hydrogen pair, from which a dipolar coupling constant of 18.6(4) kHz and inter-hydrogen distance of d(H-H)=1.86(2) Å were obtained. Superhydrous B appears to give two poorly resolved 1H MAS peaks, consistent with the presence of two distinct hydrogen pairs in the P21 mn crystal structure. Analysis of its spin-echo spectrum gives d (H-H)=1.83 (3) Å, slightly shorter than for phase B. β-Mg2SiO4, coexisting with phases B and superhydrous B, appears to give 29Si {1H} CP-MAS signal, indicating that it contains significant H concentration. The 29Si chemical shifts for phases B, superhydrous B, and chondrodite, together with those reported previously for other Mg-silicates, show a good correlation with structural parameters.

Original languageEnglish (US)
Pages (from-to)179-190
Number of pages12
JournalPhysics and Chemistry of Minerals
Volume24
Issue number3
DOIs
StatePublished - Apr 1997
Externally publishedYes

ASJC Scopus subject areas

  • Materials Science(all)
  • Geochemistry and Petrology

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