High-Resolution Multinuclear Magnetic Resonance of Inorganic Solids. Oxygen-17 Nuclear Magnetic Resonance Studies of Inorganic Oxides, Oxyanions, and Silicates
Schramm, Suzanne Elaine
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https://hdl.handle.net/2142/70283
Description
Title
High-Resolution Multinuclear Magnetic Resonance of Inorganic Solids. Oxygen-17 Nuclear Magnetic Resonance Studies of Inorganic Oxides, Oxyanions, and Silicates
Author(s)
Schramm, Suzanne Elaine
Issue Date
1984
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Abstract
High resolution (8.45 and 11.7 Tesla) oxygen-17 NMR spectra have been obtained for a variety of oxides, oxyanions, carbonyls and for crystals and glasses in the system CaO-MgO-SiO(,2) using magic-angle sample spinning (MASS) and variable-angle sample spinning (VASS) techniques. The results (obtained by observation of the 1/2, - 1/2 central spin transition) indicate that a very wide range of oxygen-17 quadrupole coupling constants (e('2)qQ/h, (TURN)0 to > 5 MHz) and linewidths ((TURN)0.3 to > 40 ppm) are to be anticipated in solid-state oxygen-17 NMR studies. The linewidth of solid Mg('17)O (0.3 ppm) is narrower than that of liquid water, due to the high symmetry of the oxygen site. The spectrum of static Si('17)O(,2) (cristobalite) indicates an oxygen-17 e('2)qQ/h = 5.8 MHz with an asymmetry parameter of 0. Because of this VASS NMR is more effective than MASS NMR in line narrowing. In the SiO(,4)('2-) unit of forsterite, each nonequivalent oxygen is partially resolved, and split by a large second-order quadrupole interaction, permitting determination of the isotropic chemical shifts, quadrupole coupling constants, and electric field gradient tensor asymmetry parameters for each of the three types of oxygen present. The oxygen-17 spectra of many glasses contain multiple peaks due to non-bridging oxygens, bridging oxygens coordinated to non-Q('4) silicons, and bridging oxygens coordinated to Q('4) silicons. The oxygen-17 quadrupole coupling constant decreases as the percent ionic character of the cation oxygen bond increases. For metasilicate crystals and glasses, the oxygen-17 chemical shift of the non-bridging oxygen becomes progressively deshielded as the ionic potential of the cation present increases. The principal elements of the oxygen-17 chemical shielding tensors have been determined for several oxyanions and transition metal carbonyls. The magnitudes of such tensors are large ((DELTA)(sigma) (TURN) 500 ppm) while the oxygen-17 quadrupole coupling constants are small ((TURN)1 MHZ). A field-dependent quadrupole-induced shift in variable-angle sample spinning NMR spectra has been observed in the boron-11 NMR study of a borosilicate glass. The results indicate that difference in electric quadrupole coupling constants may be used in variable-angle sample spinning NMR at low magnetic field strengths to provide highly resolved spectra of some nonintegral spin quadrupole nuclei.
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