title: 17O NMR and crystalline hydrates.
abstract: 17O NMR is complementary to 2H NMR for studies of hydrate structure and dynamics in solids, insofar as the quadrupole coupling parameters can be accurately determined. At a Larmor frequency of 34.2 MHz, the effects of a large 17O quadrupole coupling (e2qQ/h approximately 7 MHz) on both the orientational dependence of the central transition resonance frequency and its observation by cross-polarization are examined in powders and a single crystal of oxalic acid dihydrate. Comparison with the exact energies shows that the variation of the central transition frequency with tensor orientation is accurately described as a second-order perturbation, even when e2qQ/h and the Larmor frequency are comparable. The combined chemical and quadrupole-induced shifts of the central transition frequency are separated by their distinct transformation properties, and we report the H2(17)O quadrupole coupling tensor in alpha-oxalic acid dihydrate, which is compared with the hydrogen bonding structure. Excitation of the central transition by cross-polarization is examined in terms of the 17O nutation frequency. Distortions in powder patterns and the loss of lines in single-crystal spectra owing to the orientational dependence of the first-order quadrupole coupling are verified, and simple methods for mitigating the problem in single-crystal and powder experiments are presented.
authors.affiliation: Department of Chemistry, University of Louisville, KY 40292, USA.
authors.forename: Q W
authors.initials: QW
authors.lastname: Zhang
authors.forename: H M
authors.initials: HM
authors.lastname: Zhang
authors.forename: M G
authors.initials: MG
authors.lastname: Usha
authors.forename: R J
authors.initials: RJ
authors.lastname: Wittebort
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003460:Crystallization; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008432:Mathematical Computing; D009842:Oligopeptides / Q000737:chemistry*; D010070:Oxalates / Q000737:chemistry*; D019815:Oxalic Acid; D010103:Oxygen Isotopes; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D009842:Oligopeptides; D010070:Oxalates; D010103:Oxygen Isotopes; D014867:Water; C080939:glycyl-glycyl-valine; D019815:Oxalic Acid