Fine structure in the pure quadrupole resonance of oxygen-17 in Ba(ClO3)2⋅H2 17O by nuclear double resonance

Abstract

A technique of double resonance in the laboratory frame is applied for the measurement of the pure quadrupole resonances of oxygen-17 in polycrystalline Ba(ClO3)2⋅H2 17O at 77°K. The spectrum comprises three frequency bands displaying fine structure that is interpreted in terms of the intramolecular dipolar interactions within the hydration water molecule. The experimental results are compared with theoretical spectra calculated for various geometries of the water molecule and relative orientations of the quadrupolar and dipolar interactions. It is not possible to obtain a complete agreement between the calculated and experimental spectra, since apparently not all predicted lines show experimentally. It is suggested that the transitions involving triplet eigenstates of the proton–proton dipolar interaction are not observed, presumably due to excessive line broadening. Based on this assumption a good fit with the experimental spectrum is obtained with the following parameters: e2qQ/h (17O) = (−7.61±0.01)MHz, η=0.94±0.01, proton–oxygen distance ROH= (0.99±0.02) Å, and the HOH angle 2ϑ=110°±2°. These results are discussed in terms of the electronic and geometric structure of the hydration water molecule.

Probing Axial Water Bound to Copper in Tutton Salt Using Single Crystal 17O-ESEEM Spectroscopy

“…As discussed by others, the quadrupole coupling is a very sensitive probe of the electronic environment of the oxygen nucleus, and should be influenced by water hydrogen bonding, H–O–H angle, O–H bond length as well as interactions with nearby ions. − ,− ,, In the present system, the axial water - copper interaction is weak which may be partly responsible for the differences found between the nqi values in Table and those reported for equatorial 17 O-waters bound to copper (average values: e 2 qQ / h = 7.6 MHz, η = 0.67) 34 .…”

“…In atoms where nuclear quadrupole interactions exhibit high η, even moderate changes to the electric field gradient tensor can flip the sign and principal direction of the absolute maximum interaction. , This has also been highlighted in the early Townes–Dailey analysis of an idealized 17 O-water molecule, which predicts such a switch when the H–O–H angle extends more than 109.5° . Subsequent nqr studies of Ba­(ClO 3 ) 2 ·H 2 17 O proposed that the large H–O–H angle and long hydrogen bonds causes such an interchange in the 17 O-water z and y efg axes, and therefore the sign of e 2 qQ / h was considered negative. , Shortly thereafter a single crystal 17 O-water NMR study of enriched oxalic acid dihydrate reported that the absolute maximum quadrupole tensor component lies in the plane of the water molecule . However, more recent high-field solid state NMR investigations of 17 O hydrated systems used advanced quantum chemical calculations to argue against these earlier conclusions, and instead maintain that e 2 qQ / h for 17 O-water should be positive and directed normal to the water plane. − …”

17O NMR Investigation of Water Structure and Dynamics

“…18,25,26,65,66 However, nuclear quadrupole resonance (NQR) studies of some inorganic hydrates have determined the C Q of bound water to be significantly larger than 7 MHz, including Ba(ClO 3 ) 2 · H 2 O. 67,68 This is not the case or all hydrates that have been studied via NQR, demonstrating the sensitivity of the EFG tensor to many different factors and highlighting the complexity of the discrepancy. 69,70 The differences in temperature between the NMR (300 K, C Q = 6.92 MHz) and NQR (77 K, C Q = 7.61 MHz) experiments could explain the discrepancies in measured C Q due to changes in dynamics.…”

Water molecular reorientation in ice and tetrahydrofuran clathrate hydrate from lineshape analysis of 17O spin-echo NMR spectra

“…C Q is moderately sensitive to the local environment of the water molecules, as seen in the different values for water- 17 O in Ice-II (C Q = 6.893 MHz, h = 0.865), 48 and crystal hydrates oxalic acid dihydrate (C Q = 6.8 MHz, h = 0.93) 49 and barium chlorate monohydrate (C Q = 7.61 MHz, h = 0.94). 50 For THF clathrate hydrate at 140 K, the envelope of the spectrum is somewhat noisier than that of ice-Ih, perhaps because of an inhomogeneous orientational distribution of hydrate crystallites produced when the THF solution was frozen in the NMR probe. Nevertheless, it is clear that the lineshape is almost identical to that of ice-Ih at 150 K, and thus we conclude that the local oxygen coordination in THF clathrate hydrate is very similar to that in ice-Ih.…”