Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.594986
Title: Some structural studies by deuterium magnetic resonance
Author: Dillon, Maria da Graça Fernandes Graveirinha
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1972
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Abstract:
Single crystals of ND 4 DS0 4 and Sr(DCOO)2.2D 2 0 have been studied by deuteron magnetic resonance spectroscopy; the apparatus and techniques used are described in some detail. ND 4 DS0 4 has considerable interest because of its ferroelectric properties: spectra were recorded at 300 K and 230 K, within the paraelectric and ferroelectric phases respectively. Symmetry relationships were used in solving the structure, particularly for refining the orientation data. At room temperature, the two sets of bisu1phate deuterons were found to have (within xperimental error) the same quadrupole coupling constants and asymmetry parameters: h = 191.9 ± 3KHz, T1 = 0.094 ± 0.02 ~ h = 193.2 ± 3KHz, T1 = 0.070 ± 0.0l. The quadrupolar constants appear somewhat larger than expected from the known 0····0 distances. No evidence of disorder is apparent from the room temperature data. At 230 K, both groups of deuterons appear to have suffered small angular displacements, essentially planar and antisymmetric with relation to the room temperature positions. One type of deuteron undergoes movements of larger amplitude in a plane more favourably oriented with respect to the polar axis, [Cl], which suggests a definite contribution from these deuterons to the appearance of ferroelectricity. The Curie point has been determined independently by use of the radio frequency spectrometer; a value of 266 ± 2K was obtained, in reasonable agreement with the literature value from dielectric constant measurements. The ND4+ group is reorienting rapidly both at 230 K and 300 K. Little change seems to occur upon transition. Some distortion of the tetrahedral structure, a possible difference in the reorientation rate for the two kinds of ND4+ ions, and a slight difference in their respective environments could be the main causes for the fine structure observed in the ammonium resonance. The study of Sr(DCOO)2.2D 2 0 gave the following average values for the quadrupolar constants and asymmetry parameters at 300 K: 2 formate ion [DC(1)0(1)0(2)]- ~ = 167.6 + 3KHz 'T] = 0.043 ± 0.01, DB h = 170.3 ± 3KHz 'T] = 0.025 ± 0.01. formate ion [DC(2)0(3)0(4)]- DB= h 242.8 + 3KHz 'T] = O. 100 ± 0.005 2 ~ = 216.8 + 3KHz 'T] = O. 113 ± 0.005 Both formate ions give e.f.g. tensors very close to axial symmetry. For [DC(1)0(1)0(2)]-, the deuteron is approximately aligned with the C(1) 0(10(2) bisectrix in an essentially planar arrangement. For [DC(2)0(3)0(4)]- the deuteron shows a surprising deviation of 22̊ from the plane of the COO group, as determined from Osaki's X-ray data. A weak C-D---O bonding interaction is tentatively suggested to account for this anomaly. D 2 0(1) was easily localised in the surrounding structure as known from X-ray data; the electric field gradient constants indicate that this molecule is 'static' at room temperature. A-D-0-D angle of 107.8̊ is in good agreement with the value for H2O D 2 D0(2) gave rise to broad and rather weak resonances with marked fine structure: some poorly defined curves were analysed only approximately. The high quadrupolar constants (330 ± 30 KHz) and asymmetry parameters (0.2 ± 0.1) derived for one set of the curves suggest that this D 2 0 molecule is weakly hydrogen bonded (if at all), and may have a rather high degree of motional freedom. analysed only approximately. The high quadrupolar constants (330 ± 30 KHz) and asymmetry parameters (0.2 ± 0.1) derived for one set of the curves suggest that this D 2 0 molecule is weakly hydrogen bonded (if at all), and may have a rather high degree of motional freedom.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.594986  DOI: Not available
Keywords: QD Chemistry
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