Jones, Matthew Jonathan; (1997) Structural and dynamic properties of disordered solids. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The structural and dynamic properties of several disordered solids were investigated using a range of experimental techniques. Ni K-edge EXAFS spectroscopy was used to study the local environment of the nickel atoms in several catena-[(1,2-diaminopropane)-cadmium(II)-tetra-μ-cyanonickelate(II)] inclusion compounds containing halogenated alkane guest molecules. The main contribution to the spectra arises from the CN-units and the Cd atoms surrounding the Ni atoms. For all guest molecules studied (with one exception) a significant contribution from the halogen atoms of the guest is observed, suggesting some degree of ordering of the guest molecules with respect to the host substructure. Incoherent quasielastic neutron scattering (IQNS) was employed to study the dynamics of tetrakis (trimethylsilyl)silane (TTMSS). The dynamics at low temperature are consistent with 3-fold rotational jumps with a gyration radius of ca. 1 Å, ascribed to rotation of the methyl groups about the C-Si bond. At ca. 240 K a phase transition occurs, associated with a change of dynamics. At ambient temperature the motion is consistent with isotropic rotation on a sphere. The structure of the thiourea/chlorocyclo-hexane inclusion compound was investigated via X-ray powder diffraction. The structure of the high temperature phase is consistent with previous studies. The low temperature structure is a distorted form of the high temperature structure, and in contrast to the latter the guest molecules have well defined positions. The guest molecule dynamics in the thiourea/chlorocyclohexane and thiourea/cyclohexane inclusion compounds were studied using IQNS. For cyclohexane the motion is described by a combination of 3-fold rotational jumps about the molecular axis and 3-fold rotational jumps about the tunnel axis. The guest molecules are tilted with respect to the tunnel axis. The results for chlorocyclohexane are qualitatively similar to those for cyclohexane. For both compounds there is a change in the guest dynamics at the respective phase transition temperatures, the nature of which could not be determined.

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