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Nuclear magnetic resonance and infra-red spectroscopic studies on clathrates and weak charge transfer complexes Gilson, Denis Frank Robert

Abstract

Nuclear magnetic resonance and infra-red studies have been made of various clathrate compounds. The purpose of the investigations was to examine the extent of molecular motion which the enclathrated molecule^ may undergo. It has been shown that the benzene molecule in the clathrate with Nickel Ammonium Cyanide rotates about the six-fold axis at room temperature. The existence of shifts in the infra-red spectrum of the enclosed molecule has been confirmed but the assignment of the absorption bands at 1573 cm-¹ and 1165 cm-¹ as the Raman active E[subscript 2g] vibrations is incorrect. Studies on the quinol clathrates of methane, fluoroform, methyl alcohol and methyl cyanide and the clathrate of sulphur hexafluoride in Dianin's compound (4-p-hydroxyphenyl-2,2,4-trimethyl chroman) infer that isotropic motion of the enclathrated molecues occurs at 77°K. The infra-red spectra of these clathrates and of quinol 0-d₂ have been examined. Nuclear magnetic resonance investigations of molecular motion in weak charge transfer complexes are reported. In the dioxane complexes of bromine and mercuric chloride the structure is rigid at room temperature. In the complexes with antimony trichloride and silver perchlorate the dioxane molecule is reorienting about the O-O axis at 298°K but is rigid at 77°K. Rotation of the benzene ring at 25°C in the complex AgClO₄.C₆H₆ suggests that the reported distortion of the benzene ring may be incorrect. At low temperatures the agreement between the theoretical and and experimental second moments shows that the essential features of the structure are correct. The implication of the infra-red studies of other workers are discussed. Reorientation of both aromatic rings in the complex of benzene and hexafluorobenzene occurs down to low temperatures. The potential barrier hindering rotation of the hexafluorobenzene molecule is estimated to be 1.1 kcal/mole.

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