STRUCTURAL STUDIES ON VOLATILE, AIR AND MOISTURE SENSITIVE LIQUIDS AT AMBIENT AND ELEVATED-TEMPERATURES USING LIQUID X-RAY-SCATTERING - THE STRUCTURE OF LIQUID GALLIUM (III) CHLORIDE SYSTEMS

An X-ray scattering method is presented which provides accurate structural information on air and moisture sensitive liquids at ambient and elevated temperatures using a standard theta-theta X-ray diffractometer. The method utilizes capillary glass tubes as sample containers and requires no corrections for sample container absorption or scattering, as shown by structural studies of well-known systems such as benzene, carbon tetrachloride and antimony trichloride. Artefacts produced by the sample holder are insignificant and very easy to correct for. The major drawback of the method is the long time of experiment, due to the small (compared with the standard set-up) area/volume ratio of the liquid which contributes to the intensity of the scattered radiation. However, the time required is not unduly long except for liquids containing light elements only (very low scattering power) or very heavy ones (high linear absorptivity). Liquid GaCl3 is shown to have a dimeric structure consisting of edge-sharing GaCl4 tetrahedra. This structure is analogous to that previously found for GaCl3 in the gaseous and solid state and for AlCl3 in the gaseous and liquid state. Concentrated solutions of GaCl3 in benzene have been shown to comprise monomeric GaCl3 units with C3v symmetry. However, it is suggested that such units form as a result of a radiolytically induced cleavage of the Ga2Cl6 moieties. No Ga-C correlation is resolved, which is explained by assuming a sigma-type complex between GaCl3 and benzene and/or an ill-defined interaction between the GaCl3 unit and benzene. The former situation would most probably produce too few Ga-C correlations to be observable by the present method, whereas the latter situation would produce a very broad Ga-C correlation difficult to separate from the background. However, the deviation from the D3h symmetry adopted by GaCl3 in the gas phase indicates a specific interation between GaCl3 and benzene.