Tetra-n-butylammonium chloride (TBAC) semiclathrate hydrate was synthesized with changing TBAC concentrations. The hydration number of the obtained samples decreased as the TBAC concentration increased. Powder X-ray diffraction data showed that the crystal structure had the tetragonal symmetry and that the peak intensities of both 200 and 220 increased with decreasing hydration. Due to the large molecular size of TBA molecules, their position within the unit cell cannot be significantly changed. Crystal structure analysis by the Rietveld method indicates that chloride ions changed their atomic coordinates with changes in hydration. The chloride ion positions are effective in causing changes in the peak intensity of XRD, because chloride has the largest atomic number in TBAC semiclathrate hydrate.
