Clathrate formation-the formation of crystalline inclusion compounds-is one approach to chemical sensing of vapors and gases. The synthesis of a new diol host compound is described and absorptive clathrate formation and thermal clathrate decomposition are reported for acetone as the guest. It is shown that the sorptive uptake of a guest vapor by the crystalline host compound is not merely surface adsorption but true clathrate formation, involving a solid-state transformation. It is suggested that the use of the host as a chemical sensor is not far off.