Acetonitrile inclusion complexes of piperazine‐based macrocycles

New piperazine‐based macrocycles with single small cavities were prepared by using high dilution technique. The inclusion of acetonitrile into the cavity ( 7, 8 ) or clathrate formation ( 3 ) was studied by 1 H‐NMR spectroscopy in solution and by X‐ray diffraction in the crystalline state. The cycle 3 forms a molecular cleft, a molecular pocket, where the acetonitrile molecule is held by four weak N…H interactions reinforcing the clathrate formation. The cycles 7 and 8 contain a rigid cavity for an exact sterical fit with the methyl group of a linear compound like acetonitrile. The acetonitrile inclusion complex with 7 proved to be stable under normal conditions and was studied by means of thermogravimetry. It is stable up to 80°C and the breakdown is complete when the temperature is raised over 120°C. Solid‐state IR studies show a shift of the cyano band of 5 cm −1 to smaller wave numbers when compared with free acetonitrile. The acetonitrile methyl group is shielded and in the 1 H‐NMR spectrum its signal is shifted to δ = 1.85.