ACETONITRILE INCLUSION COMPLEXES OF PIPERAZINE-BASED MACROCYCLES

New piperazine-based macrocycles with single small cavities were prepa red by using high dilution technique. The inclusion of acetonitrile in to the cavity (7, 8) or clathrate formation (3) was studied by H-1-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 reinfo rcing the clathrate formation. The cycles 7 and 8 contain a rigid cavi ty for an exact sterical fit with the methyl group of a linear compoun d like acetonitrile. The acetonitrile inclusion complex with 7 proved to be stable under normal conditions and was studied by means of therm ogravimetry. It is stable up to 80 degrees C and the breakdown is comp lete when the temperature is raised over 120 degrees C. Solid-state IR studies show a shift of the cyano band of 5 cm(-1) to smaller wave nu mbers when compared with free acetonitrile. The acetonitrile methyl gr oup is shielded and in the H-1-NMR spectrum its signal is shifted to d elta = 1.85.