✍ Scribed by Huuskonen, Juhani ;Rissanen, Kari
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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.
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