The compound was shown to be dimeric either by matrix-assisted laser desorption ionization-time-of-flight and vapor pressure osmometry. Encapsulation studies were followed by NMR. Propionic or pivalic acid was included in the capsules, probably as head to head hydrogen-bonded dimers in mesitylene-d 12, a solvent too big to be a guest by its own. Longer dimeric carboxylic acids or larger substrates, like 2-adamantyl azide or cyclohexylcarbodiimide, do not encapsulate, but mixtures of a long and a short carboxylic acid (i.e., propionic-adamantyl or propionic-cyclohexyl) yield pairwise complexes.