Dimeric Capsules Formed by Tetra‐CMPO Derivatives of (Thia)Calix[4]arenes

Thiacalix[4]arene 2 , calix[4]arene 3 a and its tetraether fixed in the cone conformation 3 b form homo‐ and heterodimeric capsules in apolar solvents, which are held together by a seam of NH⋅⋅⋅O=P hydrogen bonds between carbamoylmethyl phospine oxide functions attached to their wide rim. Their internal volume of ∼370 Å 3 requires the inclusion of a suitable guest. Although neutral molecules such as adamantane (derivatives) or tetraethylammonium cations form kinetically stable complexes ( 1 H‐ and 31 P‐time scale), the included solvent is rapidly exchanged. The internal mobility of the included tetraethylammonium cation is distinctly higher (Δ G =42.5 and 49.7 kJ mol −1 for 3 a and 3 b ) than that for similar capsules of tetraurea calix[4]arenes 1 . Mixtures of 1 with 2 , 3 a , or 3 b contain only the two homodimers but the heterodimerization occurs with the tetraloop tetraurea 6 , which cannot form homodimers. Two dimers with cationic guests ( 2⋅ (C 5 H 5 ) 2 Co + ⋅2 and 3 a⋅ Et 3 NH + ⋅ H 2 O ⋅3 a ) were confirmed by single‐crystal X‐ray analysis.