Host–guest inclusion complexes formed between a symmetrical tetrasubstituted cucurbit[6]uril and glycine

Abstract

Herein, we have investigated the host–guest inclusion complexes formed on interaction of the symmetric tetramethyl-substituted cucurbit[6]uril (TMeQ[6]) with glycine (Gly) under different conditions. The interactions have been studied both in solution (by ¹H NMR spectroscopy and mass spectrometry) and in the solid state by single crystal X-ray diffraction. The molecular structures of two products are reported, namely TMeQ[6]·(H₂O)₂(PO₄)(NH₃CH₂COOH)₂ (1) and TMeQ[6]·Ca(H₂O)₅·(Cl)₃(NH₃CH₂COOH)·16H₂O (2). Complex 1 adopts a hydrogen-bonded dimeric structure with two glycinium ions contained within a TMeQ[6] molecule with the NH₃⁺ portions of the two molecules located just above the opposite rims of the bowl and forming hydrogen bonds with C–O. In 2, there are centrosymmetric dimers bridged by pairs of calcium ions.