The Cyclobutanocucurbit[5–8]uril Family: Electronegative Cavities in Contrast to Classical Cucurbituril while the Electropositive Outer Surface Acts as a Crystal Packing Driver

Abstract

The structural parameters for the cyclobutanoQ[5–8] family were determined through single crystal X-ray diffraction. It was found that the electropositive cyclobutano methylene protons (CH2) are important in forming interlinking crystal packing arrangements driven by the dipole–dipole interactions between these protons and the portal carbonyl O of a near neighbor. This type of interaction was observed across the whole family. Electrostatic potential maps also confirmed the electropositive nature of the cyclobutano CH2 but, more importantly, it was established that the cavities are electronegative in contrast to classical Q[5–8], which are near neutral.

Gold and Silver Chains from Tetrahydrothiophenocucurbit[6]uril as Au or Ag-Nanoparticles

“…There has long been a quest to synthesize substituted derivatives of Q­[ n ], where all their glycoluril moieties carry substitution. These types of substituted Q­[ n ] have slowly emerged over the period from 1992 to 2021. – The objectives initially were to modify the chemical and physical properties, but then these progressed to include functionality. The most accessible means to derivatization of Q­[ n ] toward functionality was through the inclusion of substitution at the equatorial methine position of the glycoluril moieties.…”

“…Prominently, the synthesis of fully substituted Q­[ n ] has been achieved where the alkyl substituent is a methyl group, or as carbocycles–cyclohexano (CyH), cyclopentano (CyP), or cyclobutano (CyB), where only the latter two and a special case of hemimethyl glycoluril unit (hMeQ [5–7]) produce ≥3 homologues (Figure ). – ,– In these examples, the equatorial region of each homologue is decorated with the carried substituent, which has the effect of maintaining symmetrical spheroidal cavities. Partially substituted Q­[ n ], with one or some of their glycoluril moieties substituted, can have the effect of distorting the cavity shape.…”

Supramolecular Self-Assembly Based on Symmetric Tetramethyl-Substituted Cucurbit[6]uril and Small Aromatic Amines

“…[1][2][3][4] They are cyclic compounds formed by glycoluril units bridged by methylene groups, which contain a hydrophobic cavity and two hydrophilic portals. 5 At present, more than 100 cucurbit[n]urils have been reported, 6 among which ordinary cucurbit[n]urils include Q [5], Q [6], Q [7], etc., 7,8 and a series of modified Q[n]s, such as methyl-, 9 cyclohexyl-, 10 cyclopentyl-, 11,12 hydroxyl-, 13 phenyl- 14 and cyclobutyl-cucurbit[n]uril 15 etc. The special structure and functional group properties of cucurbit[n]urils make them widely used in the field of host-guest chemistry, coordination chemistry and supramolecular self-assembly driven by non-covalent bonds including hydrogen bond, π•••π conjugation, ion-dipole, dipole-dipole interactions.…”