Pillar[4]pyridinium: a square-shaped molecular box

Abstract

Numerous applications of Stoddart's 'blue-box', a pyridinium containing macrocycle of rectangular shape, encouraged us to seek successors of this amazing molecule. Using a one-step cyclization reaction we synthesized a square-shaped cyclic tetramer consisting of 4-methylenepyridinium units - pillar[4]pyridinium (P[4]P). Pillar[4]pyridinium is a quadruply positively charged water-soluble macrocycle with a highly symmetric, strained structure and an electron-deficient cavity. These features impel the macrocycle to assemble into channel networks in the solid state and render it an effective fluoride receptor in water.

Base-Catalyzed, Solvent-Free Synthesis of Rigid V-Shaped Epoxydibenzo[b,f][1,5]diazocines

“…The synthetic potential of the diazocine products was demonstrated by a series of well-established transformations proceeding without affecting the diazocine core ( Scheme 4 ). First, we turned our attention to the pyridinium salt structural motif, which proved to be useful in many areas 18 such as molecular recognition, 19 catalysis, 20 and medicinal chemistry. 21 Gratifyingly, the treatment of diazocines 5a and 4b with MeI cleanly afforded salts 6a and 6b , respectively, without competitive opening of the oxygen bridge under the action of the strong alkylating agent.…”

Impact of confinement in multimolecular inclusion compounds of melamine and cyanuric acid

“…45,46 Furthermore, CA 4 -1 complex shows a cage-like cluster with a tubular cavity, alike that observed in the pillar [4]pyridinium molecular box. 24 This structure suggests that linear molecules like H 2 could fit inside the cavity. Table 2 reports some meaningful topological parameters of H-Bonds.…”

“…By far, calixarenes and cucurbituriles are the smallest molecules that can host atomic species and small molecules. Sashuk et al 24 have obtained a square shaped molecule that can capture a single water molecule or a fluoride anion. Endohedral fullerenes are also a matter of study in this field.…”

Electrostatic co-assembly of pillar[n]pyridiniums and calix[4]arene in aqueous media

“…10 Anionic p-sulfonatocalix[4]arene (C4S) is a key player in aqueous supramolecular chemistry and crystal engineering, with tremendous applications ranging from simple host-guest systems 11 to sophisticated drug delivery ensembles, 12 sensors, 13 vesicles, 14 crystals, 15 and in interactions with proteins, 16 to name a few. Given the propensity of P[n]Ps to trap water wires or clusters 8,9 and of C4S to include intracavity water molecules via non-conventional OH⋯π hydrogen bonding, 17 we anticipated a peculiar interplay between their combined supramolecular cavities and water molecules. Interestingly, our hybrid pillar[n]pyridinium/ calix[4]arene systems are devoid of any coordination or classical hydrogen bonding interactions between macrocyclic components, rendering the assembly guided, besides electrostatic attraction, by less conventional interactions, such as anion⋯π + , anion⋯π + ⋯anion, and π⋯π + .…”