Structural Tuning of Anion‐Templated Motifs with External Stimuli through Crystal‐to‐Crystal Transformation

Abstract

Protonation of trans-1,2-bis(4-pyridyl)ethylene (4,4'-bpe) with dilute sulfuric acid (33 %) afforded a protonated adduct [{4,4'-bpe⋅2 H } {HSO } {SO } {H O} ] (1). The neighboring olefinic bond in 1 is in a suitable range (3.931-4.064 Å) to undergo a photochemical [2+2] cycloaddition reaction. Upon irradiation with UV light (365 nm), 1 undergoes a molecular sliding involving the 4,4'-bpe⋅2 H units, affording 2, stabilized through O ⋅⋅⋅π interactions. Heating 1 to 50° C leads to a 3D hydrogen-bonded organic framework (HOF) (3). This process occurs through thermal dissociation of the bisulfate anion. Diffusion of iodine through the crystal lattice of 1 and 3 enables the reduction of sulfate to bisulfate, affording a 1D hydrogen-bonded chain (4). Solid-state C CPMAS NMR, IR, DSC, and powder XRD studies further support stimuli-responsive structural tuning through crystal-to-crystal transformation. All these conversions occur with significant translational and rotational movements along with a series of bond-breaking and bond-forming processes.

Supramolecular assemblies of organogelators featuring benzimidazole and long‐chain pyridine dicarboxyamide

“…The presence of polarized amide N-Hs in the gelator structures offers the possibility to tune the sol-gel interconversion by anions. Indeed, many anion probes have been designed based on the interactions between the amide functional group and various anions in the literature [14,15,17,[47][48][49][50][51][52][53][54][55][56][57][58][59]. The competition for hydrogen boning interactions between the gelator-gelator and gelator-anion allows an easy way to qualitatively identify anions capable of producing strong interactions with gelator molecules.…”

Synthon trends according to acid strength and geometry in salts of N-heterocyclic bases

“…The robustness of the primary heterosynthon III can be found in the dihydrochloride salt dihydrate of BPE, as reported previously by us, 20 and also in hexakisIJhydrogen sulfate) bisIJsulfate) tetrahydrate. 21 Therefore, we assessed if it could also be formed in other BPE salts with the same acid sources attempted for ampyz. Among the three new BPE salts obtained here, this synthon was likewise observed in two of them.…”

“…3), this synthon is found, even if the halide is replaced by oxygen in the latter, similarly to the heterosynthon III found in hexakisIJhydrogen sulfate) bisIJsulfate) tetrahydrate. 21 However, in nitrate, trifluoroacetate and three other sulfate salt forms of BPE, heterosynthon II′ is present, 22 revealing a competition between III and in BPE salts. The third new multicomponent crystal form of BPE is a phosphoric acid cocrystal of a dihydrogen phosphate salt (B3).…”