Guest Exchange through Facilitated Transport in a Seemingly Impenetrable Hydrogen-Bonded Framework

Abstract

A new inclusion compound consisting of a guanidinium 1,3,5-tri­(4-sulfophenyl)­benzene (G3TSPHB) host framework containing isophorone guests that surround isolated and seemingly inaccessible pockets was amenable to guest exchange with hexafluorobenzene (HFB) through a single crystal–single crystal transformation (SCSCT). Single-crystal X-ray diffraction of intermediate transformation states, from the parent compound G3TSPHB·(isophorone)3.7·(methanol)5.4 to the final state G3TSPHB·(isophorone)3.1·(HFB)2·(methanol)2, indicated a crystal symmetry change from monoclinic to hexagonal prior to full incorporation of HFB. Optical microscopy during the SCSCT revealed the formation of lamellae, which expanded and then coalesced into a single crystal when the phase transformation was complete. In situ Raman microscopy revealed changes in the orientation of isophorone guests during the transformation that suggested a pathway for HFB entry into the host cavities. The SCSCT occurs more rapidly than expected on the basis of simple diffusion, consistent with facilitated transport along the lamellae interfaces and a reduction in the length scale for guest exchange.

Hydrogen-bonded frameworks for molecular structure determination

“…Nonetheless, G 3 TSPHB included the conformationally flexible neryl acetate, as well as isophorone guests, to form (G 3 TSPHB) ⊃ (neryl acetate)(isophorone) 3 ( 9 ). In this example, isophorone assists the formation of the inclusion compound, similar to previous observations 40,41 . The structure of 9 was refined in the orthorhombic space group P 2 1 2 1 2 1 (Supplementary Fig.…”

Molecular Tectonics: A Node‐and‐Linker Building Block Approach to a Family of Hydrogen‐Bonded Frameworks

“…Indeed, several interesting materials have been prepared from pairs of charged components, including protonated amines with anions, and guanidinium cations with anions . Notably, Ward has used the interaction between unsubstituted guanidinium cations and polysulfonate anions to prepare a wide range of open materials including cylindrical and lamellar architectures and networked cages –. These systems show high levels of predictability, even though only one of the components (the sulfonate anion) can be varied.…”

Microporosity of a Guanidinium Organodisulfonate Hydrogen‐Bonded Framework

“…Of the 210 reported guanidinium organodisulfonate structures in the Cambridge Structural Database, only five are guest‐free, exhibiting appreciable empty space (≥25 Å 3 ), and only one of those compounds has been demonstrated to also include guests, albeit in different topologies. There are, however, a few reports of GS compounds exhibiting behavior related to porosity, including single‐crystal‐to‐single‐crystal (SC‐SC) exchange of included solvents, SC‐SC dehydration, and even a report of supposed porosity . Nevertheless, the “burden of proof” (demonstration of an open, empty structure that can be reversibly permeated by guests) has never been met.…”