title: Solvent- and Pressure-Induced Phase Changes in Two 3D Copper Glutarate-Based Metal-Organic Frameworks via Glutarate (+gauche ⇄ -gauche) Conformational Isomerism.
abstract: Two isoreticular three-dimensional copper(II) glutarate-based pillared-layered metal-organic frameworks (MOFs) with flexible pillars, [Cu2(glu)2(bpa)] and [Cu2(glu)2(bpp)] (bpa = 1,2-bis(4-pyridyl)ethane; bpp = 1,3-bis(4-pyridyl)propane), undergo spontaneous phase changes upon solvent loss at room temperature. Using single-crystal X-ray diffraction analysis (SCXRD), we show that the phase changes result in new narrow-channel forms that experience a large reduction in solvent-accessible volume. Moreover, the [Cu2(glu)2(bpa)] MOF displays a stepped sorption isotherm for the uptake of CO2at room temperature. This is indicative of reversion of the framework to the wide-channel form under CO2pressure. Supercritical CO2was used to isolate the gas-included structures, and by means of SCXRD we were able to determine the positions of the CO2molecules in the channels of the frameworks. Finally, we report the use of molecular modeling simulations to elucidate the phase-change mechanism, including the energetic changes involved. Structural limitations in both MOFs allow for only direct gauche-gauche enantiomeric interconversion of the glutarate moieties.
authors.affiliation: Department of Chemistry and Polymer Science, University of Stellenbosch , Matieland 7602, South Africa.
authors.forename: Charl X
authors.initials: CX
authors.lastname: Bezuidenhout
authors.affiliation: Department of Chemistry and Polymer Science, University of Stellenbosch , Matieland 7602, South Africa.
authors.forename: Vincent J
authors.initials: VJ
authors.lastname: Smith
authors.affiliation: Department of Chemistry and Polymer Science, University of Stellenbosch , Matieland 7602, South Africa.
authors.forename: Catharine
authors.initials: C
authors.lastname: Esterhuysen
authors.affiliation: Department of Chemistry and Polymer Science, University of Stellenbosch , Matieland 7602, South Africa.
authors.forename: Leonard J
authors.identifier: 0000-0002-6453-8331
authors.initials: LJ
authors.lastname: Barbour