title: The flexibility of modified-linker MIL-53 materials.
abstract: The flexibility of eight aluminium hydroxo terephthalates [Al(OH)(BDC-X)]·n(guest) (BDC = 1,4-benzene-dicarboxylate; X = -H, -CH3, -Cl, -Br, -NH2, -NO2, -(OH)2, -CO2H) crystallising in the MIL-53-type structure was investigated upon thermal dehydration of as-made samples, superhydration and methanol adsorption/desorption using in situ powder X-ray diffraction (PXRD). Profile fitting was used to determine lattice parameters as a function of time and/or temperature to describe their structural evolution. It has thus been shown that while methanol vapour adsorption induces an opening of all the modified frameworks, except the -NH2 material, superhydration only leads to open structures for Al-MIL-53-NO2, -Br and -(OH)2. All the MIL-53 solids, except Al-MIL-53-(OH)2 are present in the open structures upon thermal dehydration. In addition to the exploration of the breathing behavior of this MIL-53 series, the issue of disorder in the distribution of the functional groups between the organic linkers was explored. As a typical illustration, density functional theory calculations were carried out on different structures of Al-MIL-53-Cl, in which the distribution of -Cl within two adjacent BDC linkers is varied. The results show that the most energetically stable configuration leads to the best agreement with the experimental PXRD pattern. This observation supports that the distribution of the selected linker substituent in the functionalised solid is governed by energetics and that there is a preference for an ordering of this arrangement.
authors.affiliation: Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK. guillaume.maurin@univ-montp2.fr R.I.Walton@warwick.ac.uk.
authors.forename: Alexis S
authors.initials: AS
authors.lastname: Munn
authors.affiliation: Institut Charles Gerhardt Montpellier, UMR CNRS 5253, Université Montpellier, 34095 Montpellier cedex 05, France.
authors.forename: Renjith S
authors.initials: RS
authors.lastname: Pillai
authors.affiliation: Institut für Anorganische Chemie, Christian-Albrechts-Universität, Max-Eyth Straße 2, D 24118 Kiel, Germany.
authors.forename: Shyam
authors.initials: S
authors.lastname: Biswas
authors.affiliation: Institut für Anorganische Chemie, Christian-Albrechts-Universität, Max-Eyth Straße 2, D 24118 Kiel, Germany.
authors.forename: Norbert
authors.initials: N
authors.lastname: Stock
authors.affiliation: Institut Charles Gerhardt Montpellier, UMR CNRS 5253, Université Montpellier, 34095 Montpellier cedex 05, France.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Maurin
authors.affiliation: Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK. guillaume.maurin@univ-montp2.fr R.I.Walton@warwick.ac.uk.
authors.forename: Richard I
authors.initials: RI
authors.lastname: Walton