title: Vapour pressure dependence and thermodynamics of cylindrical metal-organic framework mesoparticles: an ESEM study.
abstract: Self-assembly of neodymium nitrate and 2,5-dihydroxyl-1,4-benzoquinone (DHBQ) leads to the formation of a metal organic framework (MOF) of formula [Nd2(DHBQ)3(H2O)6]·18H2O. X-ray diffraction studies show that its crystalline structure is that of a two-dimensional coordination polymer packed in parallel sheets, with organised clusters of water molecules lying between the sheets and bridging them via a dense H-bond network. However, instead of forming faceted crystals, this MOF assembles into unusually shaped cylindrical particles of micrometre size. Scanning electron microscopy revealed that the particles are indeed mesoparticles from aggregated MOF crystalline nano-grains. The mesoparticles are stimuli-responsive and shrink in size upon exposure to reduced water vapour pressure. The shrinkage is isotropic and depends on temperature, which allows measuring the coexistence curve of water inside the particles and in the gas phase. Owing to an elaborated environmental scanning-electron microscopy (ESEM) study, it was possible to determine the association energy of water in the mesoparticles. We found a value of 16 ± 6.5 kJ mol(-1). Since the only water present in the particles is the lattice water in the nano-grains, this association energy is the lattice energy of water in the nano-sized MOF crystals. This value allowed us to draw a model for the building process of these originally shaped cylindrical mesoparticles. This is the first example of determination of a thermodynamic value by ESEM.
authors.affiliation: Institut de Chimie Séparative de Marcoule, UMR 5257 CEA/CNRS/UM2/ENSCM, BP17171, 30207 Bagnols-sur-Cèze, France. caroline.genre@cea.fr.
authors.forename: Torsten K
authors.initials: TK
authors.lastname: Sievers
authors.forename: Caroline
authors.initials: C
authors.lastname: Genre
authors.forename: Florent
authors.initials: F
authors.lastname: Bonnefond
authors.forename: Thomas
authors.initials: T
authors.lastname: Demars
authors.forename: Johann
authors.initials: J
authors.lastname: Ravaux
authors.forename: Daniel
authors.initials: D
authors.lastname: Meyer
authors.forename: Renaud
authors.initials: R
authors.lastname: Podor
mesh_terms: D016227:Benzoquinones / Q000737:chemistry; D005740:Gases / Q000737:chemistry*; D008670:Metals / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D009354:Neodymium / Q000737:chemistry; D011312:Pressure; D013816:Thermodynamics; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D016227:Benzoquinones; D005740:Gases; D008670:Metals; D014867:Water; D009354:Neodymium; C004532:quinone