We report a study of the use of the porous metal–organic framework material MIL-53(Fe), FeIII(OH)0.8F0.2[O2C–C6H4–CO2], for the separation of BTEX mixtures (benzene, toluene, ethylbenzene, and the three xylene isomers). Crystal structures of the three host:guest materials MIL-53(Fe)[xylene], where xylene = the ortho, meta, or para isomer of dimethylbenzene, have been solved and refined from powder X-ray diffraction. Each exhibits a fully expanded form with a variety of host:guest and guest:guest interactions responsible for stabilizing the structure. While the ortho- and meta- isomers present a similar arrangement when occluded in the MIL-53 host, the para-xylene shows a distinctly different set of interactions with the host. Upon thermal treatment, xylenes are partially lost to give crystalline phases MIL-53(Fe)[xylene]0.5, the structures of which have also been solved. The kinetics of uptake of each xylene by MIL-53(Fe)[H2O], in which the water is replaced by the organic guest, have been studied using time-resolved energy-dispersive X-ray diffraction: this shows differences in kinetics of the adsorption of the three isomers. Under chromatographic conditions in heptane at 293 K, anhydrous MIL-53(Fe) is able to separate the three xylene isomers with elution of the para-xylene before the other two isomers, and at 323 K the host is able to resolve all components of the BTEX mixture.

An in situ, time-resolved energy dispersive powder X-ray diffraction study of the solvothermal crystallisation of the copper(II) 4,4 0 ,4 00 -benzene-1,3,5-triyl-tris(benzoate) metal-organic framework MOF-14 shows how reaction conditions must be carefully chosen to allow successful preparation of the material, since on prolonged heating at $120 C the material irreversibly collapses into Cu 2 O under solvothermal conditions in less than 2 hours. This situation is in contrast to the related Cu(II)-containing metal-organic framework HKUST-1, which shows solvothermal stability over similar temperatures and reaction times. The kinetics of crystallisation of both MOFs are examined using a mathematical model proposed by Gualtieri for zeolite crystallisation: this allows separation of the nucleation and growth regimes to yield two rate constants. Arrhenius analysis gives activation energies that reveal in both cases the crystallisations are nucleation controlled. For MOF-14 we can additionally simulate its decomposition as dissolution of the first-formed interpenetrating structure: this produces a complete picture of the solvothermal stability of MOF-14 as nucleation-growth crystallisation, with some evidence of secondary nucleation, followed by dissolution.

A time-resolved powder diffraction study of the crystallisation of porous metal organic framework materials with the CPO-27 structure ([M2(dhtp)(H2O)2]·8H2O where, dhtp=2,5-dioxoterephthalate) using the energy dispersive X-ray diffraction method is described. Crystallisation under solvothermal conditions is performed between 70 - 110 °C from clear solutions of metal salts (M=Co2+ or Ni2+) and 2,5-dihydroxyterephthalic acid in a mixture of THF-water in sealed reaction vessels, using both conventional and microwave heating. Integration of Bragg peak areas with time provides accurate crystallisation curves, which are modelled using the method of Gualtieri to determine rate constants for nucleation and for growth and then, by Arrhenius analysis, activation energies. Crystallisation is determined to be one-dimensional, consistent with the elongated morphology of the crystals produced in these reactions. With conventional heating the Co-containing CPO-27 crystallises more rapidly than the isostructural Ni-containing analogue and analysis of the kinetic parameters would suggest a complex multi-step crystallisation process. The effect of microwave heating is upon activation energies: the values for both nucleation and for crystal growth are lowered compared to reactions using conventional heating.

A layered lithium carboxylate, Li 4 [C 4 H 2 S(CO 2 ) 2 ] 2 [C 3 H 7 NO] 2 , crystallizes under solvothermal conditions (160−180 °C) from lithium nitrate and the ligand 2,5-thiophenedicarboxylate in N,N-dimethylformamide as solvent. Single-crystal X-ray diffraction (Pbca a = 10.0216(18) Å, b = 18.327(4) Å, c = 24.871(5) Å) shows that the material is constructed from lithium-centered tetrahedral units linked by edge-and corner-sharing to give tetrameric clusters. These inorganic building units are linked in two dimensions by the bidentate ligand to give a layered structure in which additionally coordinated dimethylformamide projects into the interlayer region. A study of the crystallization of the material using time-resolved in situ energy-dispersive X-ray diffraction reveals that the material crystallizes directly from solution at the reaction temperature following an induction period. Analysis of the crystallization curves suggests that nucleation does not extend far into the crystallization period and that crystal growth is one-dimensional. These findings are corroborated by the observation of relatively large, anisotropic crystals by scanning electron microscopy.

The synthesis and characterisation of a three-dimensional lithium-organic framework MIL-145 is described, which upon thermal treatment yields a second open framework, MIL-146, that contains four and three-coordinate lithium centres: the coordinatively unsaturated trigonal planar lithium centres are able to reversibly bind water with crystallinity maintained, while the dehydrated phase shows preferential adsorption of CO(2) over N(2).

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The solvothermal synthesis of a novel mixed-s-block metalorganic framework is described, with crystallization brought about by use of the sodium salt of the benzo-(1,2;3,4;5,6)tris(thiophene-2Ј-carboxylate) linker in combination with a lithium salt. The structure of the material was determined by single-crystal X-ray diffraction, which reveals an expanded [a]

The reaction of the K4[{Re6Si8}(OH)a6]·8H2O rhenium cluster salt with pyrazine (Pz) in aqueous solutions of alkaline or alkaline earth salts at 4 °C or at room temperature leads to apical ligand exchange and to the formation of five new compounds: [trans-{Re6Si8}(Pz)a2(OH)a2(H2O)a2] (1), [cis-{Re6Si8}(Pz)a2(OH)a2(H2O)a2] (2), (NO3)[cis-{Re6Si8}(Pz)a2(OH)a(H2O)a3](Pz)·3H2O (3), [Mg(H2O)6]0.5[cis-{Re6Si8}(Pz)a2(OH)a3(H2O)a]·8.5H2O (4), and K[cis-{Re6Si8}(Pz)a2(OH)a3(H2O)a]·8H2O (5). Their crystal structures are built up from trans- or cis-[{Re6Si8}(Pz)a2(OH)a4−x(H2O)ax]x−2 cluster units. The cohesions of the 3D supramolecular frameworks are based on stacking and H bonding, as well as on H3O2−bridges in the cases of (1), (2), (4), and (5) compounds, while (3) is built from stacking and H bonding only. This evidences that the nature of the synthons governing the cluster unit assembly is dependent on the hydration rate of the unit.