Adsorption of light hydrocarbons in the flexible MIL-53(Cr) and rigid MIL-47(V) metal-organic frameworks: a combination of molecular simulations and microcalorimetry/gravimetry measurements.

The adsorption of short linear alkanes has been explored in the highly flexible MIL-53(Cr) porous metal-organic framework by means of molecular simulations based on configurational bias grand canonical Monte Carlo. The unusual shape of the adsorption isotherms with the existence of steps has been successfully modelled by creating a (narrow pore, large pore) phase mixture domain, the composition of which varies with pressure. A further step consisted of combining our computational approach with several experimental tools including microcalorimetry, gravimetry and in situ X-ray diffraction, to fully characterize the adsorption behaviour of the isostructural MIL-47(V) rigid MOF, i.e. the preferential arrangement of each type of alkane inside the pores and the resulting interaction energy. Finally, relationships are established between the adsorption enthalpies and both alkyl chain length and polarisability of the alkanes that can be further utilised to predict the energetics of the adsorption process for longer alkane chains.

Complex adsorption of short linear alkanes in the flexible metal-organic-framework MIL-53(Fe).

This investigation is based on a combination of experimental tools completed by a computational approach to deeply characterize the unusual adsorption behavior of the flexible MIL-53(Fe) in the presence of short linear alkanes. In contrast to the aluminum or chromium analogues we previously reported, the iron MIL-53 solid, which initially exhibits a closed structure in the dry state, shows more complex adsorption isotherms with multisteps occurring at pressures that depend on the nature of the alkane. This behavior has been attributed to the existence of four discrete pore openings during the whole adsorption process. Molecular simulations coupled with in situ X-ray powder diffraction were able to uncover these various structural states.

A microporous scandium terephthalate, Sc2(O2CC6H4CO2)3, with high thermal stability.

A scandium terephthalate with isolated ScO6 octahedra and fully-linked carboxylate groups is prepared hydrothermally and possesses a novel hybrid framework structure with high thermal stability and a pore volume for N2 adsorption of 0.26 cm(3) g(-1) at 77 K.

[V(III)(H2O)]3O(O2CC6H4CO2)3.(Cl, 9H2O) (MIL-59): a rare example of vanadocarboxylate with a magnetically frustrated three-dimensional hybrid framework.

[V(III)(H2O)]3O(O2CC6H4CO2)3.(Cl, 9H2O) (denoted MIL-59) presents a three-dimensional framework built up from octahedral vanadium trimers joined via the isophthalate anionic linkers to delimit cages where water molecules and chlorine anions are occluded; the frustrated magnetic behaviour of MIL-59 is discussed.

VIII(OH)[O2C-C6H4-CO2].(HO2C-C6H4-CO2H)x(DMF)y(H2O)z(or MIL-68), a new vanadocarboxylate with a large pore hybrid topology: reticular synthesis with infinite inorganic building blocks?

V(III)(OH)[O(2)C-C(6)H(4)-CO(2)].(HO(2)C-C(6)H(4)-O(2)H)(x)(DMF)(y)(H(2)O)(z) or MIL-68 was solvothermally synthesised in a non-aqueous medium. Its structure, built up from octahedral chains connected by terephthalate linkers, exhibits large hexagonal channels containing different occluded moieties. Their irreversible removal releases a specific surface area of 603(22) m(2).g(-1)(BET).

[Fe2(C10O8H2)]: an antiferromagnetic 3D iron(II) carboxylate built from ferromagnetic edge-sharing octahedral chains (MIL-62).

The first three-dimensional iron(II) tetracarboxylate is built from the connection of chains of edge-sharing Fe(II) octahedra by 1,2,4,5-benzenetetracarboxylates; magnetic measurements show an antiferromagnetic coupling of ferromagnetic chains below TN = 25(1) K.

Hybrid Organic-Inorganic Frameworks (MIL-n). Hydrothermal Synthesis of a Series of Pillared Lanthanide Carboxyethylphosphonates and X-ray Powder ab Initio Structure Determination of MIL-19, Pr[O(3)P(CH(2))(2)CO(2)].

A series of lanthanide and yttrium carboxyethylphosphonates has been hydrothermally prepared (200 degrees C, 4 days) from the 1:1 mixture of carboxyethylphosphonic acid and the metal chlorides. The crystal structure of the praesodymium compound Pr(III)[O(3)P(CH(2))(2)CO(2)] has been determined ab initio from X-ray powder diffraction data and refined by the Rietveld method. The compound crystallizes in the monoclinic space group P2(1)/m (No. 11) with cell parameters at 20 degrees C a = 8.3617(2) Å, b = 7.1899(2) Å, c = 5.4586(2) Å, beta = 103.784(2) degrees, and Z = 2. The final agreement factors converged to the values R(p) = 0.139, R(wp) = 0.177, Bragg R = 0.123, R(F) = 0.055, and chi(2) = 3.50. The hybrid framework consists of inorganic Pr/O/P/C layers connected by organic groups, with an interlayer spacing of approximately 8.36 Å. The praesodymium atoms are 7-fold coordinated in this pillared layered structure. Isostructural compounds were prepared for yttrium and the entire series of the lanthanide elements.

Tetraaquabis(3,5-dicarboxybenzoato-O)cobalt(II)

The hydrothermal reaction of cobalt(II) chloride with trimesate (3, 5-dicarboxybenzoate) ions in aqueous solution gives the novel title complex, [Co(C(9)H(5)O(6))(2)(H(2)O)(4)]. The Co(II) ion lies on an inversion centre and is octahedrally coordinated to two trimesate anions and four water molecules. Hydrogen bonds ensure the three-dimensional architecture of the structure.

Open-Framework Inorganic Materials.

Aluminosilicate zeolites such as UTD-1 (structure shown) belong to a family of nanoporous inorganic materials that find utility in catalysis, separation, and ion exchange. During the last decade, the rate of discovery of new open-framework materials based, for example, on phosphates, sulfides, halides, nitrides, and coordination compounds has increased dramatically. The synthesis, structures, and properties of this remarkable class of materials are reviewed.

Al(30): A Giant Aluminum Polycation.

Simple hydrothermal treatment of the well-known aluminum polycation varepsilon-Al(13) produces the novel Al(30) structure (see picture), the largest polycation yet observed. Its characterization, by X-ray diffraction and NMR spectroscopy, also solved previously unassigned signals in (27)Al NMR spectra of other Al - O species.

Evidence of flexibility in the nanoporous iron(iii) carboxylate MIL-89.

The very large expansion upon adsorption of liquids, up to 160% in cell volume, has been observed in the iron(iii) trans,trans muconate MIL-89 [(MIL = Material Institut Lavoisier]. The structure of lutidine-containing MIL-89 (lutidine = 2,6-dimethylpyridine) has been determined using X-ray powder diffraction and computer simulations. Finally, the consequences of adsorption of various polar and apolar liquids have been evaluated using ex situ synchrotron X-ray powder diffraction data and reveals that the swelling behavior of MIL-89 is selective but slightly different from the MIL-88 analogues.

Experimental evidence supported by simulations of a very high H2 diffusion in metal organic framework materials.

Quasielastic neutron scattering measurements are combined with molecular dynamics simulations to extract the self-diffusion coefficient of hydrogen in the metal organic frameworks MIL-47(V) and MIL-53(Cr). We find that the diffusivity of hydrogen at low loading is about 2 orders of magnitude higher than in zeolites. Such a high mobility has never been experimentally observed before in any nanoporous materials, although it was predicted in carbon nanotubes. Either 1D or 3D diffusion mechanisms are elucidated depending on the chemical features of the MIL framework.

Charge distribution in metal organic framework materials: transferability to a preliminary molecular simulation study of the CO(2) adsorption in the MIL-53 (Al) system.

Density functional theory calculations have been performed in order to extract the charge distribution in the aluminium-containing MIL-53 structure, to allow further computational studies of adsorption in these materials. Both cluster and periodic methods have been used and the charges calculated for each atom constituting the organic and inorganic part of the material, were discussed. Preliminary grand canonical Monte Carlo simulations, based on a consistent set of potential parameters and this newly derived charge distribution, predicted for enthalpies of adsorption for CO(2) at low coverage in the "large" and "narrow" pore versions of MIL-53 (Al) to be significantly different. These calculated enthalpies reproduced the two distinct ranges of values observed by microcalorimetry on either side of 6 bars quite well. This agreement between experiment and simulation validated our previous assumption, suggesting a structural switching of the hybrid material during the adsorption process. The microscopic mode of interaction between the hybrid porous framework and the CO(2) adsorption was then carefully analysed in both of the MIL-53 (Al) structures.

Role of solvent-host interactions that lead to very large swelling of hybrid frameworks.

An unusually large expansion upon solvent adsorption occurs without apparent bond breaking in the network of a series of isoreticular chromium(III) or iron(III) diarboxylates labeled MIL-88A to D [dicarbox = fumarate (88A); terephthalate (1,4-BDC) (88B); 2,6-naphthalenedicarboxylate (2,6-NDC) (88C); and 4-4'-biphenyldicarboxylate (4-4'-BPDC) (88D)]. This reversible "breathing" motion was analyzed in terms of cell dimensions (extent of breathing), movements within the framework (mechanism of transformation), and the interactions between the guests and the skeleton. In situ techniques show that these flexible solids are highly selective absorbents and that this selectivity is strongly dependent on the nature of the organic linker.

A chromium terephthalate-based solid with unusually large pore volumes and surface area.

We combined targeted chemistry and computational design to create a crystal structure for porous chromium terephthalate, MIL-101, with very large pore sizes and surface area. Its zeotype cubic structure has a giant cell volume (approximately 702,000 cubic angstroms), a hierarchy of extra-large pore sizes (approximately 30 to 34 angstroms), and a Langmuir surface area for N2 of approximately 5900 +/- 300 square meters per gram. Beside the usual properties of porous compounds, this solid has potential as a nanomold for monodisperse nanomaterials, as illustrated here by the incorporation of Keggin polyanions within the cages.

Hydrothermal synthesis and structure determination from powder data of new three-dimensional titanium(IV) diphosphonates Ti(O(3)P-(CH(2))(n)-PO(3)) or MIL-25(n) (n = 2, 3).

Ti(O(3)P-(CH(2))(n)-PO(3)) or MIL-25(n) (n = 2, 3) were prepared under hydrothermal conditions (4 days, 463 K, autogenous pressure). Their structures were determined ab initio from X-ray diffraction powder data. MIL-25(2) is triclinic (space group P-1 (no. 2)), with a = 5.033(1), b = 5.092(1), c = 6.859(1) A, alpha = 95.860(1) degrees, beta = 99.994(1) degrees, gamma = 118.217(1) degrees, and Z = 2. MIL-25(3) exhibits an orthorhombic symmetry (space group Cm2m (no. 38)), with a = 5.230(1), b = 8.451(1), c = 17.400(2) A, and Z = 4. Their three-dimensional structures are built up from TiO(6) titanium(IV) octahedra linked together via diphosphonate groups. This leads to pillared structures whose inorganic sheets are closely related to those of the alphaTiP titanium phosphate structure.

Synthesis, structure, and magnetic properties of two new vanadocarboxylates with three-dimensional hybrid frameworks.

(V(III)(OH))(2)[C(6)H(2)(CO(2))(4)].4H(2)O (labeled MIL-60) and V(III)(OH)[(2)(O(2)C)C(6)H(2)(COOH)(2)].H(2)O (labeled MIL-61) were hydrothermally synthesized from mixtures of VCl(3), 1,2,4,5-benzenetetracarboxylic acid, and water heated for 3 days at 473 K. The structure of MIL-60 was solved from single-crystal X-ray diffraction data in the triclinic centrosymmetric P1 (No. 2) space group with lattice parameters a = 6.3758(5) A, b = 6.8840(5) A, c = 9.0254(5) A, alpha = 69.010(2) degrees, beta = 85.197(2) degrees, gamma = 79.452(2) degrees, V = 363.53(5) A(3), and Z = 1. The structure of MIL-61 was ab initio determined from an X-ray powder diffraction pattern. MIL-61 crystallizes in the Pnma (No. 62) orthorhombic space group with lattice parameters a = 14.8860(1) A, b = 6.9164(1) A, c = 10.6669(2) A, V = 1098.23(3) A(3), and Z = 4. Both structures contain the same inorganic building block that consists of trans chains of V(III)O(4)(OH)(2) octahedra. The three-dimensional frameworks of MIL-60 and MIL-61 are constituted by the linkage of these chains via the organic molecules so delimiting the channels or cages where the water molecules are encapsulated. The magnetic behavior of these two phases is presented: MIL-60 is paramagnetic, and MIL-61 antiferromagnetically orders below T(N) = 55(5) K.