Mohamed Haouas

The Kagomé Topology of the Gallium and Indium Metal-Organic Framework Types with a MIL-68 Structure: Synthesis, XRD, Solid-State NMR Characterizations, and Hydrogen Adsorption

The vanadium-based terephthalate analogs of MIL-68 have been obtained with gallium and indium (network composition: M(OH)(O(2)C-C(6)H(4)-CO(2)), M = Ga or In) by using a solvothermal synthesis technique using N,N-dimethylformamide as a solvent (10 and 48 h, for Ga and In, respectively, at 100 degrees C). They have been characterized by X-ray diffraction analysis; vibrational spectroscopy; and solid-state (1)H and (1)H-(1)H radio-frequency-driven dipolar recoupling (RFDR), (1)H-(1)H double quantum correlation (DQ), and (13)C{(1)H} cross polarization magic angle spinning (CPMAS) NMR spectroscopy. The three-dimensional network with a Kagomé-like lattice is built up from the connection of infinite trans-connected chains of octahedral units MO(4)(OH)(2) (M = Ga or In), linked to each other through the terephthalate ligands in order to generate triangular and hexagonal one-dimensional channels. The presence of DMF molecules with strong interactions within the channels as well as their departure upon calcination (150 degrees C under a primary vacuum) of the materials has been confirmed by subjecting MIL-68 (Ga) to solid-state (1)H MAS NMR. The (1)H-(1)H RFDR and (1)H-(1)H DQ spectra revealed important information on the spatial arrangement of the guest species with respect to the hybrid organic-inorganic network. (13)C{(1)H} CPMAS NMR of activated samples provided crystallographically independent sites in agreement with X-ray diffraction structure determination. Brunauer-Emmett-Teller surface areas are 1117(24) and 746(31) m(2) g(-1) for MIL-98 (Ga) and MIL-68 (In), respectively. Hydrogen adsorption isotherms have been measured at 77 K, and the storage capacities are found to be 2.46 and 1.98 wt % under a saturated pressure of 4 MPa for MIL-68 (Ga) and MIL-68 (In), respectively. For comparison, the hydrogen uptake for the aluminum trimesate MIL-110, which has an open framework with 16 A channels, is 3 wt % under 4 MPa.

High-Throughput Aided Synthesis of the Porous Metal−Organic Framework-Type Aluminum Pyromellitate, MIL-121, with Extra Carboxylic Acid Functionalization

A new porous metal-organic framework (MOF)-type aluminum pyromellitate (MIL-121 or Al(OH)[H(2)btec]·(guest), (guest = H(2)O, H(4)btec = pyromellitic acid) has been isolated by using a high-throughput synthesis method under hydrothermal conditions. Its structure was determined from powder X-ray diffraction analysis using synchrotron radiation (Soleil, France) and exhibits a network closely related to that of the MIL-53 series. It is a three-dimensional (3D) framework containing one-dimensional (1D) channels delimited by infinite trans-connected aluminum-centered octahedra AlO(4)(OH)(2) linked through the pyromellitate ligand. Here the organic ligand acts as tetradendate linker via two of the carboxylate groups. The two others remain non-bonded in their protonated form, and this constitutes a rare case of the occurrence of both bonding and non-bonding organic functionalities of the MOF family. The non-coordinated -COOH groups points toward the channels to get them an open form configuration. Within the tunnels are located unreacted pyromellitic acid and water species, which are evacuated upon heating, and a porous MIL-121 phase is obtained with a Brunauer-Emmett-Teller (BET) surface area of 162 m(2) g(-1). MIL-121 has been characterized by IR, thermogravimetry (TG) analyses, and solid state NMR spectroscopy employing a couple of two-dimensional (2D) techniques such as (1)H-(1)H SQ-DQ BABA, (1)H-(1)H SQ-SQ RFDR, (27)Al{(1)H} CPHETCOR and (27)Al MQMAS.

A stable hybrid bisphosphonate polyoxometalate single-molecule magnet.

The long history of polyoxometalate (POM) chemistry initially featured the characterization of diamagnetic species. However, the last few decades have seen the development of several families of paramagnetic POM molecules that display a diverse range of structures and properties. These entities can be of nanosize scale, as exemplified by the discovery of the spin-frustrated Keplerate clusters of general formula {(Mo)Mo5}12M30 (M=Fe , Cr, V). Although of smaller size than these molybdenum compounds, high-nuclearity polyoxovanadate mixed-valent species have also been characterized. The unexpectedly strong magnetic couplings observed in a number of these systems have been studied in detail both experimentally and theoretically. The third— and most extended—magnetic POM family is that of polyoxotungstates. Large clusters in which vacant polyoxotungstate ligands encapsulate 3d or 4f metals have been obtained, and most of these systems are purely inorganic. In particular, very few hybrid polynuclear 3d magnetic polyoxotungstates synthesized under mild conditions have been characterized to date. Moreover, to the best of our knowledge, no general method for the preparation of hybrid, soluble, and stable polyoxotungstates encapsulating magnetic clusters has been proposed. This contrasts with the case of the diamagnetic polyoxotungstates, for which numerous triol-functionalized, organosilyl and organostannic derivatives have been reported. Hybrid molybdenum-based POM chemistry has also been widely developed, but mainly {Mo6} Lindqvist and Anderson-type systems encapsulating a maximum of one 3d cation have been used as a platform for connecting various organic substrates. The establishment of a method allowing the rational synthesis of stable hybrid POMs incorporating several divalent or trivalent 3d metal centers thus remains a challenge. Such materials would be of interest in various fields as they would permit the covalent grafting of POMs containing 3d clusters to a range of organic substrates or surfaces, and thus the elaboration of new functional materials. For example, the covalent connection of photoactive organic groups to multi-electrochromic 3d-substituted inorganic entities may afford optical materials with new properties. Alternatively, Co-substituted polyoxotungstates have been shown to be efficient photocatalysts, which may in itself motivate the search for related hybrid materials. Clearly, hybrid 3d magnetic polyoxotungstates are also interesting in the molecular magnetism field. Since 2008, it is known that 3dor 4f-substituted polyoxotungstates can behave as single molecule magnets (SMMs). Moreover, deposition of POM SMMs on single-wall carbon nanotubes (SWCNTs) has provided evidence that individual POM molecules present a slow relaxation of the magnetization, a crucial point with respect to the potential use of such nanocomposites as information storage devices. However, in such a system, no control of the SWCNT/POM interface is possible. This is due to the purely inorganic nature of the deposited POM—a characteristic of all the 3d POM SMMs species reported to date. Indeed, the reinforcement of the interactions between the two components via covalent grafting or p–p stacking together with the control of the POM/substrate distance obviously implies the elaboration of hybrid POM SMM systems. Herein, we report the characterization of the polyanion [{(B-a-PW9O34)Co3(OH) ACHTUNGTRENNUNG(H2O)2ACHTUNGTRENNUNG(O3PC(O) ACHTUNGTRENNUNG(C3H6NH3)PO3)}2Co] 14 (1), which is built of a heptanuclear Co core sandwiched by two {PW9} units and connected to two bisphosphonato ligands, each possessing a functionalizable alkyl ammonium arm. The stability of this hybrid unit has been unambiguously assessed by using P and H NMR spectroscopy and electrochemical techniques. Single-crystal studies performed on an array of micro-SQUIDs have revealed that the ferromagnetic species 1 exhibits SMM behavior. [a] Dr. H. El Moll, Dr. A. Dolbecq, Dr. J. Marrot, G. Rousseau, Dr. M. Haouas, Dr. F. Taulelle, Prof. P. Mialane Institut Lavoisier de Versailles UMR 8180, Universit de Versailles Saint-Quentin 45 Avenue des Etats-Unis, 78035 Versailles Cedex (France) Fax: (+33)1-39-25-43-81 E-mail : mialane@chimie.uvsq.fr [b] Dr. G. Rogez Institut de Physique et de Chimie des Mat riaux de Strasbourg (IPCMS) UMR 7504, CNRS Universit de Strasbourg 23 rue du Lœss, BP 43, 67034 Strasbourg Cedex 2 (France) [c] Dr. W. Wernsdorfer Institut N el, CNRS et Universit Joseph Fourier BP 166, F-38042 Grenoble Cedex 9 (France) [d] Dr. B. Keita Laboratoire de Chimie Physique Groupe d’Electrochimie et de Photo lectrochimie, UMR 8000, CNRS Universit Paris-Sud, B timent 350, 91405 Orsay cedex (France) E-mail : bineta.keita@lcp.u-psud.fr Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201200140.

NMR of microporous compounds: From in situ reactions to solid paving

Abstract Alumino- and gallo-phosphate materials present a large variety of structures. Among them, two new families the ULM and the MIL provide a large class of microporous compounds. A systematic study has been undertaken for understanding the main steps of solids formation. As these materials form under hydrothermal conditions, we developed in-situ NMR devices and methods for following pH and concentration of species during crystal formation. Coordination state of aluminum evolution during synthesis suggests a general mechanism for the structural building unit formation. This mechanism is analyzed by quantitative evolution of liquid and solid phases in situ and ex situ. The dynamics of the different stages is therefore followed and the main steps of phase dissolution and crystallization are sequenced. Nucleation, which is the most delicate step of evolution to characterize, is shown to witness unexpected chemical bond formation not seen in steps before. These chemical bonds formed during nucleation and crystal growth are demonstrated by comparing building agents in solution and crystal structure.

Investigation of the mechanism of colloidal silicalite-1 crystallization by using DLS, SAXS, and 29Si NMR spectroscopy.

Colloidal silicalite-1 zeolite was crystallized from a concentrated clear sol prepared from tetraethylorthosilicate (TEOS) and aqueous tetrapropylammonium hydroxide (TPAOH) solution at 95 degrees C. The silicate speciation was monitored by using dynamic light scattering (DLS), synchrotron small-angle X-ray scattering (SAXS), and quantitative liquid-state (29)Si NMR spectroscopy. The silicon atoms were present in dissolved oligomers, two discrete nanoparticle populations approximately 2 and 6 nm in size, and crystals. On the basis of new insight into the evolution of the different nanoparticle populations and of the silicate connectivity in the nanoparticles, a refined crystallization mechanism was derived. Upon combining the reagents, different types of nanoparticles (ca. 2 nm) are formed. A fraction of these nanoparticles with the least condensed silicate structure does not participate in the crystallization process. After completion of the crystallization, they represent the residual silicon atoms. Nanoparticles with a more condensed silicate network grow until approximately 6 nm and evolve into building blocks for nucleation and growth of the silicalite-1 crystals. The silicate network connectivity of nanoparticles suitable for nucleation and growth increasingly resembles that of the final zeolite. This new insight into the two classes of nanoparticles will be useful to tune the syntheses of silicalite-1 for maximum yield.

Influence of [Mo6Br8F6](2-) Cluster Unit Inclusion within the Mesoporous Solid MIL-101 on Hydrogen Storage Performance

The inclusion of (TBA)(2)Mo(6)Br(8)F(6) (TBA = tetrabutylammonium) containing [Mo(6)Br(8)F(6)](2-) cluster units within the pores of the mesoporous chromium carboxylate MIL-101 (MIL stand for Materials from Institut Lavoisier) has been studied. X-ray powder diffraction, thermal analysis, elemental analysis, solid-state NMR, and infrared spectroscopy have evidenced the successful loading of the cluster. In a second step, the hydrogen sorption properties of the model cluster loaded metal organic framework (MOF) system have been analyzed and compared to those of the pure MOF sample, through a combination of adsorption isotherms (77 K, room temperature), thermal desorption spectroscopy, and calorimetry (calculated and experimental) in order to evaluate the hydrogen storage efficiency of the cluster loading.

The Extra-Framework Sub-Lattice of the Metal–Organic Framework MIL-110: A Solid-State NMR Investigation

A changeable character: Differences in the dynamics of occluded moieties within the large pores (see graphic) of aluminium 1,3,5-benzene tricarboxylate framework solid MIL-110 are a function of the synthesis pH. Host-guest proton-transfer processes lead to a reversible change in the character of the framework from cationic to neutral, depending on the nature of the extra-framework moieties.The aluminium 1,3,5-benzene tricarboxylate framework solid MIL-110, which crystallises either at pH approximately 0 or at pH approximately 4, has been investigated by solid-state NMR spectroscopy. At pH approximately 0 the solid (MIL-110{pH0}) is the unique stable thermodynamic product, whereas at pH approximately 4 MIL-110{pH4} is observed as a kinetic product in competition with the MIL-96 phase. Diffraction studies and (27)Al NMR spectroscopy prove that the framework is identical in both cases. The nature and dynamics of occluded moieties within the large pores look quite different for the two compounds. MIL-110{pH4} and MIL-110{pH0} both show the presence of occluded 1,3,5-benzene tricarboxylate (btc), with additional nitrates and water molecules. However, the proportions of btc, nitrates and water are functions of the pH, leading to an identical framework and a quite different extra-framework. With the extra-framework moieties, the framework undergoes a proton transfer which is a function of the synthesis pH. Washing the MIL-110{pH0} phase with water produces a different extra-framework structure, richer in water and poorer in btc and nitrates. The hydroxyl groups of the inorganic aluminium cluster of the framework are involved in a proton transfer, which leads for all cases to a cationic framework and an anionic extra-framework. (1)H-(1)H DQ 2D NMR spectra (DQ=double quantum) give evidence for the interaction of extra-framework btc with the terminal water carried by Al(2,3) and shows their proximity to the closest hydroxyl groups. A structure for the non-diffracting extra-framework is proposed as the most plausible topology. It provides an efficient picture for the creation of many substituted MIL-110 compounds that would have a large number of applications.

Recent advances in application of (27)Al NMR spectroscopy to materials science.

Valuable information about the local environment of the aluminum nucleus can be obtained through (27)Al Nuclear Magnetic Resonance (NMR) parameters like the isotropic chemical shift, scalar and quadrupolar coupling constants, and relaxation rate. With nearly 250 scientific articles per year dealing with (27)Al NMR spectroscopy, this analytical tool has become popular because of the recent progress that has made the acquisition and interpretation of the NMR data much easier. The application of (27)Al NMR techniques to various classes of compounds, either in solution or solid-state, has been shown to be extremely informative concerning local structure and chemistry of aluminum in its various environments. The development of experimental methodologies combined with theoretical approaches and modeling has contributed to major advances in spectroscopic characterization especially in materials sciences where long-range periodicity and classical local NMR probes are lacking. In this review we will present an overview of results obtained by (27)Al NMR as well as the most relevant methodological developments over the last 25years, concerning particularly on progress in the application of liquid- and solid-state (27)Al NMR to the study of aluminum-based materials such as aluminum polyoxoanions, zeolites, aluminophosphates, and metal-organic-frameworks.

Cubic Box versus Spheroidal Capsule Built from Defect and Intact Pentagonal Units

The high-nuclearity polyoxothiomolybdate [H(8)Mo(84)S(48)O(188)(H(2)O)(12)(CH(3)COO)(24)](32-) has been prepared and characterized by single-crystal X-ray crystallography and (1)H NMR, IR, Raman, and UV-vis spectroscopy. The solid-state structure reveals an unprecedented and intriguing arrangement consisting of a nanoscaled anionic cube. The surprisingly open structure of this {Mo(84)}-type cubic box features a large inner void that is accessible via its six open square faces with diameters of ca. 9 Å. Importantly, this molecular system appears to be highly functionalizable because of the presence of 24 exposed exchangeable acetate ligands.

Properties of a Tunable Multinuclear Nickel Polyoxotungstate Platform

A series of hybrid nickel bisphosphonate (BP) polyoxometalates (POMs) has been isolated. The complexes NaK-Ni7-Ale2 (Ale = [H2O3PC(C3H6NH2)(OH)PO3H2]) and NaNH4-Ni7-Ale2 are both made of two {PW9O34} fragments enclosing a heptanuclear Ni(II) core connected to two alendronate ligands. By pre-functionalising the alendronate moiety through the amino group, the naphthalene (napht) derivative Ni7-(AleNapht)2 and the compounds Ni7-(AlePy2 Ni)2 (py = pyridyl) and Ni7-(AleAc2Ni)2 (Ac = acyl) have been obtained. Compared with the NaK-Ni7-Ale2 species, these last two complexes contain two additional Ni(II) centres connected through two bis(2-pyridylmethyl)amine or two iminodiacetate groups, respectively. This results show that it is possible to functionalise the heptanuclear POM in a controlled manner. Quantification of the magnetic interactions in NaK-Ni7-Ale2 revealed that in the {Ni7} core, ferromagnetic interactions are predominant, with a S = 5 ground state. Magnetisation versus dc field sweeps on a single crystal of NaK-Ni7-Ale2 exhibited hysteresis at low temperature. (1)H and (31)P NMR studies in aqueous solution performed on NaK-Ni7-Ale2 and Ni7-(AleNapht)2 evidenced that the PW9/Ni7/bisphosphonate assembly is stable in solution. This was completed by (31)P magic angle spinning (MAS) investigations and confirmed by (1)H DOSY experiments. The electrochemistry of these compounds proceeds through two well-defined four-electron chemically reversible waves in a medium at pH 6. NaK-Ni7-Ale2 proved to be efficient for the electrocatalytic reduction of nitrate, nitrite and nitrous oxide. Remarkably, its electrocatalytic efficiency for nitrate reduction is approximately three times higher than those previously reported for POMs in a medium at pH >4 under the same potential. The catalytic properties of two representatives of the hybrid family were also examined. It is shown that these nickel bisphosphonate polyoxotungstates are pre-catalysts for the oxidation of alcohols into ketones or carboxylic acids, depending on the classes of alcohols considered, the stoichiometric oxidant used being H2O2. Noticeably, it has been found that an analogous cobalt bisphosphonate polyoxotungstate complex does not present any related activity, highlighting the crucial role of the 3d cations on the catalytic process.