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CO2 hydrogenation was carried out over Pt-containing UiO-67 Zr-MOFs at T = 220–280 °C and ambient pressure, with H2/CO2 = 0.2–9 and contact times, τ = 0.004–0.01 gcat·min·mL–1. The catalysts were characterized by XRD, N2 adsorption, FESEM, TEM and HRTEM, Pt L3-edge XANES and EXAFS, dissolution-NMR, CO chemisorption, IR spectroscopy, and TGA. A positive correlation was observed between the degree of Pt reduction and CO2 conversion. Contact time variation experiments showed that CO is a primary product of reaction, while CH4 is a secondary product. Testing of catalyst crystals with 0.15 and 2.0 μm crystal size, respectively, revealed no influence of diffusion on the reaction rate. Comparison to a conventional Pt/SiO2 catalyst showed very similar activation energy, with Eapp = 50 ± 3 kJ·mol–1. However, the turnover frequency over Pt/SiO2 was significantly lower, and Pt/SiO2 did not yield methane as a product. The Pt-containing UiO-67 Zr-MOF catalyst showed stable activity during 60 h of testing.

The structure of the Ruddlesden–Popper layered perovskite Li2CaTa2O7, known for its high photocatalytic water activity since its discovery in 2008, is reinvestigated. This oxide has been characterized by powder X-ray and neutron thermodiffraction, TEM, second harmonic generation (SHG), and Raman experiments on powders and single crystals. It is shown that it undergoes two structural phase transitions (i) around 220 °C, mainly characterized by the progressive emergence of SHG signal at low temperatures, and (ii) at 660 °C, mainly characterized by changes of the temperature behavior of lattice parameters and by the emergence of Raman signals that linearly increase on decreasing temperature. It is shown by powder neutron diffraction profile refinements at RT, 400, and 800 °C that the space groups of the successive phases of Li2CaTa2O7 are the acentric Pna21 (RT ≤ T ≤ 220 °C), Pnma (220 °C ≤ T ≤ 660 °C), and Cmcm (T ≥ 660 °C). A soft mode associated with the transition to the highest symmetry for this structu...

The structure and properties of two new UiO-67-type metal–organic frameworks, along with their linker synthesis and powder and single crystal synthesis, are presented. The new MOFs, UiO-67-Me and UiO-67-BN, are based on 3,3′-dimethylbiphenyl and 1,1′-binaphthyl linker scaffolds, and show a much higher stability to water than the thoroughly investigated UiO-67, which is based on the biphenyl scaffold. On the basis of structure models obtained from single crystal X-ray diffraction, it is seen that these linkers are partly shielding the Zr cluster. The new materials have higher density than UiO-67, but show a higher volumetric adsorption capacity for methane. UiO-67-BN exhibits excellent reversible water sorption properties, and enhanced stability to aqueous solutions over a wide pH range; it is to the best of our knowledge the most stable Zr-MOF that is isostructural to UiO-67 in aqueous solutions.

International audience; The structure of the Ruddlesden–Popper layered perovskite Li2CaTa2O7, known for its high photocatalytic water activity since its discovery in 2008, is reinvestigated. This oxide has been characterized by powder X-ray and neutron thermodiffraction, TEM, second harmonic generation (SHG), and Raman experiments on powders and single crystals. It is shown that it undergoes two structural phase transitions (i) around 220 °C, mainly characterized by the progressive emergence of SHG signal at low temperatures, and (ii) at 660 °C, mainly characterized by changes of the temperature behavior of lattice parameters and by the emergence of Raman signals that linearly increase on decreasing temperature. It is shown by powder neutron diffraction profile refinements at RT, 400, and 800 °C that the space groups of the successive phases of Li2CaTa2O7 are the acentric Pna21 (RT ≤ T ≤ 220 °C), Pnma (220 °C ≤ T ≤ 660 °C), and Cmcm (T ≥ 660 °C). A soft mode associated with the transition to the highest symmetry for this structural arrangement (I4/mmm) is also found in the Raman spectra. All these transitions appear continuous: the high temperature ones can be attributed to progressive vanishings of the octahedra tiltings (displacives) while the transition in the vicinity of 220 °C from Pna21 to Pnma exhibits order–disorder character.

This work reports an investigation of the localization of F atoms and OH groups in the two fluorinated aluminophosphates ULM-3(Al) and ULM-4(Al) by multinuclear and multidimensional high-resolution solid-state magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy. First, in ULM-3(Al), we show that the compound is fully fluorinated. A whole set of state-of-the-art homonuclear and heteronuclear 2D NMR experiments (19F–31P, 19F–19F, 31P–31P, 27Al–31P, and 1H–31P) have been recorded, yielding a unique line assignment of all the 31P and 19F resonances to the corresponding crystallographic sites. In a second part, ULM-4(Al) is shown to be a quite remarkable sample because it contains both fully and partially fluorinated building units. The structural differences between ULM-3(Al) and ULM-4(Al) are finally discussed in the light of the results in terms of potential templating role of water.

NMR crystallography of the fluorinated aluminophosphate cloverite is presented, with an emphasis on the description of the nonperiodic part of the compound, i.e., the fluorine and organic subnetworks, which are very difficult to access by usual X-ray powder diffraction methods. Multinuclear high-resolution 1D Al-27 and P-31 NMR support the main cloverite-type topological features previously proposed for aluminum cloverite from powder X-ray diffraction. Spatial proximities are extracted from the 2D P-31-P-31 and Al-27-P-31 NMR spectra, allowing a full assignment of the P-31 and Al-27 resonances to the corresponding phosphorus and aluminum sites in the structure. To go further into the description of the main periodic framework, C-13, N-15, and H-1 1D and H-1-H-1 and H-1-P-31 2D NMR measurements are employed, allowing the characterization and selective locations of the two costructural-directing agents in the pores and channels of the framework. The nonperiodic fluorine subnetwork is described by means of F-19-X (X = Al-27 and P-31) 2D NMR experiments. Two kinds of fluorine atoms are distinguished: F- ions trapped in D4R units and F atoms covalently bonded to terminal Al or P atoms and which interrupt the AlPO network. Through the example of aluminum cloverite, we show that, despite the considerable complexity of such systems, an extremely detailed structural model can be obtained, including the simple rules that allow the description of the nonperiodic subnetworks that tailor the structure and properties of a compound, by coupling powder X-ray diffraction and high-resolution NMR data in a generalized crystallography approach.

The structures of (enH2)2 [Al5(OH)(PO4)3 (PO3OH)4]·2H2O and (enH2)2 [Al5(PO4)5(PO3OH)2] ·H2O are determined by powder synchrotron XRD and solid state NMR spectroscopy.

International audience; The structures of four Ca-phosphonate phases are reported here: Ca(C6H5-PO3H)2 (1), Ca(C6H5-PO3)*2H2O (2), Ca(C4H9-PO3H)2 (3) and Ca(C4H9-PO3)*H2O (4). Structural models were obtained ab initio by using a combined synchrotron powder diffraction, solid-state nuclear magnetic resonance, and gauge including projector augmented wave (GIPAW) calculation approach. The 1H, 13C, 31P and 43Ca NMR parameters calculated from these structural models were found to be in good agreement with the experimental values, thereby indicating the high accuracy of the DFT-optimized structures. Correlations between the NMR parameters and structural features around the phosphonate were then analyzed, showing in particular the high sensitivity of the 31P asymmetry parameter ηCS and the 43Ca isotropic chemical shift to changes in local structure around the phosphonate groups and the Ca2+, respectively. Finally, the NMR data of a new mixed Na-Ca phosphonate phase, Ca1.5Na(C4H9-PO3)2, are reported.

MATERIAUX+ATU; The syntheses and structure resolution process of two highly complex powdered aluminophosphates with an original 5:7 Al/P ratio are presented: [Al-5(OH)(PO4)(3)(PO3OH)(4)] [NH3(CH2)(2)NH3](2) [2H(2)O], compound 1, and [Al-5(PO4)(5)(PO3OH)(2)] [NH3(CH2)(3)NH3](2) [H2O], compound 2. We have previously reported the structure of the periodic part of 1 by coupling synchrotron powder diffraction and solid-state nuclear magnetic resonance (NMR) crystallographies. With a similar strategy, that is, input of large parts of the building blocksdetermined by analysis of the Al-27-P-31 correlation pattern of the two-dimensional (2D) NMR spectrum in the structure search process, we first determine the periodic structure of 2, using the powder synchrotron diffraction data as cost function. Both 1 and 2 are layered materials, in which the inorganic layers contain five P and seven Alinequivalent atoms, with aluminum atoms that are found in three different coordination states, AlO4, AlO5, and AlO6, and the interlayer space contains the amines and water molecules. In 1, the inorganic layers are stacked on each other with a 42 element of symmetry along the c-axis, while they are stacked with a 180 degrees rotation angle in 2. By analysis of a set of high-resolution 1D and 2D NMR spectra (P-31, Al-27, H-1, N-15, C-13, Al-27-P-31, H-1-P-31, and H-1-N-14) the structure analysis of 1 and 2 is extended beyond the strict periodicity, to which diffraction is restricted, and provides localization of the hydroxyl groups and water molecules in the frameworks and an attempt to correlate the presence of these latter species to the structural features of the two samples is presented. Finally, the dehydration/rehydration processes occurring in these solids are analyzed. The methodology of the structure determination for these dehydrated forms uses the same principles, combining X-ray powder diffraction and solid-state NMR data.

The syntheses and structure resolution process of two highly complex powdered aluminophosphates with an original 5:7 Al/P ratio are presented: [Al5(OH)(PO4)3(PO3OH)4] [NH3(CH2)2NH3]2 [2H2O], compound 1, and [Al5(PO4)5(PO3OH)2] [NH3(CH2)3NH3]2 [H2O], compound 2. We have previously reported the structure of the periodic part of 1 by coupling synchrotron powder diffraction and solid-state nuclear magnetic resonance (NMR) crystallographies. With a similar strategy, that is, input of large parts of the building blocks determined by analysis of the 27Al–31P correlation pattern of the two-dimensional (2D) NMR spectrum in the structure search process, we first determine the periodic structure of 2, using the powder synchrotron diffraction data as cost function. Both 1 and 2 are layered materials, in which the inorganic layers contain five P and seven Al inequivalent atoms, with aluminum atoms that are found in three different coordination states, AlO4, AlO5, and AlO6, and the interlayer space contains the amines ...

MATERIAUX+ATU

A new two-dimensional fluorinated gallium phosphate RbGa(3)(PO(4))(2)(HPO(4))F(4)·C(5)N(2)H(16)·2H(2)O (MIL-145) has been hydrothermally synthesized (180 °C for 36 h) in the presence of 1,5-diaminopentane and rubidium fluoride. Its structural model has been determined by means of single-crystal X-ray diffraction analysis. The structure contains corrugated infinite ribbons of GaO(3)F(3) and GaO(4)F(2) octahedra linked through edge- and corner-sharing mode via fluoride anions. These chains are then connected to each other via phosphate groups to create a layered network delimiting 6-ring channels trapping rubidium cations. The inorganic sheets are intercalated by diprotonated 1,5-diaminopentane and water molecules, ensuring the three-dimensional cohesion via hydrogen bond scheme. (1)H, (13)C, (15)N and (87)Rb solid-state NMR spectra show the presence of two inequivalent amines as well as two Rb cations, confirming the choice of the space group, which was ambiguous from the diffraction data. (71)Ga NMR spectra, acquired at several magnetic fields, contain two different sets of Ga signals, corresponding to the two types of gallium environments in the structure. One-dimensional (19)F and (31)P and (19)F-(31)P two-dimensional NMR experiments have been recorded, which are in full agreement with the proposed structural model. Finally, possible assignments of the (19)F and (31)P resonances to the crystallographic sites in RbGa(3)(PO(4))(2)(HPO(4))F(4)·C(5)N(2)H(16)·2H(2)O have been determined by comparing adjacency matrices build-up from 2D NMR correlation spectra and from the structural data.

The multiple-quantum dipolar refocused-INEPT (MQ-D-R-INEPT) NMR experiment is presented. This new pulse sequence allows the generation of two-dimensional through-space NMR correlation spectra between spin-½ and quadrupolar nuclei under high-resolution. Compared to the existing sequences, the MQ-D-R-INEPT sequence benefits from increased robustness, due to the reduced sensitivity to offsets and radio-frequency field inhomogeneity of the R-INEPT recoupling scheme as compared to the classical cross-polarization transfer involving a quadrupolar nucleus, and applicability to quadrupolar nuclei with any half-integer spin value. Here, the heteronuclear dipolar couplings have been reintroduced using the rotary resonance recoupling (R(3)) sequence, chosen because it is γ-encoded, and thus robust to spinning speed instabilities and to radio-frequency inhomogeneities in the case of nuclei subjected to large chemical shift anisotropy (e.g., (31)P). In the course of the article, a new definition of γ-encoding is introduced, more general and practical than the previous ones, as it does not depend on the implementation of the recoupling sequence, and is independent of the considered frame. The efficiency of the MQ-D-R-INEPT experiment is demonstrated for the observation of (31)P-(27)Al proximities. It is first tested on AlPO4-VPI-5, and then applied to a complex aluminophosphate AlPO4-(Al5P7)-DAE of incompletely established structure. For this latter sample, the high-resolution provided by the MQMAS filter allows the resolution of a large number of (31)P-(27)Al correlations, which represent an essential step towards the determination of its structural model.

We present in this paper the structure resolution of a fluorinated inorganic-organic compound--Zn(3)Al(2)F(12)·[HAmTAZ](6)--by SMARTER crystallography, i.e. by combining powder X-ray diffraction crystallography, NMR crystallography and chemical modelling of crystal (structure optimization and NMR parameter calculations). Such an approach is of particular interest for this class of fluorinated inorganic-organic compound materials since all the atoms have NMR accessible isotopes ((1)H, (13)C, (15)N, (19)F, (27)Al, (67)Zn). In Zn(3)Al(2)F(12)·[HAmTAZ](6), (27)Al and high-field (19)F and (67)Zn NMR give access to the inorganic framework while (1)H, (13)C and (15)N NMR yield insights into the organic linkers. From these NMR experiments, parts of the integrant unit are determined and used as input data for the search of a structural model from the powder diffraction data. The optimization of the atomic positions and the calculations of NMR parameters ((27)Al and (67)Zn quadrupolar parameters and (19)F, (1)H, (13)C and (15)N isotropic chemical shifts) are then performed using a density functional theory (DFT) based code. The good agreement between experimental and DFT-calculated NMR parameters validates the proposed optimized structure. The example of Zn(3)Al(2)F(12)·[HAmTAZ](6) shows that structural models can be obtained in fluorinated hybrids by SMARTER crystallography on a polycrystalline powder with an accuracy similar to those obtained from single-crystal X-ray diffraction data.

Because solid-state nuclear magnetic resonance (ss-NMR) spectroscopy is sensitive to local order and is selective to the nature of the atoms, this technique has emerged as ideally complementary to powder diffraction for structure determination of a wide range of solids. Here, we will illustrate with the example of hybrid solids (aluminophosphates) the role of high-resolution one and two-dimensional solid-state NMR data to drive the search for a structure model from powder diffraction data. Great progresses have been made in the field of ss-NMR in the past few years (higher magnetic field, more robust pulse sequences, etc.) that now allows access to NMR spectra with very high resolution in such compounds [1]. From these NMR data, information about the cations (number, coordination number, etc) and the connectivity between the cation polyhedra are readily available. Such knowledge allows performing a more constraint structure search, thus increasing the chance to obtain a solution [2]. NMR data further provide information about the non-periodic sub-networks in hybrid compounds (water molecules, OH groups, templates...), allowing to draw very detailed pictures of the solids [3].

A summary of the recent results obtained in the field of NMR crystallography of nanoporous materials is proposed, and new original methods and strategies to perform NMR crystallography driven structure determination are presented. Although the work to reach structure resolution of a powder is much more difficult than for a single crystal, the use of NMR data associated with diffraction methods and modelling has provided significant successes in this domain. However, a general method to combine the different measurements, and overcome their respective limitations, has been only recently proposed. The structure search can therefore be organized to converge to possible structure models. This is of utmost importance for the structure determination of complex nanoporous crystals.