Nicolas Louvain

Shape-Memory Nanopores Induced in Coordination Frameworks by Crystal Downsizing

Size Affects Shape Porous molecular framework materials can adopt a different phase when guest molecules absorb and uniformly distort the framework. Usually the framework returns to its original shape when the guests desorb. Sakata et al. (p. 193) noted that because surface stress drives this process, it might be avoided in smaller crystals. Indeed, a flexible porous coordination polymer, [Cu2(dicarboxylate)2(amine)]n, could retain the structure induced by guest molecules such as methanol if crystallites were made sufficiently small (submicrometer scale) and did so to a greater degree as the crystallite dimensions decreased. A porous material retains its framework shape after guest molecules desorb if its crystallites are sufficiently small. Flexible porous coordination polymers change their structure in response to molecular incorporation but recover their original configuration after the guest has been removed. We demonstrated that the crystal downsizing of twofold interpenetrated frameworks of [Cu2(dicarboxylate)2(amine)]n regulates the structural flexibility and induces a shape-memory effect in the coordination frameworks. In addition to the two structures that contribute to the sorption process (that is, a nonporous closed phase and a guest-included open phase), we isolated an unusual, metastable open dried phase when downsizing the crystals to the mesoscale, and the closed phase was recovered by thermal treatment. Crystal downsizing suppressed the structural mobility and stabilized the open dried phase. The successful isolation of two interconvertible empty phases, the closed phase and the open dried phase, provided switchable sorption properties with or without gate-opening behavior.

Mesoscopic architectures of porous coordination polymers fabricated by pseudomorphic replication

The spatial organization of porous coordination polymer (PCP) crystals into higher-order structures is critical for their integration into separation systems, heterogeneous catalysts, ion/electron transport and photonic devices. Here, we demonstrate a rapid method to spatially control the nucleation site, leading to the formation of mesoscopic architecture made of PCPs, in both two and three dimensions. Inspired by geological processes, this method relies on the morphological replacement of a shaped sacrificial metal oxide used both as a metal source and as an architecture-directing agent by an analogous PCP architecture. Spatiotemporal harmonization of the metal oxide dissolution and the PCP crystallization allowed the preservation of very fine mineral morphological details of periodic alumina inverse opal structures. The replication of randomly structured alumina aerogels resulted in a PCP architecture with hierarchical porosity in which the hydrophobic micropores of the PCP and the mesopores/macropores inherited from the parent aerogels synergistically enhanced the materials selectivity and mass transfer for water/ethanol separation.

Structural diversity and retro-crystal engineering analysis of iodometalate hybrids

With guidance from retro-crystal engineering, iodometalate structures based on MI6 octahedra of group 14 (M = Sn(II), Pb(II)) and group 15 (M = Sb(III) and Bi(III)) are analysed. The criterion of I/M ratio, with the function of indicating the degree of condensation of octahedra in inorganic networks and the average charge density at the organic–inorganic interface, is introduced to classify all of the iodometalate networks, resulting in an easy and clear way to identify isomers with different dimensionalities. Of all iodometalates, the 2D M(II)I4 anion derived from the perovskite network is special since it can be easily stabilized by a range of common organic cations. We provide here the up-to-date progress in this extensively studied field, focusing on crystal engineering of hybrids in the aim of getting materials with a reduced band gap. Relationships between the molecular layouts of cationic entities and the structures of several non-perovskite anionic networks, focusing on the organic–inorganic interface, are highlighted. Distinct dependences between different types of cations and different types of anions are revealed, although it is still unfeasible to apply them in the actual control, design, or prediction of specific hybrid structures.

α- to β-(dmes)BiI5 (dmes = Dimethyl(2-ethylammonium)sulfonium Dication): Umbrella Reversal of Sulfonium in the Solid State and Short I···I Interchain Contacts—Crystal Structures, Optical Properties, and Theoretical Investigations of 1D Iodobismuthates

Syntheses, X-ray structural characterization, optical properties, and electronic structures of 1D metal(III) iodide hybrids, namely, alpha-((CH(3))(2)S(CH(2))(2)NH(3))BiI(5) (1a), beta-((CH(3))(2)S(CH(2))(2)NH(3))BiI(5) (1b), ((CH(3))(2)S(CH(2))(2)NH(3))SbI(5) (2), and (HO(2)C(C(6)H(4))CH(2)NH(3))BiI(4) (3), are reported. According to the results of single-crystal X-ray diffraction analyses, the 1D inorganic chains are constructed by corner-shared M(III)I(6) octahedra in 1a, 1b, and 2 and by edge-shared ones in 3. In polymorphs 1a, 1b, and 2, the polymeric BiI(5)(2-) anionic chains are charge-balanced by the dimethyl(2-ethylammonium)sulfonium (dmes) dications. Complex 1a crystallizes in the polar space group of P2(1)cn. A spectacular umbrella reversal of half sulfonium parts together with the conformational change of half polymeric anions in the crystal structure of 1a occurs at moderate temperature (73 degrees C), leading to the beta-phase 1b, through a reversible single-crystal-to-single-crystal process. Complex 1b, as well as the isotype structure of 2, crystallize in the nonpolar acentric space group of P2(1)2(1)2(1). Because of their acentric structural characteristic, second harmonic generation (SHG) optical properties are observed in the polycrystalline powder samples of 1a, 1b, and 2. It is notable that the SHG signal of 1a is much stronger than that of 1b and 2 owing to the polarity of 1a. Remarkably, the peculiar dissymmetrical dication of dmes is able to modify the bonding features of the inorganic frameworks through shortening I...I distances between adjacent chains (d(I...I) < 4A). The structure of 3, which crystallizes in the triclinic space group P1, features a polymeric anionic chain constructed from edge-shared BiI(6) octahedra. The charge is balanced by the pairs of trans-4-(ammoniummethyl)-cyclohexane-carboxylic acid, which are linked together via the H bonding between the carboxylic groups to form a pseudodication. The results of DFT calculations based on the structures of 1a and 3 indicate that the narrower band gap in 1 appears to be associated on the one hand with a sigma* I-p/Bi-s interaction that moves the Fermi level to higher energy and on the other hand with the interchain I...I contacts.

Conversion of Nanocellulose Aerogel into TiO2 and TiO2@C Nano-thorns by Direct Anhydrous Mineralization with TiCl4. Evaluation of Electrochemical Properties in Li Batteries

Nanostructured TiO2 and TiO2@C nanocomposites were prepared by an original process combining biotemplating and mineralization of aerogels of nanofibrillated cellulose (NFC). A direct one step treatment of NFC with TiCl4 in strictly anhydrous conditions allows TiO2 formation at the outermost part of the nanofibrils while preserving their shape and size. Such TiO2@cellulose composites can be transformed into TiO2 nanotubes (TiO2-NT) by calcination in air at 600 and 900 °C, or into TiO2@C nanocomposites by pyrolysis in argon at 600 and 900 °C. Detailed characterization of these materials is reported here, along with an assessment of their performance as negative electrode materials for Li-ion batteries.

Type structure, which is composed of organic diammonium, triiodide and hexaiodobismuthate, varies according to different structures of incorporated cations

Type structure of (H3N–R–NH3)2I3BiI6, which consists of sheets of organic entities together with triiodide anions separated by layers of BiI6 octahedra, is defined by triiodide, hexaiodobismuthate, and organic diammonium. The prototype structure of (H3N(CH2)2SS(CH2)2NH3)2I3BiI6 n (1) can accommodate various changes according to the nature of the organic group, such as conformation, length or size. In (H3N(CH2)2SS(CH2)2NH3)2I3BiI6·0.5H2O (2), acentric symmetry resulted from the lattice water molecules render the SHG property. Whereas in (H3N(CH2)4NH3)2(I3)0.5(I(H2O)2)0.5 BiI6 n (3), water molecules are incorporated in the main framework by substituting two iodine atoms of I3− anion, in the structure of (H3NCH2(C6H10)CO2H)4(I3)2BiI6 H3O (4), pairs of linear triiodide entities [I3⋯I3]2− n (d(I3−⋯I3−) n = 3.77(1) n A) are observed, owing to the super-long diammonium cations of two trans-4-methylammonium cyclohexane carboxylic acid linked together via hydrogen bonding between carboxylate groups.

Fluorination of anatase TiO2 towards titanium oxyfluoride TiOF2: a novel synthesis approach and proof of the Li-insertion mechanism

The reactivity of pure molecular fluorine F2 allows the creation of new materials with unique electrochemical properties. We demonstrate that titanium oxyfluoride TiOF2 can be obtained under molecular fluorine from anatase titanium oxide TiO2, while the fluorination of rutile TiO2 leads only to pure fluoride form TiF4. Contrary to most fluorides, TiOF2 is air-stable and hydrolyses poorly under humid conditions. Such a stability makes it possible for TiOF2 to be studied as an electrode material in Li-ion secondary battery systems. It shows the capacity as high as 220 mA h g−1 and good cyclability at high current rates at an average potential of 2.3 V vs. Li+/Li. At such a potential, only Li+ insertion occurs, as proven by in operando XRD/electrochemistry experiments.

Impact of crystal orientation on the adsorption kinetics of a porous coordination polymer–quartz crystal microbalance hybrid sensor

The hybridization of porous coordination polymers (PCPs) with electronic devices is a powerful strategy for developing systems that are suitable for advanced applications, such as chemical sensing. The quartz crystal microbalance (QCM) technique is one that allows minute mass changes to be resolved with a high temporal resolution, and the growth of PCP crystals that provide selective adsorption properties on a QCM substrate can facilitate the rapid detection of certain molecules from a gas or vapour mixture. Herein, we demonstrate the immobilization of the flexible PCP Zn(NO2-ip)(bpy) (Zn-CID-5; NO2-ip2− = 5-nitroisophthalate, bpy = 4,4′-bipyridine) on QCM substrates and investigate the adsorptive properties of the fabricated systems. Notably, the crystal orientation could be controlled by the anchoring of chemical functionalities on the substrate surface, or by the addition of coordination modulators (e.g. 4-phenylpyridine) at the time of growth of the PCP crystals on the substrates. Here, the crystal orientation plays a significant role in determining the detection kinetics of organic vapours (e.g. methanol), and the [010]-oriented case which displays the fastest adsorption kinetics among the samples tested is studied under mixed component (methanol–hexane) conditions to demonstrate its response profile. In all, the results demonstrate the potential utility of PCP/QCM hybrid systems in sensor applications, and also serve to highlight the importance of optimizing the physical orientation of crystal growth in such systems to maximize the overall performance of the system.

On the electrochemical encounter between sodium and mesoporous anatase TiO2 as a Na-ion electrode

Mesoporous anatase titanium dioxide (TiO2) is prepared by an easily up-scalable synthesis protocol, using relatively inexpensive precursors. We demonstrate here that submicronic anatase TiO2 crystals show unexpected performances as electrodes of Na-ion batteries (NaBs). They exhibit highly stable reversible specific capacities of up to 200 mA h g−1 and excellent cyclability at moderate current rates at an average potential of 1.0 V vs. Na+/Na. While pseudocapacitance may appear to be the main process driving the reactions between the sodium ions and TiO2 during the first discharge above 1 V vs. Na+/Na, operando Raman and X-ray diffraction studies show that the TiO2 anatase structure is nearly entirely lost below 0.25 V vs. Na+/Na. The subsequent cycling is based on amorphous sodium titanate materials.

Synthesis of Titania@Carbon Nanocomposite from Urea‐Impregnated Cellulose for Efficient Lithium and Sodium Batteries

Nanostructured TiO2 and TiO2@C nanocomposites were prepared directly from urea-impregnated cellulose by a simple reaction/diffusion process and evaluated as negative electrode materials for Li and Na batteries. By direct treatment with TiCl4 under anhydrous conditions, the urea impregnation of cellulose impacts both the TiO2 morphology and the carbon left by cellulose after pyrolysis. Hierarchical TiO2 structures with a flower-like morphology grown from-and-at the surface of the cellulose fibers are obtained without any directing agent. The resulting TiO2/cellulose composite is then transformed either into pure TiO2 flowers by calcination in air at 600 °C, or into TiO2@C nanocomposites by pyrolysis under Ar at 600 °C. Electrochemical studies demonstrate that both samples can (de)insert lithium and sodium ions and are promising electrode materials.