Mechanical bonding of rigid MORFs using a tetratopic rotaxane.

The preparation of highly rigid cobalt(II)- and copper(II)-organic frameworks incorporating a tetralactam [2]rotaxane as a ligand is described. The interlocked ligand is functionalized with two pairs of carboxylate groups placed at each counterpart, thus limiting its dynamics within the crystal. The solid structure of the metal-organic rotaxane frameworks showed different, unprecedented polycatenation modes of grids, depending on the employed metal, providing great rigidity to the structures. This rigidity has been evaluated by using single crystal X-ray diffraction analyses of the cobalt(II)-organic frameworks embedded in different solvents, observing that the lattices remain unchanged. Thus, this research demonstrates that rigid and robust materials with permanent porosity can be achieved using dynamic ligands.

An anthraquinone-based bismuth-iron metal-organic framework as an efficient photoanode in photoelectrochemical cells.

Metal-organic frameworks (MOFs) are appealing candidate materials to design new photoelectrodes for use in solar energy conversion because of their modular nature and chemical versatility. However, to date there are few examples of MOFs that can be directly used as photoelectrodes, for which they must be able to afford charge separation upon light absorption, and promote the catalytic dissociation of water molecules, while maintaining structural integrity. Here, we have explored the use of the organic linker anthraquinone-2, 6-disulfonate (2, 6-AQDS) for the preparation of MOFs to be used as photoanodes. Thus, the reaction of 2, 6-AQDS with Bi(iii) or a combination of Bi(iii) and Fe(iii) resulted in two new MOFs, BiPF-10 and BiFePF-15, respectively. They display similar structural features, where the metal elements are disposed in inorganic-layer building units, which are pillared by the organic linkers by coordination bonds through the sulfonic acid groups. We show that the introduction of iron in the structure plays a crucial role for the practical use of the MOFs as a robust photoelectrode in a photoelectrochemical cell, producing as much as 1.23 mmol H2 cm-2 with the use of BiFePF-15 as photoanode. By means of time-resolved and electrochemical impedance spectroscopic studies we have been able to unravel the charge transfer mechanism, which involves the formation of a radical intermediate species, exhibiting a longer-lived lifetime by the presence of the iron-oxo clusters in BiFePF-15 to reduce the charge transfer resistance.

Framework Adaptability and Concerted Structural Response in a Bismuth Metal-Organic Framework Catalyst.

Bismuth metal-organic frameworks (MOFs) as heterogeneous catalysts are scarce, and there is little knowledge on the influence of the MOF features on their resulting activity and behavior. Here, we present the synthesis, characterization, and catalytic activity in the one-pot multicomponent Strecker reaction with ketones of three new MOFs prepared with the combination of indium or bismuth and 4,4',4'',4'''-methanetetrayltetrabenzoic acid. One of them, denoted BiPF-7, is very robust and chemically stable, and demonstrates a high activity in the formation of the desired α-aminonitriles. The interaction of the catalytic substrates with the metal centers in this MOF has been crystallographically characterized, showcasing a concerted framework adaptability process that involves structural changes in framework components that are not directly involved in the binding of the guests.

Multi-use high/low-temperature and pressure compatible portable chamber for in situ grazing-incidence X-ray scattering studies.

The multipurpose portable ultra-high-vacuum-compatible chamber described in detail in this article has been designed to carry out grazing-incidence X-ray scattering techniques on the BM25-SpLine CRG beamline at the ESRF. The chamber has a cylindrical form, built on a 360° beryllium double-ended conflate flange (CF) nipple. The main advantage of this chamber design is the wide sample temperature range, which may be varied between 60 and 1000 K. Other advantages of using a cylinder are that the wall thickness is reduced to a minimum value, keeping maximal solid angle accessibility and keeping wall absorption of the incoming X-ray beam constant. The heat exchanger is a customized compact liquid-nitrogen (LN2) continuous-flow cryostat. LN2 is transferred from a storage Dewar through a vacuum-isolated transfer line to the heat exchanger. The sample is mounted on a molybdenum support on the heat exchanger, which is equipped with a BORALECTRIC heater element. The chamber versatility extends to the operating pressure, ranging from ultra-high vacuum (<10(-10) mbar) to high pressure (up to 3 × 10(3) mbar). In addition, it is equipped with several CF ports to allocate auxiliary components such as capillary gas-inlet, viewports, leak valves, ion gun, turbo pump, etc., responding to a large variety of experiment requirements. A movable slits set-up has been foreseen to reduce the background and diffuse scattering produced at the beryllium wall. Diffraction data can be recorded either with a point detector or with a bi-dimensional CCD detector, or both detectors simultaneously. The system has been designed to carry out a multitude of experiments in a large variety of environments. The system feasibility is demonstrated by showing temperature-dependence grazing-incidence X-ray diffraction and conductivity measurements on a 20 nm-thick La0.7Ca0.3MnO3 thin film grown on a SrTiO3(001) substrate.

Efficient mid-infrared laser operation of Li3Lu(3-x)Tm(x)Ba2(MoO4)8 disordered crystal.

Tm-doped Li(3)Lu(3)Ba(2)(MoO(4))(8) monoclinic (C2/c) crystals were grown by the TSSG-method. Details of the crystal growth and Tm(3+) spectroscopy are presented. 514 mW of laser light at 1940 nm was obtained with 71.4% of slope efficiency in quasi-cw operation mode. The laser was tuned in the 1853-2009 nm range. The crystal shows local disorder due to the shared occupancy by Li and Lu of the same 8f lattice site, this confers potential applications for mode-locked sub-200 fs laser pulses.

Hydrothermal Tm3+-Lu2O3 nanorods with highly efficient 2 µm emission.

Cubic Ia3Tm-Lu(2)O(3) porous nanorods of ∼45 µm length and 90 nm diameter have been prepared with precise compositions through a soft hydrothermal route (i.e., autogenic pressure, neutral pH, and 185 °C for 24 h) by using chloride reagents. For these nanorods, room temperature excitation and photoluminescence spectra of Tm(3+) multiplets related to the eye-safe (3)F(4)→(3)H(6) laser transition at ∼1.85-2.05 µm are similar to those of bulk crystals. Room-temperature luminescence decays of (3)H(4) and (3)F(4) exhibit nonexponential dynamics analytically reproduced by the sum of two exponential regimes, which are ascribed to the different rates of nonradiative relaxations in defects at the surface and in the body of the nanocrystals, respectively. Measured fluorescence lifetimes τ ∼ 200-260 µs and τ ∼ 2.3-2.9 ms for (3)H(4) and (3)F(4), respectively, in 0.2% mol Tm-Lu(2)O(3) nanorods, are considerably larger than in previous nanocrystalline Tm-doped sesquioxides, and they are close to values of bulk sesquioxide crystals with equivalent Tm(3+) content.