Crystal structure of a new ordered form of ammonium hydrogen succinate NH4HC4H4O4

International audienceTriclinic ammonium hydrogen succinate compound (space group P1−) is known to present very short O–H⋅⋅⋅O hydrogen bonds in association with a second-order phase transition around 170 K. Whatever the temperature, its crystal structure is characterized by a statistical distribution of the hydrogen atom belonging to the hydrogen succinate molecule on two crystallographic sites, leading to a disordered structure. In this study, we report on the crystal structure of a new ordered structural form of the title compound NH4HC4H4O4, determined by single-crystal X-ray diffraction at room temperature. This new ordered form crystallizes in the triclinic space group P1− with refined cell parameters: a = 6.4868(16) Å, b = 7.4313(17) Å, c = 7.4339(17) Å, α = 112.058(8)°, β = 96.477(9)°, γ = 109.026(8)° and V = 302.45(12) Å3. Hydrogen succinate molecules are in trans conformation in the ordered form and in gauche conformation in the disordered one. It leads to different molecular assemblies of the ammonium cations and hydrogen succinate anions, and consequently, to different hydrogen bond networks. The crystal structure stability of this new ordered structural form is discussed and compared to that of the disordered form

Flexible and Transparent Luminescent Cellulose-Transition Metal Cluster Composites

International audienceRed-NIR luminescent polymers are principally obtained from petroleum-based derivatives in which emitters, usually a critical raw material such as rare-earth or platinum group metal ions, are embedded. Considering the strong ecological impact of their synthesis and the major risk of fossil fuel energy shortage, there is an urgent need to find alternatives. We describe a luminescent nanocomposite based on red-NIR phosphorescent molybdenum nanoclusters, namely Cs(2)Mo(6)I(8)(OCOC(2)F(5))(6), embedded in an eco-friendly cellulose biopolymer matrix that is obtained by a simple solvent casting technique. While homogeneity is kept up to 20 wt% of cluster complex doping, annealing hybrids leads to a large increase of their emission efficiency, as demonstrated by quantum yield measurements

Smart emissive hybrid dynamer and nanocomposite made of complementary organic and inorganic emitters combined via a supramolecular Janus synthon

International audienceMonotopic and ditopic blue-emitting anthracene derivatives bearing one or two thymine moieties, respectively, are associated via hydrogen bonds to a red-emitting [Mo6I8(OCOC2F5)(6)](2-) anion, whose charge is counter-balanced by a Janus-type organic synthon made of an imidazolium head bearing an organic chain terminated with a complementary diamidopyridine group. The generated supramolecular hydrogen-bonded complex and dynamers show blue emission in solution and red emission in the solid state. Once embedded in the PMMA film, the dynamer emission colour is controlled by the irradiation time and power in the UV-2A region. This dynamic luminescent behaviour allows for evanescent optical writing on the film

Enhanced photoluminescence of hexamolybdenum cluster by anodic aluminum oxide photonic crystals

International audienceThe enhanced photoluminescence of the Mo6 cluster was first reported by its incorporation into the anodic aluminum oxide (AAO), a photonic structure to delocalize the emission light. Two AAO structures with different pore sizes, densities, and shapes were controlled by pore widening treatment. The deposition of the negatively charged clusters at the bottom of the ordered AAO resulted in narrowing the PL peak at 680 nm with an enhanced intensity of 230 %. In addition, the disordered AAO supported the deposition of clusters on the surface that efficiently adjusted the shift of the PL peak position, obtaining a high intensity by more than 300 % in comparison with that of clusters deposited on the ITO-coated glass. The cluster-integrated photonic crystal could be an interesting material for applications that require efficient luminescence

Effect of an Aromatic Sulfonate Ligand on the Photovoltaic Performance of Molybdenum Cluster-Sensitized Solar Cells

International audienceThe photovoltaic performance of molybdenum cluster-sensitized solar cells has been explored with the challenge of enhancing their efficiency due to the low charge transfer efficiency. Aromatic sulfonate ligands (NS = naphthalene 2,6-disulfonate = –OSO2–C10H6–SO3–) were now used for the functionalization of the {Mo6Ii8} cluster cores. The new functional [Mo6I8iI3a(H2O)2a(NS)a] cluster unit exhibits enhanced photophysical and photoelectrochemical properties compared to other homologues based on the {Mo6I8i} cluster cores. In greater detail, the role of the NS functional groups was beneficially emphasized for the improved oxidation stability of the cluster in a redox mediator, adjusting the emission lifetime to a suitable range for fast electron injection, and accelerating the charge transport process. The best as-synthesized Mo6 cluster-based solar cell resulted in a stable photocurrent of 2.38 mA cm–2 with a fill factor of 0.63 and the power conversion efficiency of 0.97% under an AM 1.5 illumination, a two times’ enhancement in comparison to the reference iodide Mo6 cluster-based cell (0.52%). Specific attention focused on the increase of the power conversion efficiency up to 1.18% after 330 s and then reached the saturation trend. The enhanced charge transfer of the metal cluster complex was obtained from facile modifications of the functional apical ligands that result in advantageous photophysical and electrochemical characteristics, specializing in optoelectronic devices. This study provides the general methodology and knowledge for the next improvement of the photovoltaic efficiency of the Mo6 cluster-based sensitized solar cells

Direct Integration of Red-NIR Emissive Ceramic-like AnM6Xi8Xa6 Metal Cluster Salts in Organic Copolymers Using Supramolecular Interactions

International audienceHybrid nanomaterials made of inorganic nanocomponents dispersed in an organic host raise an increasing interest as low-cost solution-processable functional materials. However, preventing phase segregation while allowing a high inorganic doping content remains a major challenge, and usual methods require a functionalization step prior integration. Herein, we report a new approach to design such nanocomposite in which lead-free and cadmium-free ceramic-like metallic nanocluster compounds are embedded at 10 wt % in organic copolymers, without any functionalization. Homogeneity and physical stability are ensured by weak interactions occurring between the copolymer lateral chains and the nanocluster compound. Photophysical studies show that the intrinsic properties of the native cluster (absolute quantum yield of around 0.5, phosphorescence lifetime) are fully retained in the nanocomposite. Hybrids could be ink-jet printed and casted on a blue LED. The proof-of-concept device emits in the Red-NIR area and generates singlet oxygen, of particular interest for lightings, display, sensors or photodynamic based therapy applications

Luminescent liquid crystalline hybrid materials by embedding octahedral molybdenum cluster anions with soft organic shells derived from tribenzo[18]crown-6

International audienceCrown ethers and their derivatives are versatile building blocks for the design of supramolecular materials. They can be functionalized at will and are well known for their abilities to complex with alkali cations. Here, we show that emissive lanthanide free hybrid materials can be generated by using such building blocks. The organic tribenzo[18]crown-6 central core was functionalized via six-fold Suzuki cross-coupling as a key reaction with three o-terphenyl units which could be converted into their corresponding triphenylenes by the Scholl reaction, leading to novel liquid-crystalline columnar materials. Selected tribenzo[18]crown-6 o-terphenyls could interact with emissive ternary metal cluster compound salts to generate hybrid materials combining the properties of both moieties. Due to synergistic effects and despite the anisometry of the cluster compounds, individual properties such as liquid-crystalline phase stability of the organic part and emission abilities of its inorganic counter-part are enhanced in the hybrid compounds

New ultra-violet and near-infrared blocking filters for energy saving applications: fabrication of tantalum metal atom cluster-based nanocomposite thin films by electrophoretic deposition

International audienceThis study reports the first integration of inorganic tantalum octahedral metal atom clusters into multifunctional nanocomposite coating materials and devices for window technology and energy saving applications. [Ta6Br12i](n+) (n = 2, 3 or 4) cluster-based high visible transparency UV and NIR filters are realized. Green and brown colored films are fabricated by coating on an indium-doped tin oxide glass substrate by electrophoretic deposition, an industrialized solution process. The efficiency in energy saving of the new UV-NIR filters was estimated by the determination of different figure of merit (FOM) values, such as Tvis, Tsol and Tvis/Tsol (Tsol = solar transmittance and Tvis = visible transmittance), and the color coordinates (x, y, z and L*a*b). The Tvis/Tsol ratio is equal to 1.25 for the best films. Such values are evidence of a higher energy saving efficiency than most of the inorganic composites reported in the literature. These promising results pave the way for the use of transition metal clusters as a new class of nanocoatings in energy saving window-based applications

Joint Venture of Metal Cluster and Amphiphilic Cationic Minidendron Resulting in Near Infrared Emissive Lamellar Ionic Liquid Crystals

International audienceInorganic red-NIR emissive materials are particularly relevant in many fields like optoelectronic, bioimaging or solar cells. Benefiting from their emission in devices implies their integration in easy-to-handle materials like liquid crystals, whose long-range ordering and self-healing abilities could be exploited and influence emission. Herein, we present red-NIR emissive hybrid materials obtained with phosphorescent octahedral molybdenum cluster anions electrostatically associated with amphiphilic guanidinium minidendrons. Polarized optical microscopy and X-ray analysis show that while the minidendron chloride salts self-organize into columnar phases, their association with the dianionic metal cluster leads to layered phases. Steady-state and time-resolved emission investigations demonstrate the influence of the minidendron alkyl chain length on the phosphorescence of the metal cluster core

Electrophoretic Coating of Octahedral Molybdenum Metal Clusters for UV/NIR Light Screening

International audienceThin and transparent Mo-6 cluster films with significant optical properties were prepared on indium tin oxide (ITO)-coated glass plates from the suspension of Cs2Mo6Br14 cluster precursors dispersed in methyl-ethyl-ketone (MEK) by an electrophoretic deposition (EPD) process. Two kinds of polydimethylsiloxanes (PDMS); i.e., KF-96L-1.5CS and KF-96L-2CS corresponding to the kinetic viscosity of 1.5 and 2 centistokes, respectively, were selected to topcoat the Mo-6 cluster film after the EPD. The influence of the PDMS on the durability, chemical compatibility and light absorption property of Mo-6 cluster films were characterized by means of field-emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR), and ultraviolet-visible-near infrared (UV-Vis-NIR) spectroscopy. The stabilized PDMS-coated Mo-6 cluster film could be stored for more than 6 months under ambient conditions