Synthesis,Structure, Reactivity and Catalytic Implications of a Cationic,Acetylide-Bridged Trigold–JohnPhos Species

The cationic complex [(JohnPhos–Au)₃(acetylide)][SbF₆] (JohnPhos=(2-biphenyl)di-tert-butylphosphine, L1) has been characterised structurally and features an acetylide–trigold(I)–JohnPhos system; the trinuclear–acetylide unit, coordinated to the monodentate bulk phosphines, adopts an unprecedented μ,η¹,η²,η¹ coordination mode with an additional interaction between distal phenyl rings and gold centres. Other cationic σ,π-[(gold(I)L1)₂] complexes have also been isolated. The reaction of trimethylsilylacetylene with various alcohols (iPrOH, nBuOH, n-HexOH) catalysed by cationic [Au^IL1][SbF₆] complexes in CH₂Cl₂ at 50 °C led to the formation of acetaldehyde acetals with a high degree of chemo- and regioselectivity. The reaction mechanism was studied, and several organic and inorganic intermediates have been characterised. A comparative study with the analogous cationic [Cu^IL1][PF₆] complex revealed different behaviour; the copper metal is lost from the coordination sphere leading to the formation of cationic vinylphosphonium and copper nanoparticles. Additionally, a new catalytic approach for the formation of this high-value cationic vinylphosphonium has been established.     

Complexation and Fluorescence of Tricyclic Basic Dyes Encapsulated in Cucurbiturils

Tricyclic basic dyes (proflavine, acridine orange, pyronine, pyronine Y, oxonine, thionine and methylene blue) often form one‐to‐one or two‐to‐one complexes with CB[7] and CB[8], respectively. In the case of pyronine Y, the complexes with CB[7] and CB[8] have a one‐to‐one and three‐to‐one stoichiometry, respectively. The binding constants for CB[7] complexes range from 3.07×10⁶ to 1.70×10⁷ m ^?1. In the case of CB[8], the association constant varies between 3.24×10¹³ and 2.50×10¹⁶ m ^?2. Overall, these binding constants are four orders of magnitude higher than those reported for the same dyes in β and γ‐cyclodextrins. Formation of the host–guest complexes leads to an increase in the fluorescence quantum yields in the case of CB[7], while the dimeric or trimeric dye encapsulated in CB[8] are remarkably less fluorescent than the same dye in diluted solutions.     

A Colorimetric Sensor Array for the Detection of the Date‐Rape Drug γ‐Hydroxybutyric Acid (GHB): A Supramolecular Approach

γ‐Hydroxybutyric acid (GHB), a colourless, odourless and tasteless chemical, has become one of the most dangerous illicit drugs of abuse today. At low doses, this drug is a central nervous system depressant that reduces anxiety and produces euphoria and relaxation, sedating the recipient. There is an urgent need for simple, easy‐to‐use sensors for GHB in solution. Here, we present a colorimetric sensor array based on supramolecular host–guest complexes of fluorescent dyes with organic capsules (cucurbiturils) for the detection of GHB.     

Enhancement of the photocatalytic activity of TiO2 through spatial structuring and particle size control: from subnanometric to submillimetric length scale

This review summarizes the physical approaches towards enhancement of the photocatalytic activity of titanium dioxide by controlling this semiconductor in a certain length scale from subnanometric to submillimetric distances and provides examples in which the photocatalytic activity of TiO2 is not promoted by doping or changes in the chemical composition, but rather by application of physical concepts and spatial structuring of the semiconductor. Thus, encapsulation inside the micropores and cavities of zeolites (about 1 nm) renders small titanium oxide clusters with harnessed photocatalytic activity. On the other hand, nanometric titanium particles can be ordered forming structured periodic mesoporous materials with high specific surface area and well defined porosity. Titiania nanotubes of micrometric length, either independent or forming a membrane, also exhibit unique photocatalytic activity as consequence of the long diffusion length of charge carriers along the nanotube axis. Finally, photonic crystals with an inverse opal structure and the even more powerful concept of photonic sponges can serve to slow down visible light photons inside the material, increasing the effective optical path in such a way that light absorption near the absorption onset of the material is enhanced considerably. All these physical-based approaches have shown their potential in enhancing the photocatalytic activity of titania, paving the way for a new generation of novel structured photocatalysts in which physical and chemical concepts are combined.     

Single-step preparation and catalytic activity of mesoporous MCM-41 and SBA-15 silicas functionalized with perfluoroalkylsulfonic acid groups analogous to Nafion

Preparation of hybrid organic-inorganic MCM-41 and SBA-15 silicas functionalized with perfluoroalkylsulfonic acid groups has been achieved in a single step by reacting the mesoporous silicas with 1,2,2-trifluoro-2-hydroxy-1-trifluoromethylethane sulfonic acid beta-sultone; the catalysts showed higher activity than commercial Nafion-silica composite for the esterification of long chain fatty acids with ethanol.     

The effect of extra framework species on the intrinsic negative thermal expansion property of zeolites with the LTA topology

X-Ray powder diffraction studies have been used to measure the thermal expansion properties of three zeolites with the LTA topology and provide details of the underlying structural changes. Siliceous ITQ-29 and dehydrated and hydrated silver zeolite A have large negative, moderate negative and positive thermal expansion coefficients, respectively.     

Synthesis design and structure of a multipore zeolite with interconnected 12- and 10-MR channels

A new molecular sieve, ITQ-38, containing interconnected large and medium pores in its structure has been synthesized. The rational combination of dicationic piperidine-derivative molecules as organic structure directing agents (OSDAs) with germanium and boron atoms in alkaline media has allowed the synthesis of ITQ-38 zeolite. High-resolution transmission electron microscopy (HRTEM) has been used to elucidate the framework topology of ITQ-38, revealing the presence of domains of perfect ITQ-38 crystals as well as very small areas containing nanosized ITQ-38/ITQ-22 intergrowths. The structure of ITQ-38 is highly related to ITQ-22 and the recently described polymorph C of ITQ-39 zeolite. It shares a common building layer with ITQ-22 and contains the same building unit as the polymorph C of ITQ-39. All three structures present similar framework density, 16.1 T atoms/1000 ?(3).