Search

Metalloporphyrin-containing mesoporous materials, named VTPP@SBA, were prepared via a simple anchoring of vanadyl porphyrin (5,10,15,20-Tetraphenyl-21H,23H-porphine vanadium(IV) oxide) through a SBA-15-type mesoporous material. For comparison, vanadyl porphyrin was also impregnated on SiO2 (VTPP/SiO2). The characterization results of catalysts by XRD, FTIR, DR-UV-vis, and EPR confirm the incorporation of vanadyl porphyrin within the mesoporous SBA-15. These catalysts have also been studied using electrochemical and photoelectrochemical methods. Impedance measurements confirmed that supporting the porphyrin in silica improved the electrical conductivity of samples. In fact, when using mesoporous silica, current densities associated with oxidation/reduction processes appreciably increased, implying an enhancement in charge transfer processes and, therefore, in electrochemical performance. All samples presented n-type semiconductivity and provided an interesting photoelectrocatalytic response upon illumination, especially silica-supported porphyrins. This is the first time that V-porphyrin-derived materials have been tested for photoelectrochemical applications, showing good potential for this use. [ABSTRACT FROM AUTHOR]

Extremely high electrophilic metal complexes, composed by a metal cation and very electron poor σ‐donor ancillary ligands, are expected to be privileged catalysts for oxidation reactions in organic chemistry. However, their low lifetime prevents any use in catalysis. Here we show the synthesis of fluorinated pyridine‐Pd2+ coordinate cages within the channels of an anionic tridimensional metal‐organic framework (MOF), and their use as efficient metal catalysts for the aerobic oxidation of aliphatic alcohols to carboxylic acids without any additive. Mechanistic studies strongly support that the MOF‐stabilized coordination cage with perfluorinated ligands unleashes the full electrophilic potential of Pd2+ to dehydrogenate primary alcohols, without any base, and also to activate O2 for the radical oxidation to the aldehyde intermediate. This study opens the door to design catalytic perfluorinated complexes for challenging organic transformations, where an extremely high electrophilic metal site is required. [ABSTRACT FROM AUTHOR]

Expanding the previously known family of ‐onium (ammonium, phosphonium, and sulfonium) organic structure‐directing agents (OSDAs) for the synthesis of zeolite MFI, a new member, the arsonium cation, is used for the first time. The new group of tetraalkylarsonium cations has allowed the synthesis of the zeolite ZSM‐5 with several different chemical compositions, opening a route for the synthesis of zeolites with a new series of OSDA. Moreover, the use of As replacing N in the OSDA allows the introduction of probe atoms that facilitate the study of these molecules by powder X‐ray diffraction (PXRD), solid‐state nuclear magnetic resonance (MAS NMR), and X‐ray absorption spectroscopy (XAS). Finally, the influence of trivalent elements such as B, Al, or Ga isomorphically replacing Si atoms in the framework structure and its interaction with the As species has been studied. The suitability of the tetraalkylarsonium cation for carrying out the crystallization of zeolites is demonstrated along with the benefit of the presence of As atoms in the occluded OSDA, which allows its advanced characterization as well as the study of its evolution during OSDA removal by thermal treatments. [ABSTRACT FROM AUTHOR]

Abstract: The gram‐scale synthesis, stabilization, and characterization of well‐defined ultrasmall subnanometric catalytic clusters on solids is a challenge. The chemical synthesis and X‐ray snapshots of Pt02 clusters, homogenously distributed and densely packaged within the channels of a metal–organic framework, is presented. This hybrid material catalyzes efficiently, and even more importantly from an economic and environmental viewpoint, at low temperature (25 to 140 °C), energetically costly industrial reactions in the gas phase such as HCN production, CO2 methanation, and alkene hydrogenations. These results open the way for the design of precisely defined catalytically active ultrasmall metal clusters in solids for technically easier, cheaper, and dramatically less‐dangerous industrial reactions. [ABSTRACT FROM AUTHOR]

We describe the synthesis, characterization and application as contrast agents in magnetic resonance imaging of a novel type of magnetic nanoparticle based on Gd-Si oxide, which presents high Gd3+ atom density. For this purpose, we have used a Prussian Blue analogue as the sacrificial template by reacting with soluble silicate, obtaining particles with nanorod morphology and of small size (75 nm). These nanoparticles present good biocompatibility and higher longitudinal and transversal relaxivity values than commercial Gd3+ solutions, which significantly improves the sensitivity of in vivo magnetic resonance images. [ABSTRACT FROM AUTHOR]

A novel approach to the synthesis of Gd–Si oxide mesoporous nanoparticles with a high Gd3+ atom density and pre-formed morphology is presented. Prussian blue analogue Gd(H2O)4[Fe(CN)6], a metal organic framework that crystallizes in the orthorhombic system, is used for the first time as a sacrificial template by a reaction with soluble silicate. Simultaneous and stoichiometric condensation of gadolinium hydroxide and silica takes place, leading to dense and monodispersed nanoparticles that preserve the original shape and size of the Prussian blue analogue crystals. Then, porosity is developed by incorporation of cetyltrimethylammonium bromide under hydrothermal conditions. The obtained Gd–Si mesoporous oxide particles present a dual morphology of nanocrosses and nanorods and large surface areas. [ABSTRACT FROM AUTHOR]

The Stille coupling can be carried out in a batch process using insoluble tin supports. The new type of support consists of stannylated polymers based on the vinylic polynorbornene skeleton that allow one to use a set-up where the tin reagent is immobilized in a column. The immobilized stannylated polymeric reagent can be easily reused. The coupling products are thus obtained by a very simple work-up procedure and have very low levels of tin contamination. [ABSTRACT FROM AUTHOR]

Theoretical calculations and in situsolid state NMR spectroscopy have been combined to get insight on the nature of the active sites for the Beckmann rearrangement reaction in borosilicate zeolites. The interaction of a B site in zeolite Beta with a series of probe molecules (ammonia, pyridine, acetone and water) has been modelled and the 15N and 11B NMR isotropic chemical shift of the resulting complexes calculated and compared with experimental in situNMR results. This approach has allowed validation of the methodology to model the adsorption on a zeolite boron site of molecules of varying basicity which are either protonated or non-protonated. The limitation is that theoretical calculations overestimate the effect of molecular adsorption through hydrogen bonds on the calculated isotropic 11B NMR chemical shift.Theoretical and experimental results on the adsorption of acetophenone and cyclohexanone oximes on zeolite B-Beta indicate that Brønsted acid sites protonate the oximes, changing the boron coordination from trigonal to tetrahedral. Comparison of theoretical and experimental 15N NMR chemical shifts of the adsorbed amides (acetanilide and -caprolactam) indicates that they are non-protonated, and the 11B NMR spectra show that, as expected, boron remains in trigonal coordination with an isotropic δ 11Bexpwhich differs from the calculated value δ 11Bcalc. [ABSTRACT FROM AUTHOR]

In this study, we present the synthesis, characterization, and structural analysis of a novel zeolite, ITQ‐70, using 3D electron diffraction. This unique material was synthesized under alkaline conditions, employing tetrakis(diethylamino)phosphonium as an organic structure‐directing agent, leading to the formation of a pure silica zeolite. ITQ‐70 is distinguished by its extra‐large pore apertures, which extend along all three axes and intersect one to the other. A notable feature of this zeolite is the presence of structurally ordered defects in very high concentrations (38 % of the silicon atoms). As a result, ITQ‐70 exhibits the lowest framework density (10.0 T/1000 Å3) ever reported for any zeolite except RWY (7.6 T/1000 Å3), which contains sulfur instead of oxygen connecting T‐atoms. [ABSTRACT FROM AUTHOR]

The combination of well-defined Fe 3+ isolated single-metal atoms and Ag 2 subnanometer metal clusters within the channels of a metal-organic framework (MOF) is reported and characterized by single-crystal X-ray diffraction for the first time. The resulting hybrid material, with the formula [Ag 0 2 (Ag 0 ) 1.34 Fe III 0.66 ]@Na I 2 {Ni II 4 [Cu II 2 (Me 3 mpba) 2 ] 3 }·63H 2 O ( Fe 3+ Ag 0 2 @MOF ), is capable of catalyzing the unprecedented direct conversion of styrene to phenylacetylene in one pot. In particular, Fe 3+ Ag 0 2 @MOF ─which can easily be obtained in a gram scale─exhibits superior catalytic activity for the TEMPO-free oxidative cross-coupling of styrenes with phenyl sulfone to give vinyl sulfones in yields up to >99%, which are ultimately transformed, in situ, to the corresponding phenylacetylene product. The results presented here constitute a paradigmatic example of how the synthesis of different metal species in well-defined solid catalysts, combined with speciation of the true metal catalyst of an organic reaction in solution, allows the design of a new challenging reaction.

The development of contrast agents (CAs) for Magnetic Resonance Imaging (MRI) with T1-T2 dual-mode relaxivity requires the accurate assembly of T1 and T2 magnetic centers in a single structure. In this context, we have synthesized a novel hybrid material by monitoring the formation of Prussian Blue analogue Gd(H2O)4[Fe(CN)6] nanoparticles with tailored shape (from nanocrosses to nanorods) and size, and further protection with a thin and homogeneous silica coating through hydrolysis and polymerization of silicate at neutral pH. The resulting Gd(H2O)4[Fe(CN)6]@SiO2 magnetic nanoparticles are very stable in biological fluids. Interestingly, this combination of Gd and Fe magnetic centers closely packed in the crystalline network promotes a magnetic synergistic effect, which results in significant improvement of longitudinal relaxivity with regards to soluble Gd3+ chelates, whilst keeping the high transversal relaxivity inherent to the iron component. As a consequence, this material shows excellent activity as MRI CA, improving positive and negative contrasts in T1- and T2-weighted MR images, both in in vitro (e.g., phantom) and in vivo (e.g., Sprague-Dawley rats) models. In addition, this hybrid shows a high biosafety profile and has strong ability to incorporate organic molecules on the surface with variable functionality, displaying great potential for further clinical application.