Tuning the Microenvironment of Gold Nanoparticles Encapsulated within MIL-101(Cr) for the Selective Oxidation of Alcohols with O2 : Influence of the Amino Terephthalate Linker.

This manuscript reports a comparative study of the catalytic performance of gold nanoparticles (NPs) encapsulated within MIL-101(Cr) with or without amino groups in the terephthalate linker. The purpose is to show how the amino groups can influence the microenvironment and catalytic stability of incorporated gold nanoparticles. The first influence of the presence of this substituent is the smaller particle size of Au NPs hosted in MIL-101(Cr)-NH2 (2.45±0.19 nm) compared with the parent MIL-101(Cr)-H (3.02±0.39 nm). Both materials are highly active to promote the aerobic alcohol oxidation and exhibit a wide substrate scope. Although both catalysts can achieve turnover numbers as high as 106 for the solvent-free aerobic oxidation of benzyl alcohol, Au@MIL-101(Cr)-NH2 exhibits higher turnover frequency values (12 000 h-1 ) than Au@MIL-101(Cr)-H (6800 h-1 ). Au@MIL-101(Cr)-NH2 also exhibits higher catalytic stability, being recyclable for 20 times with coincident temporal conversion profiles, in comparison with some decay observed in the parent Au@MIL-101(Cr)-H. Characterization by transmission electron microscopy of the 20-times used samples shows a very minor particle size increase in the case of Au@MIL-101(Cr)-NH2 (2.97±0.27 nm) in comparison with the Au@MIL-101(Cr)-H analog (5.32±0.72 nm). The data presented show the potential of better control of the microenvironment to improve the performance of encapsulated Au nanoparticles.

Long-Term Photostability in Terephthalate Metal-Organic Frameworks.

Prolonged (weeks) UV/Vis irradiation under Ar of UiO-66(Zr), UiO66 Zr-NO2 , MIL101 Fe, MIL125 Ti-NH2 , MIL101 Cr and MIL101 Cr(Pt) shows that these MOFs undergo photodecarboxylation of benzenedicarboxylate (BDC) linker in a significant percentage depending on the structure and composition of the material. Routine characterization techniques such as XRD, UV/Vis spectroscopy and TGA fail to detect changes in the material, although porosity and surface area change upon irradiation of powders. In contrast to BCD-containing MOFs, zeolitic imidazolate ZIF-8 does not evolve CO2 or any other gas upon irradiation.

Double-Decker Silsesquioxanes Self-Assembled in One-Dimensional Coordination Polymeric Nanofibers with Emission Properties.

The urgent needs for photoactive materials in industry drive fast evolution of synthetic procedures in many branches of chemistry, including the chemistry of silsesquioxanes. Here, we disclose an effective protocol for the synthesis of novel double-decker silsesquioxanes decorated with two (styrylethynylphenyl)terpyridine moieties (DDSQ_Ta-b). The synthesis strategy involves a series of silylative and Sonogashira coupling reactions and is reported for the first time. DDSQ_Ta-b were employed as nanocage ligands to promote self-assembly in the presence of transition metals (TM), i.e., Zn2+, Fe2+, and Eu3+ ions, to form one-dimensional (1D) coordination polymeric nanofibers. Additionally, ultraviolet-promoted and reversible E-Z isomerization of the C═C bond within the ligand structures may be exploited to tune their emission properties. These findings render such complexes promising candidates for applications in materials chemistry. This is the first example of 1D coordination polymers bearing DDSQ-based nodes with TM ions.

Subphthalocyanine encapsulated within MIL-101(Cr)-NH2 as a solar light photoredox catalyst for dehalogenation of α-haloacetophenones.

Subphthalocyanine has been incorporated into a robust metal-organic framework having amino groups as binding sites. The resulting SubPc@MIL-101(Cr)-NH2 composite has a loading of 2 wt%. Adsorption of subphthalocyanine does not deteriorate host crystallinity, but decreases the surface area and porosity of MIL-101(Cr)-NH2. The resulting SubPc@MIL-101(Cr)-NH2 composite exhibits a 575 nm absorption band responsible for the observed photoredox catalytic activity under simulated sunlight irradiation for hydrogenative dehalogenation of α-haloacetophenones and for the coupling of α-bromoacetophenone and styrene. The material undergoes a slight deactivation upon reuse. In comparison to the case of phthalocyanines the present study is one of the few cases showing the use of subphthalocyanine as a photoredox catalyst, with its activity derived from site isolation within the MOF cavities.

A highly conductive nanostructured PEDOT polymer confined into the mesoporous MIL-100(Fe).

Despite the higher efficiency, larger color range and faster stimulus response of polymeric electrochromic materials, their poor cyclability strongly hampers their application in optoelectronics. As an original strategy to stabilize and further nanostructure these polymers, herein an efficient encapsulation and in situ polymerization inside highly porous metal-organic frameworks (MOFs) is reported. In particular, the successful accommodation of poly(3,4-ethylendioxythiophene) (PEDOT) and its partially oxidized polarons inside the mesopores of the nontoxic iron trimesate MIL-100(Fe) is convincingly proved by a large panel of experimental techniques. Remarkably, the polymer-MOF interaction occurring for entrapped PEDOT within the pores (deeply assessed by experimental and simulation methods) might be responsible for the enhanced electrical conductivity of the resulting PEDOT@MIL-100(Fe) composite when compared to the insulating MIL-100(Fe) and the conductive free PEDOT. Furthermore, it was possible to observe the electrochromic properties of the PEDOT@MIL-100(Fe) composite, achieving an improved stability and good cyclability as a consequence of the effective protection by the MOF matrix.

Cu(II)-Schiff base covalently anchored to MIL-125(Ti)-NH2 as heterogeneous catalyst for oxidation reactions.

MIL-125(Ti)-NH2 has been modified by reaction of salicylaldehyde with the terephthalate amino groups to form a salicylideneimine that act as ligand of Cu2+. The success of the postsynthetic modification was assessed by FTIR spectroscopy of the MIL-125(Ti)-NH2-Sal-Cu and by analysis by 1H NMR spectroscopy of the organic linkers upon dissolution of MIL-125(Ti)-NH2-Sal-Cu. In comparison with parent MIL-125(Ti)-NH2 and MIL-125(Ti)-NH2-Sal, that exhibit a poor activity, the presence of the Cu-Schiff base complex in MIL-125(Ti)-NH2-Sal-Cu catalyst for the oxidation of 1-phenylethanol by tert-butylhydroperoxyde (TBHP, 3 eq.) increases notably the catalytic activity. Hot filtration test and reusability experiments confirm that the process is heterogeneous and that MIL-125(Ti)-NH2-Sal-Cu is stable under the reaction conditions. Quenching studies and EPR spectra using N-tbutylphenylnitrone indicate the generation of tBuOO and tBuO under the reaction conditions. The scope of MIL-125(Ti)-NH2-Sal-Cu as oxidation catalyst by tBuOOH was studied for benzyl alcohol as well as alicyclic and aliphatic alcohols and ethylbenzene.

A highly stable and hierarchical tetrathiafulvalene-based metal-organic framework with improved performance as a solid catalyst.

Herein we report the synthesis of a tetrathiafulvalene (TTF)-based MOF, namely MUV-2, which shows a non-interpenetrated hierarchical crystal structure with mesoporous one-dimensional channels of ca. 3 nm and orthogonal microporous channels of ca. 1 nm. This highly stable MOF (aqueous solution with pH values ranging from 2 to 11 and different organic solvents), which possesses the well-known [Fe3(µ3-O)(COO)6] secondary building unit, has proven to be an efficient catalyst for the aerobic oxidation of dibenzothiophenes.

Adaptability of the metal(iii,iv) 1,2,3-trioxobenzene rod secondary building unit for the production of chemically stable and catalytically active MOFs.

The use of a 5,10,15,20-tetrakis(3,4,5-trihydroxyphenyl)porphyrin has yielded a new MOF based on M-1,2,3-trioxobenzene chains that can be made of M = Zr(iv) or RE(iii) (RE = rare earth), showing a very high and limited chemical stability, respectively. The robust metallated Zr-analogue, Co-MIL-173(Zr), has proven to be a heme-like heterogeneous catalyst suitable for aerobic oxidation of hydrocarbons.