Insights into the electrochemical behaviour of composite materials: Monovacant polyoxometalates @ porous metal-organic framework

Two POM-based compounds containing Zn-capped Keggin anions as decent heterogeneous catalysts for sulfur oxidation and cycloaddition of CO2 reactions

Carbon dioxide (CO2) and the combustion of sulfide in gasoline are the main causes of air pollution. Great deal of attention has been committed to solving the problem and the...

Heterogenisation of polyoxometalates and other metal-based complexes in metal–organic frameworks: from synthesis to characterisation and applications in catalysis

This review provides a thorough overview of composites with molecular catalysts (polyoxometalates, or organometallic or coordination complexes) immobilised into MOFs via non-covalent interactions.

An Effective Hybrid Heterogeneous Catalyst to Desulfurize Diesel: Peroxotungstate@Metal-Organic Framework

A peroxotungstate composite comprising the chromium terephthalate metal–organic framework MIL-101(Cr) and the Venturello peroxotungstate [PO₄{WO(O₂)₂}₄]³⁻ (PW₄) has been prepared by the impregnation method. The PW₄@MIL-101(Cr) composite presents high catalytic efficiency for oxidative desulfurization of a multicomponent model diesel containing the most refractory sulfur compounds present in real fuels (2000 ppm of total S). The catalytic performance of this heterogeneous catalyst is similar to the corresponding homogeneous PW₄ active center. Desulfurization efficiency of 99.7% was achieved after only 40 min at 70 °C using H₂O₂ as an oxidant and an ionic liquid as an extraction solvent ([BMIM]PF₆, 2:1 model diesel/[BMIM]PF₆). High recycling and reusing capacity was also found for PW₄@MIL-101(Cr), maintaining its activity for consecutive oxidative desulfurization cycles. A comparison of the catalytic performance of this peroxotungstate composite with others previously reported tungstate@MIL-101(Cr) catalysts indicates that the presence of active oxygen atoms from the peroxo groups promotes a higher oxidative catalytic efficiency in a shorter reaction time.

Single-Molecule Magnet Behavior of Individual Polyoxometalate Molecules Incorporated within Biopolymer or Metal-Organic Framework Matrices

The chemically and structurally highly stable polyoxometalate (POM) single-molecule magnet (SMM) [(FeW9 O34 )2 Fe4 (H2 O)2 ](10-) (Fe6 W18 ) has been incorporated by direct or post-synthetic approaches into a biopolymer gelatin (Gel) matrix and two crystalline metal-organic frameworks (MOFs), including one diamagnetic (UiO-67) and one magnetic (MIL-101(Cr)). Integrity of the POM in the Fe6 W18 @Gel, Fe6 W18 @UiO-67 and Fe6 W18 @MIL-101(Cr) composites was confirmed by a set of complementary techniques. Magnetic studies indicate that the POMs are magnetically well isolated. Remarkably, in Fe6 W18 @Gel, the SMM properties of the embedded molecules are close to those of the crystals, with clear quantum tunneling steps in the hysteresis loops. For the Fe6 W18 @UiO-67 composite, the molecules retain their SMM properties, the energy barrier being slightly reduced in comparison to the crystalline material and the molecules exhibiting a tunneling rate of magnetization significantly faster than for Fe6 W18 @Gel. When Fe6 W18 is introduced into MIL-101(Cr), the width of the hysteresis loops is drastically reduced and the quantum tunneling steps are smeared out because of the magnetic interactions between the antiferromagnetic matrix and the SMM guest molecules.

Immobilization of polyoxometalates in the Zr-based metal organic framework UiO-67

We report the successful synthesis of several POM@UiO-67 composites and their characterization by a panel of complementary techniques.

Immobilization of Co-containing polyoxometalates in MIL-101(Cr): structural integrity versus chemical transformation

Complementary techniques evidenced the integrity or the evolution of polyoxometalates inside the nanocages of the metal organic framework MIL-101(Cr).

Recent advances in porous polyoxometalate-based metal–organic framework materials

POM-based MOF materials, which combine the advantages of both POMs and MOFs, have received increasing attention. In this review, we present the recent developments in porous POM-based MOF materials for the first time, including their classification, synthesis strategies and applications, especially in the field of catalysis.

Novel composite material polyoxovanadate@MIL-101(Cr): a highly efficient electrocatalyst for ascorbic acid oxidation

A novel hybrid composite material, PMo10V2@MIL-101 was prepared by the encapsulation of the tetra-butylammonium (TBA) salt of the vanadium-substituted phosphomolybdate [PMo10V2O40](5-) (PMo10V2) into the porous metal-organic framework (MOF) MIL-101(Cr). The materials characterization by powder X-ray diffraction, Fourier transform infrared spectra and scanning electron microscopy confirmed the preparation of the composite material without disruption of the MOF porous structure. Pyrolytic graphite electrodes modified with the original components (MIL-101(Cr), PMo10V2), and the composite material PMo10V2@MIL-101 were prepared and their electrochemical responses were studied by cyclic voltammetry. Surface confined redox processes were observed for all the immobilized materials. MIL-101(Cr) showed one-electron reduction process due to chromium centers (Cr(III) → Cr(II)), while PMo10V2 presented five reduction processes: the peak at more positive potentials is attributed to two superimposed 1-electron vanadium reduction processes (V(V) → V(IV)) and the other four peaks to Mo-centred two-electron reduction processes (Mo(VI) → Mo(V)). The electrochemical behavior of the composite material PMo10V2@MIL-101 showed both MIL-101(Cr) and PMo10V2 redox features, although with the splitting of the two vanadium processes and the shift of the Mo- and Cr- centered processes to more negative potentials. Finally, PMo10V2@MIL-101 modified electrode showed outstanding enhanced vanadium-based electrocatalytic properties towards ascorbic acid oxidation, in comparison with the free PMo10V2, as a result of its immobilization into the porous structure of the MOF. Furthermore, PMo10V2@MIL-101 modified electrode showed successful simultaneous detection of ascorbic acid and dopamine.

Ruthenium(II) tris(2,2'-bipyridine)-templated zinc(II) 1,3,5-tris(4-carboxyphenyl)benzene metal organic frameworks: structural characterization and photophysical properties

The ability to confine photoactive catalysts within metal organic framework (MOF) materials affords the opportunity to expand the functional diversity of these materials into solar-based applications. Here, two new Ru(II) tris(2,2'-bipyridine) (RuBpy)-based photoactive materials derived from reactions between Zn(II) ions and 1,3,5-tris(4-carboxyphenyl)benzene and templated by the presence of RuBpy (RWLC-1 and RWLC-2) are described with regard to structure and RuBpy photophysics. RuBpy cations have been successfully encapsulated within the cavities (RWLC-1) and channels (RWLC-2) of the new negatively charged frameworks, both of which are synthesized simultaneously in a single reaction vial. Single-crystal X-ray diffraction studies allowed for determination of the RuBpy position within crystal voids. RuBpy encapsulated in each of the two new MOFs exhibits biphasic triplet metal to ligand charge transfer ((3)MLCT) emission decay lifetimes (τRWLC-1-fast = 237 ns, τRWLC-1-slow = 1.60 μs, τRWLC-2-fast = 171 ns, and τRWLC-2-slow = 797 ns at 25 °C) consistent with two populations of RuBpy complexes, one being encapsulated in highly space-restricted cavities giving rise to a longer (3)MLCT lifetime, while the second is encapsulation within a larger nonperiodic pore or defect with a coencapsulated quencher giving rise to short emission lifetimes. Taken together, these results represent examples of the templating ability of RuBpy to produce novel materials with distinct photophysical environments of the encapsulated guests.