Catalytic, Spectroscopic, and Theoretical Studies of FeS-Based Coordination Polymers as Heterogenous Coupled Proton-Electron Transfer Mediators for Electrocatalysis.

Iron-sulfur clusters play essential roles in biological systems, and thus synthetic [FeS] clusters have been an area of active research. Recent studies have demonstrated that soluble [FeS] clusters can serve as net H atom transfer mediators, improving the activity and selectivity of a homogeneous Mn CO reduction catalyst. Here, we demonstrate that incorporating these [FeS] clusters into a coordination polymer enables heterogeneous H atom transfer from an electrode surface to a Mn complex dissolved in solution.

Mechanism of Benzene Hydroxylation on Tri-Iron Oxo-Centered Cluster-Based Metal-Organic Frameworks.

High-valent Fe(IV)-oxo species derived upon reactions of NO with Fe(II) centers-embedded in the framework of tri-iron oxo-centered-based metal-organic frameworks (MOFs)- selectively affect the conversion of benzene-to-phenol via electrophilic addition to arene C-H bonds akin to oxygen transfer mechanisms in the P450 enzyme. The Fe(II) species identified by Mössbauer spectroscopy can be titrated in situ by the addition of NO to completely suppress benzene oxidation, verifying the relevance of Fe(II) centers. Observed inverse kinetic isotope effects in benzene hydroxylation preclude the involvement of H atom transfer steps from benzene to the Fe(IV)-oxo species and instead suggest that the electrophilic iron-oxo group adds to an sp carbon of benzene, resulting in a change in the hybridization from sp-to-sp.

Synthesis, Characterization, Fluorescence Properties, and DFT Modeling of Difluoroboron Biindolediketonates.

We report a simple and efficient strategy to enhance the fluorescence of biocompatible biindole diketonates (bdks) in the visible spectrum through difluoroboronation (BFbdks complexes). Emission spectroscopy testifies an increase in the fluorescence quantum yields from a few percent to as much as >0.7.

The role of carbon capture, utilization, and storage for economic pathways that limit global warming to below 1.5°C.

The 2021 Intergovernmental Panel on Climate Change (IPCC) report, for the first time, stated that CO removal will be necessary to meet our climate goals. However, there is a cost to accomplish CO removal or mitigation that varies by source. Accordingly, a sensible strategy to prevent climate change begins by mitigating emission sources requiring the least energy and capital investment per ton of CO, such as new emitters and long-term stationary sources.

Experimental and computational characterization of phase transitions in CsBH.

Metal hydroborates are versatile materials with interesting properties related to energy storage and cation conductivity. The hydrides containing BH (triborane, or octahydrotriborate) ions have been at the center of attention for some time as reversible intermediates in the decomposition of BH (3BH↔ BH + 2H), and as conducting media in electrolytes based on boron-hydride cage clusters. We report here the first observation of two phase transitions in CsBH prior to its decomposition above 230 °C.

Beyond Radical Rebound: Methane Oxidation to Methanol Catalyzed by Iron Species in Metal-Organic Framework Nodes.

Recent work has exploited the ability of metal-organic frameworks (MOFs) to isolate Fe sites that mimic the structures of sites in enzymes that catalyze selective oxidations at low temperatures, opening new pathways for the valorization of underutilized feedstocks such as methane. Questions remain as to whether the radical-rebound mechanism commonly invoked in enzymatic and homogeneous systems also applies in these rigid-framework materials, in which resisting the overoxidation of desired products is a major challenge. We demonstrate that MOFs bearing Fe(II) sites within Fe-μ-oxo nodes active for conversion of CH + NO mixtures (368-408 K) require steps beyond the radical-rebound mechanism to protect the desired CHOH product.

Thermal Treatment Effect on CO and NO Adsorption on Fe(II) and Fe(III) Species in FeO-Based MIL-Type Metal-Organic Frameworks: A Density Functional Theory Study.

The properties of metal-organic frameworks (MOFs) based on triiron oxo-centered (FeO) metal nodes are often related to the efficiency of the removal of the solvent molecules and the counteranion chemisorbed on the FeO unit by postsynthetic thermal treatment. Temperature, time, and the reaction environment play a significant role in modifying key features of the materials, that is, the number of open metal sites and the reduction of Fe(III) centers to Fe(II). IR spectroscopy allows the inspection of these postsynthetic modifications by using carbon monoxide (CO) and nitric oxide (NO) as probe molecules.

Negative cooperativity upon hydrogen bond-stabilized O adsorption in a redox-active metal-organic framework.

The design of stable adsorbents capable of selectively capturing dioxygen with a high reversible capacity is a crucial goal in functional materials development. Drawing inspiration from biological O carriers, we demonstrate that coupling metal-based electron transfer with secondary coordination sphere effects in the metal-organic framework Co(OH)(bbta) (Hbbta = 1H,5H-benzo(1,2-d:4,5-d')bistriazole) leads to strong and reversible adsorption of O. In particular, moderate-strength hydrogen bonding stabilizes a cobalt(III)-superoxo species formed upon O adsorption.

Structure, Dynamics, and Reactivity for Light Alkane Oxidation of Fe(II) Sites Situated in the Nodes of a Metal-Organic Framework.

Metal organic frameworks (MOFs), with their crystalline, porous structures, can be synthesized to incorporate a wide range of catalytically active metals in tailored surroundings. These materials have potential as catalysts for conversion of light alkanes, feedstocks available in large quantities from shale gas that are changing the economics of manufacturing commodity chemicals. Mononuclear high-spin ( = 2) Fe(II) sites situated in the nodes of the MOF MIL-100(Fe) convert propane via dehydrogenation, hydroxylation, and overoxidation pathways in reactions with the atomic oxidant NO.

On the structure of superbasic (MgO) sites solvated in a faujasite zeolite.

We report the synthesis and characterisation of a HY/MgO zeolite/oxide nanocomposite material with high crystallinity and highly dispersed, highly basic MgO sites. Preparation was optimized in order to preserve sample crystallinity, to avoid the formation of mesoporosity and to minimize the formation of separate Mg-containing phases. These features were checked by means of electron microscopy, X-ray powder diffraction, porosimetry and IR spectroscopy.

Time-resolved operando studies of carbon supported Pd nanoparticles under hydrogenation reactions by X-ray diffraction and absorption.

The formation of palladium hydride and carbide phases in palladium-based catalysts is a critical process that changes the catalytic performance and selectivity of the catalysts in important industrial reactions, such as the selective hydrogenation of alkynes or alkadienes. We present a comprehensive study of a 5 wt% carbon supported Pd nanoparticle (NP) catalyst in various environments by using in situ and operando X-ray absorption spectroscopy and diffraction, to determine the structure and evolution of palladium hydride and carbide phases, and their distribution throughout the NPs. We demonstrate how the simultaneous analysis of extended X-ray absorption fine structure (EXAFS) spectra and X-ray powder diffraction (XRPD) patterns allows discrimination between the inner "core" and outer "shell" regions of the NP during hydride phase formation at different temperatures and under different hydrogen pressures, indicating that the amount of hydrogen in the shell region of the NP is lower than that in the core.

Understanding and Controlling the Dielectric Response of Metal-Organic Frameworks.

Metal-organic framework (MOF) materials have recently been shown to have promising electronic and dielectric properties. This study involves investigating a diverse range of MOFs to rationalise how the different building blocks that form the structure can affect the electronic properties and dielectric response. The analysis, based on quantum mechanical calculations, includes the contribution from the metals involved, the organic linkers and the symmetry and topology of the framework and makes suggestions for future work on low-κ dielectric MOFs.

CO Capture in Dry and Wet Conditions in UTSA-16 Metal-Organic Framework.

Water is the strongest competitor to CO in the adsorption on microporous materials, affecting their performances as CO scrubbers in processes such as postcombustion carbon capture. The metal-organic framework (MOF) UTSA-16 is considered a promising material for its capacity to efficiently capture CO in large quantities, thanks to the presence of open metal sites (OMSs). It is here shown that UTSA-16 is also able to desorb fully water already at room temperature.

Solvent-Driven Gate Opening in MOF-76-Ce: Effect on CO2 Adsorption.

A cerium-based metal-organic framework with MOF-76 topology has been synthesized by a very simple and fast solvothermal method that has been tested for a one gram yield. Variable-temperature powder XRD and X-ray absorption data, analyzed by Rietveld and multiple-scattering extended X-ray absorption fine-structure methods, revealed high thermal stability and the presence of three different stable structures. X-ray absorption near-edge structure and FTIR spectroscopy probed the presence of cerium(III), which was characterized by coordinatively unsaturated sites that, however, played no major role in carbon dioxide adsorption.

New insights into UTSA-16.

Among the metal organic framework materials proposed for CO2 separation, UTSA-16 possesses the highest CO2 volumetric density explained on the basis of favourable interactions between CO2 and structural water molecules in the material, as revealed by neutron diffraction. In this study, UTSA-16 was synthesised and extensively characterised by XRD, TEM combined with EDX analysis and DR-UV-Vis, Raman and FTIR spectroscopies, as well as by TGA measurements. The synthesised material shows XRD patterns, surface area, CO2 capacity and isosteric heat coincident to the ones reported for UTSA-16 in the original papers but a higher thermal stability and a complete removal of water upon activation under mild conditions (363 K).

Carbon dioxide adsorption in amine-functionalized mixed-ligand metal-organic frameworks of UiO-66 topology.

A series of mixed-ligand [1,4-benzenedicarboxylic acid (BDC)/2-amino-1,4-benzenedicarboxylic acid (ABDC)] UiO-66 metal-organic frameworks (MOFs) synthesized through two different methods (low (LT) and high temperature (HT)) have been investigated for their carbon dioxide adsorption properties from 0 to 1 bar to clarify the role of amino loading on carbon dioxide uptake. Volumetric CO2 isotherms show that the CO2 capacity (normalized to the Langmuir surface area) increases with a degree of functionalization of about 46%; for similar NH2 contents, the same values are found for both synthetic procedures. Microcalorimetric isotherms reveal that amino-functionalized materials have a larger differential heat of adsorption (q(diff) ) towards CO2 ; reaching 27(25) and 20(22) kJ mol(-1) on HT(LT)-UiO-66-NH2 and UiO-66, respectively, at the lowest equilibrium pressures used in this study.

Fast carbon dioxide recycling by reaction with γ-Mg(BH4)2.

γ-Mg(BH4)2 was found to be a promising material for CO2 recycling (mainly to formate and alkoxide-like compounds). CO2 conversion occurs with unprecedented fast kinetics at 30 °C and 1 bar. A multi-technique approach allowed to attribute the superior performance of γ-Mg(BH4)2 to its large specific surface area.

Silica-supported Ti chloride tetrahydrofuranates, precursors of Ziegler-Natta catalysts.

The structural and electronic properties of silica-supported titanium chloride tetrahydrofuranates samples, obtained by impregnating a polymer-grade dehydroxylated silica with TiCl4(thf)2 and TiCl3(thf)3 complexes, precursors of Ziegler-Natta catalysts, are investigated by means of FT-IR, XAS, XES and diffuse reflectance UV-Vis spectroscopy, coupled with DFT calculations. The properties of the two silica-supported samples are very similar, irrespective of the starting precursor. In both cases, most of the chlorine ligands originally surrounding the Ti sites are substituted by oxygen ligands upon grafting on silica.

Monolithic aerogels based on poly(2,6-diphenyl-1,4-phenylene oxide) and syndiotactic polystyrene.

Molecular sorption behavior of amorphous and semicrystalline samples based on poly(2,6-diphenyl-1,4-phenylene oxide) (PPPO) has been compared. Fully amorphous PPPO powders, as obtained by supercritical carbon dioxide (scCO2) extraction of concentrated solutions, present uptake of pollutants much higher than for commercial sorbent materials based on semicrystalline PPPO (Tenax TA). Robust monolithic aerogels with good handling characteristics can be easily obtained by solvent extraction by scCO2 from gels including PPPO blends with syndiotactic polystyrene (s-PS).

An alternative pathway for the synthesis of isocyanato- and urea-functionalised metal-organic frameworks.

We have developed a generic two-step post-functionalisation technique for transforming amino-functionalised MOFs into their isocyanate analogues. The first part of the synthetic pathway consists in the conversion of the amino moieties into azido groups. Next, the thermal activation of these azido groups leads to nitrene species that can react with carbon monoxide to yield the desired products.

Soft synthesis of isocyanate-functionalised metal-organic frameworks.

We have developed an original synthetic pathway for the conversion of a MIL-68(In)-NH(2) metal-organic framework into its corresponding isocyanate (-NCO) derivative. This two-step soft post-modification technique leads to highly porous isostructural materials.

Low temperature activation and reactivity of CO2 over a Cr(II)-based heterogeneous catalyst: a spectroscopic study.

A new heterogeneous catalyst for CO(2) activation was identified in the Cr(II)/SiO(2) Phillips catalyst, one of the most important catalysts used industrially for olefin polymerization. Interestingly, it was found that Cr(II)/SiO(2) strongly activates CO(2) already at room temperature, making it available for chemicals synthesis. A preliminary attempt in this direction was done by following the reaction of CO(2) with ethylene oxide at room temperature by means of FT-IR spectroscopy, which showed the formation of ethylene carbonate.

Spectroscopic and adsorptive studies of a thermally robust pyrazolato-based PCP.

The pyrazolato-based PCP [Ni(8)(μ(4)-OH)(4)(μ(4)-OH(2))(2)(μ(4)-PBP)(6)] (NiPBP, H(2)PBP = 4,4'-bis(1H-pyrazol-4-yl)biphenyl), whose 3-D architecture is built upon octametallic hydroxo clusters reciprocally connected by organic spacers, is a very promising candidate for gas adsorption applications, owing to its remarkable thermal stability (up to 400 °C in air) and its high void volume (70%). As such, NiPBP was selected as a proof-of-concept material to demonstrate how an optimized set of solid state techniques can concur to create a comprehensive and coherent picture, relating (average and local) structural features to adsorptive properties. To this aim, the response of NiPBP toward different gases, retrieved by gas adsorption measurements (N(2) at 77 K, in the low pressure region; H(2) at 77 K, in the high pressure region), was explained in terms of local-level details, as emerged by coupling electronic, X-ray (absorption and emission), and variable temperature IR spectroscopy.

H2 storage in isostructural UiO-67 and UiO-66 MOFs.

The recently discovered UiO-66/67/68 class of isostructural metallorganic frameworks (MOFs) [J. H. Cavka et al.