The preparation of secondary phosphines in an easily implemented and safe way is a challenging task. Herein, we report on the suitability of phthalimide-substituted phosphines as starting materials for the photo-catalytic production of such secondary phosphines in the presence of an IrIII photocatalyst and sacrificial electron donors. While diarylphosphines could be prepared, dialiphatic phthalimide derivatives showed a fundamentally different reactivity. They were found to undergo rearrangement of the phthalimide group, followed by cleavage, to give oxides of the secondary phosphines. Although achieving high-yielding transformations remained a challenge, unexpected mechanistic insights into the fate of the one-electron-reduced phthalimidophosphines formed as intermediates could be obtained. This knowledge is valuable for developing future benign routes to secondary phosphines.

Abstract Electrochemical CO2 reduction (eCO2R) is a sustainable strategy for converting CO2 into value-added chemicals. Here, we report the Cu-azolate metal−organic framework (MOF) CuBBTA (Cu2Cl2-bbta, MAF-X29) as a stable electrocatalyst for eCO2R in a zero-gap electrolyzer. CuBBTA was spray-coated onto carbon paper using either PTFE or Nafion binders to form gas diffusion electrodes that achieved Faradaic efficiencies of up to 50% for carbon-containing products (CH4, C2H4, and CO) at current densities as high as 100 mA cm−2 under a flow of CO2. Post-electrolysis studies confirmed retention of the MOF structure. DFT calculations reveal that CO2 reduction proceeds via COOH* and CO* intermediates, with a thermodynamically favourable and kinetically accessible CO*−CO* dimerization pathway for ethylene formation. Importantly, polymer binder selection significantly influences product selectivity. While PTFE favours methane formation, Nafion shifts selectivity toward CO, highlighting the critical yet underexplored role of electrode environment in MOF-based eCO2R catalysis.

Unidirectional electron flow is essential for applications in electron storage and reconfigurable electronics, and traditionally realized in semiconductor junctions and even single-molecule concepts. Combining aspects from both technologies, redox-conductive metal-organic frameworks (RC-MOFs) exhibit molecule-like behavior in a crystalline, porous matrix. Herein, we show that bilayer RC-MOF electrodes composed of sequentially deposited Zn(PMDI) and Zn(NDI) on fluorine-doped tin oxide (FTO) function as chemical free-energy-based rectifying junctions. Unidirectional electron flow arises from thermodynamically allowed, and spatially organized redox reactions at the Zn(PMDI)|Zn(NDI) interface. Showcasing the rectifying function, electrons that reach the outer Zn(NDI) layer in the FTO|Zn(PMDI)|Zn(NDI) configuration are trapped as NDI•− and cannot be recovered by applying an oxidative bias. Introduction of [Co(bpy)3]3+ to the electrolyte creates a source–drain situation that reveals the potential-dependent directional electron flow across the bilayer. These results position RC-MOF bilayers as programmable electrochemical diodes, with rectification governed by layer sequence and redox accessibility.

Phosphines make up one of the largest classes of organophosphorus compounds, with applications in academic research and industry. Their preparation from phosphine oxides is mechanistically and thermodynamically highly challenging but opens the possibility for phosphorus recycling. We show that phosphine oxides can be converted into their corresponding phosphonium salts and subsequently reduced in a light-driven reaction to obtain the desired phosphines in 40-80% overall yields in a one-pot procedure. The reported methodology is free of exogenously added photocatalysts and utilizes the in situ formation of a photoactive donor-acceptor complex for light absorption and charge separation. Overall, the presented photochemical approach to reducing phosphonium salts that arise from phosphine oxides represents a valuable alternative to classical thermochemical methods for phosphorus recycling.

This paper investigates the friction and wear behavior of dry-running friction systems during the run-in process, focusing on the specific adaptation of the counter-friction disk. The influence of these factors on the run-in behavior is investigated by varying the material and the finishing process of the counter-friction disk. The materials steel C45 and cast iron GGG40 as well as the application of nitrocarburizing and phosphating represent varied parameters. The results show that an improvement in wear properties, performance and coefficient of friction stability can be achieved by optimizing the counter-friction disk. These findings make it possible to increase the efficiency of friction systems.

An unexplored strategy for controlled surface patterning with porphyrinic metal-organic frameworks (MOFs), integrating atomic layer deposition (ALD) and pseudomorphic replication (PMR), is presented. Surface patterning with a sub-micrometer size resolution is enabled by translating ALD-patterned Al2O3 into a MOF pattern in the presence of a porphyrinic linker.

The ongoing demand to power our society dictates the need for fossil-free fuels. Herein, the metal-organic framework (MOF) catalyst Al2(OH)2CoTCPP was grown as a thin film on a p-type silicon semiconductor (SC) for photoelectrochemical (PEC) fuel production. The MOF@Si composite catalyzes hydrogen production under illumination at an applied potential that is 320 mV more positive than that of the same MOF on a dark conducting substrate. An interesting feature of the study relates to the product speciation, as metalloporphyrins are known to catalyze both H2 evolution as well as CO2 reduction. In aqueous bicarbonate electrolyte and in the presence of CO2, hydrogen is detected as the sole product after chronoamperometry (CA). In fact, the MOF@Si composite catalyzed H2 evolution with a faradaic efficiency of close to 100%. The role of the MOF as a catalyst could be established by comparing the current response of the MOF@Si photoelectrode with that of bare silicon, with the former showing more than 30-fold higher currents. Comprehensive characterization of the Al2(OH)2CoTCPP@Si composites by scanning electron microscopy and X-ray photoelectron spectroscopy before and after PEC experiments confirms the stability of the MOF under the experimental conditions.

Surface modification is an effective method to realize high performance photoelectrodes. While current investigations mostly aim to leverage surface layers for improved charge carrier kinetics during charge separation, interfacial charge transfer, and decreased recombination, carrier transport within the surface layer is largely unattended. Herein, we explore this charge transport process on a model photocathode consisting of p-Si and GaP semiconductors (SCs) that are coated with a redox-active Zn-NDI (NDI = naphthalene diimide bis-pyrazolate) metal-organic framework (MOF) surface layer. The MOF layer is able to accept photogenerated electrons and support a large photovoltage of the underlying SC. In addition to well-established carrier generation and interfacial transfer processes that are frequently considered to control photocurrents, experimental photoelectrochemical data of the MOF@SC electrodes expose limitations that arise from electron transport in the surface layer coating. The transport-limited regime becomes relevant when the illumination intensity is gradually increased and is sensitive to the nature of the underlying semiconductor as well as the electrolyte. The phenomenon reported in this work is likely present in other surface-modified photoelectrodes with thick cocatalysts or redox-active polymer coatings but can easily be overlooked. In the MOF@SC construct, the transition between different limiting regimes can be visualized owing to the well-behaved cation-coupled photoelectron hopping transport in the MOF layer. These findings support the design and realization of efficient photoelectrodes.

Hemithioindigo (HTI) photoswitches exhibit robust photoisomerization under visible light and relatively high thermal bistability. In this work, we report various modifications of the HTI core, namely the introduction of aldehydes and carboxylic acids at the para position of the stilbene fragment with different oxidation states of the sulfur center, and the incorporation of a Schiff base moiety. These modifications allowed tuning of the absorption properties, quantum yields of isomerization, and thermal stability of the metastable E-isomers. Notably, the formyl- and carboxyl-substituted HTI switches achieved high yields of isomerization under visible light in various solvents, while sulfur oxidation enhanced quantum yields but reduced photochromism. Schiff base formation led to red-shifted absorption and increased thermal stability. Finally, by leveraging the carboxyl substituents, we incorporated an HTI chromophore into the NU-1000 metal-organic framework (MOF), and demonstrated solid-state photoisomerization. These findings highlight key structural modifications that expand the applicability of HTI photoswitches for molecular switching in solution and solid-state environments.

The synthesis of porphyrinic Al2(OH)2MTCPP (M = Co, Cu, Fe, Zn, H2; H2TCPP refers to 5,10,15,20-tetrakis(4carboxyphenyl)porphyrin) metal-organic framework (MOF) thin films is demonstrated. Combining atomic layer deposition (ALD) and pseudomorphic replication (PMR), such thin films were for the first time grown on metallic copper substrates and gas diffusion electrodes (GDEs). The PMR process transforms an ALD-applied metal oxide layer into a MOF thin film upon exposure to a metalloporphyrin linker. Reflecting substrate requirements, MOF thin films were synthesized via conventional solvothermal heating for copper substrates or microwave-assisted heating for GDEs, with the latter significantly reducing reaction times from days to minutes. Characterization by scanning electron microscopy and X-ray photoelectron spectroscopy confirmed the structural integrity and uniformity of the films. This work expands the arsenal of methods that are available for integrating MOF thin films into functional, in particular, porous electrode materials, paving the way for future advancements in catalysis and electrochemical applications.

Electrical conductivity through redox conducting MOFs (RCMOFs) proceeds by electron hopping between linkers of differing oxidation states. While this process is treated as a purely diffusional process in the literature, we show herein that this prevalent description is an oversimplification, and that emerging electric fields under applied potential result in electron and ion migration which are sizable contributors to charge transport through RCMOFs. This insight is obtained by electrochemical experiments that are conducted under steady-state conditions, which are created by the addition of an electron acceptor to the electrolyte solution, effectively creating a source-drain architecture of the electrode|RCMOF|electrolyte system. In contrast to transient potential-step experiments, such as chronoamperometry that are ubiquitous in the literature, the steady-state conditions in our experiments avoid net ingress or exit of charge balancing counter ions, allowing the assessment of electron diffusion with negligible counter ion flux. The strategy effectively isolates the diffusional response from ion diffusion-migration and electric field effects. Most importantly, it is shown that for transient experiments, the additional flux from migration, resulting from emerging electric fields after the potential step, leads to an overestimation of the experimentally determined apparent diffusion coefficients. The work described herein also demonstrates that the separate determination of electron and ion diffusion through RCMOFs is challenging with simplified models, as the two processes are connected through migration.

The postsynthetic metalation (PSM) of metal-organic frameworks (MOFs) with intrinsic metal binding sites is an intriguing strategy to introduce catalytic function into MOFs. The spatial distribution of the catalytic sites within the MOF crystal will affect the efficiency of the material, but the factors that govern depth distribution of the introduced metal sites are often not well understood. Herein, we employ Rutherford backscattering spectrometry (RBS) to investigate the metal distribution in a series of post-synthetically metalated mixed linker bpdc/BPY UiO-67 (UiO = Universitet i Oslo, bpdc = biphenyl-dicarboxylate, BPY = 2,2'-bipyridine-5,5'-dicarboxylate) single crystals as a function of linker ratio and metalation time. The RBS spectra reveal large differences in the depth distribution of inserted Ni2+ ions, and core/shell architectures are observed in high BPY materials at shorter incubation times. The incubation times to achieve uniform metal incorporation increases with increasing BPY ratios in the materials, suggesting that the presence of the BPY linkers slow down metal uptake. We propose a combination of ionic interactions and pore clogging, where coordinated ions reduce the available pore space for further ions to diffuse deeper into the framework as reasons for the observed trends. The observations are likely relevant for other mixed-linker MOF systems, and understanding the effect that linker ratios have on PSM and cation distribution will aid in future optimizations of catalytic MOFs.

Current methods for measuring electron-hopping diffusion coefficients of planar metal-organic framework (MOF) films typically use transient potential-step experiments, assuming a simple diffusional response. However, these experiments induce a net flux of counter ions, resulting in an electric field and transport by electromigration, which can impair the accuracy of the measurement. To remedy this, we employ an alternative method based on steady-state cyclic voltammetry. By adding a mobile redox acceptor molecule to the electrolyte, the additional cross reaction between the film and the acceptor mimics a source-drain electrode configuration, generating a steady state with negligible counter ion flux. Additionally, we construct a bespoke physical model and derive an analytical expression to correct the current response for any electric field effects. Overall, this method effectively isolates the diffusional response from ionic diffusion-migration and electric field effects. We expect these results will improve the accuracy of experimentally determined electron-hopping rates of electroactive MOF films.

We evaluate a method to quantify composition depth gradients in intact metal-organic framework (MOF) single crystals and thereby derive diffusion coefficients of post synthetically incorporated active sites by nondestructive ion-beam microanalysis. Zr-based UiO-67-bpy (bpy = 2,2 '-bipyridine-5,5 '-dicarboxylic acid) MOFs were synthesized on Si substrates and then metalated post synthetically with NiCl2 for 2-48 h, resulting in different Ni depth distributions. Simultaneous micro-Rutherford backscattering spectrometry (mu-RBS) and micro-particle induced X-ray emission (mu-PIXE) analysis were used for the spatially resolved chemical analysis of the MOF single crystals. Qualitative assessment of the mu-RBS spectra indicated the presence of elemental depth gradients and hinted at the governing process of the post synthetic Ni incorporation, in the present case, molecular diffusion. Quantitative evaluation of the resulting composition depth profiles directly provided the diffusion length and, thereby, the diffusion coefficient of the system. Virtual gradients caused by overhanging tips/edges of the truncated octahedral crystal shape are considered. Furthermore, in the case of insufficient probing depth for mu-RBS, mu-PIXE was still capable of providing qualitative information. In the present system the diffusion coefficient for NiCl2 is found to be (1.72 +/- 0.18) x 10(-16) m(2)s(-1). The long-term stability of the synthesized and post synthetically modified MOFs is proved by repeated measurements.

The [2+2] cycloaddition reaction between the Si=C double bond of adamantylsilene and the carbonyl group of aliphatic, aromatic or acetylenic ketones and aldehydes is demonstrated. The product of this reaction that is central to a non-ionic version of the Peterson olefination is an unusual four-membered 1,2-silaoxetane heterocycle that was characterized spectroscopically and crystallographically. In the presence of SiO2, the silaoxetane undergoes retro-cycloaddition with the formation of alkene products. As the [2+2] cycloaddition proceeds without the necessity of any base, enolizable ketones can be converted into olefins. In addition, it is shown that the adamantylsilene can be produced in situ by a sila-Peterson reaction, providing valuable input for the development of a new one-pot silicon-based reductive carbonyl-carbonyl cross coupling methodology.

ConspectusRedox-conductive metal-organic frameworks (RC-MOFs) are a class of porous materials that exhibit electrical conductivity through a chain of self-exchange reactions between molecularly defined, neighboring redox-active units of differing oxidation states. To maintain electroneutrality, this electron hopping transport is coupled to the translocation of charge balancing counterions. Owing to the molecular nature of the redox active components, RC-MOFs have received increasing attention for potential applications in energy storage, electrocatalysis, reconfigurable electronics, etc. While our understanding of fundamental aspects that govern electron hopping transport in RC-MOFs has improved during the past decade, certain fundamental aspects such as questions that arise from the coupling between electron hopping and diffusion migration of charge balancing counterions are still not fully understood.In this Account, we summarize and discuss our group's efforts to answer some of these fundamental questions while also demonstrating the applicability of RC-MOFs in energy-related applications. First, we introduce general design strategies for RC-MOFs, fundamentals that govern their charge transport properties, and experimental diagnostics that allow for their identification. Selected examples with redox-active organic linkers or metallo-linkers are discussed to demonstrate how the molecular characteristics of the redox-active units inside RC-MOFs are retained. Second, we summarize experimental techniques that can be used to characterize charge transport properties in a RC-MOF. The apparent electron diffusion coefficient, Deapp, that is frequently determined in the field and obtained in large perturbation, transient experiments will be discussed and related to redox conductivity, σ, that is obtained in a steady state setup. It will be shown that both MOF-intrinsic (topology, pore size, and apertures) and experimental (nature of electrolyte, solvent) factors can have noticeable impact on electrical conductivity through RC-MOFs. Lastly, we summarize our progress in utilizing RC-MOFs as electrochromic materials, materials for harvesting minority carriers from illuminated semiconductors and within electrocatalysis. In the latter case, recent work on multivariate RC-MOFs in which redox active linkers are used to "wire" redox catalysts in the crystal interiors will be presented, offering opportunities to independently optimize charge transport and catalytic function.The ambition of this Account is to inspire the design of new RC-MOF systems, to aid their identification, to provide mechanistic insights into the governing ion-coupled electron hopping transport mode of conductivity, and ultimately to promote their applications in existing and emerging areas. With basically unlimited possibilities of molecular engineering tools, together with research in both fundamental and applied fields, we believe that RC-MOFs will attract even more attention in the future to unlock their full potential.

The development of redox-conductive metal-organic frameworks (MOFs) and the fundamental understanding of charge propagation through these materials are central to their applications in energy storage, electronics, and catalysis. To answer some unresolved questions about diffusional electron hopping transport and redox conductivity, mixed-linker MOFs were constructed from two statistically distributed redox-active linkers, pyromellitic diimide bis-pyrazolate (PMDI) and naphthalene diimide bis-pyrazolate (NDI), and grown as crystalline thin films on conductive fluorine-doped tin oxide (FTO). Owing to the distinct redox properties of the linkers, four well-separated and reversible redox events are resolved by cyclic voltammetry, and the mixed-linker MOFs can exist in five discrete redox states. Each state is characterized by a unique spectroscopic signature, and the interconversions between the states can be followed spectroscopically under operando conditions. With the help of pulsed step-potential spectrochronoamperometry, two modes of electron propagation through the mixed-linker MOF are identified: diffusional electron hopping transport between linkers of the same type and a second channel that arises from thermodynamically driven electron transfers between linkers of different types. Corresponding to the four redox events of the mixed-linker MOFs, four distinct bell-shaped redox conductivity profiles are observed at a steady state. The magnitude of the maximum redox conductivity is evidenced to be dependent on the distance between redox hopping sites, analogous to the situation for apparent electron diffusion coefficients, Deapp, that are obtained in transient experiments. The design of mixed-linker redox-conductive MOFs and detailed studies of their charge transport properties present new opportunities for future applications of MOFs, in particular, within electrocatalysis.

Current methods for measuring electron-hopping diffusion coefficients of planar metal-organic framework (MOF) films typically use transient potential-step experiments, assuming a simple diffusional response. However, these experiments induce a net flux of counter ions, resulting in an electric field and transport by electromigration, which can impair the accuracy of the measurement. To remedy this, we employ an alternative method based on steady-state cyclic voltammetry. By adding a mobile redox acceptor molecule to the electrolyte, the additional cross reaction between the film and the acceptor mimics a source-drain electrode configuration, generating a steady state with negligible counter ion flux. Additionally, we construct a bespoke physical model and derive an analytical expression to correct the current response for any electric field effects. Overall, this method effectively isolates the diffusional response from ionic diffusion-migration and electric field effects. We expect these results will improve the accuracy of experimentally determined electron-hopping rates of electroactive MOF films.

With the Euro 7 norm, brake wear emissions are regulated. The authors present a new method to measure wear particles in dry-running friction systems by integrating a sampling system into a test bench. The friction system is enclosed, and particles are transported to a measuring station during braking. Initial results show particle concentration depends on friction material, operating conditions, and correlates with wear. This method improves understanding of emissions, enabling the development of low-emission friction systems, which can help reduce particulate emissions and minimize health risks.