The crystal structure of a new bismuth-based light-absorbing material for the application in solar cells was determined by single crystal X-ray diffraction for the first time. (CH3NH3)3(Bi2I9) (MBI) ...is a promising alternative to recently rapidly progressing hybrid organic-inorganic perovskites due to the higher tolerance against water and low toxicity. Single crystal X-ray diffraction provides detailed structural information as an essential prerequisite to gain a fundamental understanding of structure property relationships, while powder diffraction studies demonstrate a high degree of crystallinity in thin films.
Heterogenization of molecular catalysts via their immobilization within extended structures often results in a lowering of their catalytic properties due to a change in their coordination sphere. ...Metal–organic polyhedra (MOP) are an emerging class of well-defined hybrid compounds with a high number of accessible metal sites organized around an inner cavity, making them appealing candidates for catalytic applications. Here, we demonstrate a design strategy that enhances the catalytic properties of dirhodium paddlewheels heterogenized within MOP (Rh-MOP) and their three-dimensional assembled supramolecular structures, which proved to be very efficient catalysts for the selective photochemical reduction of carbon dioxide to formic acid. Surprisingly, the catalytic activity per Rh atom is higher in the supramolecular structures than in its molecular sub-unit Rh-MOP or in the Rh-metal–organic framework (Rh-MOF) and yields turnover frequencies of up to 60 h–1 and production rates of approx. 76 mmole formic acid per gram of the catalyst per hour, unprecedented in heterogeneous photocatalysis. The enhanced catalytic activity is investigated by X-ray photoelectron spectroscopy and electrochemical characterization, showing that self-assembly into supramolecular polymers increases the electron density on the active site, making the overall reaction thermodynamically more favorable. The catalyst can be recycled without loss of activity and with no change of its molecular structure as shown by pair distribution function analysis. These results demonstrate the high potential of MOP as catalysts for the photoreduction of CO2 and open a new perspective for the electronic design of discrete molecular architectures with accessible metal sites for the production of solar fuels.
Metal–organic frameworks (MOFs) are promising materials for gas‐separation and air‐filtration applications. However, for these applications, MOF crystallites need to be incorporated in robust and ...manageable support materials. We used chitin‐based networks from a marine sponge as a non‐toxic, biodegradable, and low‐weight support material for MOF deposition. The structural properties of the material favor predominant nucleation of the MOF crystallites at the inside of the hollow fibers. This composite has a hierarchical pore system with surface areas up to 800 m2 g−1 and pore volumes of 3.6 cm3 g−1, allowing good transport kinetics and a very high loading of the active material. Ammonia break‐through experiments highlight the accessibility of the MOF crystallites and the adsorption potential of the composite indicating their high potential for filtration applications for toxic industrial gases.
Sponge bag: A composite material is formed from a metal–organic framework (MOF) and a chitin biopolymeric network extracted from a marine sponge. The inner surface functionalities of the biomatrix cause the MOF HKUST‐1 (Cu3BTC2) to crystalize inside the hollow chitin fibers, resulting in a hierarchical pore system with a surface area of up to 800 m2 g−1. The composite shows a high affinity for toxic industrial gases such as NH3.
An earth‐abundant nickel(II) bipyridine catalyst, combined with lithium hexamethyldisilazide as base, demonstrates its wide applicability in the direct arylation polymerization of di‐ and ...tri‐thiophene heteroaryls with poly(hetero)aryl halides. With a nickel catalyst loading of 2.5 mol%, a series of twenty highly cross‐linked organic polymers is obtained in 34 to 99 % yields. Using mixed polytopic coupling partners allows obtaining alternating and optically active thiophene‐based solids with intrinsic porosity.
An earth‐abundant nickel(II) bipyridine catalyst allows the direct arylation polymerization of non‐activated (poly)thiophenes with (poly)aryl halides leading to a series of 20 highly reticulated, porous and alternating conjugated polymers with yields from 50 to 99 %.
The molecular‐level structuration of two full photosystems into conjugated porous organic polymers is reported. The strategy of heterogenization gives rise to photosystems which are still fully ...active after 4 days of continuous illumination. Those materials catalyze the carbon dioxide photoreduction driven by visible light to produce up to three grams of formate per gram of catalyst. The covalent tethering of the two active sites into a single framework is shown to play a key role in the visible light activation of the catalyst. The unprecedented long‐term efficiency arises from an optimal photoinduced electron transfer from the light harvesting moiety to the catalytic site as anticipated by quantum mechanical calculations and evidenced by in situ ultrafast time‐resolved spectroscopy.
Porous organic polymers were used as photosystems to deliver a constant production rate for the CO2 to formate reduction for several days. Their photoactivation pathway is presented, including an ultrafast electronic energy transfer from the photosensitizer to the catalyst as evidenced by time‐resolved spectroscopy and quantum mechanical calculations.
A highly efficient catalyst–base pair for the C–H arylation of free (NH)-indoles in the C-3 position is reported. Ligand-free palladium acetate coupled with lithium hexamethyldisilazide (LiHMDS) ...catalyzed the regiospecific, i.e. 100% regioselective, C-3 arylation of indoles with high turnover numbers. This catalytic system has been successfully applied to a wide range of substrates, including various functional aryl halides and indolic cores. The unique role of LiHMDS as both a base and unexpected transient directing group has been revealed experimentally and elucidated computationally, in line with a Heck-type insertion–elimination mechanism.
A molecular catalyst Cp*Rh(4,4′‐bpydc)2+ and a molecular photosensitizer Ru(bpy)2(4,4′‐bpydc)2+ (bpydc=bipyridinedicarboxylic acid) were co‐immobilized into the highly porous metal–organic framework ...MIL‐101‐NH2(Al) upon easy postsynthetic impregnation. The Rh–Ru@MIL‐101‐NH2 composite allows the reduction of CO2 under visible light, while exhibiting remarkable selectivity with the exclusive production of formate. This Rh–Ru@MIL‐101‐NH2 solid represents the first example of MOFs functionalized with both a catalyst and a photosensitizer in a noncovalent fashion. Thanks to the coconfinement of the catalyst and photosensitizer into the cavity's nanospace, the MOF pores are used as nanoreactors and enable molecular catalysis in a heterogeneous manner.
Fix in a hole: A molecular catalyst Cp*Rh(4,4′‐bpydc)2+ and a molecular photosensitizer Ru(bpy)2(4,4′‐bpydc)2+ (bpydc=bipyridinedicarboxylic acid) were co‐immobilized into the highly porous MIL‐101‐NH2(Al)material. The Rh–Ru@MIL‐101‐NH2 composite effects the reduction of CO2 under visible light while exhibiting remarkable selectivity with the exclusive production of formate.
We present a toolbox for the rapid characterisation of powdered samples of paramagnetic metal–organic frameworks at natural abundance by 1H‐detected solid‐state NMR. Very fast MAS rates at room and ...cryogenic temperatures and a set of tailored radiofrequency irradiation schemes help overcome the sensitivity and resolution limits often associated with the characterisation of MOF materials. We demonstrate the approach on DUT‐8(Ni), a framework containing Ni2+ paddle‐wheel units which can exist in two markedly different architectures. Resolved 1H and 13C resonances of organic linkers are detected and assigned in few hours with only 1–2 mg of sample at natural isotopic abundance, and used to rapidly extract information on structure and local internal dynamics of the assemblies, as well as to elucidate the metal electronic properties over an extended temperature range. The experiments disclose new possibilities for describing local and global structural changes and correlating them to electronic and magnetic properties of the assemblies.
Paramagnetic DUT‐8(Ni) metal–organic frameworks were characterised over an extended temperature range with 1H‐detected NMR techniques under fast magic‐angle spinning. The sensitivity of the approach allows rapid access to structure and dynamics of the organic linkers as well as the electronic properties of the metal centres in these materials.
Conductive polymers showing stretchable and transparent properties have received extensive attention due to their enormous potential in flexible electronic devices. Here, we demonstrate a facile and ...smart strategy for the preparation of structurally stretchable, electrically conductive, and optically semitransparent polyaniline-containing hybrid hydrogel networks as electrode, which show high-performances in supercapacitor application. Remarkably, the stability can extend up to 35 000 cycles at a high current density of 8 A/g, because of the combined structural advantages in terms of flexible polymer chains, highly interconnected pores, and excellent contact between the host and guest functional polymer phase.
The integration of catalytically active centers into a solid support without any loss of performance compared to the homogeneous analogue remains a major challenge. In this context, solid ...macroligands can be regarded as the key element to combine the advantages of homogeneous and heterogeneous catalysis. Porous materials such as periodic mesoporous organosilica, metal‐organic frameworks, porous organic polymers or covalent‐organic frameworks fulfill all requirements of a macroligand acting as a solid ligand of a molecular complex. They all can be tuned at the molecular scale to adapt the properties of the catalyst for a given application. This important feature also allows to directly compare different macroligands, regardless of their nature, and to choose the most appropriate for a target application.
Molecular catalysis: In the view of porous macroligands, microporous solids possibly being MOFs, COFs or POPs behave like molecular ligands. They all can be tuned at the molecular level to adapt the properties of the catalyst for a given application. This important feature also allows to choose the most appropriate porous macroligand for a target application
PDF
