The exact chemical structure of non-crystallising natural products is still one of the main challenges in Natural Sciences. Despite tremendous advances in total synthesis, the absolute structural ...determination of a myriad of natural products with very sensitive chemical functionalities remains undone. Here, we show that a metal-organic framework (MOF) with alcohol-containing arms and adsorbed water, enables selective hydrolysis of glycosyl bonds, supramolecular order with the so-formed chiral fragments and absolute determination of the organic structure by single-crystal X-ray crystallography in a single operation. This combined strategy based on a biomimetic, cheap, robust and multigram available solid catalyst opens the door to determine the absolute configuration of ketal compounds regardless degradation sensitiveness, and also to design extremely-mild metal-free solid-catalysed processes without formal acid protons.
A novel chiral 3D bioMOF exhibiting functional channels with thio-alkyl chains derived from the natural amino acid l-methionine (1) has been rationally prepared. The well-known strong affinity of ...gold for sulfur derivatives, together with the extremely high flexibility of the thioether “arms” decorating the channels, account for a selective capture of gold(III) and gold(I) salts in the presence of other metal cations typically found in electronic wastes. The X-ray single-crystal structures of the different gold adsorbates Au III @1 and Au I @1 suggest that the selective metal capture occurs in a metal ion recognition process somehow mimicking what happens in biological systems and protein receptors. Both Au III @1 and Au I @1 display high activity as heterogeneous catalyst for the hydroalkoxylation of alkynes, further expanding the application of these novel hybrid materials.
Metal single-atom catalysts (SACs) promise great rewards in terms of metal atom efficiency. However, the requirement of particular conditions and supports for their synthesis, together with the need ...of solvents and additives for catalytic implementation, often precludes their use under industrially viable conditions. Here, we show that palladium single atoms are spontaneously formed after dissolving tiny amounts of palladium salts in neat benzyl alcohols, to catalyze their direct aerobic oxidation to benzoic acids without ligands, additives, or solvents. With this result in hand, the gram-scale preparation and stabilization of Pd SACs within the functional channels of a novel methyl-cysteine-based metal–organic framework (MOF) was accomplished, to give a robust and crystalline solid catalyst fully characterized with the help of single-crystal X-ray diffraction (SCXRD). These results illustrate the advantages of metal speciation in ligand-free homogeneous organic reactions and the translation into solid catalysts for potential industrial implementation.
The search for simple, earth-abundant, cheap, and nontoxic metal catalysts able to perform industrial hydrogenations is a topic of interest, transversal to many catalytic processes. Here, we show ...that isolated FeIII–O sites on solids are able to dissociate and chemoselectively transfer H2 to acetylene in an industrial process. For that, a novel, robust, and highly crystalline metal–organic framework (MOF), embedding FeIII–OH2 single sites within its pores, was prepared in multigram scale and used as an efficient catalyst for the hydrogenation of 1% acetylene in ethylene streams under front-end conditions. Cutting-edge X-ray crystallography allowed the resolution of the crystal structure and snapshotted the single-atom nature of the catalytic FeIII–O site. Translation of the active site concept to even more robust and inexpensive titania and zirconia supports enabled the industrially relevant hydrogenation of acetylene with similar activity to the Pd-catalyzed process.
Ferroelectrics (FEs) are materials of paramount importance with a wide diversity of applications. Herein, we propose a postsynthetic methodology for the smart implementation of ferroelectricity in ...chiral metal−organic frameworks (MOFs): following a single-crystal to single-crystal cation metathesis, the Ca2+ counterions of a preformed chiral MOF of formula Ca6 II{CuII 24(S,S)-hismox12(OH2)3}·212H2O (1), where hismox is a chiral ligand derived from the natural amino acid l-histidine, are replaced by CH3NH3 +. The resulting compound, (CH3NH3)12{CuII 24(S,S)-hismox12(OH2)3}·178H2O (2), retains the polar space group of 1 and is ferroelectric below 260 K. These results open a new synthetic avenue to enlarge the limited number of FE MOFs.
The use of the FeIII(AA)(CN)4− complex anion as metalloligand towards the preformed CuII(valpn)LnIII3+ or NiII(valpn)LnIII3+ heterometallic complex cations (AA=2,2′‐bipyridine (bipy) and ...1,10‐phenathroline (phen); H2valpn=1,3‐propanediyl‐bis(2‐iminomethylene‐6‐methoxyphenol)) allowed the preparation of two families of heterotrimetallic complexes: three isostructural 1D coordination polymers of general formula {CuII(valpn)LnIII(H2O)3(μ‐NC)2FeIII(phen)(CN)2 {(μ‐NC)FeIII(phen)(CN)3}NO3⋅7 H2O}n (Ln=Gd (1), Tb (2), and Dy (3)) and the trinuclear complex CuII(valpn)LaIII(OH2)3(O2NO)(μ‐NC)FeIII(phen)(CN)3⋅NO3⋅H2O⋅CH3CN (4) were obtained with the CuII(valpn)LnIII3+ assembling unit, whereas three isostructural heterotrimetallic 2D networks, {NiII(valpn)LnIII(ONO2)2(H2O)(μ‐NC)3FeIII(bipy)(CN)⋅2 H2O⋅2 CH3CN}n (Ln=Gd (5), Tb (6), and Dy (7)) resulted with the related NiII(valpn)LnIII3+ precursor. The crystal structure of compound 4 consists of discrete heterotrimetallic complex cations, CuII(valpn)LaIII(OH2)3(O2NO)(μ‐NC)FeIII(phen)(CN)3+, nitrate counterions, and non‐coordinate water and acetonitrile molecules. The heteroleptic {FeIII(bipy)(CN)4} moiety in 5–7 acts as a tris‐monodentate ligand towards three {NiII(valpn)LnIII} binuclear nodes leading to heterotrimetallic 2D networks. The ferromagnetic interaction through the diphenoxo bridge in the CuIILnIII (1–3) and NiIILnIII (5–7) units, as well as through the single cyanide bridge between the FeIII and either NiII (5–7) or CuII (4) account for the overall ferromagnetic behavior observed in 1–7. DFT‐type calculations were performed to substantiate the magnetic interactions in 1, 4, and 5. Interestingly, compound 6 exhibits slow relaxation of the magnetization with maxima of the out‐of‐phase ac signals below 4.0 K in the lack of a dc field, the values of the pre‐exponential factor (τo) and energy barrier (Ea) through the Arrhenius equation being 2.0×10−12 s and 29.1 cm−1, respectively. In the case of 7, the ferromagnetic interactions through the double phenoxo (NiII–DyIII) and single cyanide (FeIII–NiII) pathways are masked by the depopulation of the Stark levels of the DyIII ion, this feature most likely accounting for the continuous decrease of χMT upon cooling observed for this last compound.
Heterotrimetallic complexes of various dimensionality and topology were synthesized from {Fe(AA)(CN)4} metalloligands and 3d–4f heterobimetallic building blocks, with Schiff base compartmental ligands: {CuIILnIIIFeIII} chains (see figure; compounds 1–3), a {CuIILaIIIFeIII} discrete molecule (4), and {NiIILnIIIFeIII} 2D coordination polymers (5–7). Magnetic measurements in an ac field indicated the presence of the slow relaxation of the magnetization for 6. bipy=bipyridine, phen=phenanthroline.
Self-assembly is the most powerful force for creating ordered supramolecular architectures from simple components under mild conditions. π···π stacking interactions have been widely explored in ...modern supramolecular chemistry as an attractive reversible noncovalent tool for the nondestructive fabrication of materials for different applications. Here, we report on the self-assembly of cytidine 5’-monophosphate (CMP) nucleotide and copper metal ions for the preparation of a rare nanoporous supramolecular metal-organic framework in water. π···π stacking interactions involving the aromatic groups of the ancillary 2,2’-bipyridine (bipy) ligands drive the self-assemblies of hexameric pseudo-amphiphilic Cu6(bipy)6(CMP)2(µ-O)Br42+ units. Owing to the supramolecular geometric matching between the aromatic tails, a nanoporous crystalline phase with hydrophobic and hydrophilic chiral pores of 1.2 and 0.8 nanometers, respectively, was successfully synthesized. The encoded chiral information, contained on the enantiopure building blocks, is transferred to the final supramolecular structure, assembled in the very unusual topology 8T6. These kinds of materials, owing to chiral channels with chiral active sites from ribose moieties, where the enantioselective recognition can occur, are, in principle, good candidates to carry out efficient separation of enantiomers, better than traditional inorganic and organic porous materials.
The lack of rational design methodologies to obtain chiral rod-based MOFs is a current synthetic limitation that hampers further expansion of MOF chemistry. Here we report a metalloligand design ...strategy consisting of the use, for the first time, of preformed 1D rodlike SBUs (1) for the rational preparation of a chiral 3D MOF (2) exhibiting a rare eta net topology. The encoded chiral information on the enantiopure ligand is efficiently transmitted first to the preformed helical 1D building block and, in a second stage, to the resulting chiral 3D MOF. These results open new routes for the rational design of chiral rod-based MOFs, expanding the scope of these unique porous materials.
Ionic transition‐metal complexes based on silver(I) metal core (Ag‐iTMCs) represent an appealing alternative to other iTMCs in solid‐state lighting owing to (i) their low cost and well‐known ...synthesis, (ii) the tunable bandgap, and (iii) the highly efficient photoluminescence. However, their electroluminescence behavior is barely studied. Herein, the archetypal green‐emitting Ag‐iTMCs, namely Ag(4,4′‐dimethoxy‐2,2′‐bipyridine)(Xantphos)X (X = BF4, PF6, and ClO4), are thoughtfully investigated, revealing their electroluminescent features in light‐emitting electrochemical cells (LECs). Despite optimizing device fabrication and operation, luminance of 40 cd m−2, efficacy of 0.2 cd A−1, and a very poor stability of 30 s are achieved. This outcome encourages the comprehensive study of the degradation mechanism combining electrochemical impedance spectroscopy, X‐ray diffraction, and cyclic voltammetry techniques. These results point out the irreversible formation of silver nanoclusters under operation strongly limiting the device performance. As such, LECs are further optimized by (i) changing the counterions (PF6− and ClO4−) and (ii) decoupling electron injection and exciton formation using a double‐layered architecture. The synergy of both approaches leads to a broad exciplex‐like whitish electroluminescence emission (x/y CIE of 0.40/0.44 and color rendering index of 85) with an outstanding improved stability of ≈4 orders of magnitude (>80 h) without losing brightness (35 cd m−2).
Ionic silver(I) complexes represent an emerging class of emitters for solid‐state lighting. Herein, the first in‐depth study on the electroluminescence behavior of an silver(I) complex in light‐emitting electrochemical cells is provided. While elucidating the device degradation mechanism, a successful solution to enhance the device stability from seconds to days is proposed.
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