Search

A strategy of in situ deposition of two-dimensional covalent organic frameworks onto a supported nanocatalyst was developed for suppressing the agglomeration and sintering of metal nanoparticles without compromising their activity and selectivity.

The presence of a cyclodextrin cavity in a chelating P,N ligand promotes the exclusive formation of 1 : 1 ligand/metal complexes. A Ni(ii) complex of the ligand is a very selective catalyst for ethylene dimerisation as a result of metal confinement.

International audience; Carbonylmetallates [m]-, such as [MoCp(CO)3]-, [Mn(CO)5]-, [Co(CO)4]-, have long been successfully used in the preparation of hundreds of metal carbonyl complexes and clusters, in particular of the heterometallic type. We focus here on situations where [m]- can be viewed as a terminal, doubly- or even triply-bridging metalloligand, developing metal-metal interactions with one, two or three metal centres M, respectively. With metals M from the groups 10-12, is not straightforward or even impossible to rationalize the structure of the resulting clusters by applying the well-known Wade-Mingos rules. A very simple but global approach is presented to rationalize structures not obeying usual electron-counting rules by considering the anionic building blocks [m]- as metalloligands behaving formally as potential 2, 4 or 6 electron donors, similarly to what is typically encountered with e.g. halido ligands. Qualitative and theoretical arguments using DFT calculations highlight similarities between seemingly unrelated metal complexes and clusters and also entails a predicting power with high synthetic potential.

The presence of a permethylated α-cyclodextrin (α-CD) cavity in a chelating P,N ligand promotes exclusive formation of 1 : 1 ligand/metal complexes. In MX

The chemistry of discrete molecular chains constituted by metals in low oxidation states, displaying metal-metal proximity and stabilized by suitable metal-bridging, assembling ligands comprising at least one soft donor atom is comprehensively reviewed; complexes with a single (hard or soft) bridging atom (e.g., μ-halide, μ-sulfide, or μ-PR2etc.) as well as "closed" metal arrays (that fall in the realm of cluster chemistry) are excluded. The focus is on transition metal-based systems, with few excursions to cases combining transition and post-transition elements. Most relevant supporting ligands have neutral C, P, O, or S donor (mainly, N-heterocyclic carbene, phosphine, ether, thioether) or anionic donor (mainly phenyl, ylide, silyl, phosphide, thiolate) groups. A supporting-ligand-based classification of the metal chains is introduced, using as the classifying parameter the number of "bites" (i.e., ligand bridges) subtending each intermetallic separation. The ligands are further grouped according to the number of donor atoms interacting with the metal chain (called denticity in the following) and the column of the Periodic Table to which the set of donor atoms belongs (in ascending order). A complementary metal-based compilation of the complexes discussed is also provided in a concise tabular form.

International audience; New titanium complexes of general formula [Ti(OR)2(OiPr)2], containing functionalized alkoxido ligands, were developed for the selective catalytic dimerization of ethylene to 1-butene using a combined High Throughput Screening (HTS) / Design of Experiment (DoE) approach. First, a library of 19 ligands was elaborated and a primary screening spotted the phosphorus-functionalized alkoxido ligands as most promising. A second, more focused library containing 8 alkoxidophosphane ligands was then developed. A longer linear spacer between the alkoxido and the phosphorus functions, as in [Ti(19)2(OiPr)2], was found beneficial for this catalytic reaction. After identification of the best co-catalyst (AlEt3) and co-ligand (OnBu), final optimization of the reaction conditions was performed using a design of experiments (DoE) approach. The complex [Ti(19)2(OnBu)2] was shown to selectively dimerize ethylene in 1-butene (C4(α)=93 % (99+%)) at 30 bar C2H4 and 55 °C with AlEt3 as co-catalyst, resulting in very high activity and selectivity for a molecular titanium catalyst (13000 g gTi−1 h−1, 93 % 1-butene).

In order to examine the possibility to promote cooperative effects on catalytic activity and selectivity in ethylene dimerization through ligand design, the bisphosphino-iminato ligands syn-L and a...

Discovering and constructing novel and fancy structures is the goal of many supramolecular chemists. In this work, we propose an assembly strategy based on the synergistic effect of coordination and covalent interactions to construct a set of octahedral supramolecular cages and adjust their degree of distortion. Our strategy innovatively utilizes the addition of sulfur atoms of a metal sulfide synthon, [Et4N][Tp*WS3] (A), to an alkynyl group of a pyridine-containing linker, resulting in a novel vertex with low symmetry, and of Cu(I) ions. By adjusting the length of the linker and the position of the reactive alkynyl group, the control of the deformation degree of the octahedral cages can be realized. These supramolecular cages exhibit enhanced third-order nonlinear optical (NLO) responses. The results offer a powerful strategy to construct novel distorted cage structures as well as control the degree of distortion of supramolecular geometries.

Metal-organic framework (MOF) nanosheets with attractive chemical and structural properties have been considered as prominent oxygen evolution reaction (OER) electrocatalysts, while the insufficient exposed active sites and low electrical conductivity of MOFs limit their electrocatalytic activity and further industrial applications. Herein, a unique strategy to remarkably boost electrocatalytic OER activity of one Ni-based MOF is developed by the simultaneous incorporation of Fe

Metals are involved in various research fields of chemistry where they play key roles, as illustrated for example in transition-metal homogeneous catalysis, materials for energy storage and conversion, luminescent materials, and coordination-driven self-assembly. This special collection of Chemistry - An Asian Journal features significant contributions that chemists around the world make in this area. Working together with Professors Pierre Braunstein, Chi-Ming Che, Guo-Xin Jin, Fuwei Li and Yun Zong, Chemistry - An Asian Journal assembled 56 excellent contributions in this special collection to celebrate the 65

Designing and building unique cage assemblies attract increasing interest from supramolecular chemists but remain synthetically challenging. Herein, we propose the use of a flexible vertex with adjustable angles to selectively form highly distorted tetrahedral and octahedral cages, for the first time, in which the flexible vertex forms from the synergistic effect of coordination and covalent interactions. The inherent interligand angle of the vertex can be modulated by guest anions present, which allows for the fine-tuning of different cage geometries. Furthermore, the reversible structural transformation between tetrahedral and octahedral cages was achieved by anion exchange monitored by mass spectrometric technique, the smaller anions favoring tetrahedral cages, while the larger anions supporting octahedral cages. Additionally, the KBr-based cage thin films exhibited prominent enhancement of their third-order NLO responses in two or three orders of magnitude compared to those obtained for their corresponding solutions. This work not only provides a new methodology to build irregular polyhedral structures in a controlled and tunable way but also provides access to new kinds of promising functional optical materials.

Using a pincer platform based on a bridgehead NHC donor with functional side arms, the combined effect of increased flexibility in six-membered pyrimidine-type heterocycles compared to the more often studied five-membered imidazole, and rigidity of phosphane side arms was examined. The unique features observed include: 1) the reaction of the azolium Csp2 -H bond with [Ni(cod)2 ] affording a carbanionic ligand in [NiCl(PCsp3 H P)] (8) rather than a carbene; 2) its transformation into the NHC, hydrido complex [NiH(PCNHC P)]PF6 (9) upon halide abstraction; 3) ethylene insertion into the Ni-H bond of the latter and ethyl migration to the N-C-N carbon atom of the heterocycle in [Ni(PCEt P)]PF6 (10); and 4) an unprecedented C-P bond activation transforming the P-CNHC -P pincer ligand of 8 in a C-CNHC -P pincer and a terminal phosphanido ligand in [Ni(PPh2 )(CCNHC P)] (15). The data are supported by nine crystal structure determinations and theoretical calculations provided insights into the mechanisms of these transformations, which are relevant to stoichiometric and catalytic steps of general interest.

The poor conductivity, unsatisfactory stability and easy aggregation of metal-organic framework (MOF) nanomaterials have been recognized as the main reasons that prevent their practical application. Here, we report the highly conductive and cyclic-stable Ti

Most metal-organic frameworks (MOFs) hardly maintain their physical and chemical properties after exposure to acidic, neutral, or alkaline aqueous solutions, resulting in insufficient stability, therefore limiting their applications. Thus, the design and synthesis of stable size/morphology-controlled MOF nanocrystals is critical but challenging. In this study, dual-ligand and hard-soft-acid-base strategies were used to fabricate a variety of 3D pillared-layer [Ni(thiophene-2,5-dicarboxylate)(4,4′-bipyridine)]n MOF nanocrystals (1D nanofibers, 2D nanosheets and 3D aggregates) with controllable morphology by varying the concentration of 4,4′-bipyridine and thus controlling the crystal growth direction. Owing to the shorter ion diffusion length, enhanced electron/ion transfer and strong interactions between thiophene-2,5-dicarboxylate and 4,4′-bipyridine, the 2D nanosheets showed much larger specific capacitance than 1D nanofibers and 3D aggregates. A single device with an output voltage as high as 3.0 V and exceptional cycling performance (95% of retention after 5000 cycles at 3 mA cm–2) was realized by configuring two aqueous asymmetric supercapacitive devices in series. The excellent cycling property and charge–discharge mechanism are consistent with the hard-soft-acid-base theory.

Metal-organic frameworks (MOFs) with controllable shapes and sizes show a great potential in Li-S batteries. However, neither the relationship between shapes and specific capacity nor the influence of MOF particle size on cyclic stability have been fully established yet. Herein, MIL-96-Al with various shapes, forming hexagonal platelet crystals (HPC), hexagonal bipyramidal crystals (HBC), and hexagonal prismatic bipyramidal crystals (HPBC) were successfully prepared via co-solvent methods. Density functional theory (DFT) calculations demonstrate that the HBC shape with highly exposed (101) planes can effectively adsorb lithium polysulfides (LPS) during the charge/discharge process. By changing the relative proportion of the co-solvents, HBC samples with different particle sizes were prepared. When these MIL-96-Al crystals were used as sulfur host materials, it was found that those with the smaller size of HBC shape deliver the higher initial capacity. These investigations establish that different crystal planes have different adsorption abilities for LPS, and that the MOF particle size should be considered for a suitable sulfur host. More broadly, this work provides a strategy for designing sulfur hosts in Li-S batteries. This article is protected by copyright. All rights reserved.

Whereas the bis(imine)imidazolium salt 1·Cl is a potential precursor to a NimineCNHCNimine pincer-type ligand, it reacted with [Pt(cod)2] to give the PtII NHC hydrido complex 3, in which chloride coordination and CNHCNimine chelation is preferred over pincer formation. Unexpectedly, reaction of 1·BF4 with [Pt(cod)2] afforded the unprecedented, 56 CVE tetrahedral cluster [Pt4(μ-H)(cod)4]BF4 (7), which was fully characterized. Imidazolium salts are ubiquitous sources of the much studied NHC ligands and not expected to lead to the formation of metal clusters.

Whereas the bis(imine)imidazolium salt 1·Cl is a potential precursor to a N

Metal-organic frameworks (MOFs), which consist of central metal nodes and organic linkers, constitute a fast growing class of crystalline porous materials with excellent application potential. Herein, a series of Mn-based multimetallic MOF (bimetallic and trimetallic MIL-100) nano-octahedra are prepared by a facile one-pot synthetic strategy. The types and proportions of the incorporated elements can be tuned while retaining the original topological structure. The introduction of other metal ions is verified at the atomic level by combining X-ray absorption fine structure experiments and theoretical calculations. Furthermore, these multimetallic Mn-based MIL-100 nano-octahedra are utilized as sulfur hosts to prepare cathodes for Li-S batteries. The MnNi-MIL-100@S cathode exhibits the best Li-S battery performance among all reported MIL-100@S composite cathode materials, with a reversible capacity of ≈708.8 mAh g-1 after 200 cycles. The synthetic strategy described herein is utilized to incorporate metal ions into the MOF architecture, of which the parent monometallic MOF nano-octahedra cannot be prepared directly, thus rationally generating novel multimetallic MOFs. Importantly, the strategy also allows for the general synthesis and study of various micro-/nanoscale MOFs in the energy storage field.

This review summarizes the syntheses, crystal structures and applications of metal complexes with a specific zwitterionic thiolate ligand, 4-(trimethylammonio)benzenethiolate (Tab). The chemistry of Tab with transition metals (Fe, Co, Ni, Pd, Cu, Ag, Au, Zn, Cd, Hg), main group metals (In, Pb, Bi) and in heterometallic systems is described. The most significant structural features of the metal/Tab complexes are summarized and trends are discussed as a function of nuclearity and coordination numbers. The reactivity of specific metal/Tab complexes towards N- and P- donor ligands, organic acids, inorganic anions and metal ions is discussed. The luminescence and dielectric properties of the metal/Tab complexes and their applications as fluorescent biosensors and precursors to metal nanoparticles and catalysts for organic transformations are also illustrated.

Reactions of the phosphanyl-gold(I) precursor [(AuCl)2(bdppmapy)] (1; bdppmapy = N,N-bis(diphenylphosphanylmethyl)-2-aminopyridine) with Na2S in a 1:1 or 1:2 molar ratio gave rise to one tetradecanuclear and one octanuclear Au(I) sulfido cluster, [Au14S6(bdppmapy)5]Cl2 (2) and [Au18S8(bdppmapy)6]Cl2 (3), respectively. The former displays a new structural framework in gold cluster chemistry. Compounds 2 and 3 showed strong green luminescence and were employed as excellent imaging probes to selectively light up the lysosomes of living cells. Their long-term tracking of lysosomes can be achieved for up to 36 h, while tracking with commercial Lyso-Tracker Red under the same conditions was limited to 3 h. Our work demonstrated the possibility of constructing novel gold(I) sulfido clusters supported by special P-N hybrid ligands and the potential application of these clusters as long-term selective trackers of lysosomes in bioimaging.

International audience; With their N-amine and N’-imine substituents, the imidazolium chlorides [(ImH){C(Me)vNDipp}(C2NMe2)] Cl (1) and [(ImH){C(Me)vNDipp}(C3NMe2)]Cl (2) are suitable precursors to pincer-type tritopic NimineCNHCNamine ligands for various transition metals and allow an investigation of the influence of (i) the functionalities associated with the NHC donor and (ii) the length of the spacer connecting the amine group to the heterocycle. The mononuclear Cu(I) complexes [CuCl{Im[C(Me)vNDipp](C2NMe2)-κ1CNHC}] (3) and [CuCl{Im[C(Me)vNDipp](C3NMe2)-κ1CNHC}] (4) were prepared by the reaction of 1 and 2 with mesitylcopper(I), respectively. The reactions of 1 and 2 with Ag2O, in the presence of molecular sieves, afforded the Ag(I) complexes [AgCl{Im[C(Me)vNDipp](C2NMe2)-κ1CNHC}] (5) and [AgCl{Im[C(Me)vNDipp] (C3NMe2)-κ1CNHC}] (6), respectively. A dinuclear Cu(I) complex containing a ladder-type skeleton formed by copper and iodine atoms, [Cu4(μ2-I)2(μ3-I)2{μ-κ2-CNHC,Namine(Im){C(Me)vNDipp}(C3NMe2)}2] (7), was obtained by deprotonation of 2 using sodium trimethylsilylamide/CuI. A transmetallation reaction from 5 to [NiBr2(dme)] afforded an unexpected mixed-metal tetranuclear, centrosymmetric complex [NiCl {Im[C(Me)vNDipp](C2NMe2)-κ1CNHC}{μ2-κ3-Nimine,CNHC,NamineIm[C(Me)vNDipp](C2NMe2)}AgBr2]2 (8), which contains two mononuclear Ni(II) units, one with a κ1CNHC donor and the other with a κ2-Nimine,CNHC chelating and μ2-CNHC,Namine bridging ligand. These two monocationic complexes are connected by the dianonic, disilver unit [Ag2Br4]2−. Furthermore, the mononuclear tritopic Ni(II) pincer complexes [Ni(NCMe) {Im[C(Me)vNDipp](C2NMe2)-κ3Nimine,CNHC,Namine}][BF4]2 (9) and [Ni(NCMe){Im[C(Me)vNDipp](C3NMe2)- κ3Nimine,CNHC,Namine}][BF4]2 (10) were obtained when [Ni(NCMe)6](BF4)2 was used as a precursor in trans- metallation reaction with 9 and 10, respectively. Transmetallation from the silver complexes 5 and 6 was also applied to the synthesis of chromium complexes and whether [CrCl2(THF)2] or [CrCl3(THF)3] was used as a precursor, the same chromium(III) complexes, mer-[CrCl3{Im[C(Me)vNDipp](C2NMe2)-κ3Nimine,CNHC, Namine}] (11) and mer-[CrCl3{Im[C(Me)vNDipp](C3NMe2)-κ3Nimine,CNHC,Namine}] (12), respectively, were isolated. Moreover, silver transmetalation reactions from 5 and 6 were successfully applied to the Ir(I) pre- cursor [Ir(μ-Cl)(cod)]2 (cod = 1,5-cycloocadiene) and the Ir(I) complexes [IrCl(cod){Im[C(Me)vNDipp] (C2NMe2)-κ1CNHC}] (13) and [IrCl(cod) {Im[C(Me)vNDipp](C3NMe2)-κ1CNHC}] (14), respectively, containing a monodentate NHC ligand were isolated as yellow crystals in good yields. The cationic, Nimine,CNHC-che- lated Ir(I) complexes [Ir(cod){Im[C(Me)vNDipp](C2NMe2)-κ2Nimine,CNHC}]BF4 (15) and [Ir(cod){Im[C(Me)v NDipp](C3NMe2)-κ2Nimine,CNHC}]BF4 (16) were obtained by halide abstraction from 13 and 14, respectively. The following 10 complexes 3, 6, 7, 8·2Et2O, 9–11, 12·2C7H8, 14 and 16·THF were characterized by X-ray diffraction analysis. In catalytic ethylene oligomerization, the Ni complex 10 showed a productivity of 14 600 gC2H4 per (gNi h), giving 65% butenes and 30% hexenes. With the Cr complex 12, the productivity was up to 9200 gC2H4 per (gCr h) and a very high selectivity for α-olefins was observed, from C4 to C8.

We report on the modulation of the electrical properties of graphene-based transistors that mirror the properties of a few nanometers thick layer made of dipolar molecules sandwiched in between the 2D material and the SiO2 dielectric substrate. The chemical composition of the films of quinonemonoimine zwitterion molecules adsorbed onto SiO2 has been explored by means of X-ray photoemission and mass spectroscopy. Graphene-based devices are then fabricated by transferring the 2D material onto the molecular film, followed by the deposition of top source-drain electrodes. The degree of supramolecular order in disordered films of dipolar molecules was found to be partially improved as a result of the electric field at low temperatures, as revealed by the emergence of hysteresis in the transfer curves of the transistors. The use of molecules from the same family, which are suitably designed to interact with the dielectric surface, results in the disappearance of the hysteresis. DFT calculations confirm that the dressing of the molecules by an external electric field exhibits multiple minimal energy landscapes that explain the thermally stabilized capacitive coupling observed. This study demonstrates that the design and exploitation of ad hoc molecules as an interlayer between a dielectric substrate and graphene represents a powerful tool for tuning the electrical properties of the 2D material. Conversely, graphene can be used as an indicator of the stability of molecular layers, by providing insight into the energetics of ordering of dipolar molecules under the effect of electrical gating.

Aliphatic polyesters are a class of biorenewable, biocompatible, and biodegradable materials. The ring-opening polymerization (ROP) of lactones is one of the most powerful methods to access these materials. A novel series of benzoheterocyclic urea catalysts has been synthesized and characterized. When employed in the ROP of δ-valerolactone (δ-VL) in combination with 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD), a fast and “living”/controlled feature was observed in both solvent-free polymerization and solution polymerization, which was proved by kinetic and chain extension experiments. With benzyl alcohol as an initiator, polyvalerolactones (PVLs) were obtained with different molecular weights and narrow molecular weight distributions. In addition, the PVLs with different topological structures were prepared by varying the initiators. The structure and thermal properties of resulting polymers were determined by NMR, GPC and DSC analyses. A possible mechanism was also proposed on the basis of NMR analysis.

The development of metal–organic frameworks (MOFs) as high-efficiency electrocatalysts for water splitting has attracted special attention due to their unique structural features including high porosity, large surface areas, high concentrations of active sites, uniform pore sizes and shapes, etc. Most of the related reports focus on the in situ generation of high-efficiency electrocatalysts by annealed MOFs. However, the pyrolysis process usually destroys the porous structure of MOFs and reduces the number of active sites due to the absence of organic ligands and agglomeration of metal centers. In this work, we prepared unique NiCo-MOF hollow nanospheres (NiCo-MOF HNSs) by a solvothermal method and further fabricated Fe-doped NiCo-MOF HNSs (Fe@NiCo-MOF HNSs) by a simple impregnation-drying method. Significant enhancement of electrocatalytic activity of Fe@NiCo-MOF HNSs was witnessed because of the doped Fe. Compared with the parent NiCo-MOF HNSs, the optimized Fe@NiCo-MOF HNSs exhibited a lower overpotential of 244 mV at 10 mA·cm−2 with a smaller Tafel slope of 48.61 mV·dec−1, which was lowered by ca. 90 mV due to the influence of Fe doping on the electronic structure of the active centers of Ni and Co. The above materials also displayed excellent stability without obvious activity decay for at least 16 hours. These findings present a new entry in the design and fabrication of high-efficiency MOF-based electrocatalysts for energy conversion.

Summary Many methods exist for the synthesis of covalent organic frameworks (COFs), but precise morphology control allowing the tailoring of core-shell and yolk-shell nanostructures has been elusive, mainly due to poor control of the reaction-diffusion processes. Herein, we propose the precise regulation of the COF generation and decomposition rates and their relationship with the diffusion rate of COF species during the synthesis, which enables a successful preparation of core-shell, yolk-shell, hollow-spherical, and multiple yolk-shell COF structures with tunable sizes ranging from 200 to 1,400 nm. Formed COF structures can serve as nanoreactors or nanocontainers, with the shell layer providing molecular-size selectivity determined by the nanopore size demonstrated here using Suzuki coupling reactions with phenylboronic acid, which produce a size-cutoff efficiency for halogenated aromatics approaching 100%. The precise morphology design and control of COF particles and hybrids may help enhance application efficiencies and provide access to new functionalities for COF materials.