Construction of olefinic coordination polymer single crystal platforms: precise organic synthesis, in situ exploration of reaction mechanisms and beyond

Olefin [2+2] photocycloaddition reactions based on coordination-bond templates provide numerous advantages for the selective synthesis of cyclobutane compounds. This review outlines the recent advances in the design and construction of single crystal platforms of olefinic coordination polymers for precise organic synthesis, in situ exploration of reaction mechanisms, and possible developments as comprehensively as possible. Numerous examples are presented to illustrate how the arrangements of the olefin pairs influence the solid-state photoreactivity and examine the types of cyclobutane products. Furthermore, the photocycloaddition reaction mechanisms are investigated by combining advanced techniques such as single crystal X-ray diffraction, powder X-ray diffraction, nuclear magnetic resonance, infrared spectroscopy, fluorescence spectroscopy, laser scanning confocal microscopy and theoretical calculations. Finally, potential applications resulting from promising physicochemical properties before and after photoreactions are discussed, and existing challenges and possible solutions are also proposed.

New Pyridine Dicarbene Pincer Ligands with Ring Expanded NHCs and their Nickel and Chromium Complexes

The pincer complexes [NiIIBr(CNC)]Br (4), [CrIIIBr3(CNC)] (5 a) and [CrIIIBr2.3Cl0.7(CNC)] (5 b), where CNC=3,3'-(pyridine-2,6-diyl)bis(1-mesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene), were obtained from the novel ligand CNC, generated in situ from the precursor (CHNCH)Br2 and [NiIIBr2(PPh3)2] or from [CrII{N(SiMe3)2}2(THF)2] and (CHNCH)Br2 by aminolysis, respectively. The tetrahedrally distorted square planar (τ4≅0.30) geometry and the singlet ground state of Ni in 4 were attributed to steric constraints of the CNC backbone. Computational methods highlighted the dependence of the coordination geometry and the singlet-triplet energy difference on the size of the N-substituent of the tetrahydropyrimidine wingtips and contrasted it to the situation in 5-membered imidazolin-2-ylidene pincer analogues. The octahedral CrIII metal center in 5 a and 5 b is presumably formed after one electron oxidation from CH2Cl2. 4/MAO and 5 a/MAO were catalysts of moderate activity for the oligomerization and polymerization of ethylene, respectively. The analogous (CH^N^CH)Br2 precursor, where (CH^N^CH)=3,3'-(pyridine-2,6-diylbis(methylene))bis(1-mesityl-3,4,5,6-tetrahydropyrimidin-1-ium), was also prepared, however its coordination chemistry was not studied due to the inherent instability of the resulting free C^N^C ligand.

In situ observation of a stepwise [2 + 2] photocycloaddition process using fluorescence spectroscopy

Using highly sensitive and selective in situ techniques to investigate the dynamics of intermediates formation is key to better understand reaction mechanisms. However, investigating the early stages of solid-state reactions/transformations is still challenging. Here we introduce in situ fluorescence spectroscopy to observe the evolution of intermediates during a two-step [2 + 2] photocycloaddition process in a coordination polymer platform. The structural changes and kinetics of each step under ultraviolet light irradiation versus time are accompanied by the gradual increase-decrease of intensity and blue-shift of the fluorescence spectra from the crystals. Monitoring the fluorescence behavior using a laser scanning confocal microscope can directly visualize the inhomogeneity of the photocycloaddition reaction in a single crystal. Theoretical calculations allow us to rationalize the fluorescence behavior of these compounds. We provide a convenient strategy for visualizing the solid-state photocycloaddition dynamics using fluorescence spectroscopy and open an avenue for kinetic studies of a variety of fast reactions.

Self-Assembly of Cluster-Mediated 3D Catenanes with Size-Specific Recognition Behavior

Although interlocked three-dimensional molecules display unique properties associated with their spatial structures, their synthesis and study of their host-guest properties remain challenging. We report the formation of a novel [2]catenane, [Et4N]@[(Tp*WS3Cu3Cl)2(cis-bpype)3]2(OTf)5 ([Et4N][1](OTf)5), by self-assembly of the cluster node [Tp*WS3Cu3Cl]+ and the organic linker (Z)-1,2-diphenyl-1,2-bis(4-(pyridin-4-yl)phenyl)ethene (cis-bpype). Single-crystal X-ray and NMR analyses established that [1]4+ is formed by the interpenetration of two cluster-organic cages. Unique cation-in-cation host-guest complexes were observed with this catenane. The crystalline, empty catenane was formed by taking advantage of the electrostatic repulsion-induced weak binding of the host. Encapsulation experiments also reveal that the empty catenane can adaptively encapsulate cations such as [Et4N]+ and [Pr4N]+ in the cross cavity but is unable to encapsulate [Bu4N]+ and [Me4N]+, although the size of the latter is compatible with that of the cavity. Theoretical calculations and volume analysis allow to unravel the ingenious role of catenane structures and the interplay between electrostatic repulsion and attractive noncovalent interactions for size-specific recognition behavior in host-guest systems involving species with similar electric charges.

Gold complexes with remote-substituted amino N-heterocyclic carbenes

The 4-RN-1,3-Ar₂-imidazolium salt, R = iPr, tBu, Ar = Mes, Dipp, Mes = mesityl, Dipp = 2,6-bis-diisopropyl-phenyl was metalated by Au^I at the C2-, C5- and 4-RN positions depending on the reactants and conditions employed; a rare direct rearrangement of a Au^I aminide to an abnormal imidazol-5-ylidene Au^I complex was also observed and based on a DFT study it may involve TfO^- facilitated H⁺ transfer.

A Cut-to-Link Strategy for Cubane-Based Heterometallic Sulfide Clusters with Giant Third-Order Nonlinear Optical Response

Although the synthesis of low-dimensional metal sulfides by assembling cluster-based units is expected to promote the development of optical materials and models of enzyme active centers such as dinitrogenase, it is faced with limited assembly methodology. Herein we present a cut-to-link strategy to generate high-nuclearity assemblies, inspired by the formation of a Z-type dimer of the W-S-Cu analogues of P^N cluster through in situ release of active linkers. Four new compounds with structures based on the same {Tp*WS₃Cu₃} incomplete cubane-like units were obtained using varied combinations of mild reagents. Open-aperture Z-scan measurements demonstrated the highest-nuclearity complex has the largest nonlinear optical absorption coefficient among discrete cluster-based materials reported to date. This approach enables building high-nuclearity metal sulfide clusters through cluster-based building blocks and opens a way to the design and exploration of materials based on well-identified building blocks.

Photopolymerization-Driven Macroscopic Mechanical Motions of a Composite Film Containing a Vinyl Coordination Polymer

We report a unique vinyl coordination polymer (CP), [Zn(4-Fb)2(tkpvb)] n (1, 4-HFb = 4-fluorobenzoic acid, tkpvb = 1,2,4,5-tetrakis(4-pyridylvinyl)benzene) that undergoes a rare photopolymerization reaction to form a two-dimensional CP integrated with a one-dimensional linear organic polymer. Upon light irradiation at different wavelengths, 1 exhibits an unprecedented phenomenon of photoinduced nonlinear lattice expansion. 1 can be uniformly dispersed in polyvinyl alcohol (PVA) to form the composite film of 1-PVA. When this film is exposed to UV light, internal minute stresses within crystallites are released by lattice expansion, resulting in a variety of photopolymerization-driven macroscopic mechanical motions. The findings provide new insights into the conversion of small lattice expansions of CPs into macroscopic mechanical motions based on photopolymerization reactions, which can promote the development of CPs-based smart photoactuators in the burgeoning field of microrobotics.

Carbonylmetallates as Versatile 2-, 4- or 6-Electron Donor Metalloligands in Transition-Metal Complexes and Clusters: A Global Approach

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-metal bonded 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 centers M, respectively. With metals M from the Groups 10-12, it 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 for example halido ligands. Qualitative and theoretical arguments by using DFT calculations highlight similarities between seemingly unrelated metal complexes and clusters and also entail a predicting power with high synthetic potential.

Electrochemical activation-induced surface-reconstruction of NiOx microbelt superstructure of core-shell nanoparticles for superior durability electrocatalysis

The tailoring of intrinsic electronic structures and extrinsic hierarchical morphologies is widely recognized as a promising strategy to enhance the oxygen evolution reaction (OER) performance of electrocatalysts. It is generally accepted that the surface of the transition metal-based electrocatalyst exposed to the alkaline electrolyte is highly oxidized and reconstructed, forming an amorphous layer during the electrochemical process. This amorphous active phase is favorable for OER due to its abundant dangling bonds, vacancies and defects, which is tricky to be rationally prepared by conventional methods. Herein, a facile access to crystalline / amorphous NiO_x microbelt superstructure of core-shell nanoparticles is presented, which is assembled of crystalline NiO nanoparticles coated with amorphous Ni³⁺/Ni²⁺ oxide layer. Electrochemical activation induces the in-situ surface reconstruction of the NiO_x microbelt superstructure, resulting in a thicker outer amorphous Ni³⁺/Ni²⁺ layer further facilitating OER. Owing to the optimization of the in-situ surface reconstruction, the NiO_x microbelt superstructure with crystalline / amorphous dual phases exhibited both high electrocatalytic activity and superior durability for OER, with the original microbelt superstructure retained after 50000 s I-t test.

Surface deposition of 2D covalent organic frameworks for minimizing nanocatalyst sintering during hydrogenation

A strategy of in situ depositing 2D COFs on heterogeneous catalysts was reported for the first time to suppress the agglomeration and sintering of the supported metal nanoparticles during hydrogenation processes. The COF-decorated nanocatalysts exhibited excellent stability in various hydrogenation reactions including the reduction of dimethyl oxalate (DMO), furfural, and other chemicals.

A cavity-shaped cis-chelating P,N ligand for highly selective nickel-catalysed ethylene dimerisation

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 MX₂ complexes, one of the two halido ligands is forced to reside inside the CD hollow while the second one is pointing outside. Unlike its cavity-free analogue, a Ni(II) complex of the CD ligand is a highly selective precatalyst for ethylene dimerisation (96% C₄ selectivity with up to 95% of 1-butene within the C₄ fraction).

Experimental and Theoretical Study of Ni II ‐ and Pd II ‐Promoted Double Geminal C(sp 3 )−H Bond Activation Providing Facile Access to NHC Pincer Complexes: Isolated Intermediates and Mechanism

We report the first examples of metal‐promoted double geminal activation of C(sp³)−H bonds of the N−CH₂−N moiety in an imidazole‐type heterocycle, leading to nickel and palladium N‐heterocyclic carbene complexes under mild conditions. Reaction of the new electron‐rich diphosphine 1,3‐bis((di‐tert‐butylphosphaneyl)methyl)‐2,3‐dihydro‐1H‐benzo[d]imidazole (1) with [PdCl₂(cod)] occurred in a stepwise fashion, first by single C−H bond activation yielding the alkyl pincer complex [PdCl(PCsp3^HP)] (3) with two trans phosphane donors and a covalent Pd−Csp3 bond. Activation of the C−H bond of the resulting α‐methine Csp3 H−M group occurred subsequently when 3 was treated with HCl to yield the NHC pincer complex [PdCl(PC^NHCP)]Cl (2). Treatment of 1 with [NiBr₂(dme)] also afforded a NHC pincer complex, [NiBr(PC^NHCP)]Br (6), but the reactions leading to the double geminal C−H bond activation of the N−CH₂−N group were too fast to allow identification or isolation of an intermediate analogous to 3. The determination of six crystal structures, the isolation of reaction intermediates and DFT calculations provided the basis for suggesting the mechanism of the stepwise transformation of a N−CH₂−N moiety in the N−C^NHC−N unit of NHC pincer complexes and explain the key differences observed between the Pd and Ni chemistries.

Controllable multiple-step configuration transformations in a thermal/photoinduced reaction

Solid-state photochemical reactions of olefinic compounds have been demonstrated to represent powerful access to organic cyclic molecules with specific configurations. However, the precise control of the stereochemistry in these reactions remains challenging owing to complex and fleeting configuration transformations. Herein, we report a unique approach to control the regiospecific configurations of C = C groups and the intermediates by varying temperatures in multiple-step thermal/photoinduced reactions, thus successfully realizing reversible ring closing/opening changes using a single-crystal coordination polymer platform. All stereochemical transitions are observed by in situ single-crystal X-ray diffraction, powder X-ray diffraction and infrared spectroscopy. Density functional theory calculations allow us to rationalize the mechanism of the synergistic thermal/photoinduced transformations. This approach can be generalized to the analysis of the possible configuration transformations of functional groups and intermediates and unravel the detailed mechanism for any inorganic, organic and macromolecular reactions susceptible to incorporation into single-crystal coordination polymer platforms.

Solid-state photochemical reactions of olefinic compounds provide access to organic cyclic molecules with specific configurations but the precise control of the stereochemistry in these reactions remains challenging. Here, the authors demonstrate control of the regiospecific configurations of C=C groups and the intermediates by varying temperatures in multi-step thermal and photoinduced ring opening and closing reactions using a single-crystal coordination polymer platform.

Engineering the Electronic Structures of Metal-Organic Framework Nanosheets via Synergistic Doping of Metal Ions and Counteranions for Efficient Water Oxidation

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 Fe³⁺ ions and BF₄^- anions within its layer structure. The optimized electrocatalyst NiFe-MOF-BF₄^--0.3 NSs shows superior OER activity with a required ultralow overpotential of 237 mV at 10 mA cm^-2, a small Tafel slope of 41 mV dec^-1, and outstanding stability in an alkaline medium. The experimental and density functional theory (DFT) calculation results verify that the interactions between metal (M) ions and BF₄^- anions (defined as M···F, M = Ni or Fe) in this catalyst can adjust the adsorption abilities of oxygen intermediates and lower the free energy barrier of the potential-determining step by tailoring its electronic structure, thereby remarkably boosting its OER activity. This protocol provides new insights into surface and structure engineering of 2D MOFs, leading to greatly enhanced electrocatalytic OER performance.

Flexible Vertex Engineers the Controlled Assembly of Distorted Supramolecular Tetrahedral and Octahedral Cages

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.

In Celebration of the 65th Birthday of Professor Andy Hor

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^th birthday of Prof. Andy Hor (A*STAR, Singapore).

MIL-96-Al for Li-S Batteries: Shape or Size?

Metal-organic frameworks (MOFs) with controllable shapes and sizes show a great potential in Li-S batteries. However, neither the relationship between shape 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) are successfully prepared via cosolvent 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 cosolvents, HBC samples with different particle sizes are prepared. When these MIL-96-Al crystals are used as sulfur host materials, it is found that those with a smaller size of the HBC shape deliver 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.

Dual-ligand and hard-soft-acid-base strategies to optimize metal-organic framework nanocrystals for stable electrochemical cycling performance

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.

Rational Design and General Synthesis of Multimetallic Metal-Organic Framework Nano-Octahedra for Enhanced Li-S Battery

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.

Imidazolium salts and [Pt(cod)2]: from NHC hydrido complexes to the unprecedented olefinic tetrahedral cluster [Pt4(μ-H)(cod)4]BF4

Whereas the bis(imine)imidazolium salt 1·Cl is a potential precursor to a N^imineC^NHCN^imine pincer-type ligand, it reacted with [Pt(cod)₂] to give the Pt^II NHC hydrido complex 3, in which chloride coordination and C^NHCN^imine 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.

Transition Metal Chain Complexes Supported by Soft Donor Assembling Ligands

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-PR₂ etc.) 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.

The Covalent and Coordination Co-Driven Assembly of Supramolecular Octahedral Cages with Controllable Degree of Distortion

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.

Iron-doped NiCo-MOF hollow nanospheres for enhanced electrocatalytic oxygen evolution

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.

Quasi-ZIF-67 for Boosted Oxygen Evolution Reaction Catalytic Activity via a Low Temperature Calcination

Exposing catalytically active metal sites in metal-organic frameworks with maintained porosity could accelerate electron transfer, leading to improved performances in electrochemical energy storage and conversion. Here, we report a series of quasi-ZIF-67 obtained from low temperature calcination of ZIF-67 for electrocatalytic oxygen evolution reaction (OER) and reveal the nanostructural structure via the spherical aberration-corrected transmission electron microscopy. The quasi-ZIF-67-350 not only possesses a large Brunauer-Emmett-Teller surface area of 2038.2 m²·g^-1 but also presents an extremely low charge-transfer resistance of 15.0 Ω. In catalyzing the OER process, quasi-ZIF-67-350 displays a low overpotential of 286 mV at 10 mA cm^-2 in the electrolyte of 1.0 M KOH. The acquired quasi-ZIF-67 demonstrates a high catalytic activity in OER, and the controlled calcination strategy undoubtedly paves a way in synthesizing low-cost and efficient electrocatalysts.

Recent advances in pristine tri-metallic metal-organic frameworks toward the oxygen evolution reaction

Pristine metal-organic frameworks (MOFs) have received much attention in recent years due to their high specific surface areas, large porosity, excellent pore size distributions, flexible structure, and remarkable catalytic properties. The design of functional MOFs that can function as efficient HER and OER catalysts is significant in solving the energy crisis but remains a big challenge. Tri-metallic metal-organic frameworks show a good application prospect in water oxidation. In this review, we are going to focus on the latest progress and future trends in the development of pristine trimetallic MOFs with respect to the OER. The synergistic effect between multi-metal active sites is effective at improving the intrinsic activity of MOFs toward the OER. By summarizing the synthesis method of tri-metallic MOFs and observing their performance toward the oxygen evolution reaction, we hope that this review will trigger new developments in coordination chemistry, electrochemistry, nanomaterials and energy materials.

Manipulation of the molecular spin crossover transition of Fe(H2B(pz)2)2(bipy) by addition of polar molecules

The addition of various dipolar molecules is shown to affect the temperature dependence of the spin state occupancy of the much studied spin crossover Fe(II) complex, [Fe{H₂B(pz)₂}₂(bipy)] (pz  =  pyrazol-1-yl, bipy  =  2,2'-bipyridine). Specifically, the addition of benzimidazole results in a re-entrant spin crossover transition, i.e. the spin state starts in the mostly low spin state, then high spin state occupancy increases, and finally the high spin state occupancy decreases with increasing temperature. This behavior contrasts with that observed when the highly polar p -benzoquinonemonoimine zwitterion C₆H₂(…NH₂)₂(…O)₂ was mixed with [Fe{H₂B(pz)₂}₂(bipy)], which resulted in locking [Fe{H₂B(pz)₂}₂(bipy)] largely into a low spin state while addition of the ethyl derivative C₆H₂(…NHC₂H₅)₂(…O)₂ did not appear to perturb the spin crossover transition of [Fe{H₂B(pz)₂}₂(bipy)].

Fast and controlled ring-opening polymerization of δ-valerolactone catalyzed by benzoheterocyclic urea/MTBD catalysts

New benzoheterocyclic urea/MTBD catalysts are highly efficient and controllable in the ring-opening polymerization of δ-valerolactone under solvent-free conditions or in solution.

Tuning graphene transistors through ad hoc electrostatics induced by a nanometer-thick molecular underlayer

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.

Fabrication of Photoactuators: Macroscopic Photomechanical Responses of Metal-Organic Frameworks to Irradiation by UV Light

Photoreactive olefinic species are incorporated into a metal-organic framework (MOF), [Zn(bdc)(3-F-spy)] (1). Single crystals of 1 are shown to undergo three types of photomechanical macroscopic deformation upon illumination by UV light. To demonstrate the practical potential of this system, the inclusion of 1 in a PVA (polyvinyl alcohol) composite membrane, by exploiting hydrogen-bonding interactions, is presented. Using this composite membrane, the amplification of mechanical stress to achieve macroscopic actuation behavior is demonstrated. These results pave the way for the generation of MOF-based soft photoactuators that produce clearly defined mechanical responses upon irradiation with light. Such systems are anticipated to have considerable potential in photomechanical energy harvesting and conversion systems.

N-Heterocyclic Carbene Complexes of Copper, Nickel, and Cobalt

The emergence of N-heterocyclic carbenes as ligands across the Periodic Table had an impact on various aspects of the coordination, organometallic, and catalytic chemistry of the 3d metals, including Cu, Ni, and Co, both from the fundamental viewpoint but also in applications, including catalysis, photophysics, bioorganometallic chemistry, materials, etc. In this review, the emergence, development, and state of the art in these three areas are described in detail.

Tetradecanuclear and Octadecanuclear Gold(I) Sulfido Clusters: Synthesis, Structures, and Luminescent Selective Tracking of Lysosomes in Living Cells

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.

Cu(i), Ag(i), Ni(ii), Cr(iii) and Ir(i) complexes with tritopic NimineCNHCNamine pincer ligands and catalytic ethylene oligomerization

Potentially pincer-type tritopic N^imineC^NHCN^amine ligands with a variable length of the spacer connecting N^imidazole to the amine donor are evaluated.