Coordinative Alignment in the Pores of MOFs for the Structural Determination of N-, S-, and P-Containing Organic Compounds Including Complex Chiral Molecules

Formation, Selective Encapsulation, and Tautomerization Control of Isoindolone Utilizing Guanidinium Sulfonate Frameworks

Herein we report the use of tetrakis (guanidinium) pyrenetetrasulfonate (G4PYR) and bis (guanidinium) 1,5-napthalene disulfonate (G2NDS) to catalyze the cyclization of 2-cyanobenzamide (1) to isoindolone (2). Moreover, we demonstrate the remarkable selectivity of these guanidinium organosulfonate hosts in encapsulating 2 over 1. By thoroughly investigating the intramolecular cyclization reaction, we determined that guanidinium and the organosulfonate moiety acts as the catalyst in this process. Additionally, 2 is selectively encapsulated, even in mixtures of other structurally similar heterocycles like indole. Furthermore, the tautomeric state of 2 (amino isoindolone (2-A) and imino isoindolinone forms (2-I)) can be controlled by utilizing different guanidinium organosulfonate frameworks.

Structural Design and Energy and Environmental Applications of Hydrogen-Bonded Organic Frameworks: A Systematic Review

Hydrogen-bonded organic frameworks (HOFs) are emerging porous materials that show high structural flexibility, mild synthetic conditions, good solution processability, easy healing and regeneration, and good recyclability. Although these properties give them many potential multifunctional applications, their frameworks are unstable due to the presence of only weak and reversible hydrogen bonds. In this work, the development history and synthesis methods of HOFs are reviewed, and categorize their structural design concepts and strategies to improve their stability. More importantly, due to the significant potential of the latest HOF-related research for addressing energy and environmental issues, this work discusses the latest advances in the methods of energy storage and conversion, energy substance generation and isolation, environmental detection and isolation, degradation and transformation, and biological applications. Furthermore, a discussion of the coupling orientation of HOF in the cross-cutting fields of energy and environment is presented for the first time. Finally, current challenges, opportunities, and strategies for the development of HOFs to advance their energy and environmental applications are discussed.

Host-Guest Cocrystallization of Phenanthrene[2]arene Macrocycles Facilitating Structure Determination of Liquid Organic Molecules

Single-crystal X-ray diffraction analysis has emerged as the most reliable method for determining the structures of organic molecules. However, numerous analytes, such as liquid organic molecules, pose challenges in crystallization, making their structures directly elusive via X-ray crystallography methods. Herein, we introduced the rapid cocrystallization of a macrocycle named phenanthrene[2]arene (PTA, host) with 15 liquid organic molecules (guests). The guest liquid organic molecules were successively cocrystallized with the aid of the PTA host. Moreover, the chemical structures of the liquid organic molecules could be determined through single-crystal X-ray diffraction analysis. PTA exhibited high adaptivity and was capable of encapsulating liquid organic molecules without forming covalent bonds or strong directional interactions. The results revealed that the adaptive crystals of PTA exhibited excellent cocrystallization capacity. Weak noncovalent interactions between the host and guest molecules were crucial for organizing the guests in an ordered pattern.

Induced Aggregation, Solvent Regulation, and Supracluster Assembly of Aluminum Oxo Clusters

ConspectusRecent years have witnessed the development of cluster materials as they are atomically precise molecules with uniform size and solution-processability, which are unattainable with traditional nanoparticles or framework materials. The motivation for studying Al(III) chemistry is not only to understand the aggregation process of aluminum in the environment but also to develop novel low-cost materials given its natural abundance. However, the Al-related clusters are underdeveloped compared to the coinage metals, lanthanides, and transition metals. The challenge in isolating crystalline compounds is the lack of an effective method to realize the controllable hydrolysis of Al(III) ions. Compared with the traditional hydrolysis of inorganic Al(III) salts in highly alkaline solutions and hydrolysis of aluminum trialkyl compounds conducted carefully in an inert operating environment, we herein developed an effective way to control the hydrolysis of aluminum isopropanol through an alcoxalation reaction. By solvothermal/low melting point solid melting synthesis and using "ligand aggregation, solvent regulation, and supracluster assembly" strategies, our laboratory has established an organic-inorganic hybrid system of aluminum oxo clusters (AlOCs). The employment of organic ligands promotes the aggregation and slows the hydrolysis of Al(III) ions, which in turn improves the crystallization process. The regulation of the structure types can be achieved through the selection of ligands and the supporting solvents. Compared with the traditional condensed polyoxoaluminates, we successfully isolated a broad range of porous AlOCs, including aluminum molecular rings and Archimedes aluminum oxo cages. By studying ring expansion, structural transformation, and intermolecular supramolecular assembly, we demonstrate unique and unprecedented structural controllability and assembly behavior in cluster science. The advancement of this universal synthetic method is to realize materials customization through modularly oriented supracluster assembly. In this Account, we will provide a clear-cut definition and terminology of "ligand aggregation, solvent regulation, and supracluster assembly". Then we will discuss the discovery in this area by using a strategy, such as aluminum molecular ring, ring size expansion, ring supracluster assembly, etc. Furthermore, given the internal and external pore structures, as well as the solubility and modifiability of the AlOCs, we will demonstrate their potential applications in both the solid and liquid phases, such as iodine capture, the optical limiting responses, and dopant in polymer dielectrics. The strategy herein can be applied to extensive cluster science and promote the research of main group element chemistry. The new synthetic method, fascinating clusters, and unprecedented assembly behaviors we have discovered will advance Al(III) chemistry and will also lay the foundation for functional applications.

Benchmarking Guanidinium Organosulfonate Hydrogen-Bonded Frameworks for Structure Determination of Encapsulated Guests

Single crystal X-ray diffraction (SCXRD) is arguably the most definitive method for molecular structure determination, but it is often challenged by compounds that are liquids or oils at room temperature or do not form crystals adequate for analysis. Our laboratory previously reported a simple, cost-effective, single-step crystallization method based on guanidinium organosulfonate (GS) hydrogen bonded frameworks for structure determination of a wide range of encapsulated guest molecules, including assignment of the absolute configuration of chiral centers. Herein, we expand on those results and report a head-to-head comparison of the GS method with adamantoid "molecular chaperones", which have been reported to be useful hosts for structure determination. Inclusion compounds limited to only two GS hosts are characterized by low R1 values and Flack parameters, infrequent disorder of the host and guest, and manageable disorder when it does exist. The structures of some target molecules that were not included or resolved using the adamantoid chaperones were successfully included and resolved by the GS hosts, and vice versa. Of the 32 guests attempted by the GS method, 31 inclusion compounds afforded successful guest structure solutions, a 97% success rate. The GS hosts and adamantoid chaperones are complementary with respect to guest inclusion, arguing that both should be employed in the arsenal of methods for structure determination. Furthermore, the low cost of organosulfonate host components promises an accessible route to molecular structure determination for a wide range of users.

Assembly of Homochiral Aluminum Oxo Clusters for Circularly Polarized Luminescence

Chiral aluminum oxo clusters (cAlOCs) are distinguished from other classes of materials on account of their abundance in the earth's crust and their potential for sustainable development. However, the practical synthesis of cAlOCs is rarely known. Herein, we adopt a synergistic coordination strategy by using chiral amino acid ligands as bridges and auxiliary pyridine-2,6-dicarboxylic acid as chelating ligands and successfully isolate an extensive family of cAlOCs. They integrate molecular chirality, absolute helicity, and intrinsic hydrogen-bonded chiral topology. Moreover, they have the structural characteristics of one-dimensional channels and replaceable counteranions, which make them well combined with fluorescent dyes for circularly polarized luminescence (CPL). The absolute luminescence dissymmetry factor (glum) of up to the 10-3 order is comparable to several noble metals, revealing the enormous potential of cAlOCs in low-cost chiral materials. We hope this work will inspire new discoveries in the field of chirality and provide new opportunities for constructing low-cost chiral materials.

Novel UV-LED-driven photocatalysis-chlorine activation for carbamazepine degradation by sulfur-doped NH2-MIL 53 (Fe) composites: Electronic modulation effect and the dual role of chlorine

Chlorine activation-inefficient and the generation of disinfection by-products (DBPs) has indeed limited the application of UV/chlorine process. In this study, the typical metal-organic frameworks (MOFs) NH2-MIL53(Fe) were successfully modified with organic ligands containing sulfur functional groups and applied to construct a novel UV-LED-driven heterogeneous chlorine activation system. The generation of intermediate energy levels and the charge redistribution effect on Fe-S bond facilitated the excitation of electrons and realized the effective separation of photohole (hvb+) and photoelectron (ecb-). The involvement of S-NH2-MIL53(Fe) improved the efficiency of UV-LED/chlorine process by 6 times. The effective activation of HOCl/OCl- by hvb+ and ecb- significantly enhanced the yield of HO· and Cl·. More importantly, HOCl/OCl- played a dual role in UV-LED/chlorine/S-NH2-MIL53(Fe) process as a precursor for the generation of free radicals and a catalyst for the enhancement of HO· yield, which could achieve efficient removal of the target pollutants at lower chlorine doses. In addition, the presence of low-valent sulfur species and ecb- accelerated the cycle of Fe(II)/Fe(III) and in-situ generation of HO· and Cl·. The known generation of DBPs in UV-LED/chlorine/S-NH2-MIL53(Fe) process decreased by 37.9% compared to UV-LED/chlorine process. Developing novel UV-LED/chlorine/S-NH2-MIL53(Fe) processes provided a reliable strategy to efficiently purify actual micro-polluted water bodies.

Metal Clusters Confined in Chiral Zeolitic Imidazolate Framework for Circularly Polarized-Luminescence Inks

Chiroptical activities arising in nanoclusters (NCs) are emerging as one of the most dynamic areas of modern science. However, devising an overarching strategy that is capable of concurrently enhancing the photoluminescence (PL) and circularly polarized luminescence (CPL) of metal NCs remains a formidable challenge. Herein, gold and silver nanoclusters (AuNCs, AgNCs) are endowed with CPL, for the first time, through a universal host-guest approach─centered around perturbing a chiral microenvironment within chiral hosts, simultaneously enhancing emissions. Remarkably, the photoluminescence quantum yield (PLQY) of AuNCs has undergone an increase of over 200 times upon confinement, escalating from 0.05% to 12%, and demonstrates a CPL response. Moreover, a three-dimensional (3D) model termed "NCs@CMOF" featuring CPL activity is created using metal cluster-based assembly inks through the process of 3D printing. This work introduces a potentially straightforward and versatile approach for achieving both PL enhancement and CPL activities in metal clusters.

A GPT-4 Reticular Chemist for Guiding MOF Discovery

We present a new framework integrating the AI model GPT-4 into the iterative process of reticular chemistry experimentation, leveraging a cooperative workflow of interaction between AI and a human researcher. This GPT-4 Reticular Chemist is an integrated system composed of three phases. Each of these utilizes GPT-4 in various capacities, wherein GPT-4 provides detailed instructions for chemical experimentation and the human provides feedback on the experimental outcomes, including both success and failures, for the in-context learning of AI in the next iteration. This iterative human-AI interaction enabled GPT-4 to learn from the outcomes, much like an experienced chemist, by a prompt-learning strategy. Importantly, the system is based on natural language for both development and operation, eliminating the need for coding skills, and thus, make it accessible to all chemists. Our collaboration with GPT-4 Reticular Chemist guided the discovery of an isoreticular series of MOFs, with each synthesis fine-tuned through iterative feedback and expert suggestions. This workflow presents a potential for broader applications in scientific research by harnessing the capability of large language models like GPT-4 to enhance the feasibility and efficiency of research activities.

Chiral Materials: Progress, Applications, and Prospects

Chirality is a universal phenomenon in molecular and biological systems, denoting an asymmetric configurational property where an object cannot be superimposed onto its mirror image by any kind of translation or rotation, which is ubiquitous on the scale from neutrinos to spiral galaxies. Chirality plays a very important role in the life system. Many biological molecules in the life body show chirality, such as the "codebook" of the earth's biological diversity-DNA, nucleic acid, etc. Intriguingly, living organisms hierarchically consist of homochiral building blocks, for example, l-amino acids and d-sugars with unknown reason. When molecules with chirality interact with these chiral factors, only one conformation favors the positive development of life, that is, the chiral host environment can only selectively interact with chiral molecules of one of the conformations. The differences in chiral interactions are often manifested by chiral recognition, mutual matching, and interactions with chiral molecules, which means that the stereoselectivity of chiral molecules can produce changes in pharmacodynamics and pathology. Here, the latest investigations are summarized including the construction and applications of chiral materials based on natural small molecules as chiral source, natural biomacromolecules as chiral sources, and the material synthesized by design as a chiral source.

Highly efficient conversion of CO2 into N-formamides catalyzed by a noble-metal-free aluminum-based MOF under mild conditions

Formamides have critical application value in the chemical industry serving as solvents or reagents for the synthesis of pharmaceuticals, agrochemicals, and dyes. Herein, we selected a green-synthesis produced aluminum-based metal-organic framework (Al-MOF) material CAU-10pydc as a catalyst to study its performance in CO2 formylation reaction. At room temperature and in the green solvent acetonitrile, CAU-10pydc could highly effectively catalyze the reaction of CO2 and N-methylaniline to N-methyl-N-phenylformamide under mild conditions. CAU-10pydc could maintain its efficient catalytic performance after five catalytic cycles, and PXRD and SEM measurements demonstrated that CAU-10pydc is stable after cyclic catalysis. The universality of this catalyst was illustrated by nine substrates with high yields. The reaction mechanism was further analyzed by DFT calculations. To our knowledge, this work is the first example of a CO2 formylation reaction being catalyzed highly effectively by an Al-MOF under green conditions.

MOF-Triggered Synthesis of Subnanometer Ag02 Clusters and Fe3+ Single Atoms: Heterogenization Led to Efficient and Synergetic One-Pot Catalytic Reactions

The combination of well-defined Fe³⁺ isolated single-metal atoms and Ag₂ subnanometer metal clusters within the channels of a metal-organic framework (MOF) is reported and characterized by single-crystal X-ray diffraction for the first time. The resulting hybrid material, with the formula [Ag⁰₂(Ag⁰)_1.34Fe^III_0.66]@Na^I₂{Ni^II₄[Cu^II₂(Me₃mpba)₂]₃}·63H₂O (Fe³⁺Ag⁰₂@MOF), is capable of catalyzing the unprecedented direct conversion of styrene to phenylacetylene in one pot. In particular, Fe³⁺Ag⁰₂@MOF─which can easily be obtained in a gram scale─exhibits superior catalytic activity for the TEMPO-free oxidative cross-coupling of styrenes with phenyl sulfone to give vinyl sulfones in yields up to >99%, which are ultimately transformed, in situ, to the corresponding phenylacetylene product. The results presented here constitute a paradigmatic example of how the synthesis of different metal species in well-defined solid catalysts, combined with speciation of the true metal catalyst of an organic reaction in solution, allows the design of a new challenging reaction.

Induced CPL-Active Materials Based on Chiral Supramolecular Co-Assemblies

Circularly polarized luminescence (CPL) has attracted much interest due to its potential applications on chiral photonic techniques and optoelectronic materials science. As known, dissymmetry factor (g_em ) of CPL is one essential factor for evaluating the features of CPL-active materials. Much attention has focused on how to increase the g_em value, which is one of the most important issues for CPL practical applications. Recently, more and more works have demonstrated that chiral supramolecular could provide the significant strategy to improve the g_em value through the orderly helical superstructure of chiral building blocks. Normally, this kind of chiral supramolecular assembly process can be accompanied by chirality transfer and induction mechanism, which can promote the amplification effect on the induced CPL of achiral dyes. In this review, we fully summarized recent advances on the induced CPL-active materials of chiral supramolecular co-assemblies, their applications in circularly polarized organic light-emitting diodes (CP-OLEDs) and current challenges.

Multiple Responsive CPL Switches in an Enantiomeric Pair of Perovskite Confined in Lanthanide MOFs

Circularly polarized luminescence (CPL) switches have attracted widespread attention due to their potential applications in advanced information technologies. However, the design and fabrication of solid-state multiple-responsive CPL switches remain challenging. Here, through self-assembly of chiral metal-organic frameworks (MOFs) and perovskite nanocrystals (NCs), a pair of crystalline enantiomeric (P)-(+)/(M)-(-)-EuMOF⊃MAPbX₃ (MA = CH₃ NH₃ ⁺ , X = Cl^- , Br^- , I^- ) adducts is prepared, where the achiral MAPbBr₃ perovskite NCs embedded into chiral MOFs inherit the chirality of host MOFs by host-guest EuBr and PbO coordination bonds, which is demonstrated by synchrotron-radiation-based X-ray absorption spectroscopy. The chiral adducts show enhanced photoluminescence quantum yield (PLQY), good thermal stability of CPL in air, and photoswitchable CPL properties upon altering different UV irradiation. Based on two chiral emission centers and their different characteristics, reversible CPL switches are realized upon a diversity of external stimuli, for example, chemicals (water /CH₃ NH₃ Br solution) or temperatures (room temperature/high temperature). Benefiting from the extraordinary stimuli-responsive and highly reversible switchable CPL, multiple information encryptions and decryptions integrated with CPL, together with a chiroptical logic gate are successfully designed. This work opens a new avenue to generally fabricate solid-state CPL composite materials and develops new applications based on switchable CPL.

Combination of aluminum molecular rings with chemical reduction centers for iodine capture and aggregation

Presented herein is the designed synthesis of porous materials by the assembly of aluminum molecular rings with flexible pseudo-tetracarboxylic acid ligands and their application in atomically precise iodine capture and aggregation.

Surface chiroselective assembly of enantiopure crystalline porous films containing bichiral building blocks

The development of chiral crystalline porous materials (CPMs) containing multiple chiral building blocks plays an important role in chiral chemistry and applications but is a challenging task. Herein, we report the first example of bichiral building block based enantiopure CPM films containing metal-organic cages (MOCs) and metal complexes. The functionalized substrate was immersed subsequently into homochiral metal complex (R)- or (S)-Mn(DCH)3 (DCH = 1,2-diaminocyclohexane) and racemic Ti4L6 cage (L = embonate) solutions by a layer-by-layer growth method. During the assembly process, the substrate surface coordinated with (R)- or (S)-Mn(DCH)3 can, respectively, layer-by-layer chiroselectively connect Δ- or Λ-Ti4L6 cages to form homochiral (R, Δ)- or (S, Λ)-CPM films with a preferred [111] growth orientation, tunable thickness and homogeneous surface. The resulting enantiopure CPM films show strong chirality, photoluminescence, and circularly polarized luminescence (CPL) properties as well as good enantioselective adsorption toward enantiomers of 2-butanol and methyl-lactate. The present in situ surface chiroselective strategy opens a new route to assemble homochiral CPM films containing multiple chiral building blocks for chiral applications.

Using Postsynthetic X-Type Ligand Exchange to Enhance CO2 Adsorption in Metal-Organic Frameworks with Kuratowski-Type Building Units

Postsynthetic modification methods have emerged as indispensable tools for tuning the properties and reactivity of metal-organic frameworks (MOFs). In particular, postsynthetic X-type ligand exchange (PXLE) at metal building units has gained increasing attention as a means of immobilizing guest species, modulating the reactivity of framework metal ions, and introducing new functional groups. The reaction of a Zn-OH functionalized analogue of CFA-1 (1-OH, Zn(ZnOH)₄(bibta)₃, where bibta^2- = 5,5'-bibenzotriazolate) with organic substrates containing mildly acidic E-H groups (E = C, O, N) results in the formation of Zn-E species and water as a byproduct. This Brønsted acid-base PXLE reaction is compatible with substrates with pK_a(DMSO) values as high as 30 and offers a rapid and convenient means of introducing new functional groups at Kuratwoski-type metal nodes. Gas adsorption and diffuse reflectance infrared Fourier transform spectroscopy experiments reveal that the anilide-exchanged MOFs 1-NHPh_0.9 and 1-NHPh_2.5 exhibit enhanced low-pressure CO₂ adsorption compared to 1-OH as a result of a Zn-NHPh + CO₂ ⇌ Zn-O₂CNHPh chemisorption mechanism. The MFU-4l analogue 2-NHPh ([Zn₅(OH)_2.1(NHPh)_1.9(btdd)₃], where btdd^2- = bis(1,2,3-triazolo)dibenzodioxin), shows a similar improvement in CO₂ adsorption in comparison to the parent MOF containing only Zn-OH groups.

Multi-Light-Responsive Upconversion-and-Downshifting-Based Circularly Polarized Luminescent Switches in Chiral Metal-Organic Frameworks

Metal-organic frameworks (MOFs) have attracted tremendous attention for several novel applications. However, functional MOFs with light-responsive circularly polarized luminescence (CPL) are not examined in detail. Therefore, a dual CPL switch exhibiting both upconversion (UC) and downshifting (DS) CPL in the solid state is constructed by loading a luminescent diarylethene derivative (DAEC) and UC nanoparticles (UCNPs) into chiral MOFs. The chiral MOF⊃DAEC composites exhibit both photoswitchable luminescence and DS-CPL properties under alternating UV and visible light irradiation. Additionally, a reversible UC-CPL switch is realized using near-infrared (NIR) and visible light irradiation by introducing energy-level-matched UCNPs and DAEC into the chiral MOFs. The dissymmetry factor (g_lum ) of UC-CPL is noted to be significantly amplified through energy transfer compared to that of DS-CPL, which indicates that the information on circular polarization can be manipulated by altering the incident light. A chiroptical logic circuit with a 2D information output is designed with UV, visible, and NIR light as inputs by setting a rational threshold.

Designable Assembly of Aluminum Molecular Rings for Sequential Confinement of Iodine Molecules

Although numerous adsorbent materials have been reported for the capture of radioactive iodine, there is still demand for new absorbents that are economically viable and can be prepared by reliable synthetic protocols. Herein, we report a coordination-driven self-assembly strategy towards adsorbents for the sequential confinement of iodine molecules. These adsorbents are versatile heterometallic frameworks constructed from aluminum molecular rings of varying size, flexible copper ions, and conjugated carboxylate ligands. Additionally, these materials can quickly remove iodine from cyclohexane solutions with a high removal rate (98.8 %) and considerable loading capacity (555.06 mg g^-1 ). These heterometallic frameworks provided distinct pore sizes and binding sites for iodine molecules, and the sequential confinement of iodine molecules was supported by crystallographic data. This work not only sets up a bridge between molecular rings and infinite porous networks but also reveals molecular details for the underlying host-guest binding interactions at crystallographic resolution.

The difference in the CO2 adsorption capacities of different functionalized pillar-layered metal-organic frameworks (MOFs)

The excessive use of fossil energy has caused the CO2 concentration in the atmosphere to increase year by year. MOFs are ideal CO2 adsorbents that can be used in CO2 capture due to their excellent characteristics. Studies of the structure-activity relationship between the small structural differences in MOFs and the CO2 adsorption capacities are helpful for the development of efficient MOF-based CO2 adsorbents. Therefore, a series of pillar-layered MOFs with similar structural and different functional groups were designed and synthesized. The CO2 adsorption tests were carried out at 273 K to explore the relationship between the small structural differences in MOFs caused by different functional groups and the CO2 adsorption capacities. Significantly, compound 6 which contains a pyridazinyl group has a 30.9% increase in CO2 adsorption capacity compared to compound 1 with no functionalized group.

Coordination-induced spontaneous resolution of a TPPE-based MOF and its use as a crystalline sponge in guest determination

In this work, by virtue of a coordination-induced fixation of the propeller-like conformation of the tetraphenylethylene (TPE) backbone, we achieved a spontaneous resolution of conglomerate-forming enantiomers of [Co(TPPE)Cl2]·4DMF (1M and 1P), as unambiguously probed by single-crystal X-ray crystallography. Benefitting from the robust, accessible, and electron-rich 1D channels, the chiral MOF turned out to be a good 'crystalline sponge' to adsorb and determine six liquid guests, of which two (2-butanol and 2-butylamine) are crystallized in an enantiospecific manner.

Application of Crystalline Matrices for the Structural Determination of Organic Molecules

While single-crystal X-ray diffraction (SC-XRD) is one of the most powerful structural determination techniques for organic molecules, the requirement of obtaining a suitable crystal for analysis limits its applicability, particularly for liquids and amorphous solids. The emergent use of preformed porous crystalline matrices that can absorb organic compounds and stabilize them via host-guest interactions for observation via SC-XRD offers a way to overcome this hindrance. A topical and current discussion of SC-XRD in organic chemistry and the use of preformed matrices for the in crystallo analysis of organic compounds, with a particular focus on the absolute structure determination of chiral molecules, is presented. Preformed crystalline matrices that are covered include metal-organic frameworks (MOFs) as used in the crystalline sponge method, metal-organic polyhedra (MOPs, coordination cages), porous organic materials (POMs)/porous organic molecular crystals (POMCs), and biological scaffolds. An outlook and perspective on the current technology and on its future directions is provided.

Dual Emissive Gold(I)-Sulfido Cluster Framework Capable of Benzene-Cyclohexane Separation in the Solid State Accompanied by Luminescence Color Changes

A decanuclear gold(I)-sulfido complex, [(L^H)₄Au₁₀S₄]Cl₂ (L^H-Au₁₀S₄-Cl, where L^H = 4,5-bis(diphenylphosphanyl)-2H-1,2,3-triazole), assembled from the reaction of H₂S with the chlorogold(I) precursor obtained from the click reaction of [dppa(AuCl)₂] (where dppa = 1,2-bis(diphenylphosphino)acetylene) with NaN₃, is shown to display a bright dual green and red emission in the solid state. Single crystal X-ray diffraction (SCXRD) studies indicate a gold(I) cluster-based framework assembled through intermolecular halogen···hydrogen bonds as well as other weak interactions. The framework of L^H-Au₁₀S₄-Cl is found to display high stability toward solvent molecules, with capability to encapsulate solvent molecules, such as benzene and cyclohexane, inside the crystal lattice voids via a single-crystal-to-single-crystal (SCSC) transformation. With different degrees of influence on the dual green and red emission, crystalline solids of L^H-Au₁₀S₄-Cl exhibit remarkable solvatochromic luminescence in the presence of benzene and cyclohexane. Notably, due to the size confinement of the lattice cavities, the L^H-Au₁₀S₄-Cl solids exhibit a high selectivity (>95%) toward benzene in a mixture of equimolar concentration of benzene and cyclohexane. This work has demonstrated the promising capability of gold(I)-sulfido cluster frameworks to serve as luminescent functional materials for the separation of benzene and cyclohexane.

X-ray Crystallographic Observation of Chiral Transformations within a Metal-Peptide Pore

Porous metal complexes enable single-crystal X-ray crystallographic observation of included guests or reaction intermediates through simple soaking with the guests/substrates. Previous studies on this technique have often encountered difficulties in the observation of chiral structures because the host frameworks had no chirality. We synthesized a new metal-peptide porous complex through a folding-and-assembly strategy and utilized the chiral pore for trapping chiral guests. Chiral alcohols and ketones were successfully included within the pore. Crystallographic analyses clearly revealed not only their chemical structures but also chiral transformation events within the pore such as fixed conformations or an unstable hemiacetal formation.

Sequential Solid-State Transformations Involving Consecutive Rearrangements of Secondary Building Units in a Metal-Organic Framework (MOF)

Solid-state transformations in metal-organic frameworks (MOFs) are important and have led to the creation of new MOF structures. Solid-state transformations from interpenetrated to non-interpenetrated networks involving rearrangement of secondary building units (SBUs) in a single-crystal-to-single-crystal (SCSC) fashion have not been explored to date. Herein, we report the sequential, thermally stimulated solid-state transformations in a barium-organic framework (UPC-600). The two-fold interpenetrated framework of UPC-600 is converted at 373 K into UPC-601, a non-interpenetrated framework. This proceeds in a SCSC fashion and involves the rearrangement of two proximate rod-shaped SBUs in different nets to generate a new rod-shaped SBU. At 473 K, a continuous solid-state transformation involving a second rearrangement occurred, UPC-601 converted into UPC-602 by the rearrangement of the 1D rod-shaped SBU to a 2D layer SBU. This is the first example of such a thermally driven stepwise transformation involving simultaneous cleavage and regeneration of multiple bonds.

Ligand engineering to achieve enhanced ratiometric oxygen sensing in a silver cluster-based metal-organic framework

Ratiometric luminescent oxygen sensing based on dual fluorescence and phosphorescence emission in a single matrix is highly desirable, yet the designed synthesis remains challenging. Silver-chalcogenolate-cluster-based metal-organic frameworks that combine the advantages of silver clusters and metal-organic frameworks have displayed unique luminescent properties. Herein, we rationally introduce -NH₂ groups on the linkers of a silver-chalcogenolate-cluster-based metal-organic framework (Ag₁₂bpy-NH₂) to tune the intersystem crossing, achieving a dual fluorescence-phosphorescence emission from the same linker chromophore. The blue fluorescence component has a 100-nm gap in wavelength and 8,500,000-fold difference in lifetime relative to a yellow phosphorescence component. Ag₁₂bpy-NH₂ quantifies oxygen during hypoxia with the limit of detection of as low as 0.1 ppm and 0.3 s response time, which is visualized by the naked eye. Our work shows that metal cluster-based MOFs have great potential in luminescent sensing, and the longer-lived charge-separated states could find more photofunctional applications in solar energy transformation and photocatalysis.

Designable Aluminum Molecular Rings: Ring Expansion and Ligand Functionalization

Presented herein are the Al^III molecular ring architectures from 8-ring to 16-ring. Although there are numerous reported cyclic coordination compounds based on transition metals, gallium, or lanthanides, the Al versions are less developed due to the fast hydrolysis nature of Al³⁺ ion. With the assistant of monohydric alcohols, a series of atomic precisely Al molecular rings based on benzoates are synthesized. The ring expansion of these Al-rings from 8-ring to 16-ring is related to the monohydric alcohol structure-directing agents. Moreover, the organic ligands on the Al-rings can be modified by using various benzoate derivatives, which lead to tunable surface properties of the Al-rings from hydrophilicity to ultra-hydrophobicity. Importantly, 4-aminobenzoic acid bridged 16-ring is soluble in organic solvents and exhibits high solution stability revealed by mass spectroscopy. Ligand substitution also can be performed between these Al-rings, which reveal controllable ligand functionalization of these Al-rings.

Crystal-to-Crystal Synthesis of Photocatalytic Metal-Organic Frameworks for Visible-Light Reductive Coupling and Mechanistic Investigations

Postmodification of reticular materials with well-defined catalysts is an appealing approach to produce new catalytic functional materials with improved stability and recyclability, but also to study catalysis in confined spaces. A promising strategy to this end is the postfunctionalization of crystalline and robust metal-organic frameworks (MOFs) to exploit the potential of crystal-to-crystal transformations for further characterization of the catalysts. In this regard, two new photocatalytic materials, MOF-520-PC1 and MOF-520-PC2, are straightforwardly obtained by the postfunctionalization of MOF-520 with perylene-3-carboxylic acid (PC1) and perylene-3-butyric acid (PC2). The single crystal-to-crystal transformation yielded the X-ray diffraction structure of catalytic MOF-520-PC2. The well-defined disposition of the perylenes inside the MOF served as suitable model systems to gain insights into the photophysical properties and mechanism by combining steady-state, time-resolved, and transient absorption spectroscopy. The resulting materials are active organophotoredox catalysts in the reductive dimerization of aromatic aldehydes, benzophenones, and imines under mild reaction conditions. Moreover, MOF-520-PC2 can be applied for synthesizing gram-scale quantities of products in continuous-flow conditions under steady-state light irradiation. This work provides an alternative approach for the construction of well-defined, metal-free, MOF-based catalysts.

Hydrolase-like catalysis and structural resolution of natural products by a metal-organic framework

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.

Structural diversity of metal-organic frameworks based on a chalcone dicarboxylic acid ligand

Using chalcone dicarboxylic acid ligands, three different metal-organic frameworks have been successfully obtained. Interestingly, structural diversity has been observed. The difference between compounds 2 and 3 is the inconsistent orientation of the adjacent binuclear Cd clusters. In addition, the photocatalytic properties of compounds 1 and 2 for the degradation of several organic dyes have been explored.