Homo‐Helical Rod Packing as a Path Toward the Highest Density of Guest‐Binding Metal Sites in Metal–Organic Frameworks

Construction of a redox-active metal-organic framework with an octanuclear lithium one-dimensional building block

A stable lithium metal-organic framework, constructed using a redox-active N,N,N',N'-tetrakis(4-carboxyphenyl)-1,4-phenylenediamine linker and Li8 cluster-based one-dimensional rod secondary building unit, exhibits good stability and reversible redox activity. The Li8-MOF, which can be oxidized by AgNO3, has the potential to function as an electrochromic device, thereby advancing the development of smart MOF materials.

Toward Developing Superior Cu-Based Metal-Organic Framework-Derived Materials for Electrocatalytic Oxidation of Ethanol

This project addresses the urgent need for efficient and cost-effective development of electrocatalysts for the ethanol oxidation reaction (EOR). This reaction offers promising renewable energy solutions but faces challenges due to the slow EOR kinetics, typically requiring costly noble metal catalysts. To overcome these limitations, this study focuses on developing CuZn-based EOR catalysts derived from metal-organic frameworks (MOFs), focusing on understanding the structure-performance relationship between pristine MOF-based electrocatalysts and their pyrolyzed counterparts. Herein, bimetallic MOF materials with varying Cu/Zn ratios were synthesized, followed by pyrolysis to produce carbonized counterparts while preserving the fundamental structure but with altered physicochemical properties. Comparative EOR studies revealed the superior performance of pyrolyzed MOFs, demonstrating that optimized Zn-loading is crucial over Cu-based framework for catalyst performance and durability. Overall, this work highlights the potential of MOF-derived Cu-based catalysts for renewable energy applications and provides insights into optimizing their performance through controlled synthesis and post-treatment strategies.

Rational Design and Reticulation of Infinite qbe Rod Secondary Building Units into Metal-Organic Frameworks through a Global Desymmetrization Approach for Inverse C3 H8 /C3 H6 Separation

The development of reticular chemistry has enabled the construction of a large array of metal-organic frameworks (MOFs) with diverse net topologies and functions. However, dominating this class of materials are those built from discrete/finite secondary building units (SBUs), yet the designed synthesis of frameworks involving infinite rod-shaped SBUs remain underdeveloped. Here, by virtue of a global linker desymmetrization approach, we successfully targeted a novel Cu-MOF (Cu-ASY) incorporating infinite Cu-carboxylate rod SBUs with its structure determined by micro electron diffraction (MicroED) crystallography. Interestingly, the rod SBU can be simplified as a unique cylindric sphere packing qbe tubule made of [43 .62 ] tiles, which further connect the tritopic linkers to give a newly discovered 3,5-connected gfc net. Cu-ASY is a permanent ultramicroporous material featuring 1D channels with highly inert surfaces and shows a preferential adsorption of propane (C3 H8 ) over propene (C3 H6 ). The efficiency of C3 H8 selective Cu-ASY is validated by multicycle breakthrough experiments, giving C3 H6 productivity of 2.2 L/kg. Density functional theory (DFT) calculations reveal that C3 H8 molecules form multiple C-H⋅⋅⋅π and atypical C-H⋅⋅⋅ H-C van der Waals interactions with the inner nonpolar surfaces. This work therefore highlights the linker desymmetrization as an encouraging and intriguing strategy for achieving unique MOF structures and properties.

Synthesis of a Cd-MOF Fluorescence Sensor and Its Detection of Fe3+, Fluazinam, TNP, and Sulfasalazine Enteric-Coated Tablets in Aqueous Solution

A Cd-based metal-organic framework (Cd-MOF), named after {[Cd(ttc)(H₂O)]·H₂O}_n (ttc = 1-imidazole-1-yl-2,4,6-benzene-tricarboxylic acid), was synthesized using the solvothermal reaction. The single-crystal structure was determined by single X-ray diffraction analysis, and crystalline characteristics and composition were confirmed by powder X-ray diffraction (PXRD) and thermogravimetric analysis (TG), respectively. Structural analysis showed that the Cd²⁺ ion is in the seven-coordinated mode, in which ttc^2- ion adopts the μ₄-η¹-η¹-η²-η² coordination mode. It is worth noting that the Cd²⁺ ion is connected to ttc^2- to form a 2D network, and the adjacent 2D network is expanded into a 3D supramolecular network structure through weak hydrogen bonds. The fluorescence sensing experiments indicated that Cd-MOF could not only be used as a fluorescence sensor for Fe³⁺, fluazinam (FLU), and 2,4,6-trinitrophenolol (TNP) but also for sulfasalazine detection in aqueous solution. To verify the sensitivity of the fluorescent probe, we calculated its detection limit: 5.34 × 10^-8 M (Fe³⁺), 7.8 × 10^-8 M (FLU), 1.21 × 10^-7 M (TNP), and 2.67 × 10^-7 M (SECT). In addition, the quenching mechanism was thoroughly studied.

Facile synthesis of Co-Ni layered double hydroxides nanosheets wrapped on a prism-like metal-organic framework for efficient oxygen evolution reaction

The construction of low-cost oxygen evolution reaction (OER) electrocatalysts with high activity and good durability is a considerable challenge for facilitating the efficient utilization of green energy. Herein, the prism-like materials of institute lavoisier frameworks-88 (MIL-88) was first synthesized by a hydrothermal method. Then, Co-Ni layered double hydroxides (CoNi-LDHs) nanosheets were directly wrapped on the MIL-88 surface by electrodeposition to form core-shell MIL-88@CoNi-LDHs composites. Due to the distinct structure and synergistic effect between the MIL-88 core and CoNi-LDHs shell, it was found that MIL-88@CoNi-LDHs had outstanding OER activity with a small Tafel slope (45.55 mV dec^-1), low overpotential (314 mV) at 10 mA cm^-2, and superior durability. This study provides a prospective pathway to exploit highly efficient low-cost electrocatalysts for OER.

Induction of Chirality in Boron Imidazolate Frameworks: The Structure-Directing Effects of Substituents

By enhancing steric hindrance of substituents on the imidazole ring, the fan-shaped molecule of a tridentate boron imidazolate ligand (KBH(2-ipim)₃, 2-ipim = 2-isopropylimidazolate) with racemic chirality was obtained. Then, seven novel boron imidazolate frameworks (BIFs) were prepared by mixing KBH(2-ipim)₃ ligands with various derivatives of benzene carboxylic acid under solvothermal conditions. All of these seven materials contain a ladder-like zinc-boron-imidazolate chain as a basic building block, and the ligand BH(2-ipim)₃^- exists in the same handedness in one chain. The structural variations are associated with the position of substituents of the auxiliary ligand. Of particular interest is the spontaneous resolution of BH(2-ipim)₃^- ligands into two independent enantiomorphous homochiral structures, BIF-131-S and BIF-131-R, which contain both a chiral chain and an absolute helix embedded in the nets.

Synthesis, structure and properties of coordination polymers formed from bridging 4-hydroxybenzoic acid anions

The combination of 4-hydroxbenzoic acid with metal ions Li+, Mg2+ and Cu2+ leads to the formation of novel 2D and 3D networks.

Ionothermal synthesis of calcium-based metal–organic frameworks in a deep eutectic solvent

The ionothermal synthesis of Ca-MOFs has been performed using the 1 : 2 choline chloride : e-urea deep eutectic solvent, allowing the preparation of water sensitive materials.

Coordination polymers derived from alkali metal complexes of redox-active ligands

Treatment solutions of (dpp-bian)M (dpp-bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene; M = Li, Na, K) with 4,4′-bipyridine (4,4′-bipy) affords coordination polymers [(dpp-bian)M(4,4′-bipy)m]n, (M = Li or K, m = 1; M = Na, m = 2).

New Reticular Chemistry of the Rod Secondary Building Unit: Synthesis, Structure, and Natural Gas Storage of a Series of Three-Way Rod Amide-Functionalized Metal-Organic Frameworks

Reticular chemistry and methane storage materials have been predominately focused on finite metal-cluster-based metal-organic frameworks (MOFs). In contrast, MOFs constructed from infinite rod secondary building units (SBUs), i.e., rod MOFs, are less developed, and the existing ones are typically built from simple one-way helical, zigzag, or (mixed)polyhedron SBUs. Herein, inspired by a recent unveiled structure of Zn₆(H₂O)₃(BTP)₄ and by means of an amide-functionalized preliminary single tricarboxylate, a subsequent mixed tricarboxylate, and dicarboxylate linkers, an intricate three-way rod MOF and the next three isoreticular three-way rod MOFs have been successfully realized, namely, 3W-ROD-1 and 3W-ROD-2-X (X = -OH, -F, and -CH₃), respectively. The structural analyses disclosed that the four compounds were constructed from unprecedented three-way invariant nonintersecting trigonal rod-packing SBUs cross-linked via the noncovalent-interaction-driven self-assembly of pseudo hexacarboxylates with the original tricarboxylate or different functional ditopic linkers, resulting in cage-like pore geometries accessible via ultramicroporous apertures concomitant with the complex topology transitivity, namely, 18 42 and 18 44. Sorption studies show that the apparent surface areas of these materials are among the most highly porous materials for rod MOFs. Due to the presence of favorable pocket sites created by X, ketone, and proximal amide groups as revealed by Monte Carlo molecular dynamics (MCMD) computational calculations, the MOFs exhibit impressive methane storage working capacities, outperforming the well-known rod Ni-MOF-74 and representing the highest values among rigid rod MOFs.

Chiral induction in boron imidazolate frameworks: the construction of cage-based absolute helices

Two cage-based boron imidazolate helices were prepared in achiral reaction systems by mixing a C3 symmetric rigid ligand, KBH(bim)3, and a long flexible dicarboxylic acid ligand. The presence of an appropriate chiral inducer can control the helical orientation of bulk samples, which further acts on the enantioselective separation of racemic 1-phenylethanol.

Zeolitic octahedral metal oxide-based membranes for pervaporative desalination of concentrated brines

An all-inorganic zeolitic octahedral metal oxide based on cobalt tungstoselenate with porosity and hydrophilicity is successfully used to fabricate a membrane. The as-synthesized membrane and its ion-exchanged membranes exhibit extraordinary permeation flux with high salt rejection by pervaporative desalination for high-salinity brines up to 25 wt%.

Photochemical In Situ Exfoliation of Metal-Organic Frameworks for Enhanced Visible-Light-Driven CO2 Reduction

Two novel two-dimensional metal-organic frameworks (2D MOFs), 2D-M₂ TCPE (M=Co or Ni, TCPE=1,1,2,2-tetra(4-carboxylphenyl)ethylene), which are composed of staggered (4,4)-grid layers based on paddlewheel-shaped dimers, serve as heterogeneous photocatalysts for efficient reduction of CO₂ to CO. During the visible-light-driven catalysis, these structures undergo in situ exfoliation to form nanosheets, which exhibit excellent stability and improved catalytic activity. The exfoliated 2D-M₂ TCPE nanosheets display a high CO evolution rate of 4174 μmol g^-1  h^-1 and high selectivity of 97.3 % for M=Co and Ni, and thus are superior to most reported MOFs. The performance differences and photocatalytic mechanisms have been studied with theoretical calculations and photoelectric experiments. This study provides new insight for the controllable synthesis of effective crystalline photocatalysts based on structural and morphological coregulation.

A "Thermodynamically Stable" 2D Nickel Metal-Organic Framework over a Wide pH Range with Scalable Preparation for Efficient C2 s over C1 Hydrocarbon Separations

The design and construction of "thermodynamically stable" metal-organic frameworks (MOFs) that can survive in liquid water, boiling water, and acidic/basic solutions over a wide pH range is highly desirable for many practical applications, especially adsorption-based gas separations with obvious scalable preparations. Herein, a new thermodynamically stable Ni MOF, {[Ni(L)(1,4-NDC)(H₂ O)₂ ]}_n (IITKGP-20; L=4,4'-azobispyridine; 1,4-NDC=1,4-naphthalene dicarboxylic acid; IITKGP stands for the Indian Institute of Technology Kharagpur), has been designed that displays moderate porosity with a BET surface area of 218 m²  g^-1 and micropores along the [10-1] direction. As an alternative to a cost-intensive, cryogenic, high-pressure distillation process for the separation of hydrocarbons, MOFs have recently shown promise for such separations. Thus, towards an application standpoint, this MOF exhibits a higher uptake of C₂ hydrocarbons over that of C₁ hydrocarbon under ambient conditions, with one of the highest selectivities based on the ideal adsorbed solution theory (IAST) method. A combination of two strategies (the presence of stronger metal-N coordination of the spacer and the hydrophobicity of the aromatic moiety of the organic ligand) possibly makes the framework highly robust, even stable in boiling water and over a wide range of pH 2-10, and represents the first example of a thermodynamically stable MOF displaying a 2D structural network. Moreover, this material is easily scalable by heating the reaction mixture at reflux overnight. Because such separations are performed in the presence of water vapor and acidic gases, there is a great need to explore thermodynamically stable MOFs that retain not only structural integrity, but also the porosity of the frameworks.

Bimetallic Rod-Packing Metal-Organic Framework Combining Two Charged Forms of 2-Hydroxyterephthalic Acid

Although many rod-packing metal-organic frameworks are known, few are based on ordered heterometallic rod building unit. We show here the synthesis of CPM-76 based on an unprecedented Zn-Mg bimetallic rod with crystallographically distinguishable metal sites. The configuration of the rod offers two types of coordination site with trigonal bipyramidal and octahedral sites selectively occupied by Zn and Mg, respectively. Also unusual is the inter-connection mode between the rods, which is based on dual-charged forms (-3 and -2) of the 2-hydroxyterephthalic acid (H₃ OBDC) ligand. Interestingly, each metal site in CPM-76 binds one solvent molecule, leading to a high density of solvent binding sites.

Heterometallic multinuclear nodes directing MOF electronic behavior

Metal node engineering in combination with modularity, topological diversity, and porosity of metal–organic frameworks (MOFs) could advance energy and optoelectronic sectors. In this study, we focus on MOFs with multinuclear heterometallic nodes for establishing metal−property trends, i.e., connecting atomic scale changes with macroscopic material properties by utilization of inductively coupled plasma mass spectrometry, conductivity measurements, X-ray photoelectron and diffuse reflectance spectroscopies, and density functional theory calculations. The results of Bader charge analysis and studies employing the Voronoi–Dirichlet partition of crystal structures are also presented. As an example of frameworks with different nodal arrangements, we have chosen MOFs with mononuclear, binuclear, and pentanuclear nodes, primarily consisting of first-row transition metals, that are incorporated in HHTP-, BTC-, and NIP-systems, respectively (HHTP³⁻ = triphenylene-2,3,6,7,10,11-hexaone; BTC³⁻ = 1,3,5-benzenetricarboxylate; and NIP²⁻ = 5-nitroisophthalate). Through probing framework electronic profiles, we demonstrate structure–property relationships, and also highlight the necessity for both comprehensive analysis of trends in metal properties, and novel avenues for preparation of heterometallic multinuclear isoreticular structures, which are critical components for on-demand tailoring of properties in heterometallic systems.

Metal node engineering in combination with modularity, topological diversity, and porosity of metal–organic frameworks (MOFs) could advance energy and optoelectronic sectors.

Zinc and Cadmium Complexes of Pyridinemethanol Carboxylates: Metal Carboxylate Zwitterions and Metal-Organic Frameworks

The heterofunctional lactone furo[3,4-b]pyridin-5(7H)-one (L₁ ) undergoes a coordination-induced ring-opening reaction with Zn(NO₃ )₂  ⋅ 6H₂ O to yield the zwitterionic [Zn(L₁ ')₂ (H₂ O)₂ ] (1, L₁ '=2-(hydroxymethyl)nicotinate) with an uncoordinated carboxylate. The same reaction with Cd(NO₃ )₂  ⋅ 4H₂ O provides a two-dimensional (2D) network of [Cd(L₁ ')₂ ]_n (3) with the carboxylates coordinated to cadmium(II) propagating the assembly. The corresponding reactions of Zn(NO₃ )₂  ⋅ 6H₂ O and Cd(NO₃ )₂  ⋅ 4H₂ O with 2-(hydroxymethyl)isonicotinic acid (HL₂ ) generated zwitterionic [Zn(L₂ )₂ (H₂ O)₂ ] (2) and a 2D network [Cd(L₂ )₂ ]_n ⋅nDMF (4, DMF=N,N'-dimethylformamide), respectively. Complexes 1-4 are weakly emissive, giving ligand-centered emissions at 409 nm (1), 412/436 nm (2), 404 nm (3), and 412/436 nm (4) in CHCl₃ solutions upon excitation at 330 nm. This work points to the potential of using 'hidden' functionalities widely found in small organic molecules and natural products for the construction of coordination complexes with new functionality and potential applications.

Kinked-Helix Actinide Polyrotaxanes from Weakly Bound Pseudorotaxane Linkers with Variable Conformations

The incorporation of a mechanically interlocked molecule such as pseudorotaxane into metal-organic coordination polymers has afforded plenty of new hybrid materials with special structures and unique properties. In this work, we employ a weakly bound cucurbit[6]uril (CB[6])-bipyridinium pseudorotaxane as a supramolecular precursor to assemble with uranyl, aiming to construct uranyl-rotaxane coordination polymers (URCPs) with intriguing structures. By adjusting the synthetic conditions, a new kinked-helix uranyl rotaxane compound (URCP3), together with three other compounds URCP1, URCP2, and URCP4 varying from 1D chains to 2D interwoven networks, was obtained. Detailed structural analyses indicate that the pseudorotaxane ligand (C8BPCA@CB[6]) shows great configuration diversity in the construction of URCPs, which is most probably due to the weak binding strength between the host and guest molecules. Specifically, based on the monodentate coordination of the end carboxyl groups of C8BPCA forced by the surrounding unilaterally-chelated oxalate, the entire flexible pseudorotaxane linker will be more likely to undergo conformational change, thereby binding to the uranyl center from both sides of the uranyl equatorial plane and promoting the formation of a kinked helix structure of URCP3 that is shaped like a Chinese knot along [001]. This work enriches the library of actinide-rotaxane compounds and provides a new approach to construct metal-organic compounds with complicated structures using weakly bonded pseudorotaxanes as well.

Highly Selective and Sensitive Turn-Off-On Fluorescent Probes for Sensing Al3+ Ions Designed by Regulating the Excited-State Intramolecular Proton Transfer Process in Metal-Organic Frameworks

The concept of high-performance excited-state intramolecular proton transfer (ESIPT)-based fluorescent metal-organic framework (MOF) probes for Al³⁺ is proposed in this work. By regulating the hydroxyl groups on the organic linker step by step, new fluorescent magnesium-organic framework (Mg-MOF) probes for Al³⁺ ions were established based on the ESIPT fluorescence mechanism. It is observed for the first time that the number of intramolecular hydrogen bonds between adjacent hydroxyl and carboxyl groups can effectively adjust the ESIPT process and lead to tunable fluorescence sensing performance. Together with the well-designed porous and anionic framework, the Mg-TPP-DHBDC probe decorating with a pair of intramolecular hydrogen bonds exhibits extra-high quantitative fluorescence response to Al³⁺ through an unusual turn-off (0-1.2 μM) and turn-on (4.2-15 μM) luminescence sensing mechanism. Notably, the 28 nM limit of detection value represents the lowest record among all reported MOF-based Al³⁺ fluorescent sensors up to now. Benefited from the unique turn-off-on ESIPT fluorescence detection process, the Mg-TPP-DHBDC MOF sensor exhibits single Al³⁺ detection compared with other 16 common metal ions including Ga³⁺, In³⁺, Fe³⁺, Cr³⁺, Ca²⁺, and Mg²⁺. Impressively, such an Al³⁺ selective sensing process can even be fulfilled by the reusable MOF test paper detected by naked eyes. Overall, the quantitative Al³⁺ detection, together with the extraordinary sensitivity, selectivity, fast response, and good reusability, strongly supports our concept of ESIPT-based fluorescent MOF Al³⁺ probes and makes Mg-TPP-DHBDC one of the most powerful Al³⁺ fluorescent sensors.

One-pot synthesis of a recyclable ratiometric fluorescent probe based on MOFs for turn-on sensing of Mg2+ ions and bioimaging in live cells

This work illustrates the design and construction of a fascinating recyclable ratiometric fluorescent probe based on MOFs (Fe₃O₄/RhB@Al-MOFs) via a simple one-step approach.

A new cluster-based chalcogenide zeolite analogue with a large inter-cluster bridging angle

A new cluster-based chalcogenide zeolite analogue with a large inter-cluster bridging angle.