Network topology diversification of porous organic salts

Hydrogen-bonded organic frameworks (HOFs) are porous organic materials constructed via hydrogen bonds. HOFs have solubility in specific high-polar organic solvents. Therefore, HOFs can be returned to their components and can be reconstructed, which indicates their high recyclability. Network topologies, which are the frameworks of porous structures, control the pore sizes and shapes of HOFs. Therefore, they strongly affect the functions of porous materials. However, hydrogen bonds are usually weak interactions, and the design of the intended network topology in HOFs from their components has been challenging. Porous organic salts (POSs) are an important class of HOFs, are hierarchically constructed via strong charge-assisted hydrogen bonds between sulfonic acids and amines, and therefore are expected to have high designability of the porous structure. However, the network topology of POSs has been limited to only dia-topology. Here, we combined tetrasulfonic acid with the adamantane core (4,4',4'',4'''-(adamantane-1,3,5,7-tetrayl)tetrabenzenesulfonic acid; AdPS) and triphenylmethylamines with modified substituents in para-positions of benzene rings (TPMA-X, X = F, methyl (Me), Cl, Br, I). We changed the steric hindrance between the adamantane and substituents (X) in TPMA-X and obtained not only the common dia-topology for POSs but also rare sod-topology, and lon- and uni-topologies that are formed for the first time in HOFs. Changing template molecules under preparation helped in successfully isolating the porous structures of AdPS/TPMA-Me with dia-, lon-, and sod-topologies which exhibited different gas adsorption properties. Therefore, for the first time, we demonstrated that the steric design of HOF components facilitated the formation, diversification, and control of the network topologies and functions of HOFs.

Metal-organic Frameworks in Semiconductor Devices

Metal-organic frameworks (MOFs) are a specific class of hybrid, crystalline, nano-porous materials made of metal-ion-based 'nodes' and organic linkers. Most of the studies on MOFs largely focused on porosity, chemical and structural diversity, gas sorption, sensing, drug delivery, catalysis, and separation applications. In contrast, much less reports paid attention to understanding and tuning the electrical properties of MOFs. Poor electrical conductivity of MOFs (~10-7-10-10 S cm-1), reported in earlier studies, impeded their applications in electronics, optoelectronics, and renewable energy storage. To overcome this drawback, the MOF community has adopted several intriguing strategies for electronic applications. The present review focuses on creatively designed bulk MOFs and surface-anchored MOFs (SURMOFs) with different metal nodes (from transition metals to lanthanides), ligand functionalities, and doping entities, allowing tuning and enhancement of electrical conductivity. Diverse platforms for MOFs-based electronic device fabrications, conductivity measurements, and underlying charge transport mechanisms are also addressed. Overall, the review highlights the pros and cons of MOFs-based electronics (MOFtronics), followed by an analysis of the future directions of research, including optimization of the MOF compositions, heterostructures, electrical contacts, device stacking, and further relevant options which can be of interest for MOF researchers and result in improved devices performance.

A bifunctionalised Pb-based MOF for iodine capture and dye removal

A 2-dimensional Pb(II) metal-organic framework, [Pb(bdc)_0.5(py-Phen)NO₃]_n (SM-3), was synthesized under solvothermal conditions using a mixed ligand approach. SM-3 was assembled using dinuclear SBUs [Pb₂(COO)₂]^2-, an oxygen donor H₂bdc = 1,4-benzene dicarboxylic acid, and nitrogen donor py-Phen = pyrazino[2,3-f][1,10]-phenanthroline linkers. SM-3 was characterized by elemental analysis, FT-IR, powder-X-ray diffraction, thermal gravimetric analysis, SEM, EDS, TEM, and single-crystal X-ray diffraction techniques. Crystallographic studies confirmed that SM-3 displays a 2D layered structure with unique anagostic (Pb⋯H) interactions. Interestingly, the presence of abundant π-electron-rich rings embellished with free -N donor sites in the framework makes SM-3 an excellent adsorbent that exhibits adsorption performance for iodine and dyes. The experimental results show that SM-3 reversibly adsorbs radioactive iodine in the solution and vapor phases and exhibits selective adsorption performance for hazardous cationic dyes, namely, methylene blue (MB) and rhodamine-B (Rh-B), from aqueous solution. Moreover, the possible mechanism of iodine and dye adsorption was also discussed in detail. Thus, this work is remarkable for coordination chemists to engineer layered MOFs for adsorption purposes and expands their potential characteristics by converting them into 2D MOF nanosheets to further enhance the adsorption of hazardous pollutants for environment protection.

A Zirconium-Organic Framework Constructed from Saddle-Shaped Tetratopic Carboxylate for High-Rate and -Efficiency Iodine Capture

Metal-organic frameworks (MOFs) exhibit strong potential for applications in molecular adsorption and separation because of their highly tunable structures and large specific surface areas and have also been used for iodine capture. However, most works on MOF-based iodine capture focus on the adsorption capacity while taking little consideration of the capture rate and efficiency. Herein, we report the design of a saddle-shaped tetratopic carboxylic acid containing four thiophene groups (H₄COTTBA) and the synthesis of a 4,8-connected flu-type zirconium MOF (HIAM-4014) using this linker. HIAM-4014 exhibits highly efficient iodine capture. The large cagelike pore structure, OH^- groups on the unsaturated Zr₆ clusters, electron-rich nature of the thiophene group in the linker, and high surface area are all attributed to the tetrahedral geometry of H₄COTTBA, which endows HIAM-4014 with a relatively high iodine adsorption capacity of 2.50 g/g within 2 h and an equilibrium adsorption capacity of 2.68 g/g after 5 h. Coupled with a high elution ratio and great recyclability, HIAM-4014 is a good candidate for the efficient removal of waste iodine.

An Azo-Group-Functionalized Porous Aromatic Framework for Achieving Highly Efficient Capture of Iodine

The strong radioactivity of iodine compounds derived from nuclear power plant wastes has motivated the development of highly efficient adsorbents. Porous aromatic frameworks (PAFs) have attracted much attention due to their low density and diverse structure. In this work, an azo group containing PAF solid, denoted as LNU-58, was prepared through Suzuki polymerization of tris-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-phenyl)-amine and 3,5-dibromoazobenzene building monomers. Based on the specific polarity properities of the azo groups, the electron-rich aromatic fragments in the hierarchical architecture efficiently capture iodine molecules with an adsorption capacity of 3533.11 mg g−1 (353 wt%) for gaseous iodine and 903.6 mg g−1 (90 wt%) for dissolved iodine. The iodine uptake per specific surface area up to 8.55 wt% m−2 g−1 achieves the highest level among all porous adsorbents. This work illustrates the successful preparation of a new type of porous adsorbent that is expected to be applied in the field of practical iodine adsorption.

Adsorption of iodine in metal-organic framework materials

Nuclear power will continue to provide energy for the foreseeable future, but it can pose significant challenges in terms of the disposal of waste and potential release of untreated radioactive substances. Iodine is a volatile product from uranium fission and is particularly problematic due to its solubility. Different isotopes of iodine present different issues for people and the environment. 129I has an extremely long half-life of 1.57 × 107 years and poses a long-term environmental risk due to bioaccumulation. In contrast, 131I has a shorter half-life of 8.02 days and poses a significant risk to human health. There is, therefore, an urgent need to develop secure, efficient and economic stores to capture and sequester ionic and neutral iodine residues. Metal-organic framework (MOF) materials are a new generation of solid sorbents that have wide potential applicability for gas adsorption and substrate binding, and recently there is emerging research on their use for the selective adsorptive removal of iodine. Herein, we review the state-of-the-art performance of MOFs for iodine adsorption and their host-guest chemistry. Various aspects are discussed, including establishing structure-property relationships between the functionality of the MOF host and iodine binding. The techniques and methodologies used for the characterisation of iodine adsorption and of iodine-loaded MOFs are also discussed together with strategies for designing new MOFs that show improved performance for iodine adsorption.

Aluminum molecular rings bearing amino-polyalcohol for iodine capture

Amino-polyalcohol-solvothermal synthesis leads to the isolation of a broad range of aluminum molecular rings, which exhibit considerable affinity towards iodine molecules.

Conductive Metal-Organic Frameworks: Electronic Structure and Electrochemical Applications

Smarter and minimization of devices are consistently substantial to shape the energy landscape. Significant amounts of endeavours have come forward as promising steps to surmount this formidable challenge. It is undeniable that material scientists were contemplating smarter material beyond purely inorganic or organic materials. To our delight, metal-organic frameworks (MOFs), an inorganic-organic hybrid scaffold with unprecedented tunability and smart functionalities, have recently started their journey as an alternative. In this review, we focus on such propitious potential of MOFs that was untapped over a long time. We cover the synthetic strategies and (or) post-synthetic modifications towards the formation of conductive MOFs and their underlying concepts of charge transfer with structural aspects. We addressed theoretical calculations with the experimental outcomes and spectroelectrochemistry, which will trigger vigorous impetus about intrinsic electronic behaviour of the conductive frameworks. Finally, we discussed electrocatalysts and energy storage devices stemming from conductive MOFs to meet energy demand in the near future.

A novel CdII-based metal–organic framework as a multi-responsive luminescent sensor for Fe3+, MnO4−, Cr2O72−, salicylaldehyde and ethylenediamine detection with high selectivity and sensitivity

A luminescent Cd^II-based MOF has been synthesized.

Biocompatible MOF-808 as an iodophor antimicrobial agent with controlled and sustained release of iodine

I2@MOF-808 was prepared to investigate the amount of I2 adsorbed on MOF-808. By antibacterial tests, it was also confirmed that it could be considered as a biocide without the problem of microbial resistance and instability of iodine.

Iodine Capture Using Zr-Based Metal-Organic Frameworks (Zr-MOFs): Adsorption Performance and Mechanism

The effective capture of radioiodine, produced or released from nuclear-related activities, is of paramount importance for the sustainable development of nuclear energy. Here, a series of zirconium-based metal-organic frameworks (Zr-MOFs), with a Zr₆(μ₃-O)₄(μ₃-OH)₄ cluster and various carboxylate linkers, were investigated for the capture of volatile iodine. Their adsorption kinetics and recyclability were investigated in dry and humid environments. The structural change of Zr-MOFs during iodine trapping was studied using powder X-ray diffraction and pore structure measurements. Experimental spectra (Raman and X-ray photoelectron spectroscopy) and density functional theory (DFT) calculations for the linkers and Zr clusters were performed to understand the trapping mechanism of the framework. When interacting with iodine molecules, MOF-808, NU-1000, and UiO-66, with highly connected and/or rigid linkers, have better structural stability than UiO-67 and MOF-867, which have flexible linkers with less connectivity. Particularly, MOF-808, with a rigid and tritopic benzenetricarboxylate linker, has the highest iodine adsorption capacity (2.18 g/g, 80 °C), as well as the largest pore volume after iodine elution. In contrast, UiO-67, with long linear ditopic linkers, exhibits the weakest stability and lowest adsorption capacity (0.53 g/g, 80 °C) because of its most serious collapse of pore structures. After incorporating with strong electron-donating imidazole/pyridine ligands, both the stability and adsorption capacity of MOF-808/NU-1000 decrease. DFT calculations verify that the N-heterocycle groups could enhance the affinity toward iodine by strong charge transfer. DFT calculations also suggest that the terminal -OH in MOF-808 has a strong affinity toward iodine (-54 kJ/mol I₂) and water (-63 kJ/mol H₂O) and a weak affinity toward NO₂ (-27 kJ/mol NO₂). With high adsorption capacity and excellent stability, MOF-808 shows great potential for the sustainable removal of radioiodine.

Iodine Adsorption in a Redox-Active Metal-Organic Framework: Electrical Conductivity Induced by Host-Guest Charge-Transfer

We report a comparative study of the binding of I2 (iodine) in a pair of redox-active metal-organic framework (MOF) materials, MFM-300(VIII) and its oxidized, deprotonated analogue, MFM-300(VIV). Adsorption of I2 in MFM-300(VIII) triggers a host-to-guest charge-transfer, accompanied by a partial (∼30%) oxidation of the VIII centers in the host framework and formation of I3- species residing in the MOF channels. Importantly, this charge-transfer induces a significant enhancement in the electrical conductivity (Δσ = 700000) of I2@MFM-300(VIII/IV) in comparison to MFM-300(VIII). In contrast, no host-guest charge-transfer or apparent change in the conductivity was observed upon adsorption of I2 in MFM-300(VIV). High-resolution synchrotron X-ray diffraction of I2@MFM-300(VIII/IV) confirms the first example of self-aggregation of adsorbed iodine species (I2 and I3-) into infinite helical chains within a MOF.

Insight into the structure and bonding of copper(i) iodide clusters and a cluster-based coordination polymer

The structure and chemical bonding pattern of selected copper(i) iodide clusters and a cluster-based coordination polymer are investigated using DFT.

Charge, adsorption, water stability and bandgap tuning of an anionic Cd(ii) porphyrinic metal–organic framework

By changing the occupancies of the metal ions and counterions, the tuning of the framework charge, band-edge position and bandgap of a novel Cd(ii) porphyrinic MOF 1 was achieved.

Irreversible solvent-assisted structural transformation in 3D metal-organic frameworks: Structural modification and enhanced iodine-adsorption properties

In this work, we demonstrate a solvent-assisted structural transformation between two 3D metal-organic frameworks (MOFs) ([Zn₄(α-bptc)₂(H₂O)₃]_n (1) → {[Zn₂(α-bptc)(H₂O)₄]·(pra)}_n (2)) (α-H₄bptc = 2,3,3',4'-biphenyl tetra-carboxylic acid and pra = pyridin-2-amine) at room temperature by immersing complex 1 in a mother solution. The structural transformation involves not only solvent exchange but also the cleavage and formation of coordination bonds, which is confirmed by infrared spectroscopy, single-crystal X-ray diffraction analysis, powder X-ray diffraction patterns, and thermogravimetric analysis. Structural analyses revealed that significant modifications occurred during the transformation including the changes in lattice parameters, unit cell volume, space group, coordination number, secondary building units, and topological type. In the case of drastic structural transitions, significant changes in properties were also observed. Complex 2 displayed the interesting uptake and release of iodine with the changes in visible color, UV and fluorescence spectra, and fully reversible I2 uptake of 8.5 mg g-1, which further suggested about its future application as iodine absorbing material.

Biporous Metal-Organic Framework with Tunable CO2/CH4 Separation Performance Facilitated by Intrinsic Flexibility

In this work, we report the synthesis of SION-8, a novel metal-organic framework (MOF) based on Ca(II) and a tetracarboxylate ligand TBAPy^4- endowed with two chemically distinct types of pores characterized by their hydrophobic and hydrophilic properties. By altering the activation conditions, we gained access to two bulk materials: the fully activated SION-8F and the partially activated SION-8P with exclusively the hydrophobic pores activated. SION-8P shows high affinity for both CO₂ ( Q_st = 28.4 kJ/mol) and CH₄ ( Q_st = 21.4 kJ/mol), while upon full activation, the difference in affinity for CO₂ ( Q_st = 23.4 kJ/mol) and CH₄ ( Q_st = 16.0 kJ/mol) is more pronounced. The intrinsic flexibility of both materials results in complex adsorption behavior and greater adsorption of gas molecules than if the materials were rigid. Their CO₂/CH₄ separation performance was tested in fixed-bed breakthrough experiments using binary gas mixtures of different compositions and rationalized in terms of molecular interactions. SION-8F showed a 40-160% increase (depending on the temperature and the gas mixture composition probed) of the CO₂/CH₄ dynamic breakthrough selectivity compared to SION-8P, demonstrating the possibility to rationally tune the separation performance of a single MOF by manipulating the stepwise activation made possible by the MOF's biporous nature.

Exploring the multifunctionality in metal–organic framework materials: how do the stilbenedicarboxylate and imidazolyl ligands tune the characteristics of coordination polymers?

A synergistic effect causes MOF materials to demonstrate excellent iodine vapor retention and luminescence properties.

Iodine-loaded metal organic framework as growth-triggered antimicrobial agent

Zeolitic imidazolate framework-8 (ZIF-8) is one of easily available metal organic frameworks because of its facile preparation via mixing aqueous solutions of zinc nitrate and 2-methylimidazole. It turned into a very effective pH-responsive bactericide after loading with iodine. Approximately, 0.9g of iodine could be readily loaded into one gram of ZIF-8 from iodine dissolved n-heptane solution. Both Gram-negative Escherichia coli and Gram-positive Staphylococcus epidermidis and Staphylococcus aureus could be very effectively killed by iodine loaded ZIF-8 (ZIF-8@I) at pH6.0 within 3min. In contrast, at pH above 7.0, no appreciable antimicrobial activity could be detected. The bacteria killing effect is resulted from the iodine released from ZIF-8@I disintegrated at acidic pH. ZIF-8@I coated surface also showed its acidic pH-triggered antimicrobial activity against deposited bacterial cells. The antimicrobial activity of ZIF-8@I against actively grown bacterial lawns on a pH neutral agar plate was also observed. The result demonstrates that iodine was released from the disintegrated ZIF-8@I to kill bacteria in response to the bacterial growth-induced pH lowering.

Capture of volatile iodine by newly prepared and characterized non-porous [CuI]n-based coordination polymers

Four new non-porous copper(i) iodide coordination polymers have been synthesized and demonstrate volatile iodine capture with simultaneous fluorescence quenching.

A Zn(ii) complex with large channels based on 3′-nitro-biphenyl-3,5,4′-tricarboxylic acid: synthesis, crystal structure, fluorescence sensing of ATP, ADP, GTP, and UTP in aqueous solution and drug delivery

A 3D Zn(ii)–MOF with large cubic channels was synthesized. It showed fluorescence sensing of ATP, ADP, GTP, and UTP. Furthermore, it exhibited a remarkable capacity for and controlled release of 5-fluorouracil.

Increase in Electrical Conductivity of MOF to Billion-Fold upon Filling the Nanochannels with Conducting Polymer

Redox-active pyrrole (Py) monomers were intercalated into 1D nanochannels of [Cd(NDC)0.5(PCA)]·Gx (H2NDC = 2,6-napthalenedicarboxylic acid, HPCA = 4-pyridinecarboxylic acid, G = guest molecules) (1) - a fluorescent 3D MOF (λem = 385 nm). Subsequent activation of 1⊃Py upon immersing into iodine (I2) solution resulted in an increment of the bulk electrical conductivity by ∼9 orders of magnitude. The unusual increase in conductivity was attributed to the formation of highly oriented and conducting polypyrrole (PPy) chains inside 1D nanochannels and specific host-guest interaction in 1⊃PPy thereof. The Hall-effect measurements suggested 1⊃PPy to be an n-type semiconductor material with remarkably high-carrier density (η) of ∼1.5 × 10(17) cm(-3) and mobility (μ) of ∼8.15 cm(2) V(-1) s(-1). The fluorescence property of 1 was almost retained in 1⊃PPy with concomitant exciplex-type emission at higher wavelength (λem = 520 nm). The here-presented results on [MOF⊃Conducting Polymer] systems in general will serve as a prototype experiment toward rational design for the development of highly conductive yet fluorescent MOF-based materials for various optoelectronic applications.

Coordination polymers of 5-substituted isophthalic acid

The synthesis and characterisation of five coordination polymers - Ni2(mip)2(H2O)8·2H2O (1), Zn6(mip)5(OH)2(H2O)4·7.4H2O (2), Zn6(mip)5(OH)2(H2O)2·4H2O (3), Mn(HMeOip)2 (4), and Mn3(tbip)2(Htbip)2(EtOH)2 (5) - are reported. Preliminary nitric oxide release data on compounds 2 and 3 are also given.

Cadmium metal–organic frameworks: Ln3+ ion functionalized assembly, fluorescence tuning and polymer film preparation

We obtain size-reduced Cd-MOFs with the assistance of sodium acetate, with the use of it, luminescent and transparent polymer films are prepared for further application.

Lanthanide contraction effects on the structures, thermostabilities, and CO2 adsorption and separation behaviors of isostructural lanthanide–organic frameworks

A systematic investigation of the CO₂ adsorption and separation behaviours of fourteen isostructural lanthanide–organic frameworks of lanthanide benzenetricarboxylate is executed.

Coordination polymers of ZnIIand 5-methoxy isophthalate

Four different coordination polymers were prepared by reaction of Zn(OAc)₂and 5-methoxy isophthalic acid using various aqueous/aqueous alcohol solvent systems.

Recent advances in metal–organic frameworks based on pyridylbenzoate ligands: properties and applications

In this mini-review we discuss the properties and applications of metal–organic frameworks based on pyridylbenzoate.