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

Stability of Iodine Species Trapped in Titanium-Based MOFs: MIL-125 and MIL-125_NH2

Two titanium-based MOFs MIL-125 and MIL-125_NH2 are synthesized and characterized using high-temperature powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), N2 sorption, Fourier transformed infrared spectroscopy (FTIR), Raman spectroscopy, ultraviolet-visible spectroscopy (UV-Vis), and electron paramagnetic resonance (EPR). Stable up to 300 °C, both compounds exhibited similar specific surface areas (SSA) values (1207 and 1099 m2 g-1 for MIL-125 and MIL-125_NH2, respectively). EPR signals of Ti3+ are observed in both, whith MIL-125_NH2 also showing ─NH2 ●+ signatures. Both MOFs efficiently adsorbed iodine in continuous gas flow over five days, with MIL-125 trapping 1.9 g.g-1 and MIL-125_NH2 trapping 1.6 g.g-1. MIL-125_NH2 exhibited faster adsorption kinetics due to its smaller band gap (2.5 against 3.6 eV). In situ Raman spectroscopy conducted during iodine adsorption revealed signal evolution from "free" I2 to "perturbed" I2, and I3 -. TGA and in situ Raman desorption experiments showed that ─NH2 groups improved the stabilization of I3 - due to an electrostatic interaction with NH2 ●+BDC radicals. The Albery model indicated longer lifetimes for iodine desorption in I2@MIL-125_NH2, attributed to a rate-limiting step due to stronger interaction between the anionic iodine species and the ─NH2 ●+ radicals. This study underscores how MOFs with efficient charge separation and hole-stabilizer functional groups enhance iodine stability at higher temperatures.

Porous organic materials for iodine adsorption

The nuclear industry will continue to develop rapidly and produce energy in the foreseeable future; however, it presents unique challenges regarding the disposal of released waste radionuclides because of their volatility and long half-life. The release of radioactive isotopes of iodine from uranium fission reactions is a challenge. Although various adsorbents have been explored for the uptake of iodine, there is still interest in novel adsorbents. The novel adsorbents should be synthesized using reliable and economically feasible synthetic procedures. Herein, we discussed the state-of-the-art performance of various categories of porous organic materials including covalent organic frameworks, covalent triazine frameworks, porous aromatic frameworks, porous organic cages, among other porous organic polymers for the uptake of iodine. This review discussed the synthesis of porous organic materials and their iodine adsorption capacity and reusability. Finally, the challenges and prospects for iodine capture using porous organic materials are highlighted.

Bi0-Reduced Graphene Oxide Composites for the Enhanced Capture and Cold Immobilization of Off-Gas Radioactive Iodine

Radioactive waste management is critical for maintaining the sustainability of nuclear fuel cycles. In this study, we propose a novel bismuth-based reduced graphene oxide (Bi0-rGO) composite for the immobilization of off-gas radioactive iodine. This material synthesized via a solvothermal route exhibited a low surface area (2.96 m2/g) combined with a maximum iodine sorption capacity of 1228 ± 25 mg/g at 200 °C. The iodine sorbent was mixed with Bi2O3 powder and distilled water to fabricate waste matrices, which were cold-sintered at 300 °C under a uniaxial pressure of 500 MPa for 20 min to achieve a relative density of ∼98% and Vickers hardness of 1.3 ± 0.1 GPa. The utilized methodology reduced the iodine leaching rate by approximately 3 orders of magnitude through the formation of a chemically durable iodine-bearing waste form (BiOI). This study demonstrates the high potential of Bi0-rGO as an innovative solution for the immobilization of radioactive waste at relatively low temperatures.

Iodine Molecules within Triethylenediamine-Based Metal-Organic Frameworks for Hydrolysis/Alkylation Tandem Reactions

The integration of radionuclide iodine molecules in metal-organic frameworks (MOFs) for organic synthesis is attracting considerable research attention due to their specific catalytic performance. However, understanding the comprehensive catalytic behaviors of different types of molecular iodine encapsulated in MOFs for a sequential organic transformation is a great challenge. To address this issue, we have designed two triethylenediamine-functionalized MOFs assembled from 1,3,5-tricarboxyphenyl-2-(triethylenediaminemethyl)benzene-linker and {Cd(COO)3N} or {Cu4(u3-OH)2(COO)6N} clusters. Both MOFs show good stability and adsorption of I2 in the solution and vapor phases. Catalysts obtained after treatment with ethyl acetate present efficient catalytic activity in hydrolysis/alkylation tandem reactions in water. The mechanistic investigations disclose a sequential catalytic process comprising a "hidden" Brønsted acid catalytic hydrolysis of acetals to aldehydes followed by the I2-bonding Lewis acid catalytic alkylation of aldehydes to 3,3'-disubstituted 1H-indoles.

Electron-Donor Functional Groups, Band Gap Tailoring, and Efficient Charge Separation: Three Keys To Improve the Gaseous Iodine Uptake in MOF Materials

Metal-organic frameworks (MOFs) have been largely investigated worldwide for their use in the capture of radioactive iodine due to its potential release during nuclear accident events and reprocessing of nuclear fuel. The present work deals with the capture of gaseous I₂ under a continuous flow and its subsequent transformation into I₃^- within the porous structures of three distinct, yet structurally related, terephthalate-based MOFs: MIL-125(Ti), MIL-125(Ti)_NH₂, and CAU-1(Al)_NH₂. The synthesized materials exhibited specific surface areas (SSAs) with similar order of magnitude: 1207, 1099, and 1110 m² g^-1 for MIL-125(Ti), MIL-125(Ti)_NH₂, and CAU-1(Al)_NH₂, respectively. Because of that, it was possible to evaluate the influence of other variables over the iodine uptake capacity─such as band gap energies, functional groups, and charge transfer complexes (CTC). After 72 h of contact with the I₂ gas flow, MIL-125(Ti)_NH₂ was able to trap 11.0 mol mol^-1 of I₂, followed by MIL-125(Ti) (8.7 mol mol^-1), and by CAU-1(Al)_NH₂ (4.2 mol mol^-1). The enhanced ability to retain I₂ in the MIL-125(Ti)_NH₂ was associated with a combined effect between its amino group (which has a great affinity toward iodine), its smaller band gap (2.5 eV against 2.6 and 3.8 eV for CAU-1(Al)_NH₂ and MIL-125(Ti), respectively), and its efficient charge separation. In fact, the presence of a linker-to-metal charge transfer (LMCT) mechanism in MIL-125(Ti) compounds separates the photogenerated electrons and holes into the two distinct moieties of the MOF: the organic linker (which stabilizes the holes) and the oxy/hydroxy inorganic cluster (which stabilizes the electrons). This effect was observed using EPR spectroscopy, whereas the reduction of the Ti⁴⁺ cations into the paramagnetic Ti³⁺ species was evidenced after irradiation of the pristine Ti-based MOFs with UV light (<420 nm). In contrast, because CAU-1(Al)_NH₂ exhibits a purely linker-based transition (LBT)─with no EPR signals related to Al paramagnetic species─it tends to exhibit faster recombination of the photogenerated charge carriers as, in this case, both electrons and holes are located over the organic linker. Furthermore, the transformation of the gaseous I₂ into I_n^- [n = 5, 7, 9, ...] intermediates and then into I₃^- species was evaluated using Raman spectroscopy by following the evolution of their respective bands at about 198, 180, and 113 cm^-1. This conversion─which is favored by an effective charge separation and smaller band gaps─increases the I₂ uptake capacity of the compounds by creating specific adsorption sites for these anionic species. In fact, because the -NH₂ groups act as an antenna to stabilize the photogenerated holes, both I_n^- and I₃^- are adsorbed into the organic linker via an electrostatic interaction with these positively charged entities. Finally, changes regarding the EPR spectra before and after the iodine loading were considered to propose a mechanism for the electron transfer from the MOFs structure to the I₂ molecules considering their different characteristics.

Effect of Spatial Heterogeneity on the Unusual Uptake Behavior of Multivariate-Metal-Organic Frameworks

The uniqueness of multivariate metal-organic frameworks (MTV-MOFs) has been widely explored to discover their unknown opportunities. While mesoscopic apportionments have been studied, macroscopic heterogeneity and its spatial effects remain unexplored in MTV-MOFs. In this study, we investigated the effect of macroscopic heterogeneity on MTV-MOFs on their uptake behaviors by comparing three types of MTV-MOFs having the functional groups in inner, outer, or entire parts of crystals. Their adsorption behavior for carbon dioxide (CO₂) and water (H₂O) brought out that functional groups located in the outer part of the crystals dominantly influence the sorption behavior of MTV-MOFs. These results are also visualized by observing iodine adsorption in the three types of MTV-MOFs using scanning transmission electron microscopy-electron energy loss spectroscopy. We believe that this finding provides new ways to decipher and design MTV-MOFs for their unusual properties.

Enhanced Thermoelectric Properties of a Semiconducting Two-Dimensional Metal-Organic Framework via Iodine Loading

We report the first result of a study in which molecular iodine has been incorporated via incipient wetness impregnation into the two-dimensional semiconducting metal-organic framework (MOF) Cu₃(2,3,6,7,10,11-hexahydroxytriphenylene)₂ Cu₃(HHTP)₂ to enhance its thermoelectric properties. A power factor of 0.757 μW m^-1 K^-2 for this MOF was obtained which demonstrates that this provides an effective route for the preparation of moderate-performance thermoelectric MOFs.

Recent advances in the removal of radioactive iodine by bismuth-based materials

Nowadays, the demand for nuclear power is continue increasing due to its safety, cleanliness, and high economic benefits. Radioactive iodine from nuclear accidents and nuclear waste treatment processes poses a threat to humans and the environment. Therefore, the capture and storage of radioactive iodine are vital. Bismuth-based (Bi-based) materials have drawn much attention as low-toxicity and economical materials for removing and immobilizing iodine. Recent advances in adsorption and immobilization of vapor iodine by the Bi-based materials are discussed in this review, in addition with the removal of iodine from solution. It points out the neglected areas in this research topic and provides suggestions for further development and application of Bi-based materials in the removal of radioactive iodine.

Synthesis of a Triazaisotruxene-Based Porous Organic Polymer and Its Application in Iodine Capture

A new triazaisotruxene-based porous organic polymer (POP) was designed and successfully synthesized by a FeCl₃-promoted crosslinking reaction. As a result of its porosity and good thermal stability, the designed POP can be utilized as a promising adsorbent for iodine, not only in the gaseous phase, but also in organic and aqueous solutions. Compared to its triazatruxene (TN) analogue, the ITN-based POP shows equal iodine uptake in the gaseous phase and in hexane solution, and better uptake in aqueous solution.

Energy‐Efficient Iodine Uptake by a Molecular Host⋅Guest Crystal

Recently, porous organic crystals (POC) based on macrocycles have shown exceptional sorption and separation properties. Yet, the impact of guest presence inside a macrocycle prior to adsorption has not been studied. Here we show that the inclusion of trimethoxybenzyl-azaphosphatrane in the macrocycle cucurbit[8]uril (CB[8]) affords molecular porous host⋅guest crystals (PHGC-1) with radically new properties. Unactivated hydrated PHGC-1 adsorbed iodine spontaneously and selectively at room temperature and atmospheric pressure. The absence of (i) heat for material synthesis, (ii) moisture sensitivity, and (iii) energy-intensive steps for pore activation are attractive attributes for decreasing the energy costs. ¹ H NMR and DOSY were instrumental for monitoring the H₂ O/I₂ exchange. PHGC-1 crystals are non-centrosymmetric and I₂ -doped crystals showed markedly different second harmonic generation (SHG), which suggests that iodine doping could be used to modulate the non-linear optical properties of porous organic crystals.

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.

Leveraging Nitrogen Linkages in the Formation of a Porous Thorium-Organic Nanotube Suitable for Iodine Capture

We report the synthesis, characterization, and iodine capture application of a novel thorium-organic nanotube, TSN-626, [Th₆O₄(OH)₄(C₆H₄NO₂)₇(CHO₂)₅(H₂O)₃]·3H₂O. The classification as a metal-organic nanotube (MONT) distinguishes it as a rare and reduced dimensionality subset of metal-organic frameworks (MOFs); the structure is additionally hallmarked by low node connectivity. TSN-626 is composed of hexameric thorium secondary building units and mixed O/N-donor isonicotinate ligands that demonstrate selective ditopicity, yielding both terminating and bridging moieties. Because hard Lewis acid tetravalent metals have a propensity to bind with electron donors of rival hardness (e.g., carboxylate groups), such Th-N coordination in a MOF is uncommon. However, the formation of key structural Th-N bonds in TSN-626 cap some of the square antiprismatic metal centers, a position usually occupied by terminal water ligands. TSN-626 was characterized by using complementary analytical and computational techniques: X-ray diffraction, vibrational spectroscopy, N₂ physisorption isotherms, and density functional theory. TSN-626 satisfies design aspects for the chemisorption of iodine. The synergy between accessibility through pores, vacancies at the metal-oxo nodes, and pendent N-donor sites allowed a saturated iodine loading of 955 mg g^-1 by vapor methods. The crystallization of TSN-626 diversifies actinide-MOF linker selection to include soft electron donors, and these Th-N linkages can be leveraged for the investigation of metal-to-ligand bonding and unconventional topological expressions.

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.

Capture of Gaseous Iodine in Isoreticular Zirconium-Based UiO-n Metal-Organic Frameworks: Influence of Amino Functionalization, DFT Calculations, Raman and EPR Spectroscopic Investigation

A series of Zr-based UiO-n MOF materials (n=66, 67, 68) have been studied for iodine capture. Gaseous iodine adsorption was collected kinetically from a home-made set-up allowing the continuous measurement of iodine content trapped within UiO-n compounds, with organic functionalities (-H, -CH₃ , -Cl, -Br, -(OH)₂ , -NO₂ , -NH₂ , (-NH₂ )₂ , -CH₂ NH₂ ) by in-situ UV-Vis spectroscopy. This study emphasizes the role of the amino groups attached to the aromatic rings of the ligands connecting the {Zr₆ O₄ (OH)₄ } brick. In particular, the preferential interaction of iodine with lone-pair groups, such as amino functions, has been experimentally observed and is also based on DFT calculations. Indeed, higher iodine contents were systematically measured for amino-functionalized UiO-66 or UiO-67, compared to the pristine material (up to 1211 mg/g for UiO-67-(NH₂ )₂ ). However, DFT calculations revealed the highest computed interaction energies for alkylamine groups (-CH₂ NH₂ ) in UiO-67 (-128.5 kJ/mol for the octahedral cavity), and pointed out the influence of this specific functionality compared with that of an aromatic amine. The encapsulation of iodine within the pore system of UiO-n materials and their amino-derivatives has been analyzed by UV-Vis and Raman spectroscopy. We showed that a systematic conversion of molecular iodine (I₂ ) species into anionic I^- ones, stabilized as I^- ⋅⋅⋅I₂ or I₃ ^- complexes within the MOF cavities, occurs when I₂ @UiO-n samples are left in ambient light.

Bromine Vapor Induced Continuous p- to n-Type Conversion of a Semiconductive Metal-Organic Framework Cu[Cu(pdt)2]

Guest-promoted modulation of the electronic states in metal-organic frameworks (MOFs) has brought about a new field of interdisciplinary research, including host-guest chemistry and solid-state physics. Although there are dozens of studies on guest-promoted enhancement of the electrical conductivity properties, including stoichiometry, conductive carriers and structure-property relationships have been scarcely studied in detail. Herein, we studied the effects of continuous and controlled bromine vapor doping on structural, optical, thermoelectric, and semiconducting properties of Cu[Cu(pdt)₂] (pdt = 2,3-pyrazinedithiolate) as a function of bromine stoichiometry. We demonstrated that the same material could act as both p- and n-type semiconductors by tuning the stoichiometry of Br doped in Br_x@Cu[Cu(pdt)₂], and a change in the charge-carrier type from holes in pristine MOF to electrons upon bromine vapor doping was observed. Bromine molecules acted as an oxidant, causing the selective oxidation of [Cu^II(pdt)₂] in the host framework. In addition, a redox hopping pathway between the partially oxidized Cu^II/Cu^III center contributed to the enhancement of the electrical conductivity of the MOF.

Zn(II) and Co(II) 3D Coordination Polymers Based on 2-Iodoterephtalic Acid and 1,2-bis(4-pyridyl)ethane: Structures and Sorption Properties

Metal-organic frameworks [M₂(2-I-bdc)₂bpe] (M = Zn(II) (1), Co(II) (2), 2-I-bdc = 2-iodoterephtalic acid, and bpe = 1,2-bis(4-pyridyl)ethane) were prepared and characterized by X-ray diffractometry. Both compounds retain their 3D structure after the removal of guest DMF molecules. Selectivity of sorption of different organic substrates from the gas phase was investigated for both complexes.

Facile synthesis of novel Bi0-SBA-15 adsorbents by an improved impregnation reduction method for highly efficient capture of iodine gas

Development of high efficient adsorbents to capture iodine is of great significance for the active development of nuclear power. Herein, Bi⁰-SBA-15 was firstly synthesized and applied for capture of iodine gas. Bi⁰-SBA-15 materials were prepared by an improved impregnation reduction method. The benefit of this method was that the Bi⁰ nanoparticles with flocculent and spherical morphologies were loaded on the surface of SBA-15, which provide abundant active sites for iodine and improve the utilization rate of active sites, so as to attain a record high capture capacity (up to 925 mg/g within 60 min) and high stablitiy (91.2%) at 200 °C. The results demonstrated that the loading of Bi⁰ on the surface showed a significant impact on the structure of Bi⁰-SBA-15 and did greatly enhance the iodine capture. Furthermore, the high iodine capture capacity mainly derived from the chemical adsorption in the stable form of BiI₃. The obtained Bi⁰-SBA-15 materials exhibited excellent aqueous and irradiation stability. Thus, the results indicated that the new and highly efficient Bi⁰-SBA-15 was a potential radioactive iodine gas capture material.

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.

Heterometallic Actinide-Containing Photoresponsive Metal-Organic Frameworks: Dynamic and Static Tuning of Electronic Properties

Acquiring fundamental knowledge of properties of actinide-based materials is a necessary step to create new possibilities for addressing the current challenges in the nuclear energy and nuclear waste sectors. In this report, we established a photophysics-electronics correlation for actinide-containing metal-organic frameworks (An-MOFs) as a function of excitation wavelength, for the first time. A stepwise approach for dynamically modulating electronic properties was applied for the first time towards actinide-based heterometallic MOFs through integration of photochromic linkers. Optical cycling, modeling of density of states near the Fermi edge, conductivity measurements, and photoisomerization kinetics were employed to shed light on the process of tailoring optoelectronic properties of An-MOFs. Furthermore, the first photochromic MOF-based field-effect transistor, in which the field-effect response could be changed through light exposure, was constructed. As a demonstration, the change in current upon light exposure was sufficient to operate a two-LED fail-safe indicator circuit.

Cationic Nonporous Macrocyclic Organic Compounds for Multimedia Iodine Capture

Over the past two decades, progress in chemistry has generated various types of porous materials for removing iodine (¹²⁹ I or ¹³¹ I) that can be formed during nuclear energy generation or nuclear waste storage. However, most studies for iodine capture are based on the weak host-guest interactions of the porous materials. Here, we present two cationic nonporous macrocyclic organic compounds, namely, MOC-1 and MOC-2, in which 6I^- and 8I^- were as counter anions, for highly efficient iodine capture. MOC-1 and MOC-2 were formed by reacting 1,1'-diamino-4,4'-bipyridylium di-iodide with 1,2-diformylbenzene or 1,3-diformylbenzene, respectively. The presence of a large number of I^- anions results in high I₂ affinity with uptake capacities up to 2.15 g ⋅ g^-1 for MOC-1 and 2.25 g ⋅ g^-1 for MOC-2.

Tunable Strategies Involving Flexibility and Angularity of Dual Linkers for a 3D Metal-Organic Framework Capable of Multimedia Iodine Capture

The widespread use of nuclear power poses severe health and environmental risks owing to the nonregulated release and disposal of radioactive wastes in the environment. Among these wastes, the capture and removal of radioactive iodine poses a big challenge. To develop a novel material for capturing molecular iodine, we have strategically synthesized a nitrogen-rich three-dimensional (3D) metal-organic framework (MOF), {[Mn₂(oxdz)₂(tpbn)(H₂O)₂]·2C₂H₅OH}_n (1), utilizing a bent heterocyclic dicarboxylate linker (H₂oxdz: (4,4'-(1,3,4-oxadiazole-2,5-diyl)dibenzoic acid)) and a flexible bis(tridentate) ligand (tpbn: N, N', N″, N‴-tetrakis(2-pyridylmethyl)-1,4-diaminobutane). Based on its single-crystal structure, 1 is an eightfold interpenetrated 3D framework, consisting of a unique 4-connected {Mn₂(tpbn)} subunit, in which the pores line up with the nitrogen atoms of the oxadiazole moiety. This can be considered as a big leap for the development of 3D MOFs using flexible bis(tridentate) ligands. To emphasize the role of the flexible methylene chain length in such ligand in the dimensionality of the resultant framework, the tphn (N, N', N″, N‴-tetrakis(2-pyridylmethyl)-1,6-diaminohexane) ligand with two additional methylene groups provides a one-dimensional (1D) CP {[Mn₂(oxdz)₂(tphn)(H₂O)]·CH₃OH}_n (2). This spacer chain lengthening has a profound effect on the coordination of such ligand with Mn(II), further affecting the binding of oxdz. The inherent polarizable nature of the oxadiazole moiety and the presence of permanent pore of dimensions (19.122 × 19.253 Ų) in 1 have been exploited for the capture/removal of iodine not only from vapor and an organic solution but also from an aqueous media. It exhibits competent 100% reversible sorption of iodine with an uptake capacity of (1.1 ± 0.05) g/g of 1. The uptake value has been corroborated by both gravimetric and titrimetric analyses. The interaction of iodine with 1 has been notably studied with molecular simulations, kinetic models of sorption, field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDX) analysis. Moreover, 1 is highly stable and is recyclable without much loss of sorption capability up to five cycles.

Coordination polymers for n-type thermoelectric applications

Coordination polymers (CPs) are potential thermoelectric (TE) materials to replace the sometimes costly, brittle and toxic heavy metal inorganic TEs for near-ambient-temperature applications. Air-stable and highly conductive p-type thermoelectric CPs are relatively well known, but the their n-type counterparts are only now emerging and both are needed for most practical applications. This perspective reviews recent advances in the development of n-type thermoelectric CPs, particularly the 1D and 2D metal bisdithiolenes, and introduces a relatively new class of guest@metal-organic framework(MOF)-based composites. Low dimensional CPs with reasonable n-type thermoelectric performance are emerging with good charge mobility and air-stability but still relatively low electrical conductivity.

Electrically Conductive Metal-Organic Frameworks

Metal–organic frameworks (MOFs) are intrinsically porous extended solids formed by coordination bonding between organic ligands and metal ions or clusters. High electrical conductivity is rare in MOFs, yet it allows for diverse applications in electrocatalysis, charge storage, and chemiresistive sensing, among others. In this Review, we discuss the efforts undertaken so far to achieve efficient charge transport in MOFs. We focus on four common strategies that have been harnessed toward high conductivities. In the “through-bond” approach, continuous chains of coordination bonds between the metal centers and ligands’ functional groups create charge transport pathways. In the “extended conjugation” approach, the metals and entire ligands form large delocalized systems. The “through-space” approach harnesses the π–π stacking interactions between organic moieties. The “guest-promoted” approach utilizes the inherent porosity of MOFs and host–guest interactions. Studies utilizing less defined transport pathways are also evaluated. For each approach, we give a systematic overview of the structures and transport properties of relevant materials. We consider the benefits and limitations of strategies developed thus far and provide an overview of outstanding challenges in conductive MOFs.

Open metal site (OMS) and Lewis basic site (LBS)-functionalized copper–organic framework with high CO2 uptake performance and highly selective CO2/N2 and CO2/CH4 separation

A robust porous metal–organic framework with dual functionalities of open metal sites (OMSs) and O-rich Lewis basic sites (LBSs) has been designed and synthesized, and shows high CO₂ uptake and excellent selectivity for CO₂ over N₂ and CH₄.

Electrical conductivity and magnetic bistability in metal–organic frameworks and coordination polymers: charge transport and spin crossover at the nanoscale

This review aims to reassess the progress, issues and opportunities in the path towards integrating conductive and magnetically bistable coordination polymers and metal–organic frameworks as active components in electronic devices.

Crystal engineering of coordination-polymer-based iodine adsorbents using a π-electron-rich polycarboxylate aryl ether ligand

This work revealed that the synergy of microporous channels and convergent arrangements of halogen bonding and charge-transfer interaction sites within coordination polymers facilitated the iodine adsorption process.