New Hg(II) coordination polymers based on a thioimidazole ligand with good performance to detoxify Hg(II) and reversibly capture iodine

In the current paper, we have successfully synthesized three new mercury coordination polymers with fascinating structures and properties via a flexible sulfur donor ligand, namely, {[Hg(μ₂-Cl)(μ₂-Ls)]}_n[BF₄]_n(1), {[Hg(μ₂-Cl)(μ₂-Ls)]}_n[ClO₄]_n(2), and [Hg(SCN)₂(μ₂-Ls)]_n(3) [Ls = 1,1-bis(3-methyl-4-imidazoline-2-thione)methane]. These complexes have been characterized by means of different techniques such as single crystal X-ray crystallography, FT-IR, elemental analysis (CHNS), UV-Vis, PXRD, BET, and TGA. Suitable single crystals of all complexes were obtained using the branch tube method with a very high yield and good stability due to the high affinity of mercury to bind to the thione groups. The cationic moieties of polymers 1 and 2 were isostructural, with a HgCl₂S₂ coordination core structure. The voids of the quasi-hexagonal packing of the columnar chains were occupied by unbonded tetrahedral BF₄^- ions in 1 and perchlorate anions in polymer 2. Polymer 3 has a less distorted tetrahedral geometry than 1 and 2, with a HgS₄ core structure. By considering the thiophilicity of mercury, a thioamide-based Ls ligand was used to detoxify Hg(II) into insoluble polymers 1-3. The results of an MTT assay for (HepG2) liver cells confirmed the excellent cytoprotective effect of this ligand against mercury. Based on IC₅₀ calculations, their toxicity was in order of polymer 1 > polymer 2 > polymer 3. These polymers were also considered as adsorbents for the reversible removal of iodine from solution and the kinetics of the process has been studied in detail. Interestingly, all of them showed an excellent stability and high capacity, in order of 763.53 mg g^-1, 877.10 mg g^-1, and 905.31 mg g^-1 for polymers 1-3, respectively.

Cluster-Based Crystalline Materials for Iodine Capture

The treatment of radioactive iodine in nuclear waste has always been a critical issue of social concern. The rational design of targeted and efficient capture materials is of great significance to the sustainable development of the ecological environment. In recent decades, crystalline materials have served as a molecular platform to study the binding process and capture mechanism of iodine molecules, enabling people to understand the interaction between radioactive iodine guests and pores intuitively. Cluster-based crystalline materials, including molecular clusters and cluster-based metal-organic frameworks, are emerging candidates for iodine capture due to their aggregative binding sites, precise structural information, tunable pores/packing patterns, and abundant modifications. Herein, recent progress of different types of cluster materials and cluster-dominated metal-organic porous materials for iodine capture is reviewed. Research prospects, design strategies to improve the affinity for iodine and possible capture mechanisms are discussed.

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.

Halogen Bonding Adsorbent Pyridine N-oxides for Iodine Capture in Water

Rapid capture of ¹²⁹ I with high volatility and toxicity in the environment has attracted much attention. Herein we reported a firstly synthesized nonporous material: pyridine N-oxides (NTPO and ATPO) as iodine adsorbent. Both of NTPO and ATPO exhibit remarkable performance on the adsorption of iodine in aqueous solution, vapor state and organic solvents. Upon the capture of iodine, pyridine N-oxides were transformed to binary cocrystals combined with the pyridine N-oxides and iodine which is driven by halogen bond between iodine and oxygen atoms. Moreover, pyridine N-oxides shows high chemical, thermal and moisture stability.

Tunable Proton Conductivity and Color in a Nonporous Coordination Polymer via Lattice Accommodation to Small Molecules

Nonporous coordination polymers (npCPs) able to accommodate molecules through internal lattice reorganization are uncommon materials with applications in sensing and selective gas adsorption. Proton conduction, extensively studied in the analogue metal-organic frameworks under high-humidity conditions, is however largely unexplored in spite of the opportunities provided by the particular sensitivity of npCPs to lattice perturbations. Here, AC admittance spectroscopy is used to unveil the mechanism behind charge transport in the nonporous 1·2CH3 CN. The conductance in the crystals is found to be of protonic origin. A vehicle mechanism is triggered by the dynamics of the weakly coupled acetonitrile molecules in the lattice that can be maintained by a combination of thermal cycles, even at low humidity levels. An analogue 1·pyrrole npCP is formed by in situ exchange of these weakly bound acetonitrile molecules by pyrrole. The color and conduction properties are determined by the molecules weakly bonded in the lattice. This is the first example of acetonitrile-mediated proton transport in an npCP showing distinct optical response to different molecules. These findings open the door to the design of switchable protonic conductors and capacitive sensors working at low humidity levels and with selectivity to different molecules.

Stepwise Observation of Iodine Diffusion in a Flexible Coordination Network Having Dual Interactive Sites

We created dual interactive sites in a porous coordination network using a CuI cluster and a rotation-restricted ligand, tetra(3-pyridyl)phenylmethane (3-TPPM). The dual interactive sites of iodide and Cu ions can adsorb I₂ via four-step processes including two chemisorption processes. Initially, one I₂ molecule was physisorbed in a pore and successively chemisorbed on iodide sites of the pore surface, and then the next I₂ molecule was physisorbed and chemisorbed on Cu ions to form a cross-linked network. We revealed the four-step I₂ diffusion process by single-crystal X-ray structure determination and spectroscopic kinetic analysis.

Copper(i)–iodide cluster structures as functional and processable platform materials

This review provides a complete overview of the progress towards implementation of CuI-nanoclusters in functional materials and devices.

Capture of iodine in solution and vapor phases by newly synthesized and characterized encapsulated Cu2O nanoparticles into the TMU-17-NH2 MOF

The efficient capture and storage of radioactive iodine (¹²⁹I or ¹³¹I) formed during the extensive use of nuclear energy is of paramount importance. Therefore, it is a great deal to design new adsorbents for effectively disposing of iodine from nuclear waste. In this work, a new Cu₂O/TMU-17-NH₂ composite has been prepared by a simple encapsulation of Cu₂O nanoparticles (NPs) into the metal organic framework (MOF) TMU-17-NH₂ for the first time. The as-synthesized Cu₂O/TMU-17-NH₂ was fully characterized in details and the iodine sorption/release capability of the Cu₂O/TMU-17-NH₂ composite has been investigated both in solution and in the vapor phase. According to the FE-SEM images, the Cu₂O/TMU-17-NH₂ was obtained with same morphology to that of the pristine TMU-17-NH₂. The I₂ sorption/release experiments were examined by UV-vis spectroscopy. The optimal iodine sorption was obtained by almost complete removal of iodine with a sorption capacity of about 567 mg/g. Detailed experimental evidence demonstrating that the iodine was captured by chemisorption process. Furthermore, photoluminescence (PL) properties of Cu₂O/TMU-17-NH₂ have also been investigated in which indicate that the Cu₂O/TMU-17-NH₂ composite exhibits stronger emission than the pristine TMU-17-NH₂.

Bisimidazole-based phosphorescent thiocyanatocadmates

Simple room-temperature self-assemblies between Cd2+ salts, SCN- and bisimidazole molecules at pH = 2 created three new organically templated thiocyanatocadmates [H2(L1)][Cd(SCN)4]·H2O (L1 = 1,4-bis(1H-imidazol-1-yl)benzene) 1, [H2(L2)][Cd(SCN)4] (L2 = 1,3-bis(2-methylimidazol-1-yl)propane) 2, and [H2(L3)][Cd2(SCN)6] (L3 = 1,4-bis(2-methyl-1H-imidazol-1-yl)butane) 3. X-ray single-crystal diffraction analysis reveals that (i) in 1-3, the SCN- groups doubly bridge the Cd2+ centers to form different thiocyanatocadmates: a linear chain in 1; a zigzag chain in 2; and a 2-D layer network (63 net) in 3; and (ii) in 1, via Nbase-HNSCN interactions, the L1 molecules extend the thiocyanatocadmate chains into a 2-D supramolecular layer, whereas in 2, the zigzag thiocyanatocadmate chains self-assemble into a 3-D supramolecular network via weak SS interactions. Photoluminescence analysis indicates that the three title compounds all emit light: blue light for 1 and 2 and green light for 3. At low temperatures, the emission positions of the three compounds hardly change, but the emission intensities are largely enhanced. Interestingly, after turning off the UV lamp, 1 and 2 still briefly emit light (ca. 2 s), which means that 1 and 2 possess phosphorescence properties. Phosphorescence lifetimes at 77 K are 1619 ms for 1 and 247 ms for 2.

Copper(i)-polymers and their photoluminescence thermochromism properties

Under hydro(solvo)thermal conditions, four organic bidentate bridging N,N'-donor ligands 1,3-bis(2-methylimidazol-1-yl)propane (L1), 4,4'-di(1H-imidazol-1-yl)-1,1'-biphenyl (L2), 1,2-bis(2-methyl-1H-imidazol-1-ylmethyl)benzene (L3) and 5,6,7,8-tetrahydroquinoxaline (L4) were employed to react with CuBr/CuI, generating four 2-D layered copper(i)-polymer coordination polymer materials [Cu2Br2(L1)] 1, [CuI(L2)] 2, [CuI(L3)] 3 and [CuI(L4)0.5] 4. In 1-4, different Cu-X motifs are found: a cubic Cu4Br4 core in 1; a castellated Cu-I single chain in 2; a rhombic Cu2I2 core in 3; and a staircase-like Cu-I double chain in 4. The 2-D layer networks of 1-3 can all be simplified into a simple 44 topology (planar for 1 and 3; wave-like for 2), while the 2-D layer network of 4 has a 63 topology. The photoluminescence behaviors of 1-4 under a UV lamp suggest that 1 and 2 possess fluorescence thermochromism properties. Under the UV lamp, with the decrease in temperature, (i) 1 exhibits a yellow-to-red emission; (ii) 2 exhibits a yellow-to-green emission; (iii) 3 always emits green light; and (iv) 4 never emits light. These are further confirmed by their emission spectra. From 297 K to 77 K, the emission of 1 exhibits a large red shift from 561 nm to 623 nm; the emission of 2 exhibits a large blue shift from 571 nm to 515 nm; only a minor red shift is observed for the emission of 3; and no peaks appear in the emission spectra of 4. The crystal data of 1 and 2 at different temperatures have been collected for revealing the origination of their fluorescence thermochromism properties. Based on the above investigations, the effect of the rigidity/flexibility of the organic ligand on the fluorescence thermochromism properties of copper(i)-polymer coordination polymer materials is discussed. The quantum yields at 297 K and the photoluminescence lifetimes at 297 K and 77 K for 1-3 were also measured for better understanding their photoluminescence properties.