Novel Viologen Derivative Based Uranyl Coordination Polymers Featuring Photochromic Behaviors

Mining for Metal-Organic Systems: Chemistry Frontiers of Th-, U-, and Zr-Materials

The conceptual framework presented in this Perspective overviews the design principles of innovative thorium-based materials that could address urgent needs of the medicinal, nuclear energy, and waste remediation sectors from the lens of zirconium and uranium analogs. We survey the intersections of Zr, Th, and U chemistry with a focus on how the intrinsic behavior of each metal translates to broader material properties, including, but not limited to, structural and topological diversity, preferential metal-ligand binding, and reactivity. On the example of several classes of materials, including organometallic complexes, polyoxometalates, and the primary focus of this Perspective, metal-organic frameworks (MOFs), the design principles that govern the preparation of Zr-, Th-, and U-compounds, including oxophilicity, variation in oxidation states, and stable coordination environments have been considered. Further, we highlight how the impact of the mentioned variables may shift throughout the progression from discrete molecular systems to extended structures. We discuss the common assumption that zirconium-organic materials are typically considered a close analog of thorium-based congeners in areas such as material design and preparation. Through consideration of fundamental chemistry principles, we shed light on the relationships between Zr-, Th-, and U-based materials and highlight how a critical analysis of their distinct properties can be used to target a desired material performance. As a result, we provide a detailed understanding of Th-based materials chemistry by anchoring their fundamental properties between two well-studied reference points, zirconium- and uranium-containing analogs.

Systematic Study of Solid-State U(VI) Photoreactivity: Long-Lived Radicalization and Electron Transfer in Uranyl Tetrachloride

Reported are the syntheses, structural characterizations, and luminescence properties of three novel [UO2Cl4]2- bearing compounds containing substituted 1,1'-dialkyl-4,4'-bipyridinum dications (i.e., viologens). These compounds undergo photoinduced luminescence quenching upon exposure to UV radiation. This reactivity is concurrent with two phenomena: radicalization of the uranyl tetrachloride anion and photoelectron transfer to the viologen which constitutes the formal transfer of one electron from [UO2Cl4]2- to the viologen species. This behavior is elucidated using electron paramagnetic resonance (EPR) spectroscopy and further probed through a series of characterization and computational techniques including Rehm-Weller analysis, time-dependent density functional theory (TD-DFT), and density of states (DOS). This work provides a systematic study of the photoreactivity of the uranyl unit in the solid state, an under-described aspect of fundamental uranyl chemistry.

Unveiling Structural Diversity of Uranyl Compounds of Aprotic 4,4'-Bipyridine N,N'-Dioxide Bearing O-Donors

As an aprotic O-donor ligand, 4,4'-bipyridine N,N'-dioxide (DPO) shows good potential for the preparation of uranyl coordination compounds. In this work, by regulating reactant compositions and synthesis conditions, diverse coordination assembly between uranyl and DPO under different reaction conditions was achieved in the presence of other coexisting O-donors. A total of ten uranyl-DPO compounds, U-DPO-1 to U-DPO-10, have been synthesized by evaporation or hydro/solvothermal treatment, and the possible competition and cooperation of DPO with other O-donors for the formation of these uranyl-DPO compounds are discussed. Starting with an aqueous solution of uranyl nitrate, it is found that an anionic nitrate or hydroxyl group is involved in the coordination sphere of uranyl in U-DPO-1 ((UO₂)(NO₃)₂(H₂O)₂·(DPO)), U-DPO-2 ((UO₂)(NO₃)₂(DPO)), and U-DPO-3 ((UO₂)(DPO)(μ₂-OH)₂), where DPO takes three different kinds of coordination modes, i.e. uncoordinated, monodentate, and biconnected. The utilization of UO₂(CF₃SO₃)₂ in acetonitrile, instead of an aqueous solution of uranyl nitrate, precludes the participation of nitrate and hydroxyl, and ensures the engagement of DPO ligands (4-5 DPO ligands for each uranyl) in a uranyl coordination sphere of U-DPO-4 ([(UO₂)(CF₃SO₃)(DPO)₂](CF₃SO₃)), U-DPO-5 ([UO₂(H₂O)(DPO)₂](CF₃SO₃)₂) and U-DPO-6 ([(UO₂)(DPO)_2.5](CF₃SO₃)₂). Moreover, when combined with anionic carboxylate ligands, terephthalic acid (H₂TPA), isophthalic acid (H₂IPA), and succinic acid (H₂SA), DPO works well with them to produce four mixed-ligand uranyl compounds with similar structures of two-dimensional (2D) networks or three-dimensional (3D) frameworks, U-DPO-7 ((UO₂)(TPA)(DPO)), U-DPO-8 ((UO₂)₂(DPO)(IPA)₂·0.5H₂O), U-DPO-9 ((UO₂)(SA)(DPO)·H₂O), and U-DPO-10 ((UO₂)₂(μ₂-OH)(SA)_1.5(DPO)). Density functional theory (DFT) calculations conducted to probe the bonding features between uranyl ions and different O-donor ligands show that the bonding ability of DPO is better than that of anionic CF₃SO₃ ^-, nitrate, and a neutral H₂O molecule and comparable to that of an anionic carboxylate group. Characterization of physicochemical properties of U-DPO-7 and U-DPO-10 with high phase purity including infrared (IR) spectroscopy, thermogravimetric analysis (TGA), and luminescence properties is also provided.

Zwitterionic and Anionic Polycarboxylates as Coligands in Uranyl Ion Complexes, and Their Influence on Periodicity and Topology

The three zwitterionic di- and tricarboxylate ligands 1,1'-[(2,3,5,6-tetramethylbenzene-1,4-diyl)bis(methylene)]bis(pyridin-1-ium-4-carboxylate) (pL1), 1,1'-[(2,3,5,6-tetramethylbenzene-1,4-diyl)bis(methylene)]bis(pyridin-1-ium-3-carboxylate) (mL1), and 1,1',1″-[(2,4,6-trimethylbenzene-1,3,5-triyl)tris(methylene)]tris(pyridin-1-ium-4-carboxylate) (L2) have been used as ligands to synthesize a series of 15 uranyl ion complexes involving various anionic coligands, in most cases polycarboxylates. [(UO₂)₂(pL1)₂(cbtc)(H₂O)₂]·10H₂O (1, cbtc^4- = cis,trans,cis-1,2,3,4-cyclobutanetetracarboxylate) is a discrete, dinuclear ring-shaped complex with a central cbtc^4- pillar. While [UO₂(pL1)(NO₃)₂] (2), [UO₂(pL1)(OAc)₂] (3), and [UO₂(pL1)(HCOO)₂] (4) are simple chains, [(UO₂)₂(mL1)(1,3-pda)₂] (5, 1,3-pda^2- = 1,3-phenylenediacetate) is a daisy chain and [UO₂(pL1)(pdda)]₃·10H₂O (6, pdda^2- = 1,2-phenylenedioxydiacetate) is a double-stranded, ribbon-like chain. Both [UO₂(pL1)(pht)]·5H₂O (7, pht^2- = phthalate) and [(UO₂)₃(mL1)(pht)₂(OH)₂] (8) crystallize as diperiodic networks with the sql topology, the latter involving hydroxo-bridged trinuclear nodes. [(UO₂)₂(pL1)(c/t-1,3-chdc)₂] (9, c/t-1,3-chdc^2- = cis/trans-1,3-cyclohexanedicarboxylate) and [UO₂(pL1)(t-1,4-chdc)]·1.5H₂O (10, t-1,4-chdc^2- = trans-1,4-cyclohexanedicarboxylate) are also diperiodic, with the V₂O₅ and sql topologies, respectively. Both [(UO₂)₂(mL1)(c/t-1,4-chdc)₂] (11) and [(UO₂)₂(pL1)(1,2-pda)₂] (12, 1,2-pda^2- = 1,2-phenylenediacetate) crystallize as diperiodic networks with hcb topology, and they display threefold parallel interpenetration. [HL2][(UO₂)₃(L2)(adc)₃]Br (13, adc^2- = 1,3-adamantanedicarboxylate) contains a very corrugated hcb network with two different kinds of cells, and the uncoordinated HL2⁺ molecule associates with the coordinated L2 to form a capsule containing the bromide anion. [(UO₂)₂(pL1)(kpim)₂] (14, kpim^2- = 4-ketopimelate) is a three-periodic framework with pL1 molecules pillaring fes diperiodic subunits, whereas [(UO₂)₂(L2)₂(t-1,4-chdc)](NO₃)_1.7Br_0.3·6H₂O (15), the only cationic complex in the series, is a triperiodic framework with dmc topology and t-1,4-chdc^2- anions pillaring fes diperiodic subunits. Solid-state emission spectra and photoluminescence quantum yields are reported for all complexes.

Controllable photomechanical bending of metal-organic rotaxane crystals facilitated by regioselective confined-space photodimerization

Molecular machines based on mechanically-interlocked molecules (MIMs) such as (pseudo) rotaxanes or catenates are known for their molecular-level dynamics, but promoting macro-mechanical response of these molecular machines or related materials is still challenging. Herein, by employing macrocyclic cucurbit[8]uril (CB[8])-based pseudorotaxane with a pair of styrene-derived photoactive guest molecules as linking structs of uranyl node, we describe a metal-organic rotaxane compound, U-CB[8]-MPyVB, that is capable of delivering controllable macroscopic mechanical responses. Under light irradiation, the ladder-shape structural unit of metal-organic rotaxane chain in U-CB[8]-MPyVB undergoes a regioselective solid-state [2 + 2] photodimerization, and facilitates a photo-triggered single-crystal-to-single-crystal (SCSC) transformation, which even induces macroscopic photomechanical bending of individual rod-like bulk crystals. The fabrication of rotaxane-based crystalline materials with both photoresponsive microscopic and macroscopic dynamic behaviors in solid state can be promising photoactuator devices, and will have implications in emerging fields such as optomechanical microdevices and smart microrobotics.

Impact of Proximity Effect on Uranyl Coordination of Conformationally Variable Weakly-Bonded Cucurbit[6]uril-Bipyridinium Pseudorotaxane

To explore the proximity effect in uranyl coordination of weak-bonded cucurbit[6]uril(CB[6])-bipyridinium ligands, a new pseudorotaxane precursor C7BPCN3@CB[6] containing 1, 1'-(heptyl-1,7-diyl)bis(3-cyanopyridin-1-ium) bromide (C7BPCN3) with elongated alkyl chains and meta-substituted cyano groups,...

Proximity Effect in Uranyl Coordination of the Cucurbit[6]uril-Bipyridinium Pseudorotaxane Ligand for Promoting Host-Guest Synergistic Chelating

In the present work, we proposed regulating uranyl coordination behavior of cucurbituril-bipyridinium pseudorotaxane ligand by utilizing meta-functionalized bipyridinium dicarboxylate guest. A tailored pseudorotaxane precursor involving 1,1'-(hexane-1,6-diyl)bis(3-cyanopyridin-1-ium) bromide (C6BPCN3) and cucurbit[6]uril (CB[6]) has designed and synthesized. Through in situ hydrolysis of the pseudorotaxane ligands and their coordination assembly with uranyl cations, seven new uranyl-rotaxane coordination polymers URCP1-URCP7 have been obtained under hydrothermal conditions in the presence of different anions. It is demonstrated that the variation of carboxylate groups from para- to meta-position greatly affected the coordination behaviors of the meta-functionalized pseudorotaxane linkers, which are enriched from simple guest-only binding to host-guest simultaneous coordination and synergistic chelating. This effective regulation on uranyl coordination of supramolecular pseudorotaxane can be attributed to the proximity effect, which refers to the meta-position carboxyl group being spatially closer to the portal carbonyl group of CB[6]. Moreover, by combining other regulation methods such as introducing competing counterions and modulating solution acidity, the nuclearity of the uranyl center and the coordination patterns of the pseudorotaxane ligand can be diversely tuned, which subsequently exert great influence on the final dimensionality of resultant uranyl compounds. This work presents a large diversity of uranyl-based coordination polyrotaxane compounds with fascinating mechanically interlocked components and, most importantly, provides a feasible approach to adjust and control the metal coordination behavior of the pseudorotaxane ligand that might expand the scope of application of such supramolecular ligands.

2,5-Thiophenedicarboxylate: An Interpenetration-Inducing Ligand in Uranyl Chemistry

Seven uranyl ion complexes have been crystallized under solvo-hydrothermal conditions from 2,5-thiophenedicarboxylic acid (tdcH₂) and diverse additional, structure-directing species. [UO₂(tdc)(DMF)] (1) is a two-stranded monoperiodic coordination polymer, while [PPh₃Me][UO₂(tdc)(HCOO)] (2) is a simple chain with terminal formate coligands. Although it is also monoperiodic, [C(NH₂)₃][H₂NMe₂]₂[(UO₂)₃(tdc)₄(HCOO)] (3) displays an alternation of tetra- and hexanuclear rings. Two-stranded subunits are bridged by oxo-coordinated Ni^II cations to form a diperiodic network in [UO₂(tdc)₂Ni(cyclam)] (4), but a homometallic sql diperiodic assembly is built in [Cu(R,S-Me₆cyclam)(H₂O)][UO₂(tdc)₂]·H₂O (5), to which the counterion is hydrogen bonded only. Diperiodic networks with the hcb topology are formed in both [Zn(phen)₃][(UO₂)₂(tdc)₃]·2H₂O·3CH₃CN (6) and [PPh₄]₂[(UO₂)₂(tdc)₃]·2H₂O (7). The slightly undulating layers in 6 are crossed by oblique columns of weakly interacting counterions in polythreading-like fashion. In contrast, the larger curvature in 7 allows for three-fold, parallel 2D interpenetration to occur. These results are compared with previously reported cases of interpenetration and polycatenation in the uranyl-tdc^2- system.

Radiochromic Hydrogen-Bonded Organic Frameworks for X-ray Detection

Porous materials have been investigated as efficient photochromic platforms for detecting hazardous radiation, while the utilization of hydrogen bonded organic frameworks (HOFs) in this field has remained intact. Herein, two HOFs were synthesized through self-assembly of tetratopic viologen ligand and formic acid (PFC-25, PFC-26), as a new class of "all-organic" radiochromic smart material, opening a gate for HOFs in this field. PFC-26 is active upon both X-ray and UV irradiation, while PFC-25 is only active upon X-ray irradiation. The same building block yet different radiochromic behaviors of PFC-25 and PFC-26 allow us to gain a deep mechanistic understanding of the factors that control the detection specificity. Theoretical and experimental studies reveal that the degree of π-conjugation of viologen ligand is highly related to the threshold energy of triggering a charge transfer, therefore being a vital factor for the particularity of radiochromic materials. Thanks to its convenient processibility, nanoparticle size, and UV silence, PFC-25 can be further fabricated into a portable naked-eye sensor for X-ray detection, which shows obvious color change with the merits of high transmittance contrast, good sensitivity (reproducible dose threshold of 3.5 Gy), and excellent stability. The work exhibits the promising practical potentials of HOF materials in photochromic technology.

3D Uranyl Organic Frameworks Supported by Rigid Octadentate Carboxylate Ligand: Synthesis, Structure Diversity, and Luminescence Properties

Seven three dimensional (3D) uranyl organic frameworks (UOFs), formulated as [NH₄ ][(UO₂ )₃ (HTTDS)(H₂ O)] (1), [(UO₂ )₄ (HTTDS)₂ ](HIM)₆ (2, IM=imidazole), [(UO₂ )₄ (TTDS)(H₂ O)₂ (Phen)₂ ] (3, Phen=1,10-phenanthroline), [Zn(H₂ O)₄ ]_0.5 [(UO₂ )₃ (HTTDS)(H₂ O)₄ ] (4), and {(UO₂ )₂ [Zn(H₂ O)₃ ]₂ (TTDS)} (5), {Zn(UO₂ )₂ (H₂ O)(Dib)_0.5 (HDib)(HTTDS)} (6, Dib=1,4-di(1H-imidazol-1-yl)benzene) and [Na]{(UO₂ )₄ [Cu₃ (u₃ -OH)(H₂ O)₇ ](TTDS)₂ } (7) have been hydrothermally prepared using a rigid octadentate carboxylate ligand, tetrakis(3,5-dicarboxyphenyl)silicon(H₈ TTDS). These UOFs have different 3D self-assembled structures as a function of co-ligands, structure-directing agents and transition metals. The structure of 1 has an infinite ribbon formed by the UO₇ pentagonal bipyramid bridged by carboxylate groups. With further introduction of auxiliary N-donor ligands, different structure of 2 and 3 are formed, in 2 the imidazole serves as space filler, while in 3 the Phen are bound to [UO₂ ]²⁺ units as co-ligands. The second metal centers were introduced in the syntheses of 4-7, and in all cases, they are part of the final structures, either as a counterion (4) or as a component of framework (5-7). Interesting, in 7, a rare polyoxometalate [Cu₃ (μ₃ -OH)O₇ (O₂ CR)₄ ] cluster was found in the structure. It acts as an inorganic building unit together with the dimer [(UO₂ )₂ (O₂ CR)₄ ] unit. Those uranyl carboxylates were sufficiently determined by single crystal X-ray diffraction, and their topological structures and luminescence properties were analyzed in detail.

Controlling the secondary assembly of porous anionic uranyl-organic polyhedra through organic cationic templates

Herein, we report a new uranyl-organic polyhedron U₄L₄ (L = BTPCA) assembled from uranyl and a semirigid tritopic ligand. By adjusting the carbon chain length of organic templates, two complexes can be obtained based on the diverse secondary assembly of U₄L₄ cages. The mechanism of different arrangements of U₄L₄ cages induced by organic templates was explored in detail.

Tuning of the Network Dimensionality and Photoluminescent Properties in Homo- and Heteroleptic Lanthanide Coordination Polymers

Targeted synthesis, through a heteroleptic methodology, has resulted in three types of lanthanide (Ln) coordination polymers (CPs) with tailored dimensionality, tunable photoluminescent colors, and distinct luminescence quenching upon UV and X-ray irradiation. The homoleptic Ln(tpbz)(NO₃)₂ [CP-1; tpbz = 4-(2,2':6',2″-terpyridin-4'-yl)benzoate] is assembled from Ln cations and bridging tpbz ligands, accompanied by the decoration of NO₃^- anions, forming a one-dimensional (1D) chain structure. The presence of ancillary dicarboxylate linkers, 1,4-benzenedicarboxylate (bdc) and 2,5-thiophenedicarboxylate (tdc), promotes additional bridging between 1D chains to form a two-dimensional layer and a three-dimensional framework for Ln(tpbz)(bdc) (CP-2) and Ln(tpbz)(tdc) (CP-3), respectively. The multicolor and luminescence properties of the obtained CPs were investigated, displaying typical red Eu^III-based and green Tb^III-based emissions. The Sm^III-bearing CP-1-CP-3, however, exhibit diverse ratiometric Ln^III- and ligand-based emissions, with the photoluminescent colors varying from pink to orange to cyan. Notably, the Tb^III-containing CP-1-CP-3 display distinct luminescence quenching upon continuous exposure to UV and X-ray irradiation. To our best knowledge, CP-2-Tb represents one of the most sensitive UV dosage probes (3.2 × 10^-7 J) among all CPs.

Construction of Hybrid Bimetallic Uranyl Compounds Based on a Preassembled Terpyridine Metalloligand

Six hybrid uranyl-transition metal compounds [UO₂ Ni(cptpy)₂ (HCOO)₂ (DMF)(H₂ O)] (1), [UO₂ Ni(cptpy)₂ (BTPA)₂ ] (2), [UO₂ Fe(cptpy)₂ (HCOO)₂ (DMF)(H₂ O)] (3), [UO₂ Fe(cptpy)₂ (BTPA)₂ ] (4), [UO₂ Co(cptpy)₂ (HCOO)₂ (DMF)(H₂ O)] (5), and [UO₂ Co(cptpy)₂ (BTPA)₂ ] (6), based on bifunctional ligand 4'-(4-carboxyphenyl)-2,2':6',2''-terpyridine (Hcptpy) are reported (H₂ BTPA = 4,4'-biphenyldicarboxylic acid). Single-crystal XRD revealed that all six compounds feature similar metalloligands, which consist of two cptpy^- anions and one transition metal cation. The metalloligand M(cptpy)₂ can be considered to be an extended linear dicarboxylic ligand with length of 22.12 Å. Compounds 1, 3, and 5 are isomers, and all of them feature 1D chain structures. The adjacent 1D chains are connected together by hydrogen bonds and π-π interactions to form a 3D porous structure, which is filled with solvent molecules and can be exchanged with I₂ . Compounds 2, 4, and 6 are also isomers, and all of them feature 2D honeycomb (6,3) networks with hexagonal units of dimensions 41.91×26.89 Å, which are the largest among uranyl compounds with honeycomb networks. The large aperture allows two sets of equivalent networks to be entangled together to result in a 2D+2D→3D polycatenated framework. Remarkably, these uranyl compounds exhibit high catalytic activity for cycloaddition of carbon dioxide. Moreover, the geometric and electronic structures of compounds 1 and 2 are systematically discussed on the basis of DFT calculations.

Achieving UV and X-ray Dual Photochromism in a Metal-Organic Hybrid via Structural Modulation

Rational design and synthesis of new photochromic sensors have been active research areas of inquiry, particularly on how to predict and tailor their properties and functionalities. Herein, two thulium 2,2':6',2''-terpyridine-4'-carboxylate (TPC)-functionalized metal-organic hybrids, Tm(TPC)₂(HCOO)(H₂O) (TmTPC-1) and Tm(TPC)(HCOO)₂ (TmTPC-2) with different photochromic response behaviors, have been successfully prepared, allowing for straightforward investigations of the structure-property correlation. Single-crystal X-ray diffraction and electron paramagnetic resonance analyses revealed that the incorporation of a unique dangling decorating TPC unit in TmTPC-1 offers a shorter and more accessible π-π interaction pathway between the adjacent TPC moieties than that in TmTPC-2. Such a structural feature leads to the production of radical species via a photoinduced intermolecular electron-transfer (IeMCT) process upon UV or X-ray irradiation, which ultimately endows TmTPC-1 with a rather unusual UV and X-ray dual photochromism. A linear relationship between the change of UV-vis absorbance intensity and X-ray dose was established, making TmTPC-1 a promising dosimeter for X-ray radiation with an extremely high energy threshold (30 kGy). To advance the development for real-world application, we have fabricated polyvinylidene fluoride (PVDF) membranes incorporating TmTPC-1 for functioning either as a UV imager or as an X-ray radiation indicator. Lastly, TmTPC-1 exhibits high thermal stability (up to 400 °C) and radioresistance (at least 900 kGy), and also excellent reversibility of photochromic transformation (at least 5 cycles).

Two viologen-based photoluminescent compounds: excitation-wavelength-dependent and photoirradiation-time-dependent photoluminescent switches

We synthesized two isostructural multi-coloured photoluminescent coordination polymers. They exhibit excitation-wavelength-dependent photoluminescence emission and photoirradiation-time-dependent photoluminescence emission in solid-state.

Expanding uranyl dicyanoaurate coordination polymers into the second and third dimensions

The solvothermal synthesis and characterization of a three-dimensional, interpenetrated uranyl dicyanoaurate coordination polymer, K2(UO2)2(UO2)2(Au(CN)2)2(O)2(NO3)4, from UO2(NO3)2·6H2O and KAu(CN)2 is described. The structure contains a three-dimensional (3D) lattice of planar tetranuclear uranyl–oxo–nitrate clusters connected by dicyanoaurate linkers, with the rotation of the clusters providing the increased dimensionality. The material undergoes a reversible single-crystal to single-crystal transformation on exposure to water vapour, which is taken up in the channels of the 3D system. A second uranyl dicyanoaurate coordination polymer of the form [UO2(DMSO)3(H2O)(Au(CN)2)][Au(CN)2] was structurally characterized as a linear chain of dicyanoaurate units connected by gold–gold bonds with pendant uranyl–water–DMSO adducts that are hydrogen bonded into a two-dimensional sheet. Both materials exhibit emission arising from both the uranyl moiety and the gold(I) centre and represent the first multidimensional uranyl–dicyanoaurate coordination polymers.

Hydrothermal synthesis of two 2D uranyl coordination polymers: structure, luminescence, and photocatalytic degradation of rhodamine B

Two hydrothermal synthesized uranyl-organic coordination polymers showing effective photocatalytic activities for RhB degradation with quick equilibrium time in water.

Polyoxometalate–viologen photochromic hybrids for rapid solar ultraviolet light detection, photoluminescence-based UV probing and inkless and erasable printing

Polyoxometalate–viologen photochromic hybrids showed efficient and fast low intensity ultraviolet light detection, potential fluorescence based UV probing and inkless and erasable printing.

Occurrence of polyoxouranium motifs in uranyl organic networks constructed by using silicon-centered carboxylate linkers: structures, spectroscopy and computation

Four polyoxouranium-based uranyl carboxylates have been synthesized based on silicon-centered carboxylate linkers. Oligomerization of the uranyl units from tetrameric unit, to octameric motif and ultimately infinite polyoxouranium chain was observed.

A mixed-ligand strategy regulates thorium-based MOFs

A thorium-based MOF formed via the synergistic construction of porphyrin and bipyridyl based on the mixed-ligand strategy has the effect of enhancing photocatalysis.

Structural Diversity of Bipyridinium-Based Uranyl Coordination Polymers: Synthesis, Characterization, and Ion-Exchange Application

As well-known functional groups with excellent electro/photochromic and ion-exchange properties, bipyridinium motifs have been used in functionalized metal-organic coordination polymers, but they are still rarely applied to construct actinide coordination polymers. In this work, we utilized a bipyridinium-based carboxylic acid, 1,1'-bis(4-carboxyphenyl)-4,4'-bipyridinium bis(chloride) ([H₂bcbp]Cl₂), as the organic ligand to assemble with uranyl cations. By the introduction of different kinds of auxiliary ligands and adjustment of the pH, five novel uranyl coordination compounds, 1-5, have been synthesized through hydrothermal reactions. Starting from uranyl ions and terephthalic acid (H₂TP) and H₂bcbp ligands, [(UO₂)₂(bcbp)(TP)₂]·3H₂O (1) has a wave-shaped two-dimensional (2D) structure consisting of dinuclear units connected by terephthalate linkers and further supported by the longer H₂bcbp ligands. [(UO₂)₂(bcbp)(PA)₂]·4H₂O (2) has a zigzag chain of dimeric uranium units, and [(UO₂)₂(bcbp)(bpdc)₂]·5H₂O (3) forms a one-dimensional ribbonlike structure. The 2D structures of [(UO₂)(bcbp)(OH)(H₂O)]·Cl (4) and [(UO₂)(bcbp)Cl]·Cl (5) are similar, both of which are constructed from dinuclear uranyl units and bcbp^2- ligands. Furthermore, the performance for perrhenate removal of compound 4 with a cationic framework is assessed, and we found that compound 4 can efficiently remove ReO₄^- from an aqueous solution in a wide range of pH values. This work extends the library of viologen derivative-based uranyl coordination polymers, provides to some extent broader insights into actinide coordination chemistry of functionalized ligands, and may facilitate the ion-exchange applications of related coordination polymers.

Time-controlled synthesis of the 3D coordination polymer U(1,2,3-Hbtc)2 followed by the formation of molecular poly-oxo cluster {U14} containing hemimellitate uranium(iv)

Two coordination compounds bearing tetravalent uranium were synthesized in the presence of tritopic hemimellitic acid in acetonitrile with a controlled amount of water (H2O/U ≈ 8) and structurally characterized. Compound 1, [U(1,2,3-Hbtc)2]·0.5CH3CN is constructed around an eight-fold coordinated uranium cationic unit [UO8] linked by the poly-carboxylate ligands to form dimeric subunits, which are further connected to form infinite corrugated ribbons and a three-dimensional framework. Compound 2, [U14O8(OH)4Cl8(H2O)16(1,2,3-Hbtc)8(ox)4(ac)4] ({U14}) exhibits an unprecedented polynuclear {U14} poly-oxo uranium cluster surrounded by O-donor and chloride ligands. It is based on a central core of [U6O8] type surrounded by four dinuclear uranium-subunits {U2}. Compound 1 was synthesized by a direct reaction of hemimellitic acid with uranium tetrachloride in acetonitrile (+H2O), while the molecular species ({U14} (2)) crystallized from the supernatant solution after one month. The slow hydrolysis reaction together with the partial decomposition of the starting organic reactants into oxalate and acetate molecules induces the generation of such a large poly-oxo cluster with fourteen uranium centers. Structural comparisons with other closely related uranium-containing clusters, such as the {U12} cluster based on the association of inner core [U6O8] with three dinuclear sub-units {U2}, were performed.

In situ nitroso formation induced structural diversity of uranyl coordination polymers

This work presents three possible pathways that could exist in the in situ reaction system. Structural analysis of these compounds revealed that the introduction of nitroso group exerted significant influences on the conformations of ligands, skeletons and 3D structures.

Assembly of porphyrin-based uranium organic frameworks with (3,4)-connected pto and tbo topologies

(3,4)-Connected uranyl–organic frameworks (UOFs) with pto and tbo topologies were constructed via the utilization of triangular [(UO₂)(COO)₃]⁻ as the 3-connected node and square organic linker tetrakis(4-carboxyphenyl)porphyrin (H₄TCPP) as the 4-connected node.

A metal–organic framework constructed by a viologen-derived ligand: photochromism and discernible detection of volatile amine vapors

A Co(ii)-MOF based on a viologen-derived ligand was obtained: the Co(ii) compound exhibits photochromism, and allows the visual and differentiable detection of different volatile alkylamines.

A novel multifunction photochromic metal–organic framework for rapid ultraviolet light detection, amine-selective sensing and inkless and erasable prints

The system shows efficient and fast low intensity ultraviolet light detection, amine-selective sensing and also be used as inkless and erasable print.

Monomeric thorium chalcogenolates with bipyridine and terpyridine ligands

Thorium chalcogenolates Th(ER)4 react with 2,2'-bipyridine (bipy) to form complexes with the stoichiometry (bipy)2Th(ER)4 (E = S, Se; R = Ph, C6F5). All four compounds have been isolated and characterized by spectroscopic methods and low-temperature single crystal X-ray diffraction. Two of the products, (bipy)2Th(SC6F5)4 and (bipy)2Th(SeC6F5)4, crystallize with lattice solvent, (bipy)2Th(SPh)4 crystallizes with no lattice solvent, and the selenolate (bipy)2Th(SePh)4 crystallizes in two phases, with and without lattice solvent. In all four compounds the available volume for coordination bounded by the two bipy ligands is large enough to allow significant conformational flexibility of thiolate or selenolate ligands. 77Se NMR confirms that the structures of the selenolate products are the same in pyridine solution and in the solid state. Attempts to prepare analogous derivatives with 2,2',6',2''-terpyridine (terpy) were successful only in the isolation of (terpy)(py)Th(SPh)4, the first terpy compound of thorium. These materials are thermochromic, with color attributed to ligand-to-ligand charge transfer excitations.

Bimetallic Uranyl Organic Frameworks Supported by Transition-Metal-Ion-Based Metalloligand Motifs: Synthesis, Structure Diversity, and Luminescence Properties

A bifunctional ligand, 2,2'-bipyridine-4,4'-dicarboxylic acid (H₂bpdc), has been used in the investigation of constructing bimetallic uranyl organic frameworks (UOFs). Seven novel uranyl-transition metal bimetallic coordination polymers, [(UO₂)Zn(bpdc)₂] _n (1), [Cd(UO₂)(bpdc)₂(H₂O)₂·2H₂O] _n (2), [Cu(UO₂)(bpdc)(SO₄)(H₂O)₃·2H₂O] _n (3), [CuCl(UO₂)(bpdc)(Hbpdc)(H₂O)₂·H₂O] _n (4), [Cu(UO₂)(bpdc)₂(H₂O)] _n (5), [Co₂(UO₂)₃(bpdc)₆] _n (6), and [Co₃(UO₂)₄(bpdc)₈(Hbpdc)(H₂O)₂] _n (7), have been successfully constructed through the assembly of various transition-metal salts, uranyl ions, and H₂bpdc ligands under hydrothermal conditions. UOFs 1, 5, 6, and 7 adopt three-dimensional (3D) frameworks with different architectures; UOFs 2 and 3 exhibit two-dimensional (2D) wavelike and stairlike layers, respectively, while UOF 4 is a one-dimensional (1D) chain assembly. These UOFs include a wide range of dimensionalities (1D-3D), interpenetrated frameworks, and cation-cation interaction species, suggesting that anion-dependent structure regulation based on the metalloligand [M(bpdc) _m] ^n- motifs, the coordination modes of the metal centers and bpdc^2- ligands, along with the reaction temperature, has a remarkable influence on the formation of bimetallic UOFs, which could be a representative system for the structural modulation of UOFs with various dimensionalities and structures. Furthermore, the thermal stability and luminescent properties of compounds 1, 3, and 6 are also investigated.

Five monocyclic pyridinium derivative based halo-argentate/cuprate hybrids or iodide salts: influence of composition on photochromic behaviors

Using novel monocyclic pyridinium derivatives as structural directing agents and electron acceptors, five composition dependent photochromic compounds have been synthesized.

Improving coloration time and moisture stability of photochromic viologen–carboxylate zwitterions

The coordination compound [Zn₂LCl₄]_n (ZnLCl) showed greater moisture stability and faster color change than the viologen ligand L (N,N′-dipropionate-4,4′-bipyridinium).