Solar-Driven Nitrogen Fixation Catalyzed by Stable Radical-Containing MOFs: Improved Efficiency Induced by a Structural Transformation.

Herein we present a new viologen-based radical-containing metal-organic framework (RMOF) Gd-IHEP-7, which upon heating in air undergoes a single-crystal-to-single-crystal transformation to generate Gd-IHEP-8. Both RMOFs exhibit excellent air and water stability as a result of favorable radical-radical interactions, and their long-lifetime radicals result in wide spectral absorption in the range 200-2500 nm. Gd-IHEP-7 and Gd-IHEP-8 show excellent activity toward solar-driven nitrogen fixation, with ammonia production rates of 128 and 220 μmol h  g , respectively.

Molecular Spring-like Triple-Helix Coordination Polymers as Dual-Stress and Thermally Responsive Crystalline Metal-Organic Materials.

Elastic metal-organic materials (MOMs) capable of multiple stimuli-responsiveness based on dual-stress and thermally responsive triple-helix coordination polymers are presented. The strong metal-coordination linkage and the flexibility of organic linkers in these MOMs, rather than the 4 Å stacking interactions observed in organic crystals, causes the helical chain to act like a molecular spring and thus accounts for their macroscopic elasticity. The thermosalient effect of elastic MOMs is reported for the first time.

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

The incorporation of a mechanically interlocked molecule such as pseudorotaxane into metal-organic coordination polymers has afforded plenty of new hybrid materials with special structures and unique properties. In this work, we employ a weakly bound cucurbit[6]uril (CB[6])-bipyridinium pseudorotaxane as a supramolecular precursor to assemble with uranyl, aiming to construct uranyl-rotaxane coordination polymers (URCPs) with intriguing structures. By adjusting the synthetic conditions, a new kinked-helix uranyl rotaxane compound (), together with three other compounds , , and varying from 1D chains to 2D interwoven networks, was obtained.

Noncomplexed Cucurbituril-Mediated Structural Evolution of Layered Uranyl Terephthalate Compounds.

Template synthesis is one of the most feasible ways to explore new uranyl compounds with intriguing structures and properties. Here we demonstrate the preparation of six novel "sandwichlike" uranyl coordination polymers (UCPs) based on two-dimensional uranyl-terephthalate acid (H) networks using CB ( = 5, 6, 8) as template ligands in the presence of different cations (Na, K, Cs, or HN(CH)). Compound ([UO()][Na(CB5)(HO)](HO)) is composed of layered uranyl- networks with the complex of CB5 and sodium cations as template ligands.

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) ([Hbcbp]Cl), 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, -, have been synthesized through hydrothermal reactions.

Bipyridine-Directed Syntheses of Uranyl Compounds Containing Semirigid Dicarboxylate Linkers: Diversity and Consistency in Uranyl Speciation.

Bipyridine organic bases are beneficial to the synthesis of novel uranyl-organic hybrid materials, but the relationship between their molecular structures and specific roles as structure-directing agents, especially for the semirigid dicarboxylate systems, is still unclear. Here we demonstrate how the bipyridine ligands direct the coordination assembly of uranyl-organic compounds with a semirigid dicarboxylate linker, 4,4'-dicarboxybiphenyl sulfone (Hdbsf), by utilizing a series of bipyridine ligands, 1,10-phenanthroline (phen), 2,2'-bipyridine (2,2'-bpy), 5,5'-dimethylbipyridine (5,5'-dmbpy), 4,4'-bipyridine (4,4'-bpy), or 1,3-di(4-pyridyl)propane (bpp). Under hydrothermal conditions, eight uranyl-organic coordination polymers (UCPs), four of which [[UO(dbsf)(phen)] (1), [UO(dbsf)(phen)]·HO (1'), [UO(dbsf)][Hbpp] (6), and [UO(dbsf)][Hbpp] (6')] were reported previously, were synthesized and divided into two types based on the chelate or template effect of these bipyridine ligands.

Uranyl Compounds Involving a Weakly Bonded Pseudorotaxane Linker: Combined Effect of pH and Competing Ligands on Uranyl Coordination and Speciation.

Pseudorotaxane-type ligands with tunable structural dynamics offer an opportunity in the exploration of new actinide hybrid materials. In this work, we utilized a weakly bonded pseudorotaxane ligand involving CB[6] and 1, 1'-(heptane-1, 7-diyl)bis(4-(ethoxycarbonyl)pyridin-1-ium) bromides ([C7BPCEt]Br@CB[6]) to assemble with uranyl ion, and we systematically investigated the effect of different factors including pH and competing ligands on the hydrothermal synthesis of URCPs. Nine uranyl-rotaxane coordination polymers (URCPs) with diversity in coordination mode and topological structure were successfully prepared (two previously reported complexes, URCP1 and URCP2 are also included).

Uranyl-Organic Coordination Compounds Incorporating Photoactive Vinylpyridine Moieties: Synthesis, Structural Characterization, and Light-Induced Fluorescence Attenuation.

The fluorescence of uranyl originated from electronic transitions (S-S and S-S, v = 0-4) of the ligand-to-metal charge transfer (LMCT) process is an intrinsic property of many uranyl coordination compounds. However, light-induced regulation on fluorescence features of uranyl hybrid materials through photoactive functional groups is less investigated. In this work, the photoactive vinyl group-containing ligands, ( E)-methyl 3-(pyridin-4-yl)acrylate and ( E)-methyl 3-(pyridin-3-yl)acrylate, have been used in the construction of uranyl coordination polymers in the presence of 1,10-phenanthroline (phen).

Releasing Metal-Coordination Capacity of Cucurbit[6]uril Macrocycle in Pseudorotaxane Ligands for the Construction of Interwoven Uranyl-Rotaxane Coordination Polymers.

As an emerging type of actinide hybrid material, uranyl-rotaxane coordination polymers (URCPs) with new coordination patterns and topological structures are still desired. In this work, we propose a new strategy to construct URCPs by promoting the simultaneous coordination of both the wheel and axle moieties in pseudorotaxane linkers with metal nodes. Starting from a series of cucurbit[6]uril (CB[6])-based pseudorotaxane ligands, C nBPCA@CB[6] [C nBPCA = 1,1-(α,ω-diyl)bis[4-(ethoxycarbonyl)pyridin-1-ium] bromides, where n = 5-8] with slightly deformed CB[6], four new URCPs (URCP1, URCP3, URCP4, and URCP5) with interwoven network structures, as well as another noninterwoven polymer(URCP2), have been successfully prepared.

Stepwise ortho Chlorination of Carboxyl Groups for Promoting Structure Variance of Heterometallic Uranyl-Silver Coordination Polymers of Isonicotinate.

We report the syntheses and characterization of four new heterometallic uranyl-silver compounds from isonicotinic acid derivatives with a stepwise ortho chlorination of carboxyl group, that is, isonicotinic acid (H-PCA), 3-chloroisonicotinic acid (H-3-MCPCA), and 3,5-dichloroisonicotinic acid (H-3,5-DCPCA). Compound 1, (UO)Ag(3,5-DCPCA)(3,5-DCPy), from H-3,5-DCPCA displays a heterometallic three-dimensional (3D) framework through the connection of 3,5-DCPCA and in situ-formed 3,5-dichloropyridine (3,5-DCPy) with the aid of multiple argentophilic interactions. Compounds 2 ((UO)Ag(3-MCPCA)) and 3 ((UO)Ag(3-MCPCA)), which differ from each other in coordination modes of uranyl center, are both heterometallic 3D reticular frameworks from 3-MCPCA based on highly coordinated silver nodes.

An Unprecedented Two-Fold Nested Super-Polyrotaxane: Sulfate-Directed Hierarchical Polythreading Assembly of Uranyl Polyrotaxane Moieties.

The hierarchical assembly of well-organized submoieties could lead to more complicated superstructures with intriguing properties. We describe herein an unprecedented polyrotaxane polythreading framework containing a two-fold nested super-polyrotaxane substructure, which was synthesized through a uranyl-directed hierarchical polythreading assembly of one-dimensional polyrotaxane chains and two-dimensional polyrotaxane networks. This special assembly mode actually affords a new way of supramolecular chemistry instead of covalently linked bulky stoppers to construct stable interlocked rotaxane moieties.

The templated synthesis of a unique type of tetra-nuclear uranyl-mediated two-fold interpenetrating uranyl-organic framework.

Two novel tetra-nuclear uranyl-mediated two-fold interpenetrating networks, [U4O10(dbsf)3]2[H2bpp]2 and [U4O10(dbsf)3][H2bpp], have been hydrothermally synthesized from a semi-rigid carboxylic acid, H2dbsf, with the organic base, bpp, as the charge balancing agent and stacking template (H2dbsf = 4,4'-dicarboxybiphenyl sulfone, bpp = 1,3-di(4-pyridyl)propane).

Silver Ion-Mediated Heterometallic Three-Fold Interpenetrating Uranyl-Organic Framework.

A unique case of a uranyl-silver heterometallic 3-fold interpenetrating network (U-Ag-2,6-DCPCA) from a multifunctionalized organic ligand, 2,6-dichloroisonicotinic acid, in the presence of uranyl and silver ions is reported. It is the first report of a heterometallic uranyl-organic interpenetrating network or framework. Notably, a (4,4)-connected uranyl building unit in U-Ag-2,6-DCPCA, which is available through combined influences of structural halogenation and silver ion additive on uranyl coordination, plays a vital role in the formation of a 3-fold interpenetrating network.

Supramolecular inclusion-based molecular integral rigidity: a feasible strategy for controlling the structural connectivity of uranyl polyrotaxane networks.

The assembly of two-dimensional (2D) large channel uranyl-organic polyrotaxane networks as well as structural regulation of uranyl-bearing units using jointed cucurbit[6]uril-based pseudorotaxanes with integral rigidity based on supramolecular inclusion is presented for the first time. This construction strategy concerning controlling molecular integral rigidity based on supramolecular inclusion may afford an entirely new methodology for coordination chemistry.

The first case of actinide triple helices: pH-dependent structural evolution and kinetically-controlled transformation of two supramolecular conformational isomers.

The first actinide triple helices, including two supramolecular conformational isomers of uranium(VI), have been synthesized with the aid of a flexible V-shaped ligand and a rigid aromatic base. The isomers exhibit an intriguing pH-dependent structural evolution and a kinetically-controlled transformation via a novel conformational rearrangement of the organic base.

A novel two-component system BqsS-BqsR modulates quorum sensing-dependent biofilm decay in Pseudomonas aeruginosa.

Pseudomonas aeruginosa can grow either as planktonic- or biofilm-form in response to environmental changes. Recent studies show that switching from biofilm to planktonic lifestyle requires rhamnolipids. Here we report the identification of a novel twocomponent system BqsS-BqsR that regulates biofilm decay in P.