The coordination chemistry of f‐block elements (lanthanide and actinide) in molten salts has become a resounding topic in view of its great importance to the research and development (R&D) of molten ...salt reactors and pyroprocessing. In this Review article, a general overview of the coordination chemistry of f‐block elements in molten salts is provided including past achievements and recent advances. Particular emphases are placed on the oxidation state, speciation, and solution structure of f‐block metal ions in molten salts, as well as their relationships with the salt composition. Furthermore, this review briefly discusses the spectroscopic and theoretical methods that complement each other in revealing the coordination properties.
The coordination chemistry of f‐block elements in molten salts has become a resounding topic owing to fundamental interests and potential applications in molten salt reactors and pyroprocessing. This concept paper highlights the state‐of‐the‐art in the coordination chemistry of f‐block elements in molten salts, which may advance understanding of the nature of molten salt fuels, coolants and electrolytes.
Use of abiotic chemical systems for understanding higher order superstructures is challenging. Here we report a ring‐in‐ring(s) system comprising a hydrogen‐bonded macrocycle and ...cyclobis(paraquat‐o‐phenylene) tetracation (o‐Box) or cyclobis(paraquat‐p‐phenylene) tetracation (CBPQT4+, p‐Box) that assembles to construct discrete higher order structures with adaptive conformation. As indicated by mass spectrometry, computational modeling, NMR spectroscopy, and single‐crystal X‐ray diffraction analysis, this ring‐in‐ring(s) system features the box‐directed aggregation of multiple macrocycles, leading to generation of several stable species such as H4G (1 a/o‐Box) and H5G (1 a/o‐Box). Remarkably, a dimeric shish‐kebab‐like ring‐in‐rings superstructure H7G2 (1 a/o‐Box) or H8G2 (1 a/p‐Box) is formed from the coaxial stacking of two ring‐in‐rings units. The formation of such unique dimeric superstructures is attributed to the large π‐surface of this 2D planar macrocycle and the conformational variation of both host and guest.
Multiple 2D H‐bonded macrocycles are threaded onto a box‐like cationic cyclophane, which further assembles into higher order dimeric shish‐kebab‐like structures. Such ring‐in‐ring(s) superstructures maximize their stability through the conformational adaptivity of both host and guest.
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−1 g−1, respectively. Experiments and theoretical calculations indicate that both RMOFs have similar nitrogen fixation pathways. The enhanced catalytic efficiency of Gd‐IHEP‐8 versus Gd‐IHEP‐7 is attributed to intermediates stabilized by enhanced hydrogen bonding.
A single‐crystal‐to‐single‐crystal (SCSC) transformation of stable radical‐containing MOF Gd‐IHEP‐7 generates Gd‐IHEP‐8. It is accompanied by a marked increase in efficiency of sacrificial agent‐free photocatalytic nitrogen fixation to yield NH3 from H2O and N2 under simulated solar light irradiation at ambient temperature. The NH3 production rate of 220 μmol h−1 g−1 for Gd‐IHEP‐8 is a new record for MOF photocatalysts.
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. Crystal structure analyses at different temperatures reveal that this thermoresponsiveness is achieved by adaptive regulation of the triple‐helix chains by fine‐tuning the opening angle of flexible V‐shaped organic linkers and rotation of its lateral conjugated groups to resist possible expansion, thus demonstrating the vital role of adaptive reorganization of triple‐helix metal–organic chains as a molecular spring‐like motif in crystal jumping.
Dual‐stress and thermally responsive crystalline metal–organic materials (MOMs) based on molecular spring‐like triple‐helix coordination polymers are presented. As the first example of thermosalient effect in elastic MOMs, these compounds undergo elastic flexure upon external stress as well as cracking and jumping after thermal treatment.
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 cucurbit8uril (CB8)-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-CB8-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-CB8-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.
A series of novel uranyl coordination polymers have been synthesized by hydrothermal reactions. Both complexes 1 and 2 prosess two ipbp− ligands (H2ipbpCl=1‐(3,5‐dicarboxyphenyl)‐4,4′‐bipyridinium ...chloride), one uranyl cation, and two coordination water molecules, which can further extend to 2D networks through hydrogen bonding. In complex 1, two sets of equivalent nets are entangled together, resulting in a 2D + 2D → 3D polycatenated framework. In complex 2, the neighbouring equivalent nets interpenetrate each other, forming a twofold interpenetrated network. Complexes 3 and 4 are isomers, and both of them are constructed from (UO2)2(OH)2 dinuclear units, which are connected with four ipbp− ligands. The 3D structures of complexes 3 and 4 are similar along the b axis. Similar to other viologen‐based coordination polymers, complexes 3 and 4 exhibit photochromic and thermochromic properties, which are rarely observed in actinide coordination polymers. Unlike the monotonous coordination mode in complexes 1–4, the ipbp− ligands feature a μ3‐bridge through two kinds of coordination modes in complex 5. Notably, complex 5 presents a unique example in which terminal pyridine nitrogen atom is involved in the coordination.
A series of novel uranyl complexes were synthesized based on viologen derivative ligand by altering pH adjusters (HNO3, NaOH, triethylamine, DMF). Both complexes 3 and 4 exhibit photochromic properties, which are rarely observed in actinide coordination polymers.
Electrospray Ionization Mass Spectrometry (ESI‐MS) technique and density functional theory (DFT) calculations were combined to study the formation of the complexes of lanthanides (Ln = La, Ce, Nd, ...Sm, Eu, Yb) and actinides (UO22+, Th4+) with CyMe4‐BTBP (6,6′‐bis(5,5,8,8‐tetramethyl‐5,6,7,8‐tetrahydro‐benzo‐1,2,4‐triazin‐3‐yl)‐2,2′bipyridine) to understand the mechanisms during the extraction process. Mass spectrometry titrations showed the formation of the complexation in acetonitrile. For lanthanides, only 1:2 complexes (Ln(L)23+, Ln(L)2(CH3CN)3+), Ln(L)2(NO3)2+) were found at low Ln/L concentration ratios, whereas the 1:1 complexes (Ln(L)(NO3)2+) were observed when the Ln/L concentration ratio reached 1.0. For uranyl complexes, 1:1 complex (UO2L(NO3)+) was the only species within the measuring range. Th4+ complexes had two compositions: 1:1 and 1:2, in which 1:2 species was the dominant complex. Collision‐induced dissociation (CID) was employed to characterize the fragmentation process. The fragmentation process was unfolded sequentially on both sides of CyMe4‐BTBP ligand with the loss of alkyl groups and cleavage of triazinyl rings. The CID results of CyMe4‐BTBP complexes revealed a slight difference depending on the metal center. The DFT calculations showed that the stable complexes formed in acetonitrile solution were consistent with the ESI‐MS results.
Uranyl–organic frameworks (UOFs) have recently been the object of many research endeavors due to the unique coordination mode of uranyl ions and their attractive physicochemical properties. Here, a ...new (3,4)‐connected UOF (U‐IHEP‐4) assembled from uranyl and porphyrin ligand tetrakis(4‐carboxyphenyl)porphyrin (H4TCPP) is reported, which represents the first case of actinide porphyrinic MOFs. Adsorption experiments in DMF solution demonstrated that U‐IHEP‐4 selectively adsorbs positively charged dyes, which is in line with its negatively charged framework and large pore volume ratio (90 %). Remarkably, U‐IHEP‐4 exhibited high catalytic activity for the dehydrogenation of N‐heterocycles to synthesize the corresponding aromatic heterocycles and it can be used as an efficient heterogeneous catalyst.
A new uranyl–organic framework (U‐IHEP‐4) based on porphyrin derivative ligand was synthesized, filling the gap of porphyrinic MOFs in the field of actinide chemistry. The compound U‐IHEP‐4 was demonstrated to be a heterogeneous catalyst for dehydrogenation of N‐heterocycles.
Two highly symmetrical (3,4)‐connected uranyl–organic frameworks (UOFs) were synthesized by a judicious combination of D3h‐symmetrical triangular UO2(COO)3− and Td symmetrical tetrahedral ...tetrakis(4‐carboxyphenyl)methane (H4MTB). These two as‐synthesized UOFs possess similar structural units and coordination modes but totally different topological structures, namely ctn net and bor net. Solvent‐induced interpenetration and a morphology change are observed. The two compounds exhibit crystal transformation via a dissolution–crystallization process. Adsorption experiments in CH3OH solution indicate that both of them can selectively remove positively charged dyes over negatively charged and neutral dyes. Moreover, the electronic structural and bonding properties of the two compounds were systematically explored by density functional theory (DFT) calculations.
Two uranyl–organic frameworks (UOFs) based on the MTB4− ligand, C(p‐C6H4COO−)4, were synthesized by altering solvents. They possess similar structure units and coordination modes but totally different 3D structures, featuring ctn‐type and bor‐type topology.
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