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Covalent organic frameworks (COFs) are an innovative class of crystalline porous polymers composed of light elements such as C, N, O, etc., linked by covalent bonds. The distinctive properties of COFs, including designable building blocks, large specific surface area, tunable pore size, abundant active sites, and remarkable stability, have led their widespread applications in electrocatalysis. In recent years, COF‐based electrocatalysts have made remarkable progress in various electrocatalytic fields, including the hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, nitrogen reduction reaction, nitrate reduction reaction, and carbon dioxide reduction reaction. This review begins with an introduction to the design and synthesis strategies employed for COF‐based electrocatalysts. These strategies include heteroatom doping, metalation of COF and building monomers, encapsulation of active sites within COF pores, and the development of COF‐based derived materials. Subsequently, a systematic overview of the recent advancements in the application of COF‐based catalysts in electrocatalysis is presented. Finally, the review discusses the main challenges and outlines possible avenues for the future development of COF‐based electrocatalysts. [ABSTRACT FROM AUTHOR]

Non‐platinum noble metals are highly desirable for the development of highly active, stable oxygen reduction reaction (ORR) electrocatalysts for fuel cells and metal‐air batteries. However, how to improve the utilization of non‐platinum noble metals is an urgent issue. Herein, a highly efficient catalyst for ORR was prepared through homogeneous loading of Pd precursors by a domain‐limited method in a three‐dimensional covalent organic framework (COF) followed by pyrolysis. The morphology of the Pd nanoparticles (Pd NPs) was well maintained after carbonization, which was attributed to the rigid structure of the 3D COF. Thanks to the uniform distribution of Pd NPs in the carbon, the catalyst exhibited a remarkable half‐wave potential of 0.906 V and a Tafel slope of 70 mV dec−1 in 0.1 M KOH, surpassing the commercial Pt/C catalyst (0.863 V and 75 mV dec−1). Furthermore, a maximum power density of 144.0 mW cm−2 was achieved at 252 mA cm−2, which was significantly higher than the control battery (105.1 mW cm−2). This work not only provides a simple strategy for in‐situ preparation of highly dispersible metal catalysts in COFs, but also offers new insights into the ORR electrocatalysis. [ABSTRACT FROM AUTHOR]

Dual‐atom catalysts (DAC) are deemed as promising electrocatalysts due to the abundant active sites and adjustable electronic structure, but the fabrication of well‐defined DAC is still full of challenges. Herein, bonded Fe dual‐atom catalysts (Fe2DAC) with Fe2N6C8O2 configuration were developed through one‐step carbonization of a preorganized covalent organic framework with bimetallic Fe chelation sites (Fe2COF). The transition from Fe2COF to Fe2DAC involved the dissociation of the nanoparticles and the capture of atoms by carbon defects. Benefitting from the optimized d‐band center and enhanced adsorption of OOH* intermediates, Fe2DAC exhibited outstanding oxygen reduction activity with a half‐wave potential of 0.898 V vs. RHE. This work will guide more fabrication of dual‐atom and even cluster catalysts from preorganized COF in the future. [ABSTRACT FROM AUTHOR]

Dual‐atom catalysts (DAC) are deemed as promising electrocatalysts due to the abundant active sites and adjustable electronic structure, but the fabrication of well‐defined DAC is still full of challenges. Herein, bonded Fe dual‐atom catalysts (Fe2DAC) with Fe2N6C8O2 configuration were developed through one‐step carbonization of a preorganized covalent organic framework with bimetallic Fe chelation sites (Fe2COF). The transition from Fe2COF to Fe2DAC involved the dissociation of the nanoparticles and the capture of atoms by carbon defects. Benefitting from the optimized d‐band center and enhanced adsorption of OOH* intermediates, Fe2DAC exhibited outstanding oxygen reduction activity with a half‐wave potential of 0.898 V vs. RHE. This work will guide more fabrication of dual‐atom and even cluster catalysts from preorganized COF in the future. [ABSTRACT FROM AUTHOR]

Atmospheric moisture is a sustainable clean water source that can solve the shortage of fresh water in arid areas. Herein a 2D covalent organic framework (COF‐ok) was reported as a promising porous sorbent for solar‐driven atmospheric water harvesting. COF‐ok with ortho‐ketoenamine linkage was extremely stable in harsh environment, including in boiling water, strong acids and bases. Because of the balanced hydrophilic and hydrophobic sites in channels, COF‐ok showed a high water uptake of 0.33 g g−1 at a low relative humidity of 34 % featuring a characteristic S‐shaped water sorption isotherm with low regeneration temperature (∼45 °C) and excellent cyclic stability. A laboratory‐scale water harvesting system could collect water of 161 g kg−1 under sunlight. [ABSTRACT FROM AUTHOR]

Three metal covalent organic frameworks (MCOFs), namely RuCOF‐ETTA, RuCOF‐TPB and RuCOF‐ETTBA, were synthesized by incorporating the photosensitive RuII tris(2,2′‐bipyridine) unit into the skeleton. Interestingly, each RuCOF contains three isostructural covalent organic frameworks that interlock together with the RuII centers serving as point of registry. The covalently linked network coupling with uniformly distributed RuII units allowed the RuCOFs to exhibit superior chemical stability, strong light‐harvesting ability, and high photocatalytic activity toward hydrogen evolution (20 308 μmol g−1 h−1). This work illustrates the potential of developing versatile MCOFs‐based photocatalysts from functionalized metal complex building unit and further enriches the MCOFs family. [ABSTRACT FROM AUTHOR]

Three metal covalent organic frameworks (MCOFs), namely RuCOF‐ETTA, RuCOF‐TPB and RuCOF‐ETTBA, were synthesized by incorporating the photosensitive RuII tris(2,2′‐bipyridine) unit into the skeleton. Interestingly, each RuCOF contains three isostructural covalent organic frameworks that interlock together with the RuII centers serving as point of registry. The covalently linked network coupling with uniformly distributed RuII units allowed the RuCOFs to exhibit superior chemical stability, strong light‐harvesting ability, and high photocatalytic activity toward hydrogen evolution (20 308 μmol g−1 h−1). This work illustrates the potential of developing versatile MCOFs‐based photocatalysts from functionalized metal complex building unit and further enriches the MCOFs family. [ABSTRACT FROM AUTHOR]

Photoresponsive self‐healing polymer gels have great potential in the fields of optical information storage, artificial intelligence, and wearable flexible devices. Herein, a series of photoresponsive self‐healing gels based on dynamic imine bonds are synthesized in which the photoresponsive functions are achieved by the incorporation of the chromophore 1,2‐bis(5′‐formyl‐2′‐methylthien‐3′‐yl)perfluorocyclopentene (DEA) and the fluorophore 2,5‐dimethoxybenzene‐1,4‐diformaldehyde derivatives (DBD) through the Schiff base reactions between DEA/DBD and aminopropylmethylsiloxane‐dimethylsiloxane copolymers. The gels show ultrafast photoresponsive ability with the transition from yellow to blue within 10 s under 254 nm UV–Vis and subsequent color restoration within 20 s under visible light, derived from the fast ring‐closure and ‐opening transition of DEA. Interestingly, the molecular states of DEA have influence on the on–off intensity of the fluorescence. The gels with ring‐opened DEA show stronger blue fluorescence than the ones with ring‐closed DEA. In addition, the cross‐linked dynamic imine bond enables the gels to self‐heal quickly, and the wound disappears within 10 min without any external stimuli. [ABSTRACT FROM AUTHOR]

The construction of heteroporous covalent organic frameworks (COFs) is still a challenge. Herein, a series of 2D COFs with hexagonal and quadrilateral pores were constructed via in situ salphen or metal salphen formation. Metallized salphen-based COFs can be used as electrocatalysts towards water oxidation with an overpotential of 266 mV at 10 mA cm−2. [ABSTRACT FROM AUTHOR]

The construction of three‐dimensional (3D) covalent organic frameworks (COFs) remains challenging due to the limited types of organic building blocks. With octahedral TiIV complex as the building unit, this study reports on the first 3D anionic titanium‐based COF (Ti‐COF‐1) with an edge‐transitive (6, 4)‐connected soc topology. Ti‐COF‐1 exhibits high crystallinity, superior stability, and large specific surface area (1000.4 m2 g−1). Moreover, Ti‐COF‐1 has a broad absorption band in the UV spectrum with an optical energy gap of 1.86 eV, and exhibits high photocatalytic activity toward Meerwein addition reactions. This research demonstrates an attractive strategy for the design of 3D functional COFs. [ABSTRACT FROM AUTHOR]

The construction of three‐dimensional (3D) covalent organic frameworks (COFs) remains challenging due to the limited types of organic building blocks. With octahedral TiIV complex as the building unit, this study reports on the first 3D anionic titanium‐based COF (Ti‐COF‐1) with an edge‐transitive (6, 4)‐connected soc topology. Ti‐COF‐1 exhibits high crystallinity, superior stability, and large specific surface area (1000.4 m2 g−1). Moreover, Ti‐COF‐1 has a broad absorption band in the UV spectrum with an optical energy gap of 1.86 eV, and exhibits high photocatalytic activity toward Meerwein addition reactions. This research demonstrates an attractive strategy for the design of 3D functional COFs. [ABSTRACT FROM AUTHOR]

A ligand exchange induced single crystal to single crystal (SCSC) transformation from 3D Hofmann-type frameworks [Fe(ep)M(CN)4] (ep = ethylpyrazine; M = Pt, Pd) to 2D layer networks [Fe(mp)2M(CN)4] (mp = methoxypyrazine) was observed. Interestingly, the different pillar–ligands showed a significant influence on the structural assembly and spin-crossover properties. [ABSTRACT FROM AUTHOR]

An electron donor–acceptor covalent organic framework (TTF-COF1) was constructed by the imine condensation of electron donor tetraformyl-tetrathiafulvalene (TTF-fo) and electron acceptor 2,6-diaminoanthraquinone (DAQ). TTF-COF1 has intramolecular charge transfer, offering capacitance of 752 F g−1 at 1 A g−1 and an energy density of 57 W h kg−1 at a power density of 858 W kg−1. [ABSTRACT FROM AUTHOR]

In this work, pyrazine (A), aminopyrazine (B), quinoxaline (C), and 5,6,7,8‐tetrahydroquinoxaline (D) have been screened out among a large number of pyrazine derivatives to construct Hofmann‐type metal–organic frameworks (MOFs) Fe(L)[M(CN)4] (M=Pt, Pd) with similar 3D pillared‐layer structures. X‐ray single‐crystal diffraction reveals that the alternate linkage between M and FeII ions through cyano bridges forms the 2D extended metal cyanide sheets, and ligands A–D acted as vertical columns to connect the 2D sheets to give 3D pillared‐layer structures. Subsequently, a series of bivariate MOFs were constructed by pairwise combination of the four ligands A–D, which were confirmed by 1H NMR, PXRD, FTIR, and Raman spectroscopy. The results demonstrated that ligand size and crystallization rate play a dominant role in constructing bivariate Hofmann‐type MOFs. More importantly, the spin‐crossover (SCO) properties of the bivariate MOFs can be finely tuned by adjusting the proportion of the two pillared ligands in the 3D Hofmann‐type structures. Remarkably, the spin transition temperatures, Tc↑ and Tc↓ of Fe(A)x(B)1−x[Pt(CN)4] (x=0 to 1) can be adjusted from 239 to 254 K and from 248 to 284 K, respectively. Meanwhile, the width of the hysteresis loops can be widened from 9 to 30 K. Changing Pt to Pd, the hysteresis loops of Fe(A)x(B)1−x[Pd(CN)4] can be tuned from 9 (Tc↑=215 K, Tc↓=206 K) to 24 K (Tc↑=300 K, Tc↓=276 K). This research provides wider implications in the development of advanced bistable materials, especially in precisely regulating SCO properties. [ABSTRACT FROM AUTHOR]

A diarylethene-based photochromic cage (DPC) with an adjustable cavity upon irradiation with UV and visible light has been designed and synthesized. Au nanoparticles encapsulated in the organic cage with open and closed states (Au@o-DPC and Au@c-DPC) showed different catalytic activities for the reduction of 4-nitrophenol. [ABSTRACT FROM AUTHOR]

Two Fe II8 L12 cubic metal–organic cages were constructed with semi-rigid ligands and they further self-assembled into supramolecular assemblies with three different porous cavities. The supramolecular assemblies showed synergistic adsorption of I2 and TTF, and their solid state spin-crossover behaviors were influenced by the adsorbed guest molecules. [ABSTRACT FROM AUTHOR]

Two three-dimensional (3D) porphyrin covalent organic frameworks, PCOF-1 and PCOF-2, were synthesized via imine condensation of a planar porphyrin tetramine (TAPP or TABPP) and a rigid tetrahedral aldehyde based on the steric hindrance of 3,3′,5,5′-tetrakis(4-formylphenyl)bimesityl (TFBM). The structures of PCOF-1 and PCOF-2 were studied by FT-IR and 13C CP-MAS solid state NMR spectroscopy. Powder X-ray diffraction patterns revealed obvious crystallinity with two intense peaks at 3.28° and 3.75° for PCOF-1, and 2.63° and 2.98° for PCOF-2. Structural simulation confirmed their 3D rutile type (pts) topological structures with two different pore sizes. X-ray single crystal diffraction revealed a distorted tetrahedral structure for the building block TFBM with two dihedral angles of 119° and 107.8°, and a planar square structure for the model compound (MC) with an outspread angle of 176.5°. PCOF-1 and PCOF-2 exhibited Brunauer–Emmett–Teller (BET) surface areas of 316 and 234 m2 g−1, respectively. The morphologies of PCOF-1 and PCOF-2 were investigated by scanning electron microscopy and transmission electron microscopy methods. PCOF-1 and PCOF-2 showed a high thermal stability up to 420 °C without decomposition through thermogravimetric analysis (TGA), and high chemical stability with no obvious mass loss after three days of immersion in various solutions. Due to the large surface area and the appropriate pore size, PCOF-Fe exhibited excellent biocatalytic catalytic performance, while PCOF-Co exhibited good electrocatalytic activity towards oxygen evolution reactions. These results indicate that 3D porphyrin-based COFs constructed from the tetrahedral building block with steric hindrance are promising candidates for single-site catalysis. [ABSTRACT FROM AUTHOR]

Diarylethene polymers are an emerging class of photochromic materials which offer new opportunities for the development of optical data recording and storage. This work reports two diarylethene-based conjugated polymer networks DPP-1 and DPP-2 constructed by Schiff-base polymerization of two-connected photochromic unit 1,2-bis(5-formyl-2-methylthiophen-3-yl)perfluorocyclopentene (DEA-CHO) and tetrahedral four-connected unit tetra(p-aminophenyl)methane (TAPM) or plane three-connected unit 1,3,5-tris(4-aminophenyl)triazine (TAPT). The molecular structures of DPP-1 and DPP-2 were characterized by FT-IR and 13C CP-MAS solid state NMR spectroscopy, and the morphology was investigated through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The model compound was used to indicate the possibility of constructing DPP-1 and DPP-2. DPP-1 and DPP-2 exhibited high chemical stability in the presence of strong acid (6 M HCl) and strong base (6 M NaOH) for 5 days. DPP-1 and DPP-2 showed ultrafast photochromic transformation between the open form (yellow) and closed form (green) with alternate irradiation of ultraviolet and visible light in 50 seconds, which were measured through UV-vis-NIR experiments. X-ray photoelectron spectroscopy (XPS) demonstrated that the electronic arrangement around the sulfur atoms changed during the process of the open form to the closed form. Moreover, DPP-1 and DPP-2 displayed excellent fatigue resistance that the absorbance only lost ca. 5% after three cycles. DPP-1/PMMA and DPP-2/PMMA films fabricated by dispersing diarylethene-based conjugated polymer networks in the poly(methyl methacrylate) (PMMA) matrix also exhibited great photochromic reversibility and fatigue resistance, which provide potential applications towards the development of optical rewritable patterning and information storage devices. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) have attracted enormous attention due to their unique structures, good crystallinity, modifiable functional groups, and excellent chemical stability. Nevertheless, their low electrical conductivity impeded their potential usage in supercapacitors. Herein, a two-dimensional conductive covalent organic framework (Ni-COF) with a square-planar Ni(II) coordination geometry is developed. The electrical conductivity of Ni-COF powder and thin film is 1.3 × 10−2 and 1.2 S cm−1, respectively. The highly conjugated skeleton, ordered porous structure and numerous redox centres contribute to a high specific capacitance of 1257 F g−1 at 1 A g−1 with 94% capacitance retention after 10 000 cycles. Meanwhile, the asymmetric supercapacitor (activated carbon//Ni-COF) shows a high capacitance of 417 F g−1 at 1 A g−1, and an outstanding energy density of 130 W h kg−1 at a power density of 839 W kg−1, outperforming previously reported COF electrode materials and even comparable to metal–organic framework systems. Thus, this study opens a new way to construct highly conductive structure-controllable COF electrode materials for supercapacitors. [ABSTRACT FROM AUTHOR]

A series of metal hydroxide nanosheets have been fabricated from metal–organic layers (MOLs) through a conformal conversion process. Significantly, the MOL-derived Fe(OH)3 with an ultrathin layer structure exhibited enhanced alkaline oxygen evolution with a low overpotential of 271 mV at a current density of 10 mA cm−2. [ABSTRACT FROM AUTHOR]

An unprecedented zeolite supramolecular framework featuring truncated cuboctahedral and truncated octahedral cavities was self-assembled from tetrahedral metal–organic cationic cages and tetrahedral anions. This crystalline porous material could trap iodine and organic dye molecules, and its solid state spin-crossover behavior was affected by guest encapsulation. [ABSTRACT FROM AUTHOR]

A novel porphyrin-based porous organic polymer PPOP-1(Pd) with bifunctional catalytic sites was constructed via imine condensation of tetra(4-aminophenyl)porphyrin and acenaphthenequinone. PPOP-1(Pd) containing Pd(ii)-porphyrin and Pd(ii)-α-diimine moieties exhibits excellent catalytic activity and outstanding reusability for tandem catalytic reactions of C–H arylation and Suzuki coupling. [ABSTRACT FROM AUTHOR]

Abstract: Inorganic–organic composites have received considerable attention due to their combined properties. In this study, a N‐halamine precursor poly[5,5‐dimethyl‐3‐(3′‐triethoxysilylpropyl)‐hydantoin] (PSPH) was synthesized and used for the production of inorganic–organic hybrid particles after reacting with nano‐TiO2 by a sol–gel process. The hybrid particles were characterized by FT‐IR, XRD, and TGA‐DTG. After chlorinated in the dilute sodium hypochlorite solution, antibacterial Cl‐PSPH‐TiO2 nanoparticles (NPS) could be obtained and used for production of polyvinyl alcohol (PVA) composite membranes. The synthesized PSPH‐TiO2/PVA composite membranes were characterized by SEM, FT‐IR, XRD, and TGA‐DTG. Meanwhile, antibacterial property, UV light stability, mechanical properties, and storage stability of the composite membranes were tested. The antibacterial composite membranes with Cl‐PSPH‐TiO2 could inactivate 99.97% of Staphylococcus aureus (3.03 logs) and 100% of Escherichia coli O157:H7 (6.12 logs) within 30 min. The antibacterial composite membranes also showed good UV light stability, regeneration ability, and excellent storage stability. [ABSTRACT FROM AUTHOR]

Four pairs of chiral supramolecular coordination cages were facilely synthesized, and they could efficiently inhibit amyloid-β (Aβ) aggregation with a high inhibition rate of 0.64–0.86. This research provides a new perspective on the design of chiral Aβ inhibitors using supramolecular metal–organic cages. [ABSTRACT FROM AUTHOR]

Porous organic polymers have become promising electrode materials, but their low surface area and poor electrical conductivity limit their application in high-performance supercapacitors. This study reports the facile synthesis of two porous organic polymers (POP-1 and POP-2) via the condensation of tetra(4-aminophenyl)methane and 2-thenaldehyde or 2,2-bithiophene-5-carboxyaldehyde and their subsequent polymerization. The resulting porous organic polymer materials were characterized using FT-IR, 13C-NMR, X-ray single crystal diffraction, SEM, TEM and N2 adsorption–desorption measurements. This study shows that POP-2 has a diamond topological structure with a regular morphology and a wealth of pores, and a higher BET surface area (342 m2 g−1) when compared with POP-1 (260 m2 g−1). POP-2, when used as an electrode material for supercapacitors, also exhibits a much better electrochemical performance, including higher specific capacitance (332 F g−1) and better cycle stability (capacity retention rate of more than 94% after 10 000 successive cycles). These results verify that the structure and electrochemical properties of porous organic polymer materials can be effectively improved by altering the monomers. This study also provides an approach for building various porous organic polymer materials for use in high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

AgNWs@SCO nanocomposites were constructed by in situ growing spin-crossover (SCO) nanoparticles on silver nanowires (AgNWs). The obtained AgNWs@[Fe(Htrz)2(trz)](BF4) (AgNWs@SCO-1) and AgNWs@Fe(pz)[Pt(CN)4] (AgNWs@SCO-2) nanomaterials were characterized by FT-IR, PXRD, Raman spectroscopy, SEM and TEM. SEM images show that SCO NPs grow on the surface of the AgNWs, and their size and shape can be tuned by controlling the amount of added iron(ii) salt. The magnetic measurements exhibit hysteresis loops with 45 K (Tc↑ = 385 K, Tc↓ = 340 K) for SCO-1 and 31 K (Tc↑ = 290 K, Tc↓ = 259 K) for SCO-2. It is interesting that both AgNWs@SCO nanocomposites retain spin-crossover behaviour with hysteresis loops with 50 K (Tc↑ = 395 K and Tc↓ = 345 K) for AgNWs@SCO-1 and 34 K (Tc↑ = 289 K and Tc↓ = 255 K) for AgNWs@SCO-2. The hot pressing method is used to transfer AgNWs@SCO nanocomposites to flexible PET substrates for a four-probe conductivity test. The conductivities of AgNWs@SCO-1 and AgNWs@SCO-2 are consistent with that of the individual AgNWs over the 100–350 K range, indicating that AgNWs@SCO nanocomposites exhibit good conductivity. The combination of both spin-crossover properties and conductive properties in AgNWs@SCO materials provides a great prospect for their application in devices. [ABSTRACT FROM AUTHOR]

A novel pillared-layered entangled luminescent metal–organic framework [Zn2(bpdc)2(BPyTPE)] (1) (BPyTPE = (E)-1,2-diphenyl-1,2-bis(4-(pyridin-4-yl)phenyl)ethene) has been designed and constructed. The solvent-free 1 exhibits strong blue-green emission with an excellent fluorescence quantum yield of 99% and provides a facile and reversible method to sensitively and quantitatively detect trace pesticide of 2,6-dichloro-4-nitroaniline. [ABSTRACT FROM AUTHOR]

A metalloporphyrin-based porous organic polymer, Mn-PPOP-1, was constructed in high yield via the ketoenamine condensation of robust porphyrin tetraamines (TBPP) with 1,3,5-triformylphloroglucinol. The stable keto-enamine form in the synthesized polymer was unambiguously confirmed by 13C CP-MAS solid state NMR. Noticeably, besides the high thermal and chemical stability, this material contains both micropores and mesopores, which are favorable for mass transfer in the catalytic application. Mn-PPOP-1 exhibits significantly high catalytic oxidation of olefins and arylalkanes at room temperature. The catalytic activity and stability of Mn-PPOP-1 are apparently superior to those of the homogeneous manganese porphyrins. These results indicate that the metalloporphyrin-based porous organic polymer is a promising candidate for efficient heterogeneous catalysts. [ABSTRACT FROM AUTHOR]

Two solvent-free polymorphs of a chiral iron(ii) complex have been obtained, and their polymorphism dependent spin-crossover and ferroelectric properties have been demonstrated. Polymorph I shows a gradual spin-crossover behavior, whereas polymorph II remains in a high-spin state but shows a typical ferroelectric feature. [ABSTRACT FROM AUTHOR]

Two iron(ii) molecular isomers, namely face-Λ-[Fe(L1)3](ClO4)2 (1a) (L1 = R-1-phenyl-N-((1-hexyl-5-methyl-1H-imidazol-2-ylmethylene)ethanamine)) and face-Λ-[Fe(L2)3](ClO4)2 (1b) (L2 = R-1-phenyl-N-(1-hexyl-4-methyl-1H-imidazol-2-ylmethylene)ethanamine), are obtained via a well-designed strategy based on the tautomerization of the 4(5)-methylimidazole group. Structural investigations reveal that the two isomers are extremely similar with only differences in the methyl group position of the ligands. The iron(ii) center is surrounded by three bidentate imidazole Schiff-base ligands in the face-Λ conformation, which affords a distorted [FeN6] octahedral coordination sphere. The average Fe–N bond length of 1a (1.971 Å) is shorter than that of 1b (2.185 Å). Spectroscopy analyses, X-ray crystal structures and magnetic investigations show that 1a is in the low-spin state at room temperature due to the strong ligand field imparted by the electron-donating methyl groups at the 5-position on the imidazole moieties and undergoes a partial spin transition with an estimated T1/2 = 390 K. In contrast, 1b is stabilized in the high-spin state because of the strong steric hindrance when the three methyl “legs” are changed from the 5-position to the 4-position on the imidazole moieties. In addition, a new complex, 2, without methyl groups attached to the imidazole rings is introduced and characterized to further corroborate the steric influence on the spin state. Complex 2 exhibits a gradual spin-crossover behaviour with T1/2 = 258 K. Moreover, the diverse spin states of these complexes are computationally studied using the DFT method. The results of the calculations are consistent with the experiments, which prove that the competition of the electronic effect and steric crowding influence the spin states. [ABSTRACT FROM AUTHOR]

A hexagonal porphyrin-based porous organic polymer, namely, CPF-1, was constructed by 3+2 ketoenamine condensation of the C2-symmetric porphyrin diamine 5,15-bis(4-aminophenyl)-10,20-diphenylporphyrin and 1,3,5-triformylphloroglucinol. This material exhibits permanent porosity and excellent thermal and chemical stability. CPF-1 can be employed as a superior supporting substrate to immobilize Au nanoparticles (NPs) as a result of the strong interactions between Au NPs and the CPF support. An Au@CPF-1 hybrid was synthesized by an interfacial solution infiltration method with NaBH4 as reducing agent. Au NPs (5 nm) grew on CPF-1 and were distributed without aggregation. Moreover, Au@CPF-1 exhibits superior catalytic activity compared to many other reported Au-based catalysts for the reduction of 4-nitrophenol in the presence of NaBH4. In addition, Au@CPF-1 has excellent stability and recyclability, and it can be reused for three successive reaction cycles without loss of activity. The dense distribution of phenyl rings on the channel walls of the CPF support can reasonably be regarded as the active sites that adsorb the 4-nitrophenol molecule through hydrogen-bonding and C−H ⋅⋅⋅π interactions, as was confirmed by the X-ray structure of model compound DAPP-Benz. [ABSTRACT FROM AUTHOR]

Spin-crossover (SCO) nanorod arrays have been fabricated by a very simple construction method with cation-exchange polymer resin beads as templates. The nucleation and growth mechanism of the nanorod arrays was studied by SEM. The spin-crossover properties of nanorod arrays with different growth times were characterized by differential scanning calorimetry (DSC), Mössbauer spectroscopy, and magnetic susceptibility measurements. The transition temperatures of the obtained nanorod arrays increase as the immersion time of the nanorods increases. The hysteresis loop widths of these nanorod arrays are larger than that reported for [Fe(Htrz)2(trz)][BF4] (Htrz = 1,2,4-triazole) as bulk powder and nanoparticles. This offers a new route for the fabrication of ordered SCO nanorod arrays by a self-assembly method. [ABSTRACT FROM AUTHOR]

Four pairs of enantiomers of water-stable tetrahedral metal–organic cages [Ni4L6]8+ were facilely synthesized. They efficiently stabilized antiparallel G-quadruplex DNA with moderate enantioselectivity, and displayed promising cytotoxicity against the human cancer cell lines HCT116, HepG2 and MCF-7. These results provide a new insight into the rational design of chiral G-quadruplex-based anticancer agents. [ABSTRACT FROM AUTHOR]

The first SCO@SCO core–shell nanomaterials have been synthesized by the step-by-step microemulsion method. The observed gyroscopic core–shell nanocomposites exhibit three-step spin crossover behaviour with thermal hysteresis at around room temperature. This offers an efficient and novel strategy for the development of multistable SCO materials. [ABSTRACT FROM AUTHOR]

Through multi-component self-assembly of chiral phenylethylamine, 1-alkyl-2-imidazolecarboxaldehyde and iron(ii) ions, two couples of enantiomeric iron(ii) complexes 4R, 4S, 5R and 5S with the formula of fac-Λ or Δ-[Fe(L)3]2+(L = R or S-1-phenyl-N-(1-alkyl-1H-imidazol-2-ylmethylene)ethanamine) have been designed and synthesized as building blocks. Further binary cocrystallization of the prefabricated enantiomers enabled us to construct spin crossover co-enantiomers 4R5R and 4S5S, racemates 4RS and 5RS, and co-racemate 4RS5RS. Compared with 4R in a high spin state and 5R with spin crossover at 291 K, the co-enantiomers 4R5R exhibited gradual spin crossover at a higher temperature of 301 K, and the racemic alloys showed hysteresis loops induced by desolvation above room temperature. It was demonstrated that molecular chirality could be used effectively for stereochemical engineering of spin crossover materials. In addition, crystal packing, intramolecular π–π stacking, intermolecular C–H…π interactions and solvent effects were elucidated to be responsible for the distinct spin crossover properties. This collective structural and magnetic study not only enriched the spin crossover library, but also provided a full comparison of optically pure, homochiral, and racemic materials with similar molecular structures. [ABSTRACT FROM AUTHOR]

An effective single crystal to single crystal transformation from a tetrahedral Ni cage to an FeNi cage was demonstrated. The iron(ii) centers of the FeNi cage can be induced to display spin crossover behaviors with an increasing amount of Fe(ii) ions. The SCSC metal-center exchange provides a powerful approach to modify solid magnetic properties. [ABSTRACT FROM AUTHOR]

Inorganic ion exchangers in hydrogen forms, HLaTiO (HLTO), HTiO (HTO) and HTiO (HTO) have been prepared by acid treatment of LiLaTiO, LiTiO and LiTiO, respectively, which were synthesized by the solid-state reaction method. The selectivity of metal ions, Li ion exchange property and lithium isotopes separation property were investigated. The three ion exchangers were isotopically Li-specific, and the maximum single-stage separation factors of Li/Li, were 1.042, 1.037 and 1.035 for HLTO, HTO, and HTO, respectively. The structures of HLTO, HTO and HTO were stable and they can be regenerated and recyclable in three cycles. [ABSTRACT FROM AUTHOR]

A homochiral complex 1·MeCN was synthesized by the multicomponent self-assembly of (R)-phenylethylamine, 1-methyl-2-imidazolecarboxaldehyde and iron(ii) ions in acetonitrile solution. X-ray crystallography analysis revealed that complex 1·MeCN crystallized in the chiral space group P21. The octahedral coordination mononuclear [FeL3]2+ cations are stacked into a left-handed double helix supramolecular structure along the a axis with uncoordinated acetonitrile molecules filling the helical channel. Interestingly, when 1·MeCN redissolved in racemic lactonitrile (LN) or methylglutaronitrile (MGN), the [FeL3]2+ cations can recognize one enantiomeric alkyl nitrile by forming 1·1/3(R)-LN or 1·1/3(S)-MGN crystals. 1·1/3(R)-LN and 1·1/3(S)-MGN crystallized in the P212121 space group, and the [FeL3]2+ cations are stacked in a triple helix mode with the enantiomeric alkyl nitrile captured in the helical channel. Magnetic measurement indicated that 1·MeCN displayed spin-crossover at 355 K, while the transition temperature became 220 K after desolvation. However, 1·1/3(R)-LN and 1·1/3(S)-MGN exhibited incomplete and reversible spin-crossover behaviors at about 363 K. The results demonstrated that the mononuclear iron(ii) complex could be used as a host for racemic alkyl nitrile separation, and the spin-crossover property was influenced by the process of chiral recognition. [ABSTRACT FROM AUTHOR]

A green and efficient solid-liquid extraction method of lithium isotopes separation by porous composite materials doped with imidazolium ionic liquids and 2,2′-binaphthyldiyl-17-crown-5 has been reported in this paper. The composite materials of mesoporous silica and impregnated resin were synthesized by sol-gel and direct impregnation process, respectively. Various extraction parameters such as the concentration of lithium salt, anion of lithium salt, initial pH, time and temperature were investigated. Under optimized conditions, the maximum single-stage separation factor of Li/Li was 1.048 ± 0.002, the maximum extraction efficiency was 15.86 %. The sorbents can be regenerated easily with HCl solution and reused repeatedly. [ABSTRACT FROM AUTHOR]

By using a tetraphenylethene (TPE)-based ligand, tetrakis[4-(4-carboxyphenyl)phenyl]ethene (H4TCPPE), a porous metal–organic framework [Zn2(TCPPE)] (1) is synthesized, which exhibits strong fluorescence and is capable of gas adsorption and sensing volatile organic compounds. [ABSTRACT FROM AUTHOR]