Structure, Properties, Preparation, and Application of Layered Titanates.

As a typical cation-exchangeable layered compound, layered titanate has a unique open layered structure. Its excellent physical and chemical properties allow its wide use in the energy, environmental protection, electronics, biology, and other fields. This paper reviews the recent progress in the research on the structure, synthesis, properties, and application of layered titanates. Various reactivities, as well as the advantages and disadvantages, of different synthetic methods are discussed. The reaction mechanism and influencing factors of the ion exchange reaction, intercalation reaction, and exfoliation reaction are analyzed. The latest research progress on layered titanates and their modified products in the fields of photocatalysis, adsorption, electrochemistry, and other applications is summarized. Finally, the future development of layered titanate and its exfoliated product two-dimensional nanosheets is proposed.

Enantioselective recognition of chiral acids by supramolecular interactions with chiral AIEgens.

Novel chiral AIEgens bearing optically pure amino groups were synthesized and showed excellent discrimination for a series of chiral acidic compounds and amino acids. Interestingly, after supramolecular assembly with 4-sulfocalix[4]arene, the obtained complexes showed enhanced enantioselectivity for chiral acids.

Iodine-Mediated Cyclization of Enamines to Imidazole-4-Carboxylic Derivatives with Sequential Removal of Nitrogen Atoms from TMSN3.

An iodine-mediated oxidative [4+1] cyclization of enamines with TMSN3 for the synthesis of 2,5-disubstituted imidazole-4-carboxylic derivatives has been developed. The mechanistic studies revealed that the reaction proceeds through a sequential removal of two nitrogen atoms from TMSN3. The synthetic utility was further demonstrated with a gram-scale reaction and various derivatization transformations of the products.

Iron-Catalyzed Cycloaddition of Amides and 2,3-Diaryl-2H-azirines To Access Oxazoles via C-N Bond Cleavage.

A novel and efficient iron-catalyzed cycloaddition reaction using readily available 2,3-diaryl-2H-azirines and primary amides is reported. A wide range of trisubstituted oxazoles could be achieved in good yields with good functional group compatibility. In this transformation, two C-N bonds were cleaed and new C-N and C-O bonds were formed.

IBX-Promoted Oxidative Cyclization of N-Hydroxyalkyl Enamines: A Metal-Free Approach toward 2,3-Disubstituted Pyrroles and Pyridines.

An iodoxybenzoic acid-mediated selected oxidative cyclization of N-hydroxyalkyl enamines was developed. Through this strategy, a variety of 2,3-disubstituted pyrroles and pyridines were produced in good selectivity involving oxidation of alcohol, followed by condensation of aldehyde and α-C of enamines. Furthermore, this metal-free method has several advantages, including the use of environmentally friendly reagents, broad substrate scope, mild reaction conditions, and high efficiency.

A graphene oxide functionalized energetic coordination polymer possesses good thermostability, heat release and combustion catalytic performance for ammonium perchlorate.

A new energetic coordination polymer (ECP) composite, namely GO-Cu(ii)-AmTZ, has been synthesized by 3-amino-1,2,4-triazole (AmTZ) and multifunctional graphene oxide (GO) coordination with Cu(ii) successively. The ECP composite was further characterized through SEM, EDS and XPS analysis as well as FTIR and Raman spectroscopy. It shows high thermostability, high decomposition heat release and insensitivity to mechanical stimuli. What's more, thermal analysis data for ammonium perchlorate (AP) have been obtained by mechanically mixing GO-Cu(ii)-AmTZ and AP. The low-temperature decomposition (LTD, 335.3 °C) and high-temperature decomposition (HTD, 441.3 °C) peaks of AP were reduced to an exothermic peak at 298.4 °C at a heating rate of 10 °C min-1. GO-Cu(ii)-AmTZ exhibits outstanding catalytic performance by decreasing the activation energy from 168.7 kJ mol-1 to 122.4 kJ mol-1, indicating its promising application as a combustion catalyst for improving the thermal-catalytic decomposition performance of energetic materials largely. In addition, thermal analysis techniques including thermogravimetry coupled with mass spectrometry (TG/MS) and thermogravimetry coupled with infrared spectrometry (TG/IR) were employed to determine the decomposition mechanisms.

Crystal and Band-Gap Engineering of One-Dimensional Antimony/Bismuth-Based Organic-Inorganic Hybrids.

Hybrid halide perovskites are emerging semiconducting materials with a diverse set of remarkable optoelectronic properties. Besides the widely studied lead halide perovskites, Pb-free metal halides such as Bi- and Sb-containing hybrid organic-inorganic materials have shown potential as semiconductors and have been deemed candidates for optoelectronic devices. Here, we report a series of 1D Sb/Bi-based organic-inorganic hybrid alloys: [4ApyH]SbxBi1-xIyBr4-y, where 4ApyH stands for the 4-aminopyridine cations. These compounds are assembled by edge-sharing octahedral [MX6] units stabilizing 1D chains with organic cations filled in between. The crystallographic data of eight selected complexes show that [4ApyH]SbxBi1-xIyBr4-y has at least five phases (space group) with the difference metal and halogen content: Pbca ([4ApyH]BiI4), Pca21 ([4ApyH]Sb0.5Bi0.5I4), P21/c ([4ApyH]SbI4 (100 K), [4ApyH]BiI2Br2, [4ApyH]BiBr4, and [4ApyH]SbBr4 (100 K)), I2/a ([4ApyH]Sb0.5Bi0.5I2Br2and [4ApyH]SbI2Br2), and C2/c ([4ApyH]SbI4 (298 K) and [4ApyH]SbBr4 (298 K)). Powder X-ray diffraction shows that the phase of the sample changes with a change of the metal and halogen ratios, and the change law accords with Vegard's law. The optical band gaps are heavily affected by the metal and halide contents, ranging from 1.94 eV for [4ApyH]BiI4 to 2.73 eV for [4ApyH]SbBr4. When Sb substitutes for Bi to form an alloy, the band gap increases from 1.94 for [4ApyH]BiI4 to 1.67 eV for [4ApyH]SbI4, from 2.13 eV for [4ApyH]BiI2Br2 to 2.41 eV for [4ApyH]SbI2Br2, and from 2.55 eV for [4ApyH]BiBr4 to 2.73 eV for [4ApyH]SbBr4. The conductivity of [4ApyH]SbxBi1-xI4 increased from ∼1.00 × 10-15 to 2.14 × 10-8 S cm-1 with an increase of the Sb content. Solution-deposited thin films of the nine complexes show the same (110) orientation, displaying a parallel growth orientation with respect to the substrate. The devices of [4ApyH]Sb0.8Bi0.2I4 and [4ApyH]SbI4 demonstrated stable open-circuit photovoltages of 0.55 and 0.44 V, steady-state short-circuit photocurrent densities of 1.52 and 1.81 mA cm-2, and light-to-electrical energy conversion efficiencies of 0.29% and 0.30%, respectively.

Tracking the dimensional conversion process of semiconducting lead bromide perovskites by mass spectroscopy, powder X-ray diffraction, microcalorimetry and crystallography.

The structural information of a material in both the solid state and solution state is essential to the in-depth understanding of the properties of inorganic-organic hybrid materials. A one-dimensional (1D) lead bromide formulated as [H][NH3(CH2)2SS(CH2)2NH3][H2O][PbBr5] (1) could be converted into a new two-dimensional (2D) complex, [NH3(CH2)2SS(CH2)2NH3][PbBr4] (2), by soaking the crystals in water. The isolated 2D compound showed single-layer lead-halide perovskite structures. Electrospray ionization mass spectrometry (ESI-MS) analyses of the reaction solution revealed that the [PbBr3]- fragments are initially formed from the rapid decomposition of the 1D [PbBr5]3- chains and subsequently reassemble into 2D [PbBr4]2- layers, which was verified by powder X-ray diffraction (PXRD) and microcalorimetry. Because of the decomposition and reassembly process, complex 1 could be used as a precursor to synthesize M2+-doped 2D lead bromide perovskites, namely, Mn@2, Ni@2 and Cd@2. In addition, preliminary tests indicated that complex 2 exhibited a lower optical band gap (3.25 eV) and higher electrical conductivity (3.2 × 10-11 S cm-1) than complex 1 (3.38 eV, 5.4 × 10-12 S cm-1).

Monodisperse Bismuth-Halide Double Perovskite Nanocrystals Confined in Mesoporous Silica Templates.

Metal halide perovskites have fascinating electronic properties and have already been implemented in various devices. Although the behavior of the properties of lead halide perovskite nanocrystals has been studied, the properties of lead-free perovskite nanocrystals are less well-understood because synthesizing them is still very challenging. Here, a simple and popularizable method has been demonstrated to grow monodisperse bismuth-halide double perovskite nanocrystals, Cs2AgBiBr6 (1), inside three kinds of mesoporous silica templates. The size and morphology of nanocrystals depend on the structure and pore size of the template. Structural analysis shows that the nanocrystals of various sizes and morphologies retain the crystal structure of bimetallic perovskite. 1 exhibits different morphologies in the silicon channels of three templates: square nanoparticles in KIT-6, spherical and rodlike particles in SBA-15, and nanowires in MCM-41. UV-vis-NIR and photoluminescence measurements show us the variation of band gap and carrier recombination time due to quantum confinement of nanocrystals in mesoporous silicon materials. The band gaps of nanocrystals in the template exhibit an obvious blue shift compared with that of the bulk sample, and the carrier recombination time is significantly shortened. We show that mesoporous silicon templates can be used to prepare lead-free perovskite nanocrystals, and the controllable preparation of nanocrystals can be achieved by the template's own characteristics. This provides a new idea for us to find new functional materials of lead-free metal halide solid-state light-emitting diodes.

Brønsted-Acid-Catalyzed Synthesis of 3-Alkoxy and 3-Sulfamido Indanones via a Tandem Cyclization.

Brønsted-acid-catalyzed allylic substitution reactions of the in situ generated 3-hydroxy indanones with alcohols and sulfamides were investigated, which provided a facile route for the synthesis of a large variety of 3-alkoxy and 3-sulfamido indanones. The key intermediates, 3-hydroxy indanones, were obtained through the intramolecular Meyer-Schuster rearrangement of o-propargyl alcohol benzaldehydes. The resulting 3-benzyloxy indanone could be selectively modified by allylic sulfonamidation and reduction reactions.

The slow magnetic relaxation regulated by the coordination, configuration and intermolecular dipolar field in two mononuclear DyIII single-molecule magnets (SMMs).

Tuning the magnetic dynamics of single-molecule magnets (SMMs) is a crucial challenge for chemists. Some feasible approaches have been developed to understand parts of the magneto-structural correlations and regulate the relaxation behaviors via rational design. Herein, the syntheses, structures and magnetic properties of two mononuclear DyIII SMMs are reported. The first structural motif reveals a trigonal dodecahedron (D2d) N2O6 coordination environment in 1, while the second one displays a square antiprismatic configuration (D4d). A DyDy distance of 8.589 Å in 1 is clearly shorter than that of 2 (10.433 Å) because of the existence of ππ stacking between benzene rings from two adjacent dbpy molecules in 1. The temperature and frequency-dependent out-of-phase ac susceptibility peaks were observed in the absence of a static dc field for 1 and 2. Two distinct thermal relaxation processes were observed in 1, while 2 exhibits one thermal relaxation process. It is interesting that the quantum tunneling of magnetization (QTM) was suppressed when optimum dc fields (1000 Oe) were applied. From ab initio calculations, the energies of the first excited state (KD1) are indeed close to the experimental relaxation energy barrier (Ueff) under zero dc field, which also reveals the typical features associated with the SMM behavior. In detail, the Ueff values are 103.62 cm-1 (149.87 K) as well as 55.10 cm-1 (79.69 K) for 1 and 116.07 cm-1 (167.87 K) for 2. The KD1 of 1 (133.82 cm-1) is slightly higher than that of 2 (129.31 cm-1). Comparing 1 and 2, this discrepancy from KD1 and the experimental Ueff might come from the apparent difference in the magnitude of tunneling probability between the two compounds. In other words, the intermolecular dipolar field plays an important role in their magnetic properties.

K2S2O8/TEMPO-Induced Cascade Oxidative Cyclization/1,2-Migration of Electron-Deficient Groups: Strategy for the Construction of 1 H-Pyrrol-2(3 H)-ones.

A K2S2O8/TEMPO-induced oxidative cyclization of N-unprotected enaminoesters and enaminones that gave 1 H-pyrrol-2(3 H)-ones in good yields with broad functional group compatibility is reported. This method provides easy access to 1,2-carbon migration of ester or acyl group under transition-metal-free conditions.

Copper-Catalyzed Oxidative Cyclization/1,2-Amino Migration Cascade Reaction.

A novel and efficient copper-catalyzed tandem oxidative cyclization/1,2-amino migration of readily available enamino esters for the synthesis of substituted pyrroles has been developed. In this reaction, one C-N bond was cleaved, and two new C-N bonds and one C(sp2)-C(sp2) bond were constructed in one pot. This catalytic system has the obvious advantages of mild reaction conditions and the use of oxygen as the oxidant. The reaction tolerates a wide range of functional groups and is a reliable method for the straightforward synthesis of valuable aminomethyl-substituted pyrroles in good yields.

Modular 2,3-diaryl-2H-azirine synthesis from ketoxime acetates via Cs2CO3-mediated cyclization.

A modular 2H-azirine synthesis from ketoxime acetates via Cs2CO3-mediated cyclization has been developed. The reaction utilizes easily available starting materials and provides a general synthetic route to 2,3-diaryl-2H-azirines in good to excellent yields under mild conditions, which is complementary to the conventional approaches for the synthesis of 2H-azirines. A gram-scale reaction was performed to demonstrate the scale-up applicability of this synthetic method. Importantly, 2H-azirines can be efficiently converted to various azaheterocycles.

Iron-Catalyzed Radical Cycloaddition of 2H-Azirines and Enamides for the Synthesis of Pyrroles.

A novel and efficient Fe-catalyzed radical cycloaddition of 2H-azirines and enamides for the synthesis of substituted pyrroles has been developed. The radical cycloaddition reaction proceeded through a conceptually new Fe(II)-catalyzed homolytic cleavage of C-N bond of 2H-azirines sequential radical cyclization with enamides. The reaction used readily available starting materials, tolerated various functional groups, and afforded valuable triaryl-substituted pyrroles in good to high yields under mild reaction conditions.

KI-catalyzed oxidative cyclization of α-keto acids and 2-hydrazinopyridines: efficient one-pot synthesis of 1,2,4-triazolo[4,3-a]pyridines.

A one-pot approach to substituted 1,2,4-triazolo[4,3-a]pyridines has been developed that is based on a KI-catalyzed oxidative cyclization of α-keto acids and 2-hydrazinopyridines. This transition-metal-free procedure was highly efficient and shows good economical and environmental advantages.

Experimental and theoretical interpretation of the magnetic behavior of two Dy(iii) single-ion magnets constructed through ß-diketonate ligands with different substituent groups (-Cl/-OCH3).

Two Dy(iii) single-ion magnets, formulated as [Dy(Phen)(Cl-tcpb)3] (Cl-1) and [Dy(Phen)(CH3O-tmpd)3] (CH3O-2) were obtained through ß-diketonate ligands (Cl-tcpb = 1-(4-chlorophenyl)-4,4,4-trifluoro-1,3-butanedione and CH3O-tmpd = 4,4,4-trifluoro-1-(4-methoxyphenyl)-1,3-butanedione) with different substituent groups (-Cl/-OCH3) and auxiliary ligand, 1,10-phenanthroline (Phen). The Dy(iii) ions in Cl-1 and CH3O-2 are eight-coordinate, with an approximately square antiprismatic (SAP, D 4d) and trigonal dodecahedron (D 2d) N2O6 coordination environment, respectively, in the first coordination sphere. Under zero direct-current (dc) field, magnetic investigations demonstrate that both Cl-1 and CH3O-2 display dynamic magnetic relaxation of single-molecule magnet (SMM) behavior with different effective barriers (U eff) of 105.4 cm-1 (151.1 K) for Cl-1 and 132.5 cm-1 (190.7 K) for CH3O-2, respectively. As noted, compound CH3O-2 possesses a higher effective barrier than Cl-1. From ab initio calculations, the energies of the first excited state (KD1) are indeed close to the experimental U eff as 126.7 cm-1 vs. 105.4 cm-1 for Cl-1 and 152.8 cm-1 vs. 132.5 cm-1 for CH3O-2. The order of the calculated energies of KD1 is same as that of the experimental U eff. The superior SIM properties of CH3O-2 could have originated from the larger axial electrostatic potential (ESP(ax)) felt by the central Dy(iii) ion when compared with Cl-1. The larger ESP(ax) of CH3O-2 arises from synergic effects of the more negative charge and shorter Dy-O distances of the axial O atoms of the first sphere. These charges and distances could be influenced by functional groups outside the first sphere, e.g., -Cl and -OCH3.

Synthesis of Substituted 2-Amino-1,3-oxazoles via Copper-Catalyzed Oxidative Cyclization of Enamines and N,N-Dialkyl Formamides.

A facile synthesis of 2-amino-1,3-oxazoles via CuI -catalyzed oxidative cyclization of enamines and N,N-dialkyl formamides has been developed. The reaction proceeds through an oxidative C-N bond formation, followed by an intramolecular C(sp2 )-H bond functionalization/C-O cyclization in one pot. This protocol provides direct access to useful 2-amino-1,3-oxazoles and features protecting-group-free nitrogen sources, readily available starting materials, a broad substrate scope and mild reaction conditions.

Selective Host-Guest Co-crystallization of Pyridine-Functionalized Tetraphenylethylenes with Phthalic Acids and Multicolor Emission of the Co-crystals.

Tetraphenylethylene (TPE) and its derivatives are the most typical and most widely studied organic compounds showing aggregation-induced emission (AIE). Due to their propeller-like structures, V-like clefts exist between the aryl rings, which make them promising host compounds. However, such a possibility is seldom explored. Herein, it is reported that TPE derivatives bearing two or four pyridine rings at the para positions of the phenyl rings (TPE-Pys) can selectively include triangular (Δ-like) m-phthalic acid from a mixture of o-, m-, and p-phthalic acids due to their shape complementary to form host-guest co-crystals, which showed redder emission than the TPE-Pys themselves. The emission of co-crystals 1-5 could be reversibly switched between yellow and red by alternating exposure to HCl and ammonia vapor. The host-guest co-crystals not only exhibited great potential for selectively recognizing and separating m-phthalic acid and as multicolor emission materials, but are also suitable for use as secret ink due to their reversible color change on varying the host-guest interactions.

Synthesis of Polycarbonyl Pyrroles via K2S2O8-Mediated Oxidative Cyclization of Enamines.

A novel K2S2O8-promoted oxidative cyclization of enamines is described. A variety of enamines having diverse functional groups and substitution patterns react well using K2S2O8 as the oxidant in the absence of catalyst. This protocol provides a very simple route for the synthesis of polycarbonyl pyrroles and has the advantages of readily available starting materials, mild reaction conditions, and a wide scope of substrates.