Epoxidation vs. dehydrogenation of allylic alcohols: heterogenization of the VO(acac)2 catalyst in a metal-organic framework.

Allylic alcohol epoxidation and dehydrogenation reactivity is distinguished when VO(acac)2 is used in solution or anchored in a metal-organic framework (MOF). The chemical mechanism depends on the electronic profile of alkene substituents when the vanadyl complex is used in the homogenous phase. However, confinement effects imparted by MOF channels allow gaining control of the chemoselectivity toward the dehydrogenation product.

Lanthanide Discrimination with Hydroxyl-Decorated Flexible Metal-Organic Frameworks.

We report two new highly crystalline metal-organic frameworks (MOFs), derived from the natural amino acids serine (1) and threonine (2), featuring hexagonal channels densely decorated with hydroxyl groups belonging to the amino acid residues. Both 1 and 2 are capable of discriminating, via solid-phase extraction, a mixture of selected chloride salts of lanthanides on the basis of their size, chemical affinity, and/or the flexibility of the network. In addition, this discrimination follows a completely different trend for 1 and 2 because of the different locations of the hydroxyl groups in each compound, which is evocative of steric complementarity between the substrate and receptor. Last but not least, the crystal structures of selected adsorbates could be resolved, offering unprecedented snapshots on the capture process and enabling structural correlations with the separation mechanism.

The Effects of Carbon Nanotubes on the Mechanical and Wear Properties of AZ31 Alloy.

Carbon nanotube (CNT)-reinforced AZ31 matrix nanocomposites were successfully fabricated using a powder metallurgy method followed by hot extrusion. The influence of CNTs on microstructures, mechanical properties, and wear properties were systematically investigated by optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD), hardness test, tensile test, and wear test. The results revealed that the nanocomposites showed a slightly smaller grain size compared with the matrix and uniform distribution that CNTs could achieve at proper content. As a result, the addition of CNTs could weaken basal plane texture. However, the yield strength and ultimate tensile strength of the composites were enhanced as the amount of CNTs increased up to 2.0 wt. %, reaching maximum values of 241 MPa (+28.2%) and 297 MPa (+6.1%), respectively. The load transfer mechanism, Orowan mechanism, and thermal mismatch mechanism played important roles in the enhancement of the yield strength, and several classical models were employed to predict the theoretical values. The effect of CNT content on the friction coefficient and weight loss of the nanocomposites was also studied. The relationships between the amount of CNTs, the friction coefficient, and weight loss could be described by the exponential decay model and the Boltzmann model, respectively.

Rational Synthesis of Chiral Metal-Organic Frameworks from Preformed Rodlike Secondary Building Units.

The lack of rational design methodologies to obtain chiral rod-based MOFs is a current synthetic limitation that hampers further expansion of MOF chemistry. Here we report a metalloligand design strategy consisting of the use, for the first time, of preformed 1D rodlike SBUs (1) for the rational preparation of a chiral 3D MOF (2) exhibiting a rare eta net topology. The encoded chiral information on the enantiopure ligand is efficiently transmitted first to the preformed helical 1D building block and, in a second stage, to the resulting chiral 3D MOF. These results open new routes for the rational design of chiral rod-based MOFs, expanding the scope of these unique porous materials.

Copper-based energetic MOFs with 3-nitro-1H-1,2,4-triazole: solvent-dependent syntheses, structures and energetic performances.

The persistent challenge in the field of energetic materials is how to synthesize energetic compounds with high density, high heat of detonation and outstanding detonation performance by gathering the maximum number of energetic groups in the smallest volume. The self-assembly of energetic groups with metal ions is crucially influenced by the solvent conditions. Here, the reaction of Cu(NO3)2·3H2O with 3-nitro-1H-1,2,4-triazole (Hntz) in aqueous ammonia under hydrothermal conditions via a self-assembly strategy yielded the Cu(i) energetic compound [Cu(ntz)]n (1). In order to further enhance the energetic property, an N3- anion was introduced into the system and two Cu(ii) energetic compounds, [Cu(ntz)(N3)(DMF)]n (2) and [Cu(ntz)(N3)(H2O)]n (3), were successfully synthesized under different solvent conditions. Structural analyses show that compound 1 features a compacted 3D structure framework and compounds 2-3 exhibit 1D butterfly-like chain structures. The experimental results reveal that 1 possesses attractive thermal stability up to 315.0 °C and 1-3 present excellent insensitivity. Importantly, the heat of detonation of compound 2 has been factually improved due to the abundant energetic bonds in the coordinated DMF molecules compared to 1 and lots of energies are taken away during the release of the coordinated solvent molecules in the low temperature range resulting in the obvious decreases in detonation pressure and detonation velocity for compounds 2-3, which further exemplifies that the subtle change of reaction conditions may have a crucial effect on the resultant detonation performance. In addition, the detonation performances of 1-3 calculated by both a simple method for metal-containing explosives developed by Pang et al. and the commercial program EXPLO5 v6.01, are discussed in detail.

An Ag(I) energetic metal-organic framework assembled with the energetic combination of furazan and tetrazole: synthesis, structure and energetic performance.

A novel Ag(I) energetic MOF [Ag16(BTFOF)9]n·[2(NH4)]n () assembled with Ag(iI ions and a furazan derivative, 4,4'-oxybis[3,3'-(1H-5-tetrazol)]furazan (H2BTFOF) was successfully synthesized and structurally characterized, featuring a three-dimensional porous structure incorporating ammonium cations. The thermal stability and energetic properties were determined, revealing that the 3D energetic MOF had an outstanding insensitivity (IS > 40 J), an ultrahigh detonation pressure (P) of 65.29 GPa and a detonation velocity (D) of 11.81 km cm(-3). In addition, the self-accelerating decomposition temperature (TSADT) and the critical temperature of thermal explosion (Tb) are also discussed in detail. The finding exemplifies that the assembly strategy plays a decisive role in the density and energetic properties of MOF-based energetic materials.

High Energy Density Materials Incorporating 4,5-Bis(dinitromethyl)-Furoxanate and 4,5-Bis(dinitromethyl)-3-Oxy-Furoxanate.

3-Oxy-furoxanate is immobilized in a heterometallic energetic metal-organic framework (MOFs). Two furoxan-based MOFs ([Ag2 K4 (BDOFO)(BDFO)2 (H2 O)6 ]n , [K2 (BDFO)]n ) and a salt ([(BDFO2- )(NH2 NH3 + )2 (H2 O)]n (BDOFO2- =4,5-bis(dinitromethyl)-3-oxy-furoxanate, BDFO2- =4,5-bis(dinitromethyl)-furoxanate) are synthesized and their energetic performance evaluated. This study outlines the systematic investigation of detonation performance of 3-oxy-furoxan and its derivatives.

High-Performance Energetic Characteristics and Magnetic Properties of a Three-Dimensional Cobalt(II) Metal-Organic Framework Assembled with Azido and Triazole.

A three-dimensional metal-organic framework based, high-energy-density compound, [Co5(3-atrz)7(N3)3] (3-atrz = 3-amine-1H-1,2,4-triazole), features superior detonation properties, insensitivity, and thermostability. Magnetic studies show that the compound characterizes the coexistence of remarkable coercivity, metamagnetism, long-range ordering, and relaxation dynamics. The heat-capacity measurement confirms the typical long-range antiferromagnetic ordering below 16 K. This difunctional system exemplifies an effective attempt at developing advanced magnetoenergetic materials.

Surfactant-free scalable synthesis of hierarchically spherical Co3O4 superstructures and their enhanced lithium-ion storage performances.

Unique hierarchically porous spherical Co(3)O(4) superstructures were synthesized via a surfactant-free hydrothermal process followed by a calcination treatment, in which the concentration of reactant cobalt (II) nitrate hexahydrate is a key factor affecting the morphology of products. X-ray powder diffraction, electron microscopies (TEM and SEM), and thermogravimetric analysis were employed to investigate the formation of Co(3)O(4) spherical superstructures. Our results suggest that they formed from numerous cubic Co(3)O(4) nanocrystals via an oriented attachment mechanism. These superstructures exhibit a high specific capacity of 1750 mA h g(-1) after the first charge-discharge cycle, and the capacity retention remains at a constant of 1600 mA h g(-1) at 0.2 C after 50 cycles. The facile, scalable, energy-efficient and environmentally friendly nature of the presented approach renders it particularly attractive from a technological standpoint. In addition, this scalable and facile synthesis method could be extended to the preparation of other transition metal oxides with specific morphologies and surface textures.