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Meerwein-Ponndorf-Verley (MPV) reduction has gained much attention due to is mid reaction conditions, and this reaction can be performed without the presence of reductive atmosphere and the reaction conditions of high temperature and high pressure. Solid bases with abundant strong basic sites can be synthesized with metal-organic frameworks (MOFs) as precursors. These MOFs are immobilized with alkane metal nitrides, followed by calcination to produce the desired basic metal oxides. The basic zirconia shows highly efficient catalytic performance in MPV reduction of substrates with the carbonyl group, and benzaldehyde can be completely reduced in 6 hours with a mild reaction temperature (160 °C) in the absence of hydrogen gas. The catalytic efficiency is determined by the amounts of strong basic sites, but not the total amounts of basic sites, and this phenomenon is proved by the contrast experiments with the catalytic test of weak solid bases. Furthermore, the cooperative action between basic and acid sites can also enhance the catalytic performance in MPV reactions. With MOFs as precursors, metal oxide catalysts can be synthesized with well dispersed active sites. [ABSTRACT FROM AUTHOR]

Microwave dielectric ceramics Ba(M1/32+M2/35+)O3 have been studied for many years, but the exact relations between the B-site ions and the ceramics’ dielectric properties are still unclear. We take 2:1-ordered Ba(Zn1/3Nb2/3)O3 (BZN) and Ba(Mg1/3Nb2/3)O3 (BMN) as examples and discuss their static permittivity and intrinsic loss based on first-principles calculation. The larger mode-effective charges and lower frequencies of the normal modes are found to be responsible for the larger permittivity in BZN, but further analysis indicates that the dipole interaction, which is strengthened by the covalent bonding among Zn, Nb, and O, is the origin of these phenomena. In fact, the measured loss is found to be very close to the intrinsic loss in both BZN and BMN; we conclude that the difference in the measured loss is mainly the reflection of the difference in the intrinsic loss which is caused by the difference in permittivity between BZN and BMN. Moreover, our calculation results are in good agreement with the experimental values, a characterization of the Raman spectra of BZN and BMN is suggested based on our results. [ABSTRACT FROM AUTHOR]

Microwave dielectric ceramics Ba(M1/32+M2/35+)O3 have been studied for many years, but the exact relations between the B-site ions and the ceramics’ dielectric properties are still unclear. We take 2:1-ordered Ba(Zn1/3Nb2/3)O3 (BZN) and Ba(Mg1/3Nb2/3)O3 (BMN) as examples and discuss their static permittivity and intrinsic loss based on first-principles calculation. The larger mode-effective charges and lower frequencies of the normal modes are found to be responsible for the larger permittivity in BZN, but further analysis indicates that the dipole interaction, which is strengthened by the covalent bonding among Zn, Nb, and O, is the origin of these phenomena. In fact, the measured loss is found to be very close to the intrinsic loss in both BZN and BMN; we conclude that the difference in the measured loss is mainly the reflection of the difference in the intrinsic loss which is caused by the difference in permittivity between BZN and BMN. Moreover, our calculation results are in good agreement with the experimental values, a characterization of the Raman spectra of BZN and BMN is suggested based on our results. [ABSTRACT FROM AUTHOR]

Abstract: This paper discusses the difference in permittivity at infrared frequencies between Ba(Mg1/3Ta2/3)O3 (BMT) and Ba(Mg1/3Nb2/3)O3 (BMN) based on a first-principles calculation. The permittivity, far-infrared and Raman spectra are successfully computed. Analysis of these results shows that the smaller amplitude of O in the low frequency mode Eu 2 (BMT), which is caused by the larger polarizability of Ta5+, is the origin of the smaller permittivity of BMT. [Copyright &y& Elsevier]

The structural change in phase transition of hybrid (Cl2H25NH3)2MnCl4 was investigated. The temperature and the structures of the phase transition is investigated by thermal gravimetry (TG) and differential scanning calorimetry (DSC), infrared spectrum (IR) and X-ray diffraction (XRD). The results suggest that the phase transition is reversible and the structural change arises from the conformation change of the organic chain. The interlayer distance increases when the hybrid transforms from low temperature phase to high temperature phase. This is explained by the diffusion of gauche-bond along the organic chains and they move away from each other when the phase transition occurs. Combining the experimental data with theoretical calculation, we propose that organic chain of the hybrid in high temperature phase is the conformation of gauche-bond alternating with trans bond (noted as GTG′TGTG′TGTG′T). [ABSTRACT FROM AUTHOR]

Abstract: The series of the hybrids (C n H2 n +1NH3)2FeCl4, where n=2, 4, 6, 8, 10 and 12, were synthesized in HCl solutions. The optimum conditions of synthesis were investigated including the sequence of adding reactants, the stoichiometric ratio of the reactants, the reaction time and the drying procedures. The results demonstrate that the order of adding reactants, the drying temperature and drying time have little effect on the structures of the products. But for the hybrids of n⩾10, longer reaction time is needed to form the layered structures. The X-ray diffraction (XRD) patterns and the images of scanning electron microscopy of the products demonstrate that the hybrids crystallize well with typical layered structures. Chemical analysis of C, H and N confirms that the hybrids consist of the elements in the ratio of the molecular formulas. The d values, the interlayer distance between the two adjacent inorganic sheets of each hybrid, are obtained from the XRD patterns and they suggest that the organic chains interdigitate between the inorganic sheets. The longer the organic chains are, the more interdigitations there are. This can be explained by the different interaction strengths between the organic species when the chain lengths change. These different interactions can also explain the phenomena observed in the synthesis and the decomposing temperatures of the hybrids. [Copyright &y& Elsevier]

Graphene and other two-dimensional materials have been proved to be able to offer low friction. Here we assembled van der Waals heterostructures with graphene and molybdenum disulphide monolayers. The Raman spectrum together with a modified linear chain model indicate a two-orders-of-magnitude decrease in the interlayer lateral force constant, as compared with their homogeneous bilayers, indicating a possible routine to achieve superlubricity. The decrease in the interlayer lateral force constant is consistent with the ultrasmall potential energy corrugation during sliding, which is derived from density functional theory calculations. The potential energy corrugation is found to be determined by the sliding-induced interfacial charge density fluctuation, suggesting a new perspective to understand the physical origin of the atomic scale friction of two-dimensional materials.