High-pressure NMR study of migratory CO-insertion in palladium-methyl complexes modified with Cs-symmetrical 1,4-diphosphines

Carbonylation of the palladium complexes [PdCH₃(P^∧P′)Cl] (P^∧P′ = 1a, 1b, 1c, 1d, 1e) and [PdCH₃(P^∧P′)(CH₃CN)](OTf) was investigated by means of high-pressure NMR with the determination of the half-life times t_1/2. The results were rationalized on the basis of the electronic properties of the diphosphines and the nature of the solvento ligand in the first coordination sphere. The crystal structures of the complexes [Pd(1b)Cl₂] and [Pd(1b)(H₂O)₂](OTf)₂ are described (1b = 1-(diphenylphosphinomethyl)-2-[bis(3- trifluoromethylphenyl)phosphinomethyl]benzene).     

26 ℃和常压至1.5 GPa压力下2-甲基戊烷拉曼光谱研究

利用碳化硅压腔在常压至1.5 GPa和26 ℃条件下对液态2-甲基戊烷进行了拉曼光谱测量,讨论了C—H拉曼峰频率、强度、面积、以及谱峰宽度随压力升高的变化规律。实验结果表明,2-甲基戊烷的拉曼位移在2 800～30 00 cm-1范围内的CH₃和CH₂的伸缩振动谱峰随着压力的增大均连续向高波数位移,其拉曼位移与压力的关系可以表示为ν_as(CH₃)=0.013 1p+2 960.1,ν_s(CH₃)=0.008 8p+2 871.0,ν_as(CH₂)=0.008 9p+2 930.2,ν_as(CH₂)’=0.007 0p+2 903.1和ν_s(CH₂)=0.007 9p+2 844.7。另外处理实验结果时发现,在0～1.5 GPa条件下,2-甲基戊烷的ν_as(CH₃)拉曼位移可以进行压力标定,其方程为：P(MPa)=76.2(Δν_p)_{2 960}+21.65(r2=0.995 8)。该压力体标定剂,适合于不希望有Si和Al等元素出现的体系。     

CuCl nanocrystals in alkali-halide matrices under hydrostatic pressure

CuCl nanocrystals in crystalline alkali-halide matrices have been investigated under hydrostatic pressures up to 18 GPa. The pressures of structural phase transitions in CuCl have been determined both for different nanocrystal sizes and for different matrices (NaCl, LiCl, KCl). For CuCl nanocrystals in NaCl an increase of the transition pressure with decreasing nanocrystal size is observed, which is explained by the increasing importance of surface pressure for small nanocrystals. We found higher transition pressures for the LiCl matrix than for the NaCl matrix. The reason for this is that the pressure which acts on the nanocrystal differs from the external pressure. A simple elastic model describes the effective pressure transmitted from the matrix to the nanocrystal. With CuCl nanocrystals embedded in KCl we have studied the behavior of nanocrystals during a phase transition of the matrix. Additionally we have determined the pressure coefficients of the exciton energies of the CuCl nanocrystals, which depend on the elastic properties of the matrix. Received 4 March 1999     

Neural network learning dynamics in a path integral framework

Using the local-density approximation, calculating the Hellmann-Feynman forces and applying the direct method, the phonon dispersion relations for the rutile-like structure of crystalline SnO₂ have been derived for the first time. The phonon frequencies at the point agree very well with Raman and infrared data and other phenomenological model calculations. The LO/TO splitting is estimated by calculating phonons from an elongated supercell. The computations under pressure reveal a soft mode of B_1g symmetry which leads to a ferroelastic phase transition. The pressure-dependence of the lattice constants and the Grüneisen parameters of the modes are calculated. Received 18 July 1999     

Mn_(3)Sn的高压物性研究

非共线三角晶格的反铁磁体Mn_(3)Sn,由于其动量空间中非零的贝里曲率而表现出反常霍尔效应.利用金刚石对顶砧研究压力对Mn_(3)Sn低温电输运性质和反常霍尔效应的影响.结果表明:Mn_(3)Sn在0~60GPa压力范围内保持金属导电行为;从非共线磁有序到螺旋磁有序的转变温度随压力增加先降低,在5.5GPa以上迅速升高,对应一个等结构电子拓扑转变;Mn_(3)Sn的反常霍尔效应在5.5GPa被完全抑制.     

Exploration of synthetic strategies for the stereoselective preparation of novel tetrahydrofuran-containing biaryls: A high-pressure promoted Diels-Alder approach

Three stereoselective synthetic approaches to tetrahydrofuran-containing biaryl scaffolds are described. All approaches involve a high-pressure promoted Diels-Alder reaction of substituted diene with methyl propiolate to give, after aromatization, the corresponding biaryl. The tetrahydrofuran moiety can be created starting from aryl-Br or aryl-CO₂Me functional groups through a γ-phenylseleno ketone intermediate.     

Fluid phase equilibria in the binary system trifluoromethane + 1-phenyloctane

Vapour–liquid, liquid–liquid and liquid–liquid–vapour equilibria in the binary system consisting of trifluoromethane (refrigerant R23) and 1-phenyloctane were determined in the temperature range T = 250–400 K and at pressures up to 15 MPa. The experiments were carried using a Cailletet apparatus according to the synthetic method. The investigated system exhibits type III phase behaviour according to the classification of van Konynenburg and Scott. Modelling of the equilibrium data was done with the Peng–Robinson (PR) and Soave–Redlich–Kwong (SRK) equations of state coupled with classical van der Waals mixing rules. In order to predict the global phase behaviour of the system, one single set of binary parameters was used. The topology of the phase behaviour was correctly reproduced.     

High-pressure synthesis and single-crystal structure refinement of gadolinium holmium silicate hydroxyapatite Gd4.33Ho4.33(SiO4)6(OH)2

Single crystals of gadolinium holmium silicate hydroxyapatite Gd_4.33Ho_4.33(SiO₄)₆(OH)₂ have been synthesized at 2.0 GPa and 1450 °C using a piston-cylinder-type high-pressure apparatus. The crystal symmetry by single-crystal X-ray diffraction analysis is hexagonal, space group P6₃/m (No. 176), with a=9.3142(5) Å, c=6.7010(4) Å, Z=1. Gadolinium and Ho are disordered over the two large cation positions, A(1) and A(2), and charge balance in this silicate apatite is maintained by cation vacancies in A(1). Two other apatite-structure crystals investigated have and Imma symmetry, and represent either partially ordered Gd-Ho distributions or crystal strain induced during quenching.     

Cotunnite-Structured Titanium Dioxide

Combined theoretical and experimental studies led to discovery of a new polymorph modification of titanium dioxide with nine-coordinated titanium. Among polycrystalline materials, it is one of the least compressible (with a bulk modulus of 431 GPa) and hardest (with a microhardness of 38 GPa).     

Compressibility of orthorhombic perovskites. The effect of transition metal ions (TMI)

Interest in perovskites evenly spans Materials Science and Geophysics. Due to their inimitably lattice flexibility enabling small as well as large ions to be accommodated, perovskites have become a base structure for new technological applications. Understanding the mechanisms governing their evolution at non-ambient conditions (such as high-pressure and high-temperature) is fundamentally important both for devising functional materials and in order to provide the most reliable possible deep-Earth model. With particular attention being paid to the chemical nature of the constituent ions, a suite of orthorhombic perovskites has been selected and contrasted using several parameterizations and models. A new perspective on the pressure-induced distortion of orthorhombic perovskite structures has enabled their compressional behaviour to be redefined.