Synthesis and structural characterization of CsAg5Se3 and RbAg3Te2

The syntheses and structure determinations of CsAg₅Se₃ (I) and RbAg₃Te₂ (II) are reported. Both compounds were prepared by using supercritical ethylenediamine at 300°C for 6 days reacting alkali polychalcogenides with silver. For the compound I; tetragonal space group P4₂/mnm, a = 14.083(2)Å, c = 4.410(2)Å, V = 874.5(4)ų, Z = 4, D = 6.905 Mg/m³, MoK radiation, = 0.71073, = 27.493 mm^–1, F(000) = 1568, R = 0.022, Rw = 0.026 for 472 independent reflection. For compound II; monoclinic space group C2/m, a = 17.546(2)Å, b = 4.617(2)Å, c = 9.165(2)Å, = 113.04(2)°, V = 683.31(12)ų, Z = 2, D = 6.457 Mg/m³, MoK radiation, = 0.71073, = 23.825 mm^–1, F(000) = 1128, R = 0.019, Rw = 0.027 for 690 independent reflection.     

从卫星STARLETTE的激光测距推得1980年8—10月的地球自转参数值

本文分析了在1980年8—10月,即地球自转短期联测(MERIT Short Campaign)期间,全世界13个测站对卫星STARLETTE进行激光测距所获得的631圈共54189个数据。由此推得了在这期间的极移两分量(x_p和y_p)以及日长的变化量(D=日长—86400秒)。经多项式拟合以后,所得解中,x_p的残差的均方值是0″.014;y_p的残差的均方值是0″.013;D的残差的均方值是0⁵.0005。     

Nucleophilic Aromatic Substitution with Dianions: Reactions Driven by the Release of Coulomb Repulsion

The reactions of a nucleophilic dianion with a series of activated aryl bromides were studied in the gas phase. Nucleophilic aromatic substitution (S_NAr) as well as proton transfer reactions were observed. Rate constants and branching ratios were determined for all the reactions and the experimental data are supported by ab initio calculations. Reactions with bis-trifluoromethylbromobenzenes give only S_NAr reactions and the rate constants follow the expected pattern, with substituents at the ortho and para positions having the greatest impact. Reactions of polyfluorobromobenzenes give a mix of proton transfer (when possible) and S_NAr, with both bromide and fluoride acting as leaving groups. The latter is much less thermodynamically favorable but is the dominant pathway in each case. The selectivity of the reactions indicate that the products are determined early on the potential energy surface, before there is significant cleavage of the bond to the leaving group—the reaction is potentially directed by the initial formation of a hydrogen bond with the arene. The computational data also suggest that hydrogen bonding in the product ion–ion complexes can stabilize the system until there is sufficient charge separation to use the internal Coulomb repulsion to drive the reactions to products. Overall, the results highlight (1) the ability of multiply-charged systems to efficiently funnel their Coulomb repulsion into reaction processes that are intrinsically unfavorable, and (2) the high degree of selectivity that can be attained even in systems with multiple, low-barrier pathways.

Structural Characterization of Pb6Sb6Se17

The ternary selenide Pb₆Sb₆Se₁₇ was synthesized hydrothermally from the binaries (PbSe and Sb₂Se₃) and crystallizes in the orthorhombic space group Pbam (a = 15.835(3), b = 24.043(5), c = 4.134(2)Å, Z = 2). The main building blocks of the crystal structure are ribbons made of square pyramidal [(Pb,Sb)Se₅] groups running along [010].     

Separation,identification and determination of short-chained calcium polyphosphates from pyrolyzed calcium-deficient hydroxyapatite

Two liquid-liquid partition chromatography systems were employed to separate calcium ortho-, pyro- and tripolyphosphates on thin layers of micro-crystalline cellulose. Chromatography on anion-exchange thin layers of polyethyleneimine was unsuccessful. The liquid-liquid partition system was used to demonstrate that the major condensation product produced on pyrolysis of calcium-deficient hydroxyapatite is calcium pyrophosphate.