Numerical examination of performance of some exchange-correlation functionals for molecules containing heavy elements

The performance of 17 exchange-correlation functionals for molecules containing heavy elements are numerically examined through four-component relativistic density DFT calculations. The examined functionals show the similar accuracy as they do for the molecules containing light elements only except for bond lengths. LDA and OP86 produce good results for bond lengths and frequencies but bad bond energies. Different functionals do not show much different performance for bond energies except LDA. BP86 and GP86 produce results with average accuracy while LYP does not perform well. Although encouraging results are obtained with functional B97GGA-1, other heavily parameterized and meta-GGA functionals do not produce impressive results.     

Ga3(HPO3)4F4(H3DETA) (DETA=diethylenetriamine): A new open-framework fluorinated gallium phosphite with pentameric building unit

Ga₃(HPO₃)₄F₄(H₃DETA) is a new open-framework fluorinated gallium phosphite obtained by mild hydrothermal synthesis using diethylenetriamine as templated agent and characterized by single crystal X-ray diffraction, the powder X-ray diffraction, IR spectroscopy, TGA, ICP and elemental analyses. It crystallizes in the monoclinic space group C2/c, a=12.741(6) Å, b=12.068(6) Å, c=11.988(5) Å, β=94.902(8)^o, V=1836.6(15) Å³, Z=4. The construction of 3D open-framework structure in the title compound may be viewed as the assembly of pentameric building units and HPO₃ groups. The pentameric building unit is the first to be found, which lead to form the three types of channels along a-, b- and c-axes, respectively, in gallium phosphite. The triprotonated DETA cations are inserted within the 10-membered ring channels and interact with anions of the framework via hydrogen bonds.     

端视ICP－AES系统分析性能研究──Ⅰ．在稀土分析中的应用

本工作通过比较端视与侧视ＩＣＰ的分析性能，研究了端视ＩＣＰ系统对稀土元素的分析特性。高频发生器输出功率与载气流量对端视与侧视ＩＣＰ激发特性的影响没有明显差异，取光方式的不同是二者分析性能差异的根本原因。端视ＩＣＰ由于取光时避开了产生连续背景的环形热区和截取了整个中心通道的光谱，其背景减小，谱线强度增强，获得较好的测定下限。对１４种稀土元素测定下限的比较表明：端视ＩＣＰ比铡视ＩＣＰ下降１０－３０倍。     

DABCO-catalyzed reaction of alpha-halo carbonyl compounds with dimethyl acetylenedicarboxylate: a novel method for the preparation of polysubstituted furans and highly functionalized 2H-pyrans

[Chemical reaction: see text] Polysubstituted furans and highly functionalized 2H-pyrans were prepared in good yields by DABCO-catalyzed reactions of alpha-halo carbonyl compounds with dimethyl acetylenedicarboxylate (DMAD) at room temperature.     

Electronic effects steer the mechanism of asymmetric hydrogenations of unfunctionalized aryl-substituted alkenes

Density functional theory (PBE and B3LYP) was used to study asymmetric hydrogenations of alkenes catalyzed by an iridium imidazolylidine oxazoline complex. The calculation predicts that the alkene preferentially coordinates to the site trans to the carbene. The coordinated alkene then reacts first with the H2 ligand, then with the hydride to form alkane. Finally, the alkane is released by equilibrating with extrinsic H2 and alkene. Enantioface selectivities for hydrogenations of trisubstituted alkenes seem to be driven primarily by steric interactions with the adamantyl part of the ligand; only the smallest substituents can adopt a site close to it. Application of this theoretical model leads to correct predictions regarding the experimentally observed sense and magnitude of the enantioselectivities.     

A first synthesis of thiophene dendrimers

[structure: see text] Thiophene dendrons and dendrimers were designed and synthesized using a convergent approach. Metal-mediated coupling reactions were used in the synthesis. A rational approach allowed the formation of alphaalpha, betabeta, and alphabeta linkages between the dendrons and thiophene units.     

Sonochemical synthesis of mass single-crystal PbS nanobelts

Based on sonochemical technique, large-scale PbS nanobelts are successfully synthesized in the mixed solution of PbCl₂ and Na₂S₂O₃. These nanobelts are characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), selected area electronic diffraction, energy dispersive X-ray spectroscopy, and high-resolution TEM. The as-synthesized PbS nanobelts have width of about 80 nm, length up to several millimeters, and width-to-thickness ratio of about 5. In addition, the growth mechanism of PbS nanobelts is suggested.     

Quinine/selectfluor combination induced asymmetric semipinacol rearrangement of allylic alcohols: an effective and enantioselective approach to alpha-quaternary beta-fluoro aldehydes

A quinine/Selectfluor combination inducing rearrangement reaction of allylic alcohols was discovered, which involved a moderate yield with good enantioselective construction of alpha-quaternary carbon center and beta-fluoro aldehyde under base condition.