Why does spontaneous resolution take place? (empirical force-field calculations)

Empirical force-field calculations were performed on [Ag{Co(aet)(en)₂}](NO₃)₃ (aet?=?H₂NCH₂CH₂S^?) systems to further understand the occurrence of spontaneous resolution . Results of the calculations reveal that the?ΛΛΛΛ?strand is more stable than the?ΛΔΛΔ?strand. Furthermore, the spontaneously crystallized system?ΛΛΛΛ, with six constitutional repeating units (CRUs),?ΛΛΛΛΛΛ, was more stable than the hetero-chiral system,?ΔΔΔΔ, with the same six units as above. In addition, the calculations revealed that electrostatic interactions contributed most of the stability to the system.     

通道中并列旋转圆柱的LB-DF/FD模拟

通过结合格子Boltzmann方法(LBM)和DF(Direct Forcing)/FD(Fictitious Domain)思想,建立了一种新的LB-DF/FD方法。采用两套网格系统,欧拉网格用于流体,拉格朗日网格用于固体,有效地避免了计算中重新生成网格的步骤,同时在处理流固问题方面优于LBM方法。通过模拟通道中单圆柱旋转的流场,验证了该方法的正确性;并利用该方法模拟了低雷诺数下通道中并列旋转圆柱周围的流场,分析了圆柱距离壁面间距gw和雷诺数Re对流场结构的影响。研究结果表明:gw显著影响了流场的结构及圆柱的受力;而Re对圆柱升力及Stokes单元数目的影响较大。     

Predicting an Antiaromatic Benzene Ring in the Ground State Caused by Hyperconjugation

Benzene, the prototype of aromatics, has six equivalent C?C bonds (1.397 Å), which are intermediate between a C?C double bond and a C?C single bond. For over 80 years, chemists have spent much effort on freezing a localized structure to obtain a distorted bond‐length alternating benzene ring in the ground state, leading to various localized trisannelated benzene rings. However, most of the central benzene rings are still aromatic or nonaromatic. Here we report an antiaromatic benzene ring caused by hyperconjugation. Specifically, symmetric annulation of 5,5‐difluorocyclopentadiene results in an antiaromatic benzene ring, which is supported by various aromaticity indices, including nucleus‐independent chemical shift, anisotropy of the induced current density, π‐separated electron‐localization function and heat of hydrogenation. Our findings highlight a strong power of hyperconjugation, a “weak” interaction in organic chemistry, paving the way for designing and realizing more novel (anti)aromatics.     

Role of Ab Initio Calculations in the Design and Development of Organometallic Lanthanide‐Based Single‐Molecule Magnets

Single‐molecule magnets based on lanthanides are very attractive due to their potential applications proposed in the area of microelectronic devices. Very recent advances in this area are due to the blend of conventional lanthanide chemistry with organometallic ligands, and several breakthrough achievements are attained with this combination. Ab initio methods based on multi‐reference CASSCF calculations are playing a vital role in the design and development of such molecules. In this minireview, we aim to appraise various contributions in the area of organometallic lanthanide complexes (those containing lanthanide‐carbon bonds) and describe how these robust wavefunction‐based methods have played a constructive role not only in rationalizing the observed magnetic properties but also proven to be a potential predictive tool with some selected examples.     

The Z<Superscript>-1</Superscript> expansions of the total non-relativistic energies for three- and four-electron systems

Analytical formulas are derived for the Z^-1 (Q^-1) expansions of the total energies in the two-, three- and four-electron atomic systems. The coefficients in these formulas are determined from the results of accurate and highly accurate computations with correlated wave functions. The accuracy of our formulas is sufficient to evaluate the total ground state energy of an arbitrary non-relativistic ion with two, three and four electrons.     

Evaluation of two-center electric field gradient integrals over STOs using elliptical coordinates

In this study, analytical expressions are obtained for two different types of two-center EFG integrals and the integrals are calculated using these expressions. Analytical expressions for the integrals are given in terms of auxiliary J and K functions defined by Özmen et al. [Int. J. Quantum Chem. 91, 13 (2003)] for the evaluation of two-center Coulomb integrals using elliptical coordinates. Results are compared and found to be in good agreement for small quantum numbers with the existing results from the literature. Numerical stability of the proposed method is very good and therefore we also present results for higher quantum numbers, however there is no previous results found in the literature to compare.     

New organic FET-like photoactive device, experiments and DFT modeling

We present the possible construction of an organic FET-like photoactive device in which source-drain current through a phthalocyanine ( H₂Pc film is affected by a photo-induced dipolar field in a photoactive “gate” electrode. The influence of the dipolar electric field on charge transfer between H₂Pc molecules is modeled by DFT quantum-chemical calculations on H₂Pc dimers and tetramers.     

DF激光器光栅选线实验研究

基于闪耀光栅的分光原理,利用小型直流放电驱动化学激光器,在平凹稳定腔内插入闪耀光栅,建立了选择激光器光栅谱线的实验装置.实验中共获得了14条谱线,测量了每条谱线的功率,计算了波长,分析了选线后谱线条数减少、谱线功率降低的原因.该装置尺寸小,使用比较方便,可以满足连续波DF化学激光器性能研究的需要.     

Theoretische Untersuchungen zur Basizität substituierter Pyridine

The applicability of the MINDO/3 method for the interpretation of the basicity of a series of substituted pyridines is critically discussed. Special attention is paid to the difference in thepK _a -values of the two isomeric 4,6-diamino-2-methoxy-(2) and 2,4-diamino-6-methoxy-3-pyridine-carbonitrile (3) (2=2.01,3=4.17). Based on the concept of charge- and orbital-controlled reactions this difference can be explained readily.

     

Darstellung,Charakterisierung, quantenchemische Berechnungen und chemische Reaktionen von Schwefeldiimin,dessen Ag‐ und Tl‐Salze sowie TlNSO

Preparation, Characterisation, Quantum Chemical Calculations, and Chemical Reactions of Sulfurdiimine, its Silver and Thallium Salts as well as TlNSO Reactions of (CH₃)₃SiNSNSi(CH₃)₃ with Ag[CF₃C(O)O] or TlF respectively have allowed the formation of the highly explosive compounds M₂[SN₂] (M = Ag, Tl) in nearly quantitative yields. Under analogous conditions (CH₃)₃SiNSO and TlF formed non‐explosive TlNSO again in about 100% yield. The reaction between (CH₃)₃SiNSNSi(CH₃)₃ and ICl was found to be easily reproducable and gave INSNI in good yields. INSNI was obtained also from K₂[SN₂] and ICl in 40% yield. The reaction of (CH₃)₃SiNSNSi(CH₃)₃ with CsF resulted in monosubstitution and the formation of CsNSNSi(CH₃)₃. INSNI reacted with HX (X = Cl, I) in closed systems to give S₄N₄, NH₄X, IX and N₂ as final products. Similar results were observed when M₂[SN₂] was treated with HX in Carius tubes. Besides higher yields of S₄N₄ small amounts of S₄N₃Cl and other not identified SN compounds were detected. In open systems HX reacted with M₂[SN₂] in dynamic vacuo explosively. Under matrix conditions preliminary tests showed that TlNSO formed with HX pure HNSO, characterised by a high quality matrix IR‐spectrum. With the help of this metathetical reaction, the conditions for matrix‐spectroscopic studies of the system MNSNM and HX could be optimized. If M₂[SN₂] was treated with HX analogously HNSNH was produced. The diimine was characterized by bands of comparable intensities, appearing in spectra of the products of the reaction which were assigned to the molecule. Identical bands were also observed when INSNI was treated with excess HX. If the procedure was carried out with 1 : 1 molar quantities, the formation of the primary produced HNSNI could be evidenced by IR‐spectroscopy. Detailed quantum chemical ab inition calculations about structures, relative energies and vibrational spectra of the HNSNH‐conformers as well as other possible SN₂H₂ isomeres were carried out. They confirmed the experimental results and assignments and strengthened the conclusion that HNSNH was present as a mixture of E,Z‐ and Z,Z‐conformers.