Novel supramolecular isomerism in coordination polymer synthesis from unsymmetrical bridging ligands: solvent influence on the ligand placement orientation and final network structure

The assembly of Co(NCS)(2) with 1-methyl-1'-(3-pyridyl)-2-(4-pyridyl)ethene (L(1)) exhibits a novel supramolecular isomerism of [Co(L(1))(2)(NCS)(2)](infinity) caused by different placement orientation of L(1) around metal centers. The reaction in MeOH/H(2)O and EtOH/H(2)O resulted in a double chain structure of 1, and that in EtOH/CH(3)NO(2) led to an open framework structure of 2. The reaction in MeOH/CH(3)NO(2) solvent system concomitantly afforded 1 and 2. The assemblies of 1-(3-pyridyl)-2-(4-pyrimidyl)ethene (L(2)) with Co(NCS)(2) created the water-coordinated complexes of Co(L(2))(2)(H(2)O)(2)(NCS)(2) (3 and 4), an MeOH coordinated complex of Co(L(2))(2)(H(2)O)(2)(NCS)(2) (5), and an open framework coordination polymer of [Co(L(1))(2)(NCS)(2)](infinity) (6) depending on the reaction solvent system. From these observations, it is suggested that in the formation of 1, the solvent-coordinated intermediate species would be generated first and its trans coordination configuration should define the placement orientation of L(1) in the resulting polymer of 1. On the other hand, it is presumed that the solvent-coordinated intermediate would not be produced during the formation of 2 due to the weaker coordination ability of EtOH and CH(3)NO(2) molecules. The open framework coordination polymers of 2 and 6 are converted in the solid state into the isomeric coordination polymer of 1 and hydrogen bonded network structure of 3, respectively.     

应用键轨道连接矩阵方法预测烷烃折光率.

应用键轨道连接矩阵方法提取结构参数PX1CC和PX1CH， 并用于建立预测烷烃折光率的QSPR模型．该模型不仅预测精度较高(其误差仅为0.0048)，而且模型中采用的参数表达了直接与分子的折光能力相关的结构信息(即烷烃分子中电子被极化的能力)．此参数提取简单，既具备拓扑指数简单、易算，物理意义明确．     

The bond force constants and elastic properties of boron nitride nanosheets and nanoribbons using a hierarchical modeling approach

A hierarchical approach bridging the atomistic and nanometric scales is used to compute the elastic properties of boron nitride nanosheets and nanoribbons, examining the effect of sheet size, aspect ratio and anisotropy. The approach consists in obtaining the bond force (force field) constants by dedicated computations based on density functional theory (DFT) and using such constants as input for larger scale structural models solved by finite element analysis (FEA). The bond force constants calculated by DFT are 616.9 N/m for stretching, 6.27×10⁻¹⁹ Nm/rad² for in-plane rotation and 1.32×10⁻¹⁹ Nm/rad² for dihedral rotation. Using these constants, the elastic properties of boron nitride nanosheets and nanoribbons predicted by FEA are almost independent of the sheet size, but strongly dependent on their aspect ratio. The sheet anisotropy increases with increased aspect ratio, with nanoribbons of aspect ratios of 10 exhibiting a ratio of elastic moduli along both in-plane directions of 1.7.     

Room‐Temperature Alkyne–Nitrile Metathesis and Unambiguous Proof for the Existence of a High‐Valent Iron‐Nitrido Dication in the Gas Phase. Short Communication

An unprecedented alkyne–nitrile metathesis takes place when the high‐valent iron‐nitrido dication [Fe(L)N]²⁺, with L=2,6‐bis(2‐methyl‐1,3‐diaminopropan‐2‐yl)pyridine, is reacted with alkynes in the gas phase under thermal conditions. While the detailed role of the alkyne substrate with respect to relative rates, regioselectivities, and branching ratios remains to be elucidated, the very existence of this novel metathesis reaction provides additional experimental evidence of a genuine, long‐lived, formal iron(V)‐nitrido dication.     

New Sesquiterpenoids from Hedychium yunnanense gagnep

Hedychium yunnannense Gagnep is the unique species of Zingiberaceae occurring only in Yunnan province of China and its wild resource is very abundant. Several sesquiterpenoids and diterpenoids from the petroleum ether fraction of the ethanol extract of the plant have been reported1, 2 by Zhao Qing et al. Some of them show antioxidant and cytotoxic activities. In order to use the wild plant resources efficiently, we made further systematic investigations on the chemical constituents of the rh…     

Competitive Intramolecular Aryl‐ and Alkyl‐C?H Bond Activation and Ligand Evaporation from Gaseous Bisimino Complexes [Pt(L)(CH3)((CH3)2S)]+ (L=C6H5NC(CH3)?C(CH3)NC6H5)

Mechanistic details for the formation of methane from the title compound as well as the combined elimination of (CH₃)₂S/CH₄ are derived from various mass‐spectrometric experiments including deuterium‐labeling studies and DFT calculations. For the first process, i.e., methane formation, we have identified three competing pathways in which the intact, Pt‐bonded methyl group combines with a H‐atom that originates from a phenyl substituent (ca. 7%), the dimethyl sulfide ligand (ca. 41%), and a methyl group of the diazabutadiene backbone (ca. 52%). In contrast, in the combined (CH₃)₂S/CH₄ elimination, the methane is specifically formed from the Pt‐bound CH₃ group and a H‐atom provided by one of the phenyl groups (‘cyclometalation’).     

Relative Thermodynamic Stabilities of Isomeric Vinyl Ethers Derived from 2-Acetyland 2-Isobutyryltetrahydrofurans. An Experimental and DFT Study

The relative thermodynamic stabilities of four isomeric vinyl ethers obtained by acid-catalyzed cleavage of MeOH from the dimethyl acetals of both 2-acetyltetrahydrofuran and 2-isobutyryltetrahydrofuran have been determined by chemical equilibration in cyclohexane solution. In addition, the structures and relative energies of many of these compounds have also been studied theoretically by DFT calculations. In each series of compounds, the endocyclic isomers, 5-(1-methoxyethyl)-2,3-dihydrofuran and 5-(1-methoxy-2-methylpropyl)-2,3-dihydrofuran, respectively, show the highest thermodynamic stabilities. This is particularly prominent for the vinyl ethers derived from 2-isobutyryltetrahydrofuran in which the equilibrium mixture consists of 90% of the endocyclic isomer at room temperature. The geometrical (exocyclic) isomers of the latter series of compounds show unexpected relative thermodynamic stabilities, but on the basis of the geometry-optimized structures provided by the DFT calculations, a reasonable explanation can be found.