Energetic and topological analyses of the oxidation reaction between Mo(n) (n = 1, 2) and N2O

The interaction between molybdenum, atom, and dimer, with nitrous oxide has been investigated using density functional theory. The analysis of the potential energy surfaces for both reactions has revealed that a single molybdenum atom can activate the N--O bond of N2O requiring a small activation energy. However, the presence of several intersystem crossings between three different spin states, namely, septet, quintet and triplet states, seems to be the major constraint to the Mo + N2O reaction. Contrarily, the low-lying excited states (triplet and quintet) do not participate in the reaction between the molybdenum dimer and N2O. The latter reaction fully evolves on the singlet spin surface. Three different regions have been distinguished along the pathway: formation of an adduct complex, formation of an inserted compound, and the N2 detachment. The connection between the two first regions has been characterized by the formation of a special complex in which the N--O bond is so weakened that it could be considered as a first step in the insertion process. It has been shown that the topological changes along the pathways provide a clear explanation for the geometrical changes that occur along the reaction pathway. In summary, the detachment of the N2 molecule is found to be kinetically an effective process for both reactions, owing to the high exothermicity and consequently to the high internal energy of the insertion intermediates. However, in the case of Mo atom, the reaction should be a slow process due to the presence of spin-forbidden transitions. These results fully agree with previous experimental works.     

Intermolecular-medium and intramolecular-weak hydrogen bonding chains in the crystals of chiral trifluoromethylated amino alcohols

A structural feature of hydrogen bonding chains found in the crystals of trifluoromethylated amino alcohols is reported. Hydrogen bondings of 3-(N,N-dialkylamino)-1,1,1-trifluoro-2-propanols construct chiral spiral hydrogen bonding chains. Lone pairs on the nitrogen atoms of the amino alcohols participate in two hydrogen bondings. Detailed structural analysis of the hydrogen bonds of the 3-(N,N-dimethylamino)-1,1,1-trifluoro-2-propanol suggested that the chain built up with alternating intermolecular-medium and intramolecular-weak hydrogen bonds. The medium intermolecular hydrogen bond, which transfers a proton from the hydroxy group to the amino nitrogen, would make a tentative zwitterionic form of the molecule. Then, electrostatic attraction between the charges in the zwitterion centers induced a weak intramolecular hydrogen bond.     

Insight into the cation–anion interaction in 1,1,3,3-tetramethylguanidinium lactate ionic liquid

In order to deepen the understanding of cation–anion interaction in ionic liquids (ILs), the structure and interionic interaction of 1,1,3,3-tetramethylguanidinium lactate ([tmg][L]) ion pair, including stable configuration, hydrogen bond, frontier molecular orbital, electron density, ion interaction energy and charge transfer, are studied by using ab initio calculations. It is found that more charge-localized character of [tmg][L], especially the C1 carbocation on [tmg]⁺, and the intermolecular –NH₂-associated hydrogen bonds can substantially increase the cation–anion interaction, the interaction energy is 65.3–109.3 kJ/mol higher than that of 1-n-butyl-3-methylimidazolium-based ILs. It is also found that the frontier molecular orbitals, i.e., the HOMO, HOMO + 1 of [L]⁻ and the LUMO, LUMO + 1 of [tmg]⁺, can effectively interact and more charges are transferred between cation and anion. Based on the above results, the physical property of ILs is discussed.     

Trifluoroethylene Sultone: Structure and Chemistry

The gas phase structure of trifluoroethylene sultone, ( 1 ) (3,4,4-trifluoro-1,2-oxathietane-2,2-dioxide) was determined by gas electron diffraction, and the four-membered ring was found to be planar. The following ring parameters (r_a distances and ∠_α angles with 3σ uncertainties) were derived in the electron diffraction analysis: C? O = 1.41 Å (ass.), C? C = 1.541(18) Å, S? O = 1.652(5) Å, S? C = 1.822(8) Å, S? C? C = 86.2(15)°, C? C? O = 97.1(28)°, C? O? S = 97.5(21)°, and O? S? C = 79.1(8)°. New spectral data (IR, NMR) of 1 , its acyclic isomer FSO₂CFHC(O)F ( 2 ), and the related anhydride, FSO₂OSO₂CFHC(O)F ( 3 ), are reported. New esters containing the fluorosulfonyl function, FSO₂CFHC(O)OCH₂CF₃ ( 4 ), FSO₂CFHC(O)OCH₂CH = CH₂ ( 5 ), and (FSO₂CFHC(O)OCH₂CH? CH₂? )_n ( 6 ) have been prepared and characterized.     

Structural Patterns and Dimensionality in Magnesium Borophosphates: The Crystal Structures of Mg2(H2O)[BP3O9(OH)4] and Mg(H2O)2[B2P2O8(OH)2]·H2O

Hydrothermal investigations in the system MgO/B₂O₃/P₂O₅(/H₂O) yielded two new magnesium borophosphates, Mg₂(H₂O)[BP₃O₉(OH)₄] and Mg(H₂O)₂[B₂P₂O₈(OH)₂]·H₂O. The crystal structures were solved by means of single crystal X‐ray diffraction. While the acentric crystal structure of Mg₂(H₂O)[BP₃O₉(OH)₄] (orthorhombic, P2₁2₁2₁ (No. 19), a = 709.44(5) pm, b = 859.70(4) pm, c = 1635.1(1) pm, V = 997.3(3) × 10⁶ pm³, Z = 4) contains 1D infinite chains of magnesium coordination octahedra interconnected by a borophosphate tetramer, Mg(H₂O)₂[B₂P₂O₈(OH)₂]·H₂O (monoclinic, P2₁/c (No. 14), a = 776.04(5) pm, b = 1464.26(9) pm, c = 824.10(4) pm, β = 90.25(1)°, V = 936.44(9) × 10⁶ pm³,Z = 4) represents the first layered borophosphate with 6³ net topology. The structures are discussed and classified in terms of structural systematics.     

Molecular structure of simple mono- and diphenyl meso-substituted porphyrin diacids: influence of protonation and substitution on the distorsion

The crystal and molecular structures of three simple porphyrin diacids have been determined from X-ray diffraction data to delineate how the peripheral substituents of the porphyrin affect the overall molecular flexibility. Di-meso-substituted [DPPH₄]²⁺(CF₃CO₂⁻)₂ and, mono-meso-substituted [MPPH₄]²⁺(CF₃CO₂⁻)₂ and [dedmMPPH₄]²⁺(CF₃CO₂⁻)₂ porphyrin diacids show increasingly saddled core conformation. Some of the spectroscopic properties (NMR and UV-visible) of the porphyrin diacids are also discussed in terms of the observed structures.     

MORPHOLOGICAL STUDIES ON THERMOTROPIC LIQUID CRYSTALLINE POLYESTER——MORPHOLOGY OF SHEAR ORIENTED FILMS

The morphology of shear-oriented films of a thermotropic liquid crystalline polyester containing a triad ester mesogenic unit and a flexible spacer has been investigated in details. The formation conditions and process, the fine structures and the relaxation process of mat structure in the oriented films have been observed and discussed.     

On a class of least-element complementarity problems

The present paper studies the linear complementarity problem of finding vectorsx andy inR ₊ ⁿ such thatc + Dx + y 0,b – x 0 andx ^T (c + Dx + y) = y ^T (b – x) = 0 whereD is aZ-matrix andb > 0. Complementarity problems of this nature arise, for example, from the minimization of certain quadratic functions subject to upper and lower bounds on the variables. Two least-element characterizations of solutions to the above linear complementarity problem are established first. Next, a new and direct method to solve this class of problems, which depends on the idea of least-element solution is presented. Finally, applications and computational experience with its implementation are discussed.Research partially supported by the National Science Foundation Grant MCS 71-03341 A04 and the Air Force Office of Scientific Research Contract F 44620 14 C 0079.     

Comparison of the Structural Evolution of β Polypropylene during the Sequential and Simultaneous Biaxial Stretching Process

In this work, the lamellar structural evolution and microvoids variations of β polypropylene(β-PP) during the processing of two different stretching methods, sequential biaxial stretching and simultaneous biaxial stretching, were investigated in detail. It was found that different stretching methods led to significantly different lamellae deformation modes, and the microporous membranes obtained from the simultaneous biaxial stretching exhibited better mechanical properties. For the sequential biaxial stretching, abundant coarse fibers originated from the tight accumulation of the lamellae parallel to the longitudinal stretching direction, whereas the lamellae perpendicular to the stretching direction were easily deformed and separated. Those coarse fibers were difficult to be separated to form micropores during the subsequent transverse stretching process, resulting in a poor micropores distribution. However, for the simultaneous biaxial stretching, the β crystal had the same deformation mode, that is, the lamellae distributed in different directions were all destroyed, forming abundant microvoids and little coarse fibers.     

聚氯乙烯/层状双氢氧化物纳米复合材料研究进展

聚氯乙烯(PVC)/层状双氢氧化物(LDHs)纳米复合材料相比于纯聚氯乙烯具有更好的热稳定性、力学性能、阻燃抑烟性、耐候性与耐光性等,是一种性能优异并具有广泛应用前景的新型聚合物基纳米复合材料。本文首先介绍了LDHs的化学组成和结构特点,并对其制备过程和性质特点进行了分析和探讨;然后综述了PVC/LDH纳米复合材料的制备、结构表征及性能等方面的最新研究进展,重点阐述了LDHs的表面有机化处理及其对PVC/LDH纳米复合材料制备与性能的重要作用;最后对其应用前景进行展望。