Infrared spectroscopic studies of transition metal complexes and polarizability effect

The literature data on substituent influence on the CS, CN, NC, NN, and NO stretching frequencies (ν) in the IR spectra and in specific cases on their respective stretching force constants (k) have been analyzed for 28 series of the transition metal complexes. The ν and k values were first established to depend not only on the inductive and resonance effects but on the polarizability of substituents as well. The contribution of the polarizability effect varies from 0 to 57% with the type of series.     

Hydrolytic Ring Opening Reactions of Pyromellitic Dianhydride for Divalent Transition Metal Carboxylate Complexes

The hydrolytic ring opening reactions of pyromellitic dianhydride is an effective method to prepare transition metal carboxylate complexes. In this paper, two dinuclear complexes [Ni₂(2,2′‐bipy)₂(btec)(H₂O)₆] · 2H₂O ( 1 ) and [Cd₂ (phen)₄(H₂O)₂(H₂btec)] · H₂btec · 2H₂O ( 2 ) (H₄btec = 1,2,4,5‐benzenetetracarboxylic acid, phen = 1,10‐phenanthroline, and 2,2′‐bipy = 2,2′‐bipyridine) were synthesized by slow diffusion methods and their structures were determined byX‐ray structure analysis. In both structures metal atoms are in distorted octahedral environments and they are linked by bis‐monodentately coordinated 1,2,4,5‐benzentetracarboxylate ligands as bridging units. The crystalline compounds, which are insoluble in water as well as common organic solvents, have been characterized in the solid‐state by elemental analysis, thermogravimetric analysis, IR, and diffuse reflectance UV/Visspectroscopy. Moreover, the study of the physical properties of complex 2 demonstrates that it exhibits blue fluorescence emission in the solid state at room temperature.     

The synthesis of transition metal nitrides via thermolysis of metal-ammine complexes, Part I: Chromium nitride

The thermal decomposition of a CrN precursor, hexaammine chromium(II) chloride, in ammonia has been investigated via a combination of thermogravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy, and X-ray diffraction. Upon heating, [Cr(NH₃)₆]Cl₂ sequentially loses ammonia ligands, ultimately forming CrCl₂·NH₃ at ∼400 °C. When heat-treated to 500 °C in ammonia, this compound ammonolyzes to form nanocrystalline CrN.     

Transition to turbulence, small disturbances, and sensitivity analysis I: A motivating problem

For over 100 years, researchers have attempted to predict transition to turbulence in fluid flows by analyzing the spectrum of the linearized Navier-Stokes equations. However, for many simple flows this approach fails to match experimental results. Recently, new scenarios for transition have been proposed that are based on the interaction of the linearized equations of motion with small disturbances to the flow system. These new “mostly linear” theories have increased our understanding of the transition process, but the role of nonlinearity has not been explored in detail. This paper is the first of a two part work in which sensitivity analysis is used to study the effects of small disturbances on transition to turbulence. In this part, we study a highly sensitive one-dimensional Burgers' equation as a motivating problem. Sensitivity analysis is used to predict the large changes in solutions in the presence of a small disturbance. Also, sensitivity analysis is shown to provide more information about the disturbed nonlinear problem than a purely linear analysis of the problem. In the second part of this work, this analysis will be extended to the three-dimensional Navier-Stokes equations to show that small disturbances have great potential to trigger transition to turbulence.     

Integration of equipment planning and project scheduling

It is common to schedule project activities first, then the utilization of equipment and its operating crew is planned based on such schedule. Real world experiences indicate that activity scheduling can be heavily impacted by the resources needed. In particular, if a project requires highly specialized and expensive equipment type, then one needs to take into account the schedule and cost of such resources in developing the project schedule.     

Cotunnite-Structured Titanium Dioxide and the Hardest known Oxide

Combined theoretical and experimental investigations led to the discovery of a new polymorph of titanium dioxide with titanium nine-coordinated to oxygen in the cotunnite (PbCl 2 ) structure. Hardness measurements on the cotunnite-structured TiO 2 synthesized at pressures above 60 GPa and temperatures above 1000 K reveal that this material is the hardest oxide yet discovered. Furthermore, it is one of the least compressible (with a measured bulk modulus of 431 GPa) and hardest (with a microhardness of 38 GPa) polycrystalline materials studied thus far.     

Polymerization of 4-Dimethylamino-N-propargylpyridinium Bromide by Transition Metal Catalysts

The polymerization of an ionic propargyl derivative, 4-dimethylamino-N-propargylpyridinium bromide (DMAPPB), was carried out by palladium, platinum, and ruthenium chlorides. The polymerization of DMAPPB by these transition metal catalysts proceeded well to give a relatively high polymer yield. The chemical structure of the resulting polymer was characterized by such instrumental methods as elemental analysis, infrared, NMR, UV–visible spectroscopies to have conjugated polymer backbone system bearing 4-dimethylamino-N-methylenepyridinium bromide. The polymer was soluble in DMF, DMSO, and formic acid, and found to be less hygroscopic than those of similar homologues having more smaller substituents. The resulting polymers were mostly black powders and showed the amorphous morphology.     

Exact solutions to Landau-Zener problems by evolution operator method

Various analytic approaches have been developed to solve the famous Landau-Zener (LZ) problem. Here, we introduce a time-evolution operator method to investigate such a problem by numerically solving the induced algebraic equations (by Runge-Kutta method). Based on these calculations, transitions between two levels driven by various time-dependent external fields can be simulated in detail, typically near the so-called avoided crossing points. Far from these points, our results reduce to the original Landau-Zener transition (LZT).     

HeNa及HeNa~+光谱的理论研究

利用从头算Molecule-UHF程序计算得到HeNa分子的基态~2∑3s及激发态~2∏3p和HeNa~+的~1∑2p、~3∑3s及~t∑3s态的势能曲线,并在此基础上利用自编的程序计算了态-态间光谱跃迁的Franck-Condon因子.结果说明HeNa分子的基态是不稳定的,激发态2∏3p有一个较浅的势阱,HeNa~+的1∑2p有一个较浅的势阱,而~3∑3s态及~t∑3s态分别存在一个很深的势阱.     

Synthesis, reactions and structural features of monofluorinated cyclopropanecarboxylates

Monofluorinated cyclopropanecarboxylates are available in racemic or optically active form by transition metal-catalyzed reactions of vinylfluorides with diazoacetates. From α-fluorostyrene and tert-butyl diazoacetate in the presence of 2 mol% of an enantiopure bis(oxazoline) copper complex, a 81:19 mixture of tert-butyl trans- and cis-2-fluoro-2-phenylcyclopropanecarboxylates was obtained with high enantiomeric excess (ee) of 93 or 89%, respectively. The corresponding racemic ethylesters were used as starting materials for the synthesis of carboxamides, of the cis- and trans-isomers of analogues of tranylcypromine, an anti-depressive drug and several of its homologous fluorinated cyclopropylmethyl and cyclopropylethyl amines. Corresponding enantiopure cyclopropylmethanols and several of their derivatives were synthesized also. Solid state structures of a selection of these compounds were examined by X-ray crystallography. Particularly, the cis-configurated fluorinated phenylcyclopropane derivatives showed extremely close intermolecular CH?FC contacts. The shortest of such distances (2.17 Å) was found in the N-(4-bromophenyl)carbamate of (1S,2R)-(2-fluoro-2-phenylcyclopropyl)methanol.