New chromophores based on 2-(4-vinylchromen-2-ylidene)malononitrile and 2-(2-vinylchromen-4-ylidene)malononitrile

New derivatives of 2-(4-vinylchromen-2-ylidene)malononitrile and 2-(2-vinylchromen-4-ylidene)malononitrile were synthesized using the Knoevenagel reaction of 2-(4-methyl-chromen-2-ylidene)malononitrile and 2-(2-methylchromen-4-ylidene)malononitrile, respectively, with the participation of [1-(2-n-butoxyethyl)-2,2,4,7-tetramethyl-1,2,3,4-tetrahydroquinolin-6-yl)]-carbaldehyde. First hyperpolarizability (β) was calculated for the obtained compounds using the M05-2X functional and 6-31+G (d) basis. Optical properties and solvatochromism in solvents of different polarity (toluene, 1,4-dioxane, chlorobenzene, dichloromethane, DMF, and ethanol) were also investigated.

     

On the studies of the vibrational spectra of cluster [Mo2O2S2(S2)2]2-

IR and Raman spectra of [Mo₂O₂S₂(S₂)₂]^2- were reported. The resonance Raman spectra and the depolarization ratios in CH₃CN solution were measured. By using the data of crystal structure, the simplified normal coordinate calculation of the stretching vibrations for anion [Mo₂O₂S₂(S₂)₂]^2- was performed. The results obtained are useful to assign the vibrational bands of some Mo-Fe-S clusters.     

Superconductivity in the intermetallic borocarbides YPd2B2C,YPt2B2C and LaPt2B2C

We report a detailed study of the thermodynamic properties of the conventional phonon-mediated superconductors YPd₂B₂C, YPt₂B₂C and LaPt₂B₂C. Our calculations conducted within the framework of the Migdal-Eliashberg formalism show that the experimental values of the critical temperature cannot be properly reproduced using commonly accepted value of Coulomb pseudopotential. Moreover, we proved that the values of universal ratios of conventional superconductivity appearing in the Bardeen-Copper-Schrieffer (BCS) theory are inconsistent with our results obtained from the investigated borocarbides. The observed differences are connected with the strong/medium-coupling and retardation effects existing in the studied systems.     

Facile Preparation of Indolyl-2/3-methylsulfoxides Using HF/H2O2

A variety of indolyl-2/3-methylsulfides tethered with sensitive functionalities were oxidized to the corresponding sulfoxides using a hitherto unexplored HF/H₂O₂ system.     

Synthesis of (2-chlorophenyl)(phenyl)methanones and 2-(2-chlorophenyl)-1-phenylethanones by Friedel-Crafts acylation of 2-chlorobenzoic acids and 2-(2-chlorophenyl)acetic acids using microwave heating

Several 2-(2-chlorophenyl)-1-phenylethanones and (2-chlorophenyl)(phenyl)methanones were prepared by the Friedel-Crafts acylation reaction of 2-(2-chlorophenyl) acetic acids and 2-chlorocarboxylic acids, respectively, in the presence of cyanuric chloride, pyridine, and AlCl₃ or FeCl₃ using microwave heating. The yields of the ketones were significantly higher than those obtained using conventional heating. In addition, similar reactions carried out with the less inexpensive and less toxic FeCl₃ gave titled ketones in comparable yields. Interestingly, the FeCl₃ catalyzed reactions gave pure ketones (no chromatographic purification required), whereas the AlCl₃ catalyzed reaction gave impure product that required chromatographic purification.     

Thermische Zersetzung von CuInSe2, LiInSe2 und LiInTe2

The thermal decompositions of CuInSe₂, LiInSe₂ and LiInTe₂ in vacuum at high temperatures were studied by using TG/DTG coupled with mass spectrometry. For CuInSe₂, two steps were found to be significant. Up to 1000 °C Se₂ and In₂Se evaporate, followed later by Cu₂Se. The Li-containing compounds show similar behaviour. However, Li⁺ was already detected during the first step. Obviously, Li₂Se dissociates more readily than Cu₂Se. No Cu⁺ species were detected up to the complete evaporation of CuInSe₂.     

Propene homo- and copolymerization using homogeneous and supported metallocene catalysts based on Me2Si(2-Me-Benz[e]lnd)2ZrCl2

The isoselective propene polymerization using the supported catalyst SiO₂/MAO/Me₂Si(2-Me-Benz[e]Ind)₂ZrCl₂/AlR₃ was investigated and compared with propene polymerization using the corresponding homogeneous catalyst system. The influence of propene concentration, polymerization medium, temperature, comonomer, and external aluminium alkyls on polymerization kinetics and polypropene properties such as molecular mass, stereo- and regioselectivity, morphology, and bulk density was studied. © 1997 John Wiley & Sons, Inc.     

An Ab Initio Study of C2H2.H2, C2H2.N2, and C2H2.Ar Complexes

Ab initio calculations at the post Hartree–Fock level were performed on complexes of acetylene with hydrogen, nitrogen, and argon. Total energies, optimum geometries, and binding energies were calculated, using the 6-311G** and the 6-31+G(2df,2pd) basis sets. Calculations showed the complexes to be more stable than the separate entities, with the exception of the acetylene–hydrogen complex.     

High-level ab initio versus DFT calculations on (H2O2)2 and H2O2–H2O complexes as prototypes of multiple hydrogen bond systems

The performance of B-LYP, B-P86, B3-LYP, B3-P86, and B3-PW91 density functionals to describe multiple hydrogen bond systems was studied. For this purpose we have chosen the dimers of hydrogen peroxide and the hydrogen peroxide–water complexes. The geometries and vibrational frequencies obtained with a 6-311+G(d,p) basis set were compared with those obtained at the MP2 level using the same basis set expansion. The corresponding dimerization energies were obtained using a 6-311+G(3df,2p) basis set and compared with those obtained using the G2(MP2) theory. Red shiftings of the OH donor stretching frequencies were predicted by all approaches investigated; however, in all cases, the DFT values were sizably larger than the MP2 ones. Similarly, the blue shifting of the torsion of the hydrogen peroxide subunit was larger when evaluated at the DFT level. All functionals reproduced the G2(MP2) relative stabilities of the different local minima quite well. With the exception of the B-LYP and B3-PW91 approaches, all functionals yielded binding energies which deviated from the G2(MP2) values by less than 0.5 kcal/mol, provided that G2-type basis sets were used and that the corresponding BSSE corrections were included. © 1997 John Wiley & Sons, Inc. J Comput Chem 18: 1124–1135     

Diastereoselective synthesis of 2-fluoroaziridine-2-carboxylates by Reformatsky-type aza-Darzens reaction

The reaction of ethyl dibromofluoroacetate with imines using zinc metal gave 2-fluoroaziridine-2-carboxylates via aza-Darzens reaction of the primary product of the Reformatsky reaction with high diastereoselectivity in excellent yields (quantitative yield and Dr = 85:15). This chemoselective formation of 2-fluoroaziridines was achieved by using CH₃CN as a solvent. Interestingly, the reaction proceeded without activation of zinc metal, which was necessary for the Reformatsky reaction of bromodifluoroacetate. None of α-bromo-α-fluoro-β-lactams, four-membered cyclization products, and noncyclized 3-amino-2-bromo-2-fluorocarboxylic esters, usual Reformatsky adducts, were formed.     

Zur Thermodynamik der Dimerisierung von gasförmigem CrI2, MnI2, FeI2 und CoI2: experimentelle und quantenchemische Untersuchungen

Thermodynamic Data of the Dimerisation of Gaseous CrI₂(g), MnI₂(g), FeI₂(g), and CoI₂(g), Experimental and Quantum Chemical Investigations By means of quantum chemical methods molar heats and entropies as a function of temperature for the monomeric and dimeric diiodides of 3d‐metals have been calculated. From mass‐spectrometric measurements of the dimerisation equilibria of gaseous CrI₂, MnI₂, FeI₂, and CoI₂ using the Knudsen‐effusion method the heats of dimerisation and the heats of formation of the monomeric and dimeric iodides could be derived using the results of the quantum chemical calculations.     

Assembly of 3D Coordination Polymers from 2D Sheets by [2+2] Cycloaddition Reaction

The synthesis of three 2D interdigitated Zn^II coordination polymers (CPs), by using three monotopic ligands containing C?C bonds, is reported. Among these, two CPs with 4spy (4‐styryl pyridine) and 2F‐4spy (a 2′‐fluoro derivative of 4spy) ligands showed quantitative formation of cyclobutane rings, thus demonstrating a unique synthetic procedure to synthesize metal–organic frameworks (MOFs) by using this photochemical reaction. Interestingly, these compounds can also be synthesized by mechanochemical grinding procedures by using Zn(OAc)₂. In contrast, Zn(NO₃)₂ did not yield the required product, unlike in the solution route. In addition, compounds with 4vpy (4‐vinylpyridine), 4spy and 2F‐4spy ligands created different units in the CPs; 4vpy and 2F‐4spy furnished paddle wheel units, whereas 4spy yielded tetrahedral Zn^II repeating units. Furthermore, the change in coordination geometry manifests in the photoluminescence properties, attributed to the difference in charge‐transfer and ligand‐centered fluorescent phenomenon.     

六方类钙钛矿体系La2Ca2MnO7-Sm2Ca2MnO7的结构变化和相关系

利用柠檬酸盐前驱物法制备了La2-xSmxCa2MnO7系列样品,并利用Rietveld方法对结构进行了精修.结果表明,体系中存在两个单相区(x≤0.8和x≥1.0)和一个两相区(O.8相似文献   

ZnCl2 Promoted Formal (3+2) Cycloaddition Reactions of 2-Alkoxy-1,4-benzoquinones with 2H-Chromenes

A simple, mild, inexpensive and highly efficient method for the synthesis of 2,2-dimethyldihydropyranopterocarpans (4a–h and 5a–b) by formal (3+2) cycloaddition reactions of 2-alkoxy-1,4-benzoquinones (3a–b) with 2H-chromenes (1a–d and 2) using ZnCl₂ at room temperature has been developed.     

Comparative study of TmI2, SmI2, and SmI2/HMPA in the cross-coupling reactions of 2-acetylthiophene and thiophene-2-carboxylate with carbonyl compounds

The cross-coupling reactions of acetylthiophene or ethyl thiophene-2-carboxylate with aldehydes or ketones were achieved in a regioselective manner by using thulium diiodide in THF solution. Similar coupling reactions were also realized by using samarium diiodide together with excess amounts of hexamethylphosphoramide (HMPA). However, ethyl thiophene-2-carboxylate was inert in SmI₂/THF solution, and acetylthiophene was simply reduced to thienylethanol by SmI₂ in the absence of HMPA.     

The elusive methene ylides CH2CIH,CH2FH and CH2OH2

The possible existence of the ylides CH₂CIH, CH₂₅FH and CH₂OH₂ as stable neutral species in the gas phase has been investigated by the neutralization–reionization (NR) mass spectrometry of their radical cations using a double-focusing mass spectrometer of reversed geometry. The experiments were, for the most part, performed under single-collision conditions with Xe as the neutralization target gas and He and O₂ as reionization agents. For each ylidion a peak was observed in their NR mass spectrum which indicated that the neutral ylide had apparently been produced. However for CH₂FH⁺˙ and CH₂OH₂⁺˙ the m/z 34 and m/z 32 peaks, respectively, were attribut-able to interferences from the natural isotopic abundance of ions of lower mass. For CH₂CIH⁺˙, the NR recovery signal was found to arise from the presence of CH₃CI⁺˙ as an impurity in the ylidion flux. This was proved by examination of the collisional activation mass spectra of the [C, H₃, CI]⁺˙ ions produced in the NR mass spectra of the conventional ions and ylidions, an experiment performed using a triple-sector mass spectrometer.     

Covalent Cross-Linking of 2H-MoS2 Nanosheets

The combination of 2D materials opens a wide range of possibilities to create new-generation structures with multiple applications. Covalently cross-linked approaches are a ground-breaking strategy for the formation of homo or heterostructures made by design. However, the covalent assembly of transition metal dichalcogenides flakes is relatively underexplored. Here, a simple covalent cross-linking method to build 2H-MoS₂–MoS₂ homostructures is described, using commercially available bismaleimides. These assemblies are mainly connected vertically, basal plane to basal plane, creating specific molecular sized spaces between MoS₂ sheets. Therefore, this straightforward approach gives access to the controlled connection of sulfide-based 2D materials.     

Probable mechanism for alkane oxidation with H2O2 over VS-2

Metallosilicate zeolites containing Ti and V, TS-2 and VS-2, have been synthesized using tetrabutylammonium cation as the template. Although both Ti and V exist in zeolite framework in a highly dispersed state, V easily leaches by K₂CO₃ or H₂O₂ treatments in contrast to Ti. Spin trapping experiments and relative reactivity of linear/cyclic alkanes indicate that the oxidation of alkanes over TS-2 and VS-2 proceed by different mechanisms; it is conceivable that the oxidation occurs by way of the attack of ·OH species produced from the V species in the zeolite framework with H₂O₂.     

Stable conformations of CH3CH2OCH2CH2OH: A comparison of theoretical methods

This article presents the results of an extensive examination of the stable conformations of CH₃CH₂OCH₂CH₂OH at various levels of theory. In particular, 41 initial conformations are optimized using the MM2 force field in BIGSTRN-3; the MINDO/3, MNDO, and AM1 Hamiltonians in AMPAC 2.2; the PM3 Hamiltonian in MOPAC 7.0; and at the HF/STO-3G and HF/3-21G levels using Gaussian 92. The optimized HF/3-21G structures are reoptimized at the HF/6-31G(d) level, and the unique structures are optimized again at the MP2 = FULL/6-31G(d) level. In addition, single-point MP2/6-31G(d) calculations are performed using the HF/6-31G(d) geometries. The goal is to determine the relative accuracy of each method and discuss their strengths and weaknesses. © 1994 by John Wiley & Sons, Inc.     

Synthesis and properties of CeO2-SnO2 films

The formation of CeO₂-SnO₂ thin films from film-forming solutions (FFSs) using the sol-gel method is studied. The effects of SnO₂ content on the thickness and refractive index of films are shown.