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排序方式: 共有106条查询结果,搜索用时 15 毫秒
1.
Let B(N) be the power set of the set of natural numbers endowed with the usual structure of a compact abelian group and letμ be the normed Haar measure on it. The paper studies the properties ofμ-measurable additive maps of B(N) into Hausdorff abelian groups. 相似文献
2.
De novo structural prediction of transition metal complexes is investigated. Technetium complexes are chosen given their importance in medical imaging and nuclear waste remediation and for the chemical diversity they display. A new conformational searching algorithm (LIGB) for transition metals is described that allows one to search for different conformational and geometric isomers within a single simulation. In the preponderance of cases, both conformational searching techniques (LIGB and high-temperature molecular dynamics/simulated annealing) provide comparable results, while LIGB is superior for macrocyclic complexes. A genetic algorithm-optimized PM3(tm) parametrization for Tc is compared with the standard implementation and found to yield a significant improvement in predictive ability for the most prevalent Tc structural motifs. The utility of a coupled molecular mechanics-semiempirical quantum mechanics protocol is demonstrated for very rapid, efficient, and effective de novo prediction of transition metal complex geometries. 相似文献
3.
Treatment of CrCl(2)(THF)(2) with NaOSi(t)Bu(3) afforded the tetrameric "box" [Cr(mu-Cl)(mu-OSi(t)Bu(3))](4) (1, X-ray). THF cleaved 1 to provide trans-(silox)ClCr(THF)(2) (2), whereas degradation of 1 with 4-picoline caused disproportionation and the generation of trans-Cl(2)Cr(4-pic)(2) and trans-(silox)(2)Cr(4-pic)(x) (n = 2, 3; 3, 3-4-pic). Chromous centers in 1 were antiferromagnetically coupled, and density functional calculations on the high-spin (multiplicity = 17) model [Cr(mu-Cl)(mu-OH)](4) (1') revealed that its singly occupied 3d orbitals spanned an energy range of approximately 2 eV. The addition of 8 equiv of Na(silox) to 1 yielded [((t)Bu(3)SiO)Cr(mu-OSi(t)Bu(3))(2)]Na.C(6)H(6) (4, Y shaped, angle OCrO(Na) = 91.28(7) degrees), and treatment of 4 with dibenzo-18-crown-6 produced [(silox)(3)Cr][Na(dibenzo-18-crown-6)] (5, angle OCrO = approximately 120 degrees, (120 + alpha) degrees, (120 - alpha) degrees). Calculations of [((t)Bu(3)SiO)Cr(mu-OSi(t)Bu(3))(2)]Na (4') and Cr(silox)(3)(-) (5') provided reasonable matches with the experimental geometries (X-ray). The trigonal chromic derivative (silox)(3)Cr (6) was synthesized from CrCl(3)(THF)(3) for structural and calculational comparisons to the chromous derivatives. 相似文献
4.
Buda C Kazi AB Dinescu A Cundari TR 《Journal of chemical information and modeling》2005,45(4):965-970
Several hypotheses to elucidate the linkage isomer preference of the thiocyanate (SCN(-)) ion have been offered. For complexes with small coordination numbers (i.e., 1 and 2) and groups 11 (Cu-triad) and 12 (Zn-triad) metals, different levels of theory and a variety of basis sets have been employed to study linkage isomerism. Similar results are obtained for all density functionals tested, pure and hybrid. Overall, good agreement, vis-à-vis experimentally identified linkage isomers, is achieved for ab initio techniques, whereas semiempirical quantum mechanical methods show a bias toward S-ligated isomers. Despite the seeming ease for the a priori prediction of the most stable thiocyanate isomers using acid/base principles, this research highlights the sensitivity of quantitative calculations of transition-metal linkage isomerism to the choice of basis set and electron correlation, particularly with post-Hartree-Fock treatments. 相似文献
5.
Stanciu C Hino SS Stender M Richards AF Olmstead MM Power PP 《Inorganic chemistry》2005,44(8):2774-2780
The synthesis and characterization of the first divalent germanium, tin, and lead monoamide derivatives of the parent amide group -NH(2) are presented. They have the general formula (ArMNH(2))(2) (M = Ge, Ar = Ar'(C(6)H(3)-2,6-Pr(i)(2)) or Ar* (C(6)H(3)-2,6(C(6)H(2)-2,4,6-Pr(i)(3))); M = Sn, Ar = Ar*; M = Pb, Ar = Ar*). For germanium and tin, they were obtained by reacting the corresponding terphenyl halides of the group 14 elements with liquid ammonia in diethyl ether. The lead amide derivative (Ar*PbNH(2))(2) was synthesized by reaction of LiNH(2) with Ar*PbBr in diethyl ether. The compounds were characterized by IR and multinuclear NMR spectroscopies and by X-ray crystallography in the case of the (Ar'GeNH(2))(2) or (Ar*SnNH(2))(2) derivatives. They possess dimeric structures with two -NH(2) groups bridging the germanium and tin centers. For lead, the reaction with ammonia led to isolation of a stable ammine complex of formula Ar*PbBr(NH(3)) which was characterized by IR and NMR spectroscopies and by X-ray crystallography. It is the first structural characterization of a divalent lead ammine complex. 相似文献
6.
Ionela-Daniela Carja Corneliu Hamciuc Tachita Vlad-Bubulac Maria Bruma Inga A. Ronova 《Structural chemistry》2013,24(5):1693-1703
Heteroaromatic polymers are considered to be high performance organic materials due to their unique and highly attractive properties, including outstanding thermal and mechanical resistance, that arise from their aromatic structure and strong interactions between macromolecular chains. Modification or designing new molecular architectures with tailored physico-chemical characteristics allows expanding the applications of these materials in various advanced technologies. Herein, a series of polymers containing bulky phenoxyphthalonitrile pendant units was synthesized and their physical properties were studied and correlated with their conformational parameters, as well as free and van der Waals volumes. For comparison, the related polymers without lateral moieties were also investigated to highlight the effect of bulky substituent on the polymer rigidity. Thus, it is shown that conformational rigidity determines the packing of macromolecules in solid state, and, therefore, the free volume, glass transition, and decomposition temperatures. The values found experimentally for T g correlate well with those obtained using the conformational rigidity parameters. The dependence of T g of these polymers on Kuhn segment is described by linear equations, with very good factors of convergence. The correlations established by Monte Carlo method allow obtaining the T g values for related polymers where the experimental measurement of this parameter is difficult. 相似文献
7.
8.
Atoumane Ndiaye Alle Dioum Corneliu I. Oprea Anca Dumbrava Jeanina Lungu Adrian Georgescu Florin Moscalu Mihai A. Gîru Aboubaker Chedikh Beye Issakha Youm 《Molecules (Basel, Switzerland)》2021,26(1)
The theoretical study of chrysanthemin (cyanidin 3-glucoside) as a pigment for TiO2-based dye-sensitized solar cells (DSSCs) was performed with the GAUSSSIAN 09 simulation. The electronic spectra of neutral and anionic chrysanthemin molecules were calculated by density functional theory with B3LYP functional and DGDZVP basis set. A better energy level alignment was found for partially deprotonated molecules of chrysanthemin, with the excited photoelectron having enough energy in order to be transferred to the conduction band of TiO2 semiconductor in DSSCs. In addition, we used the raw aqueous extracts of roselle (Hibiscus sabdariffa) calyces as the source of chrysanthemin and the extracts with various pH values were tested in DSSCs. The extracts and photosensitized semiconductor layers were characterized by UV-Vis spectroscopy, and DSSCs based on raw extracts were characterized by current density-voltage measurements. 相似文献
9.
The title compound is the first stable structural analogue for the monobridged isomer of a heavier group 14 alkene analogue. 相似文献
10.
Corneliu Balan 《Continuum Mechanics and Thermodynamics》2001,13(6):399-414
Received March 25, 2001 / Published online November 15, 2001 相似文献