Molecular structures of alumina nanoballs and nanotubes: a theoretical study

Molecular structures of alumina nanoballs and nanotubes have been determined. Tetrahedral, octahedral, and icosahedral alumina nanostructures were derived from Platonic solids and Archimedean polyhedra and were optimized by quantum chemical methods. I(h)-symmetric balls, resembling their isovalence electronic analogues, fullerenes, are preferred. The nanoballs consist of adjacent Al(5)O(5) and Al(6)O(6) rings, similar to C(5)- and C(6)-rings of fullerenes. The structural characteristics of alumina nanoballs are dominated by pi-electron donation from oxygen to aluminum. Alumina nanotubes can be derived from icosahedral nanoballs. The tubes alternate between D(5d)- and D(5h)-symmetries and are capped by halves of the icosahedral balls.     

Crystal and molecular structures of dicyclohexyltin dichloride and dibromide

The crystal structures of (C₆H₁₁)₂SnCl₂ (A) and (C₆H₁₁)₂SnBr₂ (B) have been determined. The compounds are isomorphous, and the molecules have nearly the same geometry. In both cases the coordination can be regarded as tetrahedral on the basis of the geometrical parameters. The data are critically analysed with that published for analogous compounds.     

Crystal and molecular structures of the copper dichloride complex with 1-isopropenylimidazole

Crystal and molecular structures of the [CuL₂Cl₂] complex (L is 1-isopropenylimidazole) (I) are determined (R = 0.038, (wR ₂ = 0.092 for 2026 reflections with F _o ≥ 4σ(F _o); R ₁ = 0.123, wR ₂ = 0.117 for all reflections)) and compared with the structure of the known cobalt complex of analogous composition [CoL₂Cl₂] (II). Unlike complex II with the usual tetrahedral environment of the cobalt atom, the structure of the coordination polyhedron of the copper atom in compound I is intermediate between tetrahedron and square (the average dihedral angle between the ClCuN planes is 35.9°, and the ClCuCl (147.5°) and NCuN (163.1°) angles are much larger than the ClCuN angle of 90.1°–93.1°). The Cu-N (1.975(3), 1.959(3) Å) and Cu-Cl bonds (2.291(1), 2.278(1) Å) in complex I are typical of the copper(II) compounds. Different spatial structures of the 1-alkenylimidazole cycles in complexes I and II are found. Different short intermolecular contacts in crystals of compounds I (Cu…Cl, Cu…H) and II (Cl…C) result in the formation of chains with different mutual arrangements of molecules of the complexes.     

Spectroscopic characterization of hydroxylated nanoballs in methanol

In this report, the photophysical properties of self-assembled [Cu(2)(5-OH-bdc)(2)L(2)](12) [where (5-OH-bdc)(2-) = 5-hydroxybenzene-1,3-dicarboxylate and L is a dimethyl sulfoxide, methanol, or water ligand] hydroxylated nanoballs (OH-nanoball) were examined in methanol using optical absorption and steady-state and time-resolved fluorescence methods. The optical spectrum of the OH-nanoball is dominated by ligand absorbance at 305 nm and a weaker Cu(2+)-to-ligand charge-transfer transition at approximately 695 nm, which are distinct from the absorption of either the free ligand (approximately 312 nm) or Cu(2+)(NO(3))(2) (>750 nm) in methanol. The corresponding emission spectrum of the OH-nanoball originates from the emission of the ligand and is centered at approximately 360 nm with a shoulder at approximately 390 nm. The emission from the OH-nanoball is significantly quenched relative to the free ligand [Phi(5-OH-H(2)bdc) = 0.014 and Phi(OH-nanoball) = (5.6 +/- 0.5) x 10-5]. The addition of bases such as imidazole results in an increase in the emission intensity of the OH-nanoball solution, indicating dissociation of the [Cu(2)(5-OH-bdc)(2)L(2)](12) units. Although the mechanism of (5-OH-bdc)(2-) quenching within the OH-nanoball is not clear, it is likely due to interactions between the ligand pi system and the Cu d orbitals. Fluorescence polarization studies further suggest that the OH-nanoball retains a spherical shape in solution. This is evident by the fact that the fluorescence anisotropy of the nanoball is nearly identical with that of the free ligand, suggesting rapid energy transfer (homogeneous fluorescence resonance energy transfer) between ligands within the OH-nanoball.     

Molecular dynamics simulation of liquid methylene dichloride (EMLG Publication)

The molecular dynamics and interactions of liquid methylene dichloride (CH₂Cl₂) have been computer simulated with atom—atom interaction potentials, with and without charges, at three EMLG pilot project state points, 293K 1 bar; 177K, 1 bar; and 323K, 5 k bar. A wide variety of static and dynamic results have been lodged in the EMLG data bank and in this paper we summarise the work to date and suggest areas of further investigation.     

Molecular electronic structure of diphenyllead(IV) dichloride and comparison with diphenyltin(IV) dichloride by the SCF-MS molecular-orbital method

SCF-MS calculations on diphenyllead(IV) dichloride for two hypothetical monomers and the dimer of the Ph₂PbCl₂ polymeric compound elucidate the molecular electronic structure. Quasirelativistic wave functions and the Vosko-Wilk-Nusair (VWN) exchange-correlation potential were used. Ph₂PbCl₂ and Ph₂SnCl₂ have been compared to show the difference between the polymeric lead molecule, which is bonded through chlorine, and the monomeric tin molecule. The nuclear quadrupole resonance frequencies and asymmetry parameters of ³⁵Cl were calculated and interpreted. The asymmetry parameters and the molecular electronic structures of Ph₂PbCl₂ and Ph₂SnCl₂ highlighted the differences which results between the tin and lead molecules when diphenyllead(IV) dichloride polymerizes.     

Syntheses and structures of magnesium pyridine thiolates--model compounds for magnesium binding in photosystem I

Novel magnesium pyridine-2-thiolates were prepared by using alkane elimination chemistry. The resulting complexes display a metal coordination environment composed of sulfur/nitrogen bonding from the intramolecularly stabilized mercaptopyridine ligand, in addition to coordination by the oxygen centers from two THF donors. The compounds are well-suited model compounds for the magnesium centers in Photosystem I, in which magnesium, situated in the central chlorophyll ligand, is bound to sulfur from a nearby methionine residue. All compounds were characterized by (1)H, (13)C NMR, and IR spectroscopy, in addition to Xray crystallography.     

Molecular shapes and molecular structures

The first part is a response to E.B. Wilson's remarks about molecular structure at the 1979 Sanibel Symposium; his proposed extension of the notion of “potential energy surface” is a convention, not a part of fundamental molecular quantum theory. An energy surface has no essential role in a non-adiabatic theory which, both in principle and practice, can account for the spectroscopic term formulae with greater accuracy than models based on PE surfaces. Results obtained from the generator coordinate method are cited as confirmation of this conclusion. Claverie and Diner's distinction between “quantum structure” and “classical molecular structure” is discussed; it is the latter that is problematic in molecular quantum theory. The use of molecular structure is optional, and determined by utility, rather than essential in chemical physics; photoelectron spectroscopy is an example where this appreciation has proved fruitful.     

Crystal and molecular structures of the complexes of cobalt dichloride with 1-isopropenylimidazole and 1-vinylimidazole

The crystal and molecular structures of bis(1-isopropenylimidazole)dichlorocobalt (C₁₂H₁₆Cl₂·N₄Co) [R 0.036 (R _W 0.089) for 3229 unique reflections with I > 2σ(I)] and tetra(1-vinylimidazole)dichlorocobalt (C₂₀H₂₄Cl₂N₈Co) [R 0.031 (R _W 0.072) for 1863 unique reflections with I > 2σ(I)] were determined. In these molecular complexes, the monodentate terminal 1-alkenylimidazole ligands coordinate to the metal via a “pyridine” nitrogen atom. In C₁₂H₁₆Cl₂N₄Co, the Co atom has a distorted tetrahedral 2N,2Cl coordination. The coordination polyhedron of cobalt in C₂₀H₂₄Cl₂N₈Co is a strongly elongated 4N,2Cl octahedron. The Co-N and Co-Cl bonds [Co-N 2.015(2) and 2.032(4) Å; Co-Cl 2.229(2) Å] in the tetrahedral complex C₁₂H₁₆Cl₂N₄Co are shorter than those in the octahedral complex C₂₀H₂₄Cl₂N₈Co [Co-N 2.134(2) and 2.157(2) Å; Co-Cl 2.518(1) Å]. In the structures of both complexes there are short contacts involving the Cl atoms.     

The structures of lithium and magnesium organocuprates and related species

Organocuprates are excellent reagents for the formation of carbon–carbon bonds and have been used extensively in synthetic methodology for over fifty years. However, despite their long pedigree the structures, solution behavior, and mechanism of operation of these reagents have often remained opaque. This review concentrates upon the resting-state structures of organocuprates as determined using X-ray crystallographic studies, and provides a comprehensive survey of all solid-state structural characterizations of these species and the intricate nature of their supramolecular assemblies. In addition, solution state experimental data is also presented where it pertains directly to the presented solid-state structures or where it illustrates key points crucial to the understanding of organocuprate reactivity. The structures of all the main classes of organocuprate reagent will be discussed including lithium and magnesium homo-cuprates, cyano-cuprates and hetero-cuprates.     

Molecular structures of adsorbed water

A method previously developed for calculating molecular nanostructures in liquid and adsorbed fluids based on the combination of molecular dynamics with graph theory is modified. In terms of the modified method, the concentrations of associates in water adsorbed in model pores of active carbon are calculated as functions of the degree of pore filling and temperature.     

Molecular structures of trinitromethane derivatives

The molecular structures of trinitromethane derivatives XC(NO₂)₃ (X = F, Cl, Br, NC, NF₂, N₃) were studied using the density functional approach. The rules for changing the configurations of substituents in these compounds were revealed. Acceptability of the method employed for the calculations of trinitromethane derivatives is discussed.     

Molecular and crystal structures of argolide epoxide

The sesquiterpene lactone argolide has been converted into its 1(10)-epoxide. The structure of the latter has been investigated by NMR, x-ray structural analysis, and molecular mechanics.Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 60–64, January–February, 1998.     

Molecular structures and hypochromism of two purinophanes

The structures of purinophane 1 and its higher homolog 2 were determined by X-ray crystallographic analysis. Hypochroism of 1 and 2 in various media reported.     

Ethylene polymerization over supported catalysts [2,6‐bis(imino)pyridyl iron dichloride/magnesium dichloride] with AlR3 as an activator

Data on ethylene polymerization over supported LFeCl₂/MgCl₂ catalysts {L = 2,6‐bis[1‐(2,6‐dimethylphenylimino)ethyl]pyridyl} containing AlR₃ (R = Me, Et, i‐Bu, or n‐Oct) as an activator are presented. These catalysts are highly active (100–300 kg of polyethylene/g of Fe h bar of C₂H₄) and stable in ethylene polymerization at 70–80 °C. Data on the effects of the iron content, AlR₃ type, Al(i‐Bu)₃ concentration, and hydrogen presence on the catalyst activity are presented. The molecular structure of polyethylene produced with these catalysts (including the molecular masses, molecular mass distribution, branching, and number of C?C bonds) has been studied; data on the effects of AlR₃ and hydrogen on the molecular structure are presented. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2128–2133, 2005     

Crystal and molecular structures of the binuclear complex of rhodium(III) chloride with selenium dichloride and the complex of iridium(III) chloride with sulfur dichloride and tetrachloride

Institute of General and Inorganic Chemistry, Ukrainian Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 3, pp. 146–148, May–June, 1992.     

Molecular and crystal structures of hemigossypolone and gossypolone

The results are given of an x-ray structural investigation of hemigossypolone isolated from the stems of a wiltinfected cotton plant and of gossypolone obtained by oxidizing gossypol.