Computational modeling of mixed-ligand cobalt diketonate complexes with pyrene-4,5,9,10-tetraimine

Quantum-chemical modeling (DFT UB3LYP*/6-311++G(d,p)) of binuclear mixed-ligand cobalt diketonate complexes with pyrene-4,5,9,10-tetraimine has been performed. Equilibrium geometries and stabilization energies of all the electromeric forms of the studied adducts have been calculated, and the exchange spin coupling constants have been evaluated. Compounds capable of undergoing one- or two-step valence tautomeric rearrangements accompanied by a change in magnetic properties have been revealed by varying the substituents in the bis(chelate) moiety.     

Reactions of trichloromethyl radicals with organosilicon compounds

The photolysis of carbon tetrachloride in the presence of a number of organosilicon compounds has been investigated in the gas phase. The products obtained from the photolysis experiments were those expected from a chain reaction in which trichloromethyl radicals abstract hydrogen atoms from the organosilane. Arrhenius parameters for hydrogen atom transfer were determined relative to those for trichloromethyl radical combination. The activation energies for the reaction of methyl, trifluoromethyl, and trichloromethyl radicals with organosilicon compounds are compared and the results rationalized in terms of polar effects.     

Investigation of organosilicon radicals : II. Methylsilyl radicals

CNDO/2 calculations for a series of Me_xH₃?_xSi (where x = 0,1,2,3) free radicals confirm the suggestion, based on electron spin resonance measurements and chemical evidence, that these radicals are not planar. The deviation from planarity decreases with increasing number of methyl groups, but the angle between the carbonsilicon bond and the plane of an assumed planar configuration is the same for methylsilyl, dimethylsilyl, and trimethylsilyl radicals.     

Investigation of organosilicon radicals : I. Methylphenylsilane anion radicals

CNDO/2 calculations with an spd basis set have been carried out on methyl-phenylsilane anion radicals, and the calculated spin density values compared with the experimental hyperfine coupling constants. The CNDO method overestimates the role of d orbitals and the partial charges on hydrogen atoms attached to silicon atom. The partial charge distribution and the carbonsilicon bond order in the anion radicals and the corresponding neutral molecules are discussed. The equilibrium carbonsilicon bond distance in the trimethylphenylsilane molecule and corresponding anion radical have also been investigated.     

Computational modeling of isotropic electron paramagnetic resonance spectra of doublet state main group radicals

The combined use of theoretical and mathematical methods in the analysis of electron paramagnetic resonance data has greatly increased the ability to interpret even the most complex spectra reported for doublet state inorganic main group radicals. This personal account summarizes the theoretical basis of such an approach and provides an in-depth discussion of some recent illustrative examples of the utilization of this methodology in practical applications. The emphasis is on displaying the enormous potential embodied within the approach.     

Metal-alane adducts with zero-valent nickel, cobalt, and iron

Coordination complexes that pair a zero-valent transition metal (Ni, Co, Fe) and an aluminum(III) center have been prepared. They add to the few examples of structurally characterized metal alanes and are the first reported metallalumatranes. To understand the M-Al interaction and gauge the effect of varying the late metal, the complexes were characterized by X-ray crystallography, electrochemistry, UV-Vis-NIR and NMR spectroscopies, and theoretical calculations. The M-Al bond strength decreases with varying M in the order Ni > Co > Fe.     

Reaction of sterically hindered o-benzoquinones with diazomethane

Conclusions In contrast to certain o-benzoquinones, the sterically hindered o-quinones react with CH₂N₂ both at the oxygen atoms to give cyclic ethers, and at the C=C and C=O bonds of the quinoid ring; the predominant direction of the reaction depends on the ratio of the reactants.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2360–2362, October, 1981.     

An ESR study of the adducts of phosphonyl radicals with fullerene-70

A. N. Nesmeyanov Institute of Organometallic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1938–1940, August, 1992.     

ESR study of the radicals obtained from adducts of dialkyl itaconates with bromotrichloromethane

Three kinds of bromides were prepared from the reaction of dialkyl itaconates with bromotrichloromethane as precursors of analogous radicals for the propagating radicals of some dialkyl itaconates, i.e., the methyl, deuterated methyl, and adamantyl ester derivatives. The radicals were generated by photoirradiation of a toluene solution of the bromides in the presence of hexabutylditin at −60 to 60°C, and ESR spectra were recorded. Hyperfine splitting and the temperature dependence of the linewidth were determined. The β-deuterated radicals were also characterized to determine a coupling to β-hydrogens. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1969–1978, 1999     

Synthesis and optical properties of fluorene‐based polymers incorporating organosilicon unit

The synthesis and optical properties of polymers bearing the repeating unit of terfluorene and various organosilicon groups were investigated. Polymers with high molecular weight and good solubility could be obtained by Suzuki coupling polymerization from silylene‐containing fluorene‐based dibromo monomers and 9,9‐dihexylfluorene‐2,7‐bis(trimethyleneborate). From UV spectra of polymers bearing acyclic silylene bridge, the organosilicon units not only interrupted a π‐conjugation but also contributed to an electronic communication between connected fluorenes. The emission maximum wavelengths (ca. 400 nm) blue‐shifted when compared with that of polyfluorene (418 nm) and the fluorescence quantum yields were considerably high (>0.82) in the CHCl₃ solution. On the other hand, rather broad emission was observed at 480 nm and the fluorescence quantum yield was quite low (0.004) in the solution‐state PL spectrum of tetraphenylsilole‐containing polymer. The polymer emitted visible green light in the spin‐coated film. The fluorescence peak intensity at 486 nm gradually decreased when the film was illuminated with the UV light of 359 nm in air. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4786–4794, 2007     

Spin adducts of group IVB organometallic radicals with Thioketones. an esr study

The radical adducts resulting from the reaction between group IVB organometallic radicals MR₃ (M = Si, Ge, Sn; R = alkyl or aryl) and a number of thioketones of the chromone and flavone series have been investigated by ESR spectroscopy. The spectral parameters obtained for these species have been compared with those of similar adducts of the corresponding ketones. Both classes of radicals adopt an orthogonal conformation, and the differences between the former and the latter paramagnetic species can be accounted for by the different electronegativity of oxygen and sulphur. the effects of substitution of the heterocyclic oxygen with a sulphur or selenium atom on the spin density distribution are likewise explained. INDO calculations have been carried out on the model systems CH₂XSiH₃ (X = O, S).     

ESR study of radicals obtained from vinylalkoxysilanes and their adducts with branched fluoroalkenes

ESR spectra of radicals obtained by abstracting a hydrogen atom from methylvinyldimethoxysilane and methylvinyldiethoxysilane through the action of thetert-butoxy radical were studied. It was shown that the radicals appearing react with branched fluorinated olefins to give relatively stable radical adducts.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 538–540, March, 1994.     

Computational modeling of nanorod growth

In this computational study, we used molecular dynamics and the embedded atom method to successfully reproduce the growth of gold nanorod morphologies from starting spherical seeds in the presence of model surfactants. The surfactant model was developed through extensive systematic attempts aimed at inducing nonisotropic nanoparticle growth in strictly isotropic computational growth environments. The aim of this study was to identify key properties of the surfactants which were most important for the successful anisotropic growth of nanorods. The observed surface and collective dynamics of surfactants shed light on the likely growth phenomena of real nanoprods. These phenomena include the initial thermodynamically driven selective adsorption, segregation, and orientation of the surfactant groups on specific crystallographic surfaces of spherical nanoparticle seeds and the kinetic elongation of unstable surfaces due to growth inhibiting surfactants on those surfaces. Interestingly, the model not only reproduced the growth of nearly all known nanorod morphologies when starting from an initial fcc or fivefold seed but also reproduced the experimentally observed failure of nanorod growth when starting from spherical nanoparticles such as the I(h) morphology or morphologies containing a single twinning plane. Nanorod morphologies observed in this work included fivefold nanorods, fcc crystalline nanorods in the [100] direction and [112] directions and the more exotic "dumbell-like" nanorods. Non-nanorod morphologies observed included the I(h) and the nanoprism morphology. Some of the key properties of the most successful surfactants seemed to be suggestive of the important but little understood role played by silver ions in the growth process of real nanorods.     

Computational modeling of extended systems

Advancements in computing architecture and in theoretical techniques allow for the modeling of complex, extended systems. This section of the 50th anniversary issue of Theoretical Chemistry Accounts highlights modeling work performed on nanostructured systems and underscores the enormous potential for synergy between theory and experiment in modern nanoscience.     

The hetero Diels-Alder reactions of masked o-benzoquinones with nitroso compounds

The first examples of hetero Diels-Alder reaction of masked o-benzoquinones with nitroso dienophiles leading to novel and highly functionalized heterocycles, which are potential intermediates for nitrogenous natural products are reported.     

Formation of radicals in the reaction of oxygen with styrene and cobalt

Conclusions A radical-forming reaction in hydrocarbon solution between styrene, oxygen, and Co^II in the form of its stearate and acetylacetonate has been established. The kinetic laws of this reaction have been studied. A mechanism has been proposed which consists in the formation of a complex between the oxygen and the Co^II by a reversible reaction, with the subsequent reaction of this complex with styrene to form free radicals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1095–1097, June, 1966.The authors express their thanks to I. I. Uskov and A. L. Aleksandrov for help in performing some of the experiments.