Structural effects in the electron absorptio and luminescence spectra of decaborane(14) derivatives B10H12L2

The electron absorption and luminescence spectra of some adducts B₁₀H₁₂L₂ with L-alkylsubstituted pyridines are compared. In each subgroup with mono- and disubstituted pyridines, the largest hypsochromic shift of the long-wave edge of the charge transfer band (CTB) and the increased fluorescence yield correspond to the maximum basicity of L. Steric strains between the ortho methyl group of L and |B₁₀H₁₂| result in an insignificant bathochromic shift of the CTB and decrease the fluorescence yield. The optimal interactions |B₁₀H₁₂|→L, which are responsible for the absorption and emission properties of the adducts, should correspond to conformations where the planes of the heterocyclic system of L make an angle of 30° and are symmetric relative to the |B₁₀H₁₂| plane. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 1, pp. 59–67, January–February, 1996. Translated by I. Izvekova     

Halide ion complexes of decaborane (B10H14) and their derivatives: noncovalent charge transfer effect on second-order nonlinear optical properties

Quantum molecular engineering has been performed to determine the second-order nonlinear optical (NLO) properties in different halo complexes of decaborane (B(10)H(14)) and their derivatives using the density functional theory (DFT) method. These decaborane halo complexes of X(-)@B(10)H(14) (X = F, Cl, Br, and I) are found to possess noncovalent charge transfer interactions. The static polarizability (α(0)) and first hyperpolarizability (β(0)) among these complexes increase by moving down the group from F to I, partly due to the increase in size of their anionic radii and the decrease in their electron affinities. A two-level approximation has been employed to investigate the origin of β(0) values in these halo complexes, which show very consistent results with those by the finite-field method. Furthermore, in the same line, two experimentally existing complexes, I(-)@B(10)H(14) and I(-)@2,4-I(2)B(10)H(12), are found to have considerably large β(0) values of 2859 and 3092 a.u., respectively, which are about three times larger than a prototypical second-order NLO molecule of p-nitroaniline, as reported by Soscun et al. [Int. J. Quantum Chem.2006, 106, 1130-1137]. Besides this, the special effects of solvent, counterion, and bottom substitutions have also been investigated. Interestingly, 2,4-alkali metal-substituted decaborane iodide complexes show remarkably large second-order NLO response with β(0) amplitude as large as 62436 a.u. for I(-)@2,4-K(2)B(10)H(12) complex, which are explained in terms of their transition energies, frontier molecular orbitals and electron density difference plots. Thus, the present investigation provides several new comparative insights into the second-order NLO properties of halo complexes of decaborane, which possess not only large first hyperpolarizabilities, but also high tunability to get a robustly large second-order NLO response by alkali metal substitution effects.     

0(3P) attack on Boranes. III. B10H14

As in our previous studies, 0(³P), generated by titration with NO of microwave discharged N₂ (He carrier), was mixed with B₁₀H₁₄ vapor (Ar carrier) in a flow-tube reactor. Levels of product OH were determined via LIF on an absolute basis, for dwell times 4 to 18 ms. The system was calibrated with C₂H₆, run under identical conditions. The reactants comprised approximately 1% of the flowing mixture. OH production is ≈62 greater from B₁₀H₁₄ than from B₅H₉ (under similar conditions but at somewhat lower temperature). FTIR analyses of a solid product that condensed downstream on cold surfaces showed the presence of ? B? O? H ?O? B? hydrogen bonds and matched (but not perfectly) the calculated frequencies of HB(OH)₂. © 1994 John Wiley & Sons, Inc.     

Homogeneous isotope exchange between thiourea and bis(thiourea)mercury(II) complex

The isotope exchange behavior of thiourea with bis(thiourea)mercury(II) complex has been studied. The concentrations of both the metal ion and the complex were varied. The results show that the complex is labile in the kinetic sense. An increase in concentration increases the rate of exchange. Increase in temperature also results in an increase of the rate of exchange.     

H/D isotope exchange in 9-R-sym-octahydro-10-oxonia(chalcogenonia)anthracene perchlorates

The method of controlled H/D isotope exchange in acid media has been used to study the effect of the heteroatom and the substituents in 9-R-sym-octahydro-10-oxonia(chalcogenonia)anthracene perchlorates on the mobility of hydrogen atoms in the -methylene units of alicyclic rings condensed with heteroaromatic rings. It has been established that in a group of aryl-substituted salts the mobility of the hydrogen atoms increases in the series S⁺++, which corresponds to a decrease in thermodynamic stability of the chalcogenopyrylium cations. In a group of unsubstituted salts (R=H) the order of reactivity of the methylene groups is O⁺++ and corresponds to the increasing orbital electrophilicity and complexing ability of these cations.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 463–467, April, 1993.     

Homogeneous isotope exchange between nickel(II) and bis(resacetophenone phenylhydrazone) nickel(II) complex

Isotope exchange behavior of bis-resacetophenone phenylhydrazone) nickel(II) complex with nickel(II) in tri-n-butyl phosphate and methanol medium has been studied. The studies were carried out at different temperatures varying the concentration of both metal ion and the complex. The results show that the complex is labile in the kinetic sense. Increase in temperature increases the isotope exchange rate. The increase in concentration also results in an enhancement of the rate of reaction.     

Homogeneous isotope exchange between copper(II) and bis(resacetophenone oxime)copper(II) complex

Isotope exchange behavior of bis(resacetophenone oxime)copper(II) complex with copper(II) in tri-n-butyl-phosphate and methanol medium has been studied. The studies were carried out at different temperatures varying the concentration of both metal ion and complex. The results show that the complex is labile in the kinetic sense. Increase in temperature increases the isotope exchange rate. The increase in concentration also results in enhancement of the rate of reaction.     

Kinetic isotope effect in hydrogen isotope exchange between water and phosphines

The kinetic parameters of the tritium exchange between^*H₂O(^*D₂O) and (CH₃)₂PH in the gas phase and between^*H₂O(^*D₂O) and (C₆H₅)₂PH in liquid were measured. Both reactions appeared to be heterogeneous ones. The^*HH/^*DD kinetic isotope effects were estimated and compared with the results of exchange between methanol and phosphines. The differences in isotope effects are explained by the change of the symmetry of the four center cyclic transition complex resulting from the various type of solvation of this complex.     

Homogeneous isotope exchange between tungsten(VI) and Keggin and Dawson type uranium polyoxotungstophosphates

The present paper is concerned with the isotope exchange between¹⁸⁵W and tungsten, and³²P and phosphorus respectively, in uranium(IV) trivacant Keggin and Dawson polyoxotungstophosphate complexes, in water. These studies were carried out at different concentrations and temperature. The isotope exchange rate increases with the temperature and the reagents' concentration. The experimental results show that the complexes are labile kinetically.     

Homogeneous isotope exchange reaction between hydrogen and deuterium

The isotope exchange reaction between hydrogen and deuterium was studied in incident and reflected shock waves over the temperature range 1200–1800 K by vacuum ultraviolet absorption spectroscopy. The observed exchange reaction ensued after long induction periods at rates that proved to account for the amounts of exchange previously seen in single-pulse shock-tube and reflected-wave mass-spectrometric investigations. From the absence of detectable reaction during the induction period, lower bounds of 70 and 45 kcal were placed on the barriers to molecular exchange in four- and six-center transition structures, respectively.     

Luminescent and Photoredox-Active Molybdenum(0) Complexes Competitive with Isoelectronic Ruthenium(II) Polypyridines

Ruthenium(II) complexes with chelating polypyridine ligands are among the most frequently investigated compounds in photophysics and photochemistry, owing to their favorable luminescence and photoredox properties. Equally good photoluminescence performance and attractive photocatalytic behavior is now achievable with isoelectronic molybdenum(0) complexes. The zero-valent oxidation state of molybdenum is stabilized by carbonyl or isocyanide ligands, and metal-to-ligand charge transfer (MLCT) excited states analogous to those in ruthenium(II) complexes can be established. Microsecond MLCT excited-state lifetimes and photoluminescence quantum yields up to 0.2 have been achieved in solution at room temperature, and the emission wavelength has become tunable over a large range. The molybdenum(0) complexes are stronger photoreductants than ruthenium(II) polypyridines and can therefore perform more challenging chemical reductions. The triplet nature of their luminescent MLCT states allows sensitization of photon upconversion via triplet-triplet annihilation, to convert low-energy input radiation into higher-energy output fluorescence. This review summarizes the current state of the art concerning luminescent molybdenum(0) complexes and highlights their application potential. Molybdenum is roughly 140 times more abundant and far cheaper than ruthenium, hence this research is relevant in the greater context of finding more sustainable alternatives to using precious and rare transition metals in photophysics and photochemistry.     

Mechanism of isotope exchange reaction between methane and deuterium

The rate of CH₄ disappearance in a shock-heated CH₄:D₂:Ar = 9.70:9.86:80.44 mixture was monitored by coincidence absorption of the 2948 cm^?1 He-Ne laser line over the shockfront temperature range of 1900–2300K. Comparison with CH₄ pyrolysis results by means of computer simulations suggested that atom and free radical chains are responsible for the homogeneous D/H exchange reaction on CH₄. Additional simulations for the experimental conditions of previous single-pulse shock tube experiments led to the recognition of a high sensitivity of the exchange rate to trace amounts of hydrocarbon impurity and to the dissociation rate of CH₄.     

Kinetics of deuterium isotope exchange between t-butylthiol and diphenylphosphine

The rate constant k (dm³ mol^–3 s^–1)=(3.7±0.4)×10²exp[–38(kJ mol^–1)/RT] for the bimolecular reaction of H-iosotope exchange between t–C₄H₉SD and (C₆H₅)₂PH in the temperature region 283–343 K was established by means of¹HNMR. The possible mechanisms of exchange are briefly discussed.

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–C₄H₉SD (C₆H₅)₂PH 283–343 ¹H (³·^–1·^–1)=(3,7±0,4)·10² exp [–38(·^–1)/RT]. .

     

Nitrogen isotope exchange between nitric oxide and nitric acid

The rate of nitrogen isotope exchange between NO and HNO₃ has been measured as a function of nitric acid concentration of 1.5–4M·1^–1. The exchange rate law is shown to beR=k[HNO₃]²[N₂O₃] and the measured activation energy isE=67.78kJ ·M^–1 (16.2 kcal·M^–1). It is concluded that N₂O₃ participates in¹⁵N/¹⁴N exchange between NO and HNO₃ at nitric acid concentrations higher than 1.5M·1^–1.