Synthesis and characterization of mixed iodide-naphthalene complexes of lanthanides

The [LnI₂(THF)₃]₂(-C₁₀H₈) complexes were obtained by reactions of LnI₃(THF)₃ (Ln = Ce, Pr, Nd, or Gd) with lithium and excess naphthalene. The magnetic moments of these complexes correspond to the oxidation state +3 of the metal atoms. The Yb^II complex, [YbI(DME)₂]₂(-C₁₀H₈), was synthesized by the reaction of YbI₂(DME)₂ with an equimolar amount of naphthalenelithium.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2573–2574, October 1996.     

Non-equilibrium rate coefficients and isotope effect with bimolecular ion-(polar) molecule reactions in xenon

Using the Fokker-Planck version of an approximate Boltzmann equation for the ion (translational) energy distribution function f _I the departure, k, of the non-equilibrium ion-(polar) molecule reaction rate coefficient k _non from its equilibrium value k ^(eq) is calculated. k enhances considerably with an increase of the dipole moment of the reacting molecular species (locked dipole reaction model). But the k-values, e.g. for reactions of H^–(D^–) and nitromethane in xenon enhance also with increasing ratio of the concentrations of CH₃NO₂ and Xe and decrease with enhancing gas temperature T. The reaction-induced (translational) non-equilibrium effect leads to a (non-equilibrium) kinetic isotope effect depending on and T. At T=300 K the example yields k _H /k _d =1.345(=5 · 10^–4),=1.409 (=10^–5) and=1.414–k _H ^/(eq) /k _D ^(eq) (10^–6).     

Density functional and molecular orbital study of physical process of inversion of nitrogen trifluoride (NF3) molecule

The physical process of the umbrella inversion of the nitrogen trifluoride molecule has been studied invoking the formalisms of the density functional theory, the frontier orbital theory, and the molecular orbital theory. An intuitive structure and dynamics of evolution of the transition state for the event of inversion is suggested. The physical process of dynamic evolution of the molecular conformations between the equilibrium (C_3v) shape and the planar (D_3h) transition state has been followed by a number of molecular orbital and density functional parameters like the total energy, the eigenvalues of the frontier orbitals, the highest occupied molecular orbital and lowest unoccupied molecular orbital, the (HOMO–LUMO) gap, the global hardness and softness, and the chemical potential. The molecular conformations are generated by deforming the ∠FNF angle through steps of 2° from its equilibrium value, and the cycle is continued till the planar transition state is reached, and the geometry of each conformation is optimized with respect to the length of the N? F bond. The geometry optimization demonstrates that the structural evolution entails an associated slow decrease in the length of the N? F bond. The dipole moment at the equilibrium form is small and that at the transition state is zero and shows a strange behavior with the evolution of conformations. As the molecular structure begins to distort from its equilibrium shape by opening of the ∠FNF angle, the dipole moment starts increasing very sharply, and the trend continues very near to the transition state but abruptly vanishes at the transition state. A rationale of the strange variation of dipole moment as a function of evolution of conformations could be obtained in terms of quantum mechanical hybridization of the lone pair on the N atom. The pattern of charge density reorganization as a function of geometry evolution is a continuous depletion of charge from the F center and piling up of charge on the N center. The continuous shortening of bond length and the pattern of variation of net charge densities on atomic sites with evolution of molecular conformations predicts that the bond moment would decrease continuously. The quantum mechanical hybridization of the lone pair of the central N atom shows that the percentage of s character of the lone‐pair hybrid on the N atom decreases at a very accelerated rate, and the lone pair at the transition state is accommodated in a pure p orbital. The result of the continued destruction of asymmetry of charge distribution in the lone pair on the central N atom due to the elimination of contribution of the s orbital with evolution of molecular conformations is the sharp decrease in lone‐pair moment. The decrease in bond moment is overcompensated by the sharp fall of its offsetting component, the lone‐pair moment, resulting in a net gain in dipole moment with the evolution of molecular geometry. Since the offsetting component decreases very sharply, the net effect is a sharp rise of dipole moment with the evolution of molecular conformations just before the transition state. The lone‐pair moment is zero by virtue of the symmetry of the pure p orbital, the lone pair of the central atom in the transition state, and the sum of the bond moments is zero by symmetry of the geometry. The barrier height is quite high at ～65.45 kcal/mol, which is close to values computed through more sophisticated methods. It is argued that an earlier suggestion regarding the development of high barrier value of NF₃ system seems to be misleading and confronting with the conclusions of the density functional theory. An analysis and a comparative study of the physical components of the one‐ and two‐center energy terms reveals that the pattern of the charge density reorganization has the principal role in deciding the origin and the magnitude of barrier of inversion of the molecule and the barrier originates not from a particular energetic effect localized in a particular region of the molecule, rather the barrier originates from a subtle interplay of one‐ and two‐center components of the total energy. The decomposed energy components show that the F?F nonbonded interaction and N? F bonded interaction favor the formation of transition state, while the one‐center energy terms prohibit the formation of the transition state. The barrier principally develops from the one‐center energy components. The profile of the HOMO is isomorphic and that of the LUMO is homomorphic with the potential energy curve for the physical process of the event of umbrella inversion of the molecule. The variation of the HOMO–LUMO gap, ?ε, the global hardness, η, and the softness, S, as a function of the reaction coordinates of angular deformation of NF₃ molecule are quite consistent with the predictions of the molecular orbital and the density functional theories in connection with the deformation of molecular geometry. The profiles of ?ε, η, and S, as a function of reaction coordinates, mimic the potential energy curve of the molecule. The eigenvalues of the frontier orbitals, and the ?ε, η, S parameters are found to be equally effective theoretical parameters, like the total energy, to monitor the physical process of the inversion of pyramidal molecules. The nature of the variation of the global hardness parameter between the equilibrium shape and the transition state form for the inversion is in accordance with the principle of maximum hardness (PMH). © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2002     

烯烃气相色谱保留指数的QSRR研究

通过对184个烯烃类化合物在不同固定相不同柱温下的617个样本的气相色谱保留指数值(RI)与其部分参数:拓扑指数(mQ)、偶极矩(DPL)、固定液极性值(CP)及柱温(T)建立定量-色谱保留相关(QSRR)模型.分别利用多元线性回归(MLR)、偏最小二乘回归(PLSR)、人工神经网络(ANN)建模,同时采用内部及外部双重验证的办法对所得模型稳定性能进行深入分析和检验,建模计算值、留一法(LOO)交互检验(CV)预测值和外部样本的复相关系数Rcum,QLOO和Rext分别为0.999 2,0.998 4和0.999 2(MLR);0.999 0,0.998 0和0.999 1(PLSR);0.999 4,0.998 7和0.999 2(ANN).结果表明:所建定量结构保留关系(QSRR)模型具有良好的稳定性和预测能力,较好地揭示了烯烃类化合物在不同固定相不同柱温上气相色谱保留指数的变化规律.     

The orientational state of uniaxially stretched PMMA

Uniaxially stretched samples of PMMA were investigated by Brillouin Spectroscopy (BS). From the velocity of hypersound we could determine most of the elastic constants. Using a recently developed analysis [1] it is demonstrated that the properties of this polymer can be well described by the aggregate model. This result offers the possibility of mapping the mechanical properties by birefringence measurements. The dependence of the fourth momentP ₄ on the second momentP ₂ is identical with that determined for PC [2] and follows, in the measured range, that of an affine orientational state. Nevertheless, the dependence on the stretching ratio differs for different molecular weights. Thus the partition of the deformation into an orientational and an elongational contribution, as has been proposed [3], seems to be well founded.The partition depends on the stretching conditions.     

Electronic transition moment with spin‐orbit coupling of the molecular ion KRb+

By using the electronic wave functions obtained from an ab initio calculation, including the spin‐orbit coupling, the electronic transition moments have been investigated for two bound states of symmetry Ω = 1/2 and Ω = 3/2 of the molecular ion KRb⁺. Based on a canonical functions approach for the determination of the vibrational wave functions, the matrix elements have been calculated for the bound states considered for v = 0, 10, 20 with v′‐ v = 0, 1, 2, …, 6; by using the same canonical approach, the eigenvalues and abscissas of the corresponding turning points (r_min and r_max) have been investigated for these states that obtained from a theoretical ab initio calculation up to v = 105. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Thermal,Magnetic, FTIR and XRD Study of New Co(II) and Ni(II) Theophyllinato Complexes with Benzylamine or Ethanolamine

Four new theophyllinato (th) complexes of Co(II) and Ni(II) were synthesized containing ethanolamine (2-aminoethanol, ea) or benzylamine (ba). Comprehensive FTIR spectroscopic, powder XRD, magnetic and thermal studies on these mixed ligand complexes have been carried out to get structural information. The almost identical FTIR spectra and XRD patterns of Co and Ni compounds with same composition have indicated that Co(th)2(ba)2·2H2O (1) and Ni(th)2(ba)2·2H2O (2) or Co(th)2(ea)2 (3) and Ni(th)2(ea)2 (4) have very similar structure pair wise. The infrared spectra and X-ray diffraction patterns of thermally dehydrated 1 and 2containing benzylamine have allowed only to suggest that the co-ordination number around the metal centres is four, while the high thermal stability of complexes 3and 4have indicated that they contain two of bidentate ethanolamine molecules in octahedral co-ordination. A big difference observed between the magnetic moments of Co compounds 1and 3have proven that the inner co-ordination sphere of complexes with benzylamine (1and 2) is tetrahedral, whilst that with ethanolamine (3and 4) is basically octahedral, independent of the cation centres (Co or Ni). This revised version was published online in July 2006 with corrections to the Cover Date.     

OBSERVATION OF ENERGY DISSIPATION PEAK IN POLYSTYRENE MELT ABOVE Tg

In this paper two different kinds of dynamic mechanical techniques(inversed torsion pendulum and energy dissipation apparatus)were used to study the dynamic behavior of atactic monodisperse polystyrene above glass transition. The plots of energy dissipation versus temperature were presented for two atactic polystyrene samples.An apparent energy dissipation peak occurred above T_g in each plot measured by the inversed torsion pendulum,and simultaneously the sample was found to flow assuredly at the moment.To exclude the influence of the flow and demonstrate there was a peak indeed above T_g,the energy dissipation apparatus was used,in which the samples were put into a cup.An obvious peak appeared, and it was in agreement with the peak observed by the inversed torsion pendulum.On basis of the results measured by the two kinds of apparatus,a conclusion is drawn that a peak occurrs above T_g,which gives a manifestation for the existence of the liquid-liquid transition.     

Dielectric Relaxation of Aqueous Trimethylamineoxide Solutions

Dielectric relaxation was examined for aqueous trimethylamineoxide (TMAO) solutions over a wide concentration (c) range. The dielectric relaxation of TMAO was described by a Debye-type function with a relaxation time of about 3 × 10^–11 s, with the strength proportional to c. The number of water molecules tightly hydrated to unprotonated TMAO was estimated to be two. Ab initio calculations predict the magnitudes of the dipoles for individual TMAO and TMAO tightly hydrated by two water molecules, to be 4.9 and 4.2 D, respectively. When the amount of HBr added was increased, dielectric spectra were described by two modes with relaxation times, about 3 × 10^–11 and the about 8 × 10^–10. The fast relaxation was assigned to the rotational mode of unprotonated TMAO tightly hydrated by two water molecules, and the slow mode to the rotational mode of dimers formed between a protonated and unprotonated TMAO due to hydrogen bonding.     

1，4－二羟基蒽醌与稀土离子的配位聚合物制备和性质

制备了三价稀土离子Ｌｎ￣（３＋）（Ｌｎ＝Ｌａ，Ｃｅ，Ｐｒ，Ｎｂ，Ｓｍ，Ｅｕ，Ｇｄ，Ｔｂ，Ｄｙ和Ｙ）与１，４－二羟基蒽醌的配位聚合物。考察了这些配合物的热稳定性、磁性、导电性和红外光谱。