不同类型协萃剂与PMBP协同萃取铀和稀土元素的研究及其应用

PMBP(1-苯基3-甲基-4-苯甲酰基吡唑酮-5)是萃取稀土、钛、锆、铀和钍等金属离子的优良萃取剂,国内外已有报导。为使PMBP能直接从含有易水解的铌、钽、钛和锆等溶液中萃取分离出稀土、铀和钍,我们曾研究在酒石酸等络合剂存在下用PMBP萃取铌、钽、钛、锆、钨、钼、铁、铀和稀土     

电热板消解与密闭罐消解对土壤中49种矿质元素ICP-MS法检测的影响

分别采用电热板消解和密闭罐消解进行土壤样品前处理,根据加标回收实验和国家标准物质(GBW07403)验证实验,结果显示,使用电热板消解-ICP-MS法分析土壤中铍、锂、钒、铬、锰、钴、镍、铜、锌、镓、锗、砷、硒、锶、锆、铌、钼、钯、银、镉、铟、锡、钡、钽、钨、铼、铊、铅、铀可获得较好的准确性和精密度,而密闭消解罐消解-ICP-MS法则更适于土壤中钪、钇、镧、铈、镨、钕、钷、钐、铕、钆、铽、钬、铒、铥、镱、镥、铱、铂、金、钍的检测,各元素的检出限为0.311～94.36 ng/L,相对标准偏差为0.55%～5.03%.表明不同消解方法适于土壤中不同矿质元素的检测.应用所建立的方法,对新疆地区2个葡萄园的土壤样品中49种矿质元素进行了分析.     

铬族金属氢化物中M-H 键键能的从头计算

铬族金属氢化物M-H 键的均裂是在自由基环化反应中的关键过程, 它直接影响反应的催化效率和选择性. 使用理论方法精确预测铬族金属氢化物M-H 键键能不仅有助于了解这类催化剂的结构与性能关系, 而且对进一步发展高效的自由基环化反应催化剂具有重要的指导意义. 为达此目的, 我们使用不同的理论方法计算14 个有可靠实验值的铬族金属氢化物M-H键键能, 通过比较发现B3P86/lanl2dz+p 方法表现最佳(计算精度为1.6 kcal/mol). 之后我们运用这个理论方法系统地研究了铬族金属氢化物M-H 键键能的构效关系. 就周期性规律而言, 在铬族金属氢化物中, 金属对于M-H 键能的影响大于配体的影响. M-H 键键裂解能的大小顺序为:铬氢络合物<钼氢络合物<钨氢络合物.此外, 我们发现含双茂配体的铬氢化合物中Cr-H 键键能与伸缩振动频率呈良好的线性相关. 有趣的是, 在含双茂配体的铬族金属氢化物中, M-H 键能与键长呈现出良好的正线性相关性. 即“键长越小, 键能越弱”. 通过自然成键轨道分析, 这可能是因为杂化缺失造成原子半径收缩程度比成键变弱引起的扩张程度大.     

过渡金属与非金属之间dπ-dπ键合作用的趋向

本文对金属和非会属原子之间形成dπ-dπ键的趋向根据其间的键能、电离势、重迭积分以及金属-非金属化合物中羰基的红外振动谱带的频率加以判断,并对金属锰、铁、钴、镍、铬、钼和钨与非金属硅、磷和硫作了探讨。     

氮配位过渡金属配合物在硅氢加成反应中的应用研究

氮配位过渡金属配合物在近十几年来得到迅速的发展。 通过设计不同的含氮配体与不同过渡金属进行配位形成的氮配位过渡金属配合物,在硅氢加成反应中有很大应用研究价值。本文综述了氮配位铑、铁、铼、钴、锌等过渡金属配合物在酮或者烯烃的硅氢加成反应中的新进展。二 NFDA1 唑啉及二氢吡咯等含氮配体的优化设计必将大大促进含氮铁、铼、钴配合物在酮或者亚胺的硅氢加成反应中的应用。     

光度络合滴定(Ⅰ)——微量铁(Ⅲ)的滴定

本文提出在pH=0.8和波长540nm,以二甲酚橙作指示剂,用铋盐作回滴剂光度滴定3-100微克铁。本法选择性很高,大量铝、钛(Ⅳ)、铬(Ⅲ)、铜、铅、锌、镉、锰、镧、铈(Ⅲ)、钨(Ⅶ)、钼(Ⅵ)、钒(Ⅴ)、砷(Ⅲ)、镁、钙、银以及适量的汞、钍、锑(Ⅲ)、镍、氟离子、氯离子和磷酸根等不干扰,应用适当的隐蔽剂,400倍于铁的铝以及适量的钍、锆和锡也不干扰。应用本法,不必分离便可滴定石英石、石英砂、铝合金、纯铝以及水样中的铁。     

过渡金属催化硼-氢键活化合成含硼-杂原子键邻碳硼烷衍生物的研究进展

十二顶点碳硼烷是一类含有碳、氢及硼原子的簇合物,具有特殊的热稳定性和化学稳定性,在医药、材料、能源、配位化学及金属有机化学中都得到广泛的应用.近年来,过渡金属催化的碳硼烷直接硼-氢键活化发展迅速,为硼顶点选择性官能团化提供了一系列新的高效路径.总结了利用过渡金属催化硼-氢键活化策略来实现邻碳硼烷硼-硼、硼-氮、硼-氧、硼-硫及硼-卤键构建的研究进展,同时对部分反应机理进行了讨论,并就该研究领域所面临的挑战和发展前景进行了展望.     

复杂矿样中锡钨的联合测定

砷、锑、铜、氟等对锡的碘量法和钨的硫氰酸盐比色法均有干扰,当分析上述元素含量较高的矿样时,需要预先分离。为此进行加硫酸铵焙烧除砷的试验,並用含磷酸钠或EDTA而适当提高碱度的浸出液浸出以减少铁、钙、镁对锡、钨的吸附和有利于锡转化为锡酸钠于溶液中。试样经焙烧后砷、锑、氟等被驱除,再碱熔水浸则使铁、钙、镁、钛、锰、锆、钡、银、金、铋、镉、钴、汞、镍、钍、铌、钽和稀土元素,以及绝大部份铜进入沉淀,只有铝、锌、钼、铬     

必需微量元素与儿童健康研究进展

就14种必需微量元素对儿童健康的利弊进行了综述，其中包括：铁、锌、锰、碘、铜和钼，铬、镍和钴，硒和锡，氟和钒，硅。必需微量元素与儿童生长发育息息相关，但过量则会对儿童产生不利影响。     

高能偏振能量色散X射线荧光光谱法分析古陶瓷

以国家地质标准样品制作工作曲线,用粉末压片法制样,高能偏振能量色散X射线荧光光谱法测定古陶瓷中包括15种稀土元素在内的56种元素,通过对6个陶瓷胎标准样品分析,结果表明:钪、钒、锰、铬、锌、镓、锗、铷、锶、钇、锆、铌、镉、锡、铯、钡、镧、铈、镨、钕、钆、钬、铒、铥、镱、镥、钍、铀等28种痕量元素测定值均在参考值的不确定度3～4倍范围,其他痕量元素如镍、铜、钼、锑、钐、铕、铽、铪、铅、铋等10种元素合格率为50%～83%。钠、镁、钾、钙、铁的氧化物和钛等6个项目均在允许误差范围内。氯、硫、磷的合格率均为66.6%。二氧化硅和三氧化二铝测定值和波长色散X射线荧光光谱熔融法测定结果相比,绝对误差分别在0.95%～4.46%和0.60%～1.66%之间。     

Spin crossover in a four-coordinate iron(II) complex

The four-coordinate iron(II) phosphoraniminato complex PhB(MesIm)(3)Fe-N═PPh(3) undergoes an S = 0 to S = 2 spin transition with T(C) = 81 K, as determined by variable-temperature magnetic measurements and Mo?ssbauer spectroscopy. Variable-temperature single-crystal X-ray diffraction revealed that the S = 0 to S = 2 transition is associated with an increase in the Fe-C and Fe-N bond distances and a decrease in the N-P bond distance. These structural changes have been interpreted in terms of electronic structure theory.     

Organometallic reactivity: the role of metal-ligand bond energies from a computational perspective

The association and dissociation of ligands plays a vital role in determining the reactivity of organometallic catalysts. Computational studies with density functional theory often fail to reproduce experimental metal-ligand bond energies, but recently functionals which better capture dispersion effects have been developed. Here we explore their application and discuss future challenges for computational studies of organometallic catalysis.     

Bond energies and formation enthalpies of mono- and polyradicals in nitroalkanes 1. Nitromethanes

The enthalpies of formation of nitromethane derivatives were obtained on the basis of experimental and literature data. The procedure for the calculation of the bond dissociation energies in nitromethanes from the atomization enthalpies and energies of nonvalent interactions of nitro groups was proposed. The calculated values were compared with the data on the thermal decomposition kinetics. The atomization enthalpies and energies of nonvalent interactions of nitro groups were also used for the calculation of the bond dissociation energies in radicals.     

Bond energies and the enthalpies of formation of mono- and polyradicals in nitroalkanes 2. Nitro derivatives of ethane and propane

Based on the experimental results and the published data, the enthalpies of formation of ethane and propane nitro derivatives were obtained for both the standard state and gas phase. The bond dissociation energies of the ethane and propane nitro derivatives were calculated using the enthalpies of atomization and the energies of nonvalent interactions of nitro groups. The calculated values were compared with the kinetic data on thermal decomposition. The bond dissociation energies in radicals of the ethane and propane nitro derivatives were also calculated using the enthalpies of atomization and the energies of nonvalent interactions of nitro groups. Regularities of changes in the bond dissociation energies of the ethane and propane nitro derivatives and their radicals were established.     

Density functionals for inorganometallic and organometallic chemistry

We present a database of 21 bond dissociation energies for breaking metal-ligand bonds. The molecules in the metal-ligand bond energy database are AgH, CoH, CoO+, CoOH+, CrCH3+, CuOH2+, FeH, Fe(CO)5, FeO, FeS, LiCl, LiO, MgO, MnCH3NiCH2+, Ni(CO)4, RhC, VCO+, VO, and VS. We have also created databases of metal-ligand bond lengths and atomic ionization potentials. The molecules used for bond lengths are AgH, BeO, CoH, CoO+, FeH, FeO, FeS, LiCl, LiO, MgO, RhC, VO, and VS and the ionization potentials are for the following atoms: C, Co, Cr, Cu, Ni, O, and V. The data were chosen based on their diversity and expected reliability, and they are used along with three previously developed databases (transition metal dimer bond energies and bond lengths and main-group molecular atomization energies) for assessing the accuracy of several kinds of density functionals. In particular, we report tests for 42 previously defined functionals: 2 local spin density approximation (LSDA) functionals, 14 generalized gradient approximation (GGA) methods, 13 hybrid GGA methods, 7 meta GGA methods, and 8 hybrid meta GGA methods. In addition to these functionals, we also examine the effectiveness of scaling the correlation energy by testing 13 functionals with scaled or no gradient-corrected correlation energy, and we find that functionals of this kind are more accurate for metal-metal and metal-ligand bonds than any of the functionals already in the literature. We also present a readjusted GGA and a hybrid GGA with parameters adjusted for metals. When we consider these 57 functionals for metal-ligand and metal-metal bond energies simultaneously with main-group atomization energies, atomic ionization potentials, and bond lengths we find that the most accurate functional is G96LYP, followed closely by MPWLYP1M (new in this article), XLYP, BLYP, and MOHLYP (also new in this article). Four of these five functionals have no Hartree-Fock exchange, and the other has only 5%. As a byproduct of this work we introduce a convenient diagnostic, called the B1 diagnostic, for ascertaining the multireference character in a bond.     

Are cyclopentadienyl complexes more stable than their pyrrolyl analogues?

Metal-η⁵-cyclopentadienyl (M-Cp) and metal-η⁵-pyrrolyl (M-pyr) bond dissociation enthalpies in group 4 complexes were determined from DFT/B3LYP calculations with a VTZP basis set. Thermochemical cycles involving calculated enthalpies of ligand exchange reactions and experimental values of ligand electron affinities and M-Cl bond dissociation enthalpies were applied to [M(η⁵-X)Cl₃] piano stool complexes (M = Ti, Zr, Hf; X = pyr, Cp), allowing a comparative study of those metal-ligand bond strengths. The results indicate that both ligands establish weaker bonds with Ti than with the heavier elements, Zr and Hf. Very similar bond dissociation enthalpies were obtained for pyrrolyl and cyclopentadienyl (within 1 kcal mol⁻¹), suggesting that the well known difference in reactivity between those families of complexes should derive from kinetic rather than thermodynamic causes.     

N—O键解离焓的密度泛函理论研究

在高精度计算方法G3和G3B3的基础上,比较了密度泛函理论(DFT)十几种方法对N—O键解离焓(BDE)相对于实验值的计算精度,发现用B3P86方法计算15种化合物N—O键的BDE,均方根误差最小,仅为6.36kJ·mol-1,计算值与实验值的线性相关系数为0.991.在此基础上,用该方法分别计算了非芳香化合物及芳香化合物的N—O键BDE.通过自然键轨道分析,发现部分N—O键的BDE与N—O键的键长、原子电荷密度及键级之间存在定量关系.此外,在B3P86方法的基础上预测了几种典型的杂环芳香化合物N—O键BDE值.     

Thermochemistry and bond dissociation energies of ketones

Ketones are a major class of organic chemicals and solvents, which contribute to hydrocarbon sources in the atmosphere, and are important intermediates in the oxidation and combustion of hydrocarbons and biofuels. Their stability, thermochemical properties, and chemical kinetics are important to understanding their reaction paths and their role as intermediates in combustion processes and in atmospheric chemistry. In this study, enthalpies (ΔH°(f 298)), entropies (S°(T)), heat capacities (C(p)°(T)), and internal rotor potentials are reported for 2-butanone, 3-pentanone, 2-pentanone, 3-methyl-2-butanone, and 2-methyl-3-pentanone, and their radicals corresponding to loss of hydrogen atoms. A detailed evaluation of the carbon-hydrogen bond dissociation energies (C-H BDEs) is also performed for the parent ketones for the first time. Standard enthalpies of formation and bond energies are calculated at the B3LYP/6-31G(d,p), B3LYP/6-311G(2d,2p), CBS-QB3, and G3MP2B3 levels of theory using isodesmic reactions to minimize calculation errors. Structures, moments of inertia, vibrational frequencies, and internal rotor potentials are calculated at the B3LYP/6-31G(d,p) density functional level and are used to determine the entropies and heat capacities. The recommended ideal gas-phase ΔH°(f 298), from the average of the CBS-QB3 and G3MP2B3 levels of theory, as well as the calculated values for entropy and heat capacity are shown to compare well with the available experimental data for the parent ketones. Bond energies for primary, secondary, and tertiary radicals are determined; here, we find the C-H BDEs on carbons in the α position to the ketone group decrease significantly with increasing substitution on these α carbons. Group additivity and hydrogen-bond increment values for these ketone radicals are also determined.     

Computational methods in organic chemistry. 3. Correction of computed enthalpies for multiple conformations

The first explicitly calculated G3(MP2) enthalpies and Gibbs energies of formation for undecane through eicosane are presented. These values, when corrected for the presence of multiple conformations, are found to be within 4 and often 2 kJ/mol of the experimental values. The derivation of the corrections for the enthalpies, which differ from those of the Gibbs energies published earlier, is presented and also applied to the first 10 homologues of the alkene, alkyne, alcohol, and thiol families.     

The degree of fragmentation of metallocomplexes with cleavage of the metal-ligand bond

A new method for estimating the degree of fragmentation of metallocomplexes under electron impact with cleavage of the metal-ligand bond was suggested. The method is based on mass spectrometric data. Using a representative selection of 67 organometallic compounds of different classes such as metal carbonyls, metallocenes, and cymantrene and bensenechrometricarbonyl derivatives, a correlation between the degree of fragmentation and the dissociation energy of metal-ligand bonds was developed. The correlation is evidence that the parameter can be used for quantitative estimation of the reactivity of metallocomplexes in the gas phase. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1374–1377, July, 1998.