Experimental and four‐component relativistic DFT studies of tungsten carbonyl complexes

We present a theoretical and experimental study of the structure and nuclear magnetic resonance (NMR) parameters of the pentacarbonyltungsten complexes of η¹‐2‐(trimethylstannyl)‐4,5‐dimethylphosphinine, η²‐norbornene, and imidazolidine‐2‐thione. The three complexes have a pseudo‐octahedral molecular structure with the six ligands bonded to the tungsten atom. The η¹‐2‐(trimethylstannyl)‐4,5‐dimethylphosphinine‐pentacarbonyl tungsten complex was synthesized for the first time. For all compounds, we present four‐component relativistic calculations of the NMR parameters at the Dirac–Kohn–Sham density functional level of theory using hybrid functionals. These large‐scale relativistic calculations of NMR chemical shifts and spin–spin coupling constants were compared with available experimental data, either taken from the literature or measured in this work. The inclusion of solvent effects modeled using a conductor‐like screening model was found to improve agreement between the calculated and experimental NMR parameters, and our best estimates for the NMR parameters are generally in good agreement with available experimental results. The present work demonstrates that four‐component relativistic theory has reached a level of maturity that makes it a convenient and accurate tool for modeling and understanding chemical shifts and indirect spin–spin coupling constants of organometallic compounds containing heavy elements, for which conventional non‐relativistic theory breaks down. Copyright © 2015 John Wiley & Sons, Ltd.     

取代基效应对脂肪醇13C NMR化学位移的影响

用原子电负性、静电作用、极化度作为基本参数,并结合表征原子空间连接方式的立体效应参数,对醇分子中不同环境碳原子的化学位移进行关联, 将120个模型化合物(91个脂肪一元醇, 29个二元醇)中747个碳原子相关参数值和化学位移值带入模型中得到如下估算方程:  δ_C=42.947 9 + 63.064 0Q_i-3.628 6F+5.121 3Σα_x-6.584 8Q_iΣα_x -4.842 7N^α_H-0.585 5N^γ_H-4.104 6N^γ_OH (R=0.998 1 R²=0.996 1 S=1.14 F=27 125.2 n=747)  方程中各参数物理意义比较明确. 通过用“留一法”(LOO)检验(R_cv=0.998 0,R²_cv = 0.996 0,S_cv=1.16)及对样本外5个化合物69个碳原子化学位移的预测值和实验值比较, 结果表明模型方程具有很好的稳定性和预测精度, 该模型的提出为以后计算更加复杂化合物的¹³C NMR化学位移奠定了良好的基础.     

Approximations in the theoretical interpretation of Mössbauer spectra

An account is given how semiempirical molecular orbital calculations and accurate relativistic atomic calculations can be utilized to understand Mössbauer spectra of the heavy main-group elements Sn, Sb, Te and I. The various approximations are described and it is shown in which way experimental and semiempirical theoretical information can be combined consistently to gain insight into the electronic structure of the respective compounds. A set of qualitative correlations between calculated valence orbital occupations, effective charges, coordination numbers and measured isomer shifts is derived and the limited applicability of phenomonological models is elucidated.     

系列Mo-Cu(Ag,Au)-Se簇合物的95Mo和31P NMR研究

报道了含硬币金属和四硒代钼酸盐的异金属硒簇合物的⁹⁵Mo NMR研究结果和含膦配体Mo(W)-Cu(Ag,Au)-Se配合物的³¹P NMR谱学性能。发现不同硬币金属对⁹⁵Mo核的化学屏蔽效应顺序为Au > Cu > Ag;对系列Mo-Cu-Se化合物的⁹⁵Mo NMR研究结果表明:⁹⁵Mo NMR的化学位移和线宽不仅与配位的Cu原子数目有关,而且对结构的变化特别敏感;[MoSe₄]^2-离子的相对四个方向被Cu⁺配位后,其Mo核的屏蔽基本饱和;外围配体对⁹⁵Mo NMR数据影响甚微。同时还用动态⁹⁵Mo NMR谱技术跟踪配体的取代反应和从MoCu₄到MoCu₁₀核的簇骼转变过程。此外,还讨论了这些化合物在不同构型之间,同一构型不同金属中心和不同配体基团的³¹P NMR化学位移的变化特征。     

Atomic C 6 dispersion coefficients: a four-component relativistic Kohn–Sham study

We present C ₆ homo- and heteroatomic dispersion coefficients for all closed-shell atoms of the periodic table based on dipole–dipole polarizabilities at imaginary frequencies calculated using our recent extension of the complex polarization propagator approach to the four-component relativistic Kohn–Sham approach. Lack of proper reference data bars definite conclusions as to which density functional shows the overall best performance, and we therefore call for state-of-the-art wave function-based correlated calculations of dispersion coefficients. Scalar relativistic effects are significant already for elements as light as zinc, whereas spin–orbit effects must be taken into account only for very heavy elements.     

原小檗属类生物碱13C核磁共振化学位移的模拟

将表征分子局部化学微环境的原子电性作用矢量(AEIV)和原子所处状态的原子杂化状态指数(AHSI)用于原小檗属类生物碱¹³C核磁共振(NMR)波谱模拟中,所得5参数回归模型的r, q, RMSEE和RMSCV分别为0.982 9, 0.982 1, 7.732 9和7.884 3. 采用留分法(LMO)和交叉测试(cross test, CT)相结合的方式对模型稳定性和预测能力的检验结果较为满意,LMO及CT对样本原子化学位移预测值与实验值的相关系数rpred分别为0.982 9, 0.986 5和0.982 1. 进一步采用该模型对¹³C NMR未知的4个小檗碱类化合物共计58个等价共振碳原子进行预测,所得结果与谱学模拟软件gNMR计算值较为接近.     

Characterization of silicon sites in monoclinic zeolite ZSM-5 using 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) and molecular modelling

An attempt has been made to correlate the experimentally observed 29Si MAS NMR chemical shifts of monoclinic phase of highly siliceous ZSM-5 with their electronic properties. In order to incorporate the influence of next neighbor atoms on the 29Si chemical shielding of central SiO4, a pentameric cluster model (H12Si5O16) has been chosen. Each of the 24 crystallographically distinct Si sites, of ZSM-5 framework has been modelled by such cluster models. Based on semi-empirical quantum chemical calculations, a multiple linear regression analysis of the various electronic properties with the 29Si chemical shifts has been attempted. The relative difference in 29Si chemical shifts for the Si sites in ZSM-5 is reasonably accounted, although quantitative prediction may require non-empirical quantum chemical calculations.     

N‐shell ionization cross sections by proton impact in the BEA

The N‐subshell ionizations cross sections of heavy elements by proton impact have been calculated in the binary‐encounter approximation. The momentum distribution of target electrons is taken into account by the use of the nonrelativistic and relativistic hydrogenic models and the Hartree–Fock–Roothaan and the relativistic Hartree–Fock–Roothaan methods. The obtained subshell ionization cross sections are compared with the experimental data and other theoretical calculations. The electronic relativistic effect and the wave‐function effect on N‐shell ionization cross sections are discussed.     

Calculations of dynamic multipolar polarizabilities of the Cd clock transition levels

The pursuit of a systematic frequency uncertainty beyond 10^-18 clock has triggered a multitude of investigations on the multipolar and higher-order lattice light shifts. The Cd atom has been proposed as a new candidate for the development of a lattice clock because of its smaller blackbody radiation shift at room temperature. Here, we apply an improved combined method of the Dirac-Fock plus core polarization and relativistic configuration interaction methods to calculate the dynamic multipolar polarizabilities of the Cd clock states. The effects of the high-order core-polarization potentials on the energies, reduced matrix elements, and multipolar polarizabilities have been evaluated systematically. The detailed comparison with available literature demonstrates that taking into account of the high-order core-polarization potentials is a simple and effective approach to improve the results of atomic properties for heavy atoms.     

2(1H)喹啉酮化合物及其开环衍生物的13C NMR研究

本文报道了16种2(1H)喹啉酮及其开环衍生物的碳谱研究,归属了取代喹啉酮母核骨架及侧链上每个碳原子的化学位移,并就卤素取代对母核骨架碳的化学位移影响规律进行了探讨.文中所有化合物的核磁数据迄今未见文献报道.     

新型萘酰亚胺衍生物的13C NMR研究

报道了四种新的萘酰亚胺衍生物的¹³C NMR谱. 应用¹H、¹³C、DEPT、HMQC、HMBC 等谱确定了这四种化合物的分子结构,并对全部谱峰进行了归属,探讨了分子结构对¹³C NMR化学位移的影响.     

双环磷酸酯类化合物NMR结构效应研究

用现有理论说明不了双环磷酸酯类化合物³¹P NMR化学位移的变化。本文在我们提出的核外电子云球对称效应原理基础上,用量子化学和分子力学计算的参数,表达了这类化合物³¹P化学位移变化的规律,同时还研究了它们的¹³C NMR化学位移和偶合常数的取代基效应。     

Electric moments of carbon dichalcogenides

The dipole and quadrupole moments and parallel dipole polarizabilities of the carbon dichalcogenides XCY (X, Y = O, S, Se and Te) are evaluated at the level of the CCSD(T) approximation with HyPolX basis sets. The relativistic effects are taken into account by using the scalar version of the two-component Douglas–Kroll method. The reported calculations provide a systematic study of the electron correlation and relativistic effects in the investigated series of carbon dichalcogenides and their results agree well with best-known experimental data. Particular attention has been given to the OCS molecule and the present calculations combined with recent studies by other authors may help to resolve the ambiguities concerning its quadrupole moment. Changes of dipole and quadrupole moments in the studied series of molecules are interpreted in terms of the electronegativities of the chalcogene atoms and their changes due to relativistic effects. The latter have been found to lead to significant changes in the calculated quadrupole moments of the heavy members of the series of molecules. Study of the basis set dependence of the calculated data shows that both the earlier PolX and the recently developed HyPolX basis sets are suitable for calculations of reliable values of the low-multipole moments and dipole polarizabilities of molecules containing heavy elements.     

On the significant relativistic heavy atom effect on 13C NMR chemical shifts of β- and γ-carbons in seleno- and telluroketones

Unexpectedly large ‘Heavy Atom on Light Atom’ (HALA) effects have been found in ¹³C NMR (Nuclear Magnetic Resonance) chemical shifts of β- and γ-carbons of seleno- and telluroketones established by means of the high-accuracy calculations of ¹³C NMR chemical shifts in three representative real-life compounds, 2,2,5,5-tetramethyl-3-cyclopentene-1-selone, selenofenchone and 1,1,3,3-tetramethyl-1,3-dihydro-2H-indene-2-tellurone. The proposed computational scheme consists of the combination of accurately correlated coupled-cluster singles and doubles model approach for the non-relativistic calculations of shielding constants taking into account the solvent, vibrational and relativistic corrections, the latter obtained within the 4-component fully relativistic gauge-including atomic orbitals KT2 approach resulting in a very good agreement of the performed calculations with the experiment. The stereochemical dependence of the ‘long-range’ γ-HALA effect on the dihedral angle has been established in the model seleno- and telluroketones providing the largest shielding effect in the orthogonal orientation of the X=C_α–C_β–C_γ (X=Se, Te) moiety.     

An accurate determination of the K‐shell X‐ray fluorescence yield of silicon

A measurement of the K‐shell fluorescence yield of silicon is undertaken in which identified sources of systematic errors in previous measurements are reduced or eliminated. This enables a stringent test of the only two sets of theoretical predictions available for atomic numbers less than 18. Our result ω_K = 0.0495 ± 0.0015 is very slightly lower than the non‐relativistic Hartree‐Fock‐Slater (HFS) prediction of 0.0514. This stringent test of the HFS predictions helps to refine the fundamental parameter database of the X‐ray fluorescence analysis technique, whose importance for light elements is increasing. Our work indicates the need for new theoretical calculations of K‐shell fluorescence yields for these elements. Copyright © 2012 John Wiley & Sons, Ltd.     

含铀化合物UAl3和USn3电子结构的密度泛函研究

用第一性原理的全势能LMTO密度泛函能带计算方法研究了具有简单立方Cu₃Au 结构的含U化 合物UX₃(X=Al, Sn)的电子结构.对于重原子U的相对论效应，除了用标量相对论 加以修正 外，还加入了自旋-轨道耦合的修正.研究结果定性地说明了由于不同的交换关联电子势场的 作用，在这两种结构相同的含U合金中，U的5f电子态具有完全不同的性质，即在UAl_{3< /sub>和US n3中U的5f态分别表现为巡游扩展态和局域态行为，通过St 关键词： 铀化合物 电子态 密度泛函理论 自旋-轨道耦合}     

Tautomeric populations of the charged species of 1,12‐diamino‐3,6,9‐triazadodecane (SpmTrien) studied with computer simulations and cluster expansions

Correct net charge and protonation pattern in the polyamine backbone is one of the major factors that define the interactions of this class of compounds. 1,12‐diamino‐3,6,9‐triazadodecane (SpmTrien) is a isosteric charge deficient analogue of naturally occurring spermine (Spm) with different biological features. The tautomeric populations of each SpmTrien charge state were estimated with computer simulations, molecular dynamics (MD) and quantum mechanical calculations, and cluster expansions separately. In the computer simulations, tautomeric populations of each charge state were obtained by constrained least‐squares fitting the theoretically calculated (GIAO B3LYP/6‐311 + G**) ¹⁵ N NMR chemical shieldings of SpmTrien tautomers to the experimentally measured chemical shifts. Theoretical chemical shieldings were calculated for water complexes of SpmTrien obtained from MD simulations in explicit water. Both methods gave highly similar realistic results. SpmTrien has many major populations of tautomers at biologically relevant charge states of three (+3) and four (+4) thus enabling a large variety of structures for specific ionic interactions. Copyright © 2013 John Wiley & Sons, Ltd.     

Simple method for obtaining electron scattering phase shifts from energies of an atom in a cavity

We present a simple method for obtaining elastic scattering phase shifts and cross sections from precise ab initio many-body perturbation theory energies of atoms in variable cavities. This method does not require calculations of wave functions of continuum states, can be generalized to many atoms and ions, and is extremely convenient because existing codes developed for energy calculations can be used without modification. The high precision of the method and close agreement with experiment are illustrated on examples of e-Ar and e-Kr scattering. Correlations as well as relativistic corrections are systematically considered.     

1H NMR study of the hetero‐association of non‐symmetrical diols with pyridine; GIAO/DFT calculations on diols

The ¹H NMR titration method is used to investigate the association of non‐symmetrical 1,2‐ and 1,3‐diols with pyridine in benzene. These diols give well‐defined titration curves for the two non‐equivalent OH protons, but it is not possible to determine individual association constants. Only the sum of the first association constants for the two protons and the product of the first and second association constants are accessible. The sum is significantly higher than that of the association constants of the corresponding primary and secondary alcohols, but close to an estimate based on symmetrical diols. The product leads to second association constants similar to those found for symmetrical diols. The sum of the chemical shifts of the associated and non‐associated OH protons in either 1:1 pyridine complex is higher than that of the shifts in the free diol and the 2:1 complex. These features are consistent with small cooperative effects, amounting to an average increase in the reaction free energy of 1.3 kJ mol^?1 compared to monohydric alcohols. Infrared (IR) spectra of non‐symmetrical diols and quantum mechanical (QM) calculation of the energies and ¹H NMR shifts of the OH protons in several conformers of propan‐1,2‐ and butan‐1,3‐diols indicate that both the primary and the secondary OH groups act as “donor” or “acceptor” in the free molecule. Gauche interactions in propan‐1,2‐diol enhance chemical shifts considerably less than does the intramolecular hydrogen bond in butan‐1,3‐diol. Copyright © 2011 John Wiley & Sons, Ltd.