Crystal Structure of Tris(2,2'-bipyridine)nickel (Ⅱ) Tetrachlorozincate

A bimetallic complex Ni[C10H8N2]3[ZnCl4] has been synthesized and its crystal structure determined at room temperature. The complex crystallizes in the trigonal system, space group R3c, with a = 13.343(2), b = 13.343(2), c =58. 932(12) A, V= 9087(3) A 3, Z = 12, NiZnC30N6CI14H24, Mr=734.30, Dc=1.611 g/cm3, μ= 1. 799 mm-1, F(000)=4464. Least-squares refinement of the structure leads to the agreement factors R1=0. 0278 and wR2=0. 0741 for the observable reflections. The complex consists of discrete tris (2, 2'-bipyridine) nickel (Ⅱ)cation, [Ni-(bipy)3]2+, and tetrachlorozincate anion, [ZnCl4]2-. Each nickel (Ⅱ)atom is six coordinated in an octahedron with six nitrogen atoms of three 2,2'-bipyridine ligands. The mean Ni(Ⅱ)-N bond length is 2. 089(2) A. The zinc(Ⅱ) atom is coordinated with four chloride atoms in tetrahedral geometry. The mean Zn (Ⅱ)- Cl bond length is 2. 264(1) A.     

Chlorosilanes: Development and application of MM2 force field parameters

The geometries, relative conformational energies, and dipole moments of mono and polychlorosilanes have been calculated using ab initio molecular orbital (MO) theory. Calculations at the HF/3–21G(*) level, with the exception of dipole moments, give reasonable agreement with experimental data. A new MM2 force field for chlorosilanes, which includes terms for bond length shortening and bond angle compression due to the attachment of electronegative Cl atoms, has been developed on the basis of experimental and ab initio results. The new force field is generally successful in predicting structural parameters, but is unable to reproduce the dipole moments of several model systems. While dipole moment predictions are not the authors' main interest, this failure defines a shortcoming in the MM2 method. The new parameters have been applied to problems in the prediction of stereochemistries of cyclic systems, and compared with experimental results where data are available.     

ArH＋势能曲线的从头计算

ArnH^ 是非常重要而又较简单的簇体系,对于它们的深入研究,有助于人们认识质子在溶液中的溶剂化行为,该簇中最为简单而又重要的存在形式是ArH^ 和ArnH^ 。ArH^ 可以在气相中稳定存在,在所有的ArnH^ 族中被研究得最早,实验数据也最为齐全,人们对ArH^ 体系进行了许多理论计算,但只局限于平衡键长、简正振动频率、解离能等分子参数,计算结果与已知的振动－转动光谱数据基本符合。     

ArH~ 势能曲线的从头计算

ArnH＋是非常重要而又较简单的簇体系 .对于它们的深入研究 ,有助于人们认识质子在溶液中的溶剂化行为 .该簇系中最为简单而又重要的存在形式是 ArH＋和 Ar2H＋ .ArH＋可以在气相中稳定存在 ,在所有的 ArnH＋簇中被研究得最早 [1],实验数据也最为齐全 [2].人们对 ArH＋体系进行了许多理论计算 [3－ 6],但只局限于平衡键长、简正振动频率、解离能等分子参数 .计算结果与已知的振动转动光谱数据 [2]基本符合 . 　　为了给 ArnH＋体系的动力学研究打基础 ,我们利用 Gaussian98[7]程序包 ,对 ArH＋和 Ar2H＋体系的势能面进行了研究 .…     

Gas phase chemistry in gallium nitride CVD: Theoretical determination of the Arrhenius parameters for the first Ga-C bond homolysis of trimethylgallium

Experimental evidence suggests that the energy of activation for the first homolytic Ga-C bond fission of GaMe3 of Ea = 249 kJ/mol, measured by Jacko and Price in a hot-wall tube reactor, is affected by surface catalytic effects. In this contribution, the rate constant for this crucial step in the gas-phase pyrolysis of GaMe3 has been calculated by variational transition state theory. By a basis set extrapolation on the MP2/cc-pVXZ level and a correlation correction from CCSD(T)/cc-pVDZ level, a theoretical "best estimate" for the bond energy of Delta H(289K) = 327.2 kJ/mol was derived. For the VTST calculation on the B3LYP/cc-pVDZ level, the energies were corrected to reproduce this bond energy. Partition functions of the transitional modes were approximated by a hindered rotor approximation to be valid along the whole reaction coordinate defined by the Ga-C bond length. On the basis of the canonical transition state theory, reaction rates were determined using the maxima of the free energy Delta G++. An Arrhenius-type rate law was fitted to these rate constants, yielding an apparent energy of activation of Ea = 316.7 kJ/mol. The preexponential factor A = 3.13 x 10(16) 1/s is an order of magnitude larger than the experimental results because of a larger release of entropy at the transition state as compared to that of the unknown surface catalyzed mechanism.     

Ab initio study of the structure, bonding, vibrational spectra, and energetics of XBS+ (where X=H, F, and Cl)

High level ab initio electronic structure calculations at the CCSD(T) level with augmented correlation-consistent basis set extrapolated to complete basis set limit have been performed on XBS and XBS+ for X=H, F, and Cl. The geometries have been optimized up through the aug-cc-pV5Z level and the vibrational frequencies have been calculated with the aug-cc-pVQZ basis sets. Analysis of the bonding in XBS and XBS+ using natural bond orbital analysis shows that the BS bond in XBS is a triple bond, while in XBS+ it is a double bond. The energetic properties of XBS cation and its first excited state are reported. The calculated adiabatic ionization potential is 11.11+/-0.01 eV as compared to the experimental value of 11.11+/-0.03 eV for HBS. The adiabatic ionization potentials for FBS and CIBS are 10.89+/-0.01 and 10.57+/-0.01 eV, respectively.     

Ab initio quantum dynamical study of the vinylidene-acetylene isomerization

The dynamics of vinylidene-acetylene isomerization has been studied quantum mechanically, based on a new ab initio calculated potential energy surface (PES). The grid underlying the PES and the dynamic treatment rest on planar 4-atom Jacobi-like coordinates. Three degrees of freedom, the C-C bond length and the two Jacobi-like angles are treated explicitly, while the two other coordinates relating to the C-H bond lengths have been optimized in the ab initio treatment. The energies of the resulting 3D grid have been computed with the CCSD(T) method, using a cc-pVTZ basis set, while selected stationary points have been characterized at a higher level of theory. The subsequent dynamic treatment reproduces very satisfactorily the experimental photodetachment spectrum of Lineberger and coworkers. Preliminary results are also reported for the lifetime of vinylidene. Received: 5 June 1998/Accepted: 23 July 1998 / Published online: 9 October 1998     

Bond lengthening and through-bond interactions in p,p'-dibenzene and related molecules

The structure of p,p'-dibenzene (PDB) has been investigated by full geometry optimizations using the empirical force field (EFF) and MINDO/3 methods. While other structural parameters are in good agreement, the central bond length calculated by MINDO/3 (1.595 Å), as confirmed by an ab initio (STO-3G basis set) optimization (1.596 Å), is in striking contrast to the corresponding length calculated by EFF (1.543 Å). A detailed analysis of the electronic structure of PDB based on a quantitative perturbational molecular orbital treatment reveals that through-bond coupling of the four π systems is responsible for an elongation of the σ bond which mediates this interaction. Further studies using the EFF and MINDO/3 approaches demonstrate that extended C-C single bonds can arise even in structures with fewer than four π systems. The effect of substituents on the central bond length in PDB has been briefly investigated. (MINDO/3). A variety of other structures have been identified in which bond lengthening may result from through-bond coupling.     

GVVPT2 multireference perturbation theory description of diatomic scandium, chromium, and manganese

With relatively simple model spaces derived from valence bond models, a straightforward zero-order Hamiltonian, and the use of moderate-sized Dunning-type correlation consistent basis sets (cc-pVTZ, aug-cc-pVTZ, and cc-pVQZ), the second order generalized Van Vleck perturbation theory (GVVPT2) method is shown to produce potential energy curves (PECs) and spectroscopic constants close to experimental results for both ground and low-lying excited electronic states of Sc(2), Cr(2) and Mn(2). In spite of multiple quasidegeneracies (particularly for the cases of Sc(2) and Mn(2)), the GVVPT2 PECs are smooth with no discontinuities. Since these molecules have been identified as ones that widely used perturbative methods are inadequate for describing well, due to intruder state problems, unless shift parameters are introduced that can obfuscate the physics, this study suggests that the conclusion about the inadequacy of multireference perturbation theory be re-evaluated. The ground state of Sc(2) is predicted to be X(5)∑(u)(-), and its spectroscopic constants are close to the ones at the MRCISD level. Near equilibrium geometries, the 1(3)∑(u)(-) electronic state of Sc(2) is found to be less stable than the quintet ground state by 0.23 eV. The Cr(2) PEC has several features of the Rydberg-Klein-Rees (RKR) experimental curve (e.g., the pronounced shelf at elongated bond lengths), although the predicted bond length is slightly long (R(e) = 1.80 ? with cc-pVQZ compared to the experimental value of 1.68 ?). The X(1)∑(g)(+) ground state of Mn(2) is predicted to be a van der Waals molecule with a long bond length, R(e), of 3.83 ? using a cc-pVQZ basis set (experimental value = 3.40 ?) and a binding energy, D(e), of only 0.05 eV (experimental value = 0.1 eV). We obtained R(e) = 3.40 ? and D(e) = 0.09 eV at the complete basis set (CBS) limit for ground state Mn(2). Low lying excited state curves have also been characterized for all three cases (Cr(2), Mn(2), and Sc(2)) and show similar mathematical robustness as the ground states. These results suggest that the GVVPT2 multireference perturbation theory method is more broadly applicable than previously documented.     

熔融ZnCl2结构的分子动力学模拟研究

熔融ZnCl2作为一种离子性共价性参半的典型熔盐, 其近邻结构在实验测量和分子动力学模拟方面均作过一些研究。本文依据新近EXAFS实验结果, 比较了不同的有效势下模拟得到的径向分布函数,表明KDR势可作为一种实用势。并进一步在KDR势模拟产生的瞬态构型基础上, 使用键序参数方法研究了晶态和熔融态ZnCl2中的近邻结构。结果表明, 和晶态ZnCl2一样, 在熔融ZnCl2中存在稳定的Zn/Cl正四面体结构, 但熔态和晶态Zn/Cl近邻结构热波方差σ不同。计算表明300K晶态σ=5.0℃, 613K熔融态σ=12.2℃。也对熔融ZnCl2的网络状结构和宏观输运性质进行了讨论。     

The conformation of alkyl cyclohexanones and terpenic ketones. Interpretation for the ‘alkylketone effect’ based on the CH/π(CO) hydrogen bond

Ab initio MO calculations were carried out, at the MP2/6-311++G(d,p)//MP2/6-311G(d,p) level, to investigate the Gibbs free energy of the conformational isomers of 2-alkyl, 3-alkyl, and 4-alkyl cyclohexanones. The calculation gave results consistent with the general trend experimentally found. The genesis of stabilization of the axial conformers in 2- and 3-alkyl cyclohexanones, as compared to the structurally corresponding cyclohexane derivatives, was sought in the context of the attractive CH/π(CO) hydrogen bond. In support of this hypothesis, short nonbonded distances have been noted between CHs in the alkyl group and the carbonyl carbon in the relevant axial conformers. Calculations were also carried out to study the conformational energies of several terpenic ketones. For isomenthone, more than a half molecular fraction (ca. 55%) has been suggested to be in the isopropyl-axial conformation, while for isocarvomenthone ca. 77% has been suggested to be in the axial-isopropyl conformation; this is consistent with bibliographic experimental data. A crystallographic database search has provided results compatible with this conclusion. We suggest that the relative stability of the axial alkyl substituent, often observed in terpenic and steroidal ketones is rationalized in terms of an attractive molecular force, the CH/π(CO) hydrogen bond.     

Density functional theoretical (DFT) study for the prediction of spectroscopic parameters of ClCCCN

DFT(B3LYP, B3PW91) calculations in conjunction with three different basis sets have been utilized to investigate the variations in the bond lengths, dipole moment, rotational constants, IR frequencies, IR intensities and rotational invariants of ClCCCN. The nuclear quadrupole constants of chlorine ((35)Cl, (37)Cl) and nitrogen ((14)N) of ClCCCN have been calculated on the experimental r(s) structure as well as on the B3PW91/6-311++g(d,p) optimized geometry and were found to be within the scale length of the experimental uncertainty. The slope and intercept obtained from the regression analysis between the B3LYP/6-311++g(d,p) level calculated and experimental B(o) values of ClCCCN were used to calculate reasonable values of rotational constants of all the rare isotopic species of ClCCCN having standard deviation +/-0.048 MHz. All the spectroscopic parameters obtained from DFT calculations show satisfactory agreement with the available experimental data.     

Second-order Møller-Plesset evaluation of the bond length alternation of several series of linear oligomers

We investigate, at the second-order M?ller-Plesset level, the bond length alternation of 30 series of increasingly long linear oligomers for a total of more than 250 compounds, polyacetylene, polymethineimine, polyphosphinoborane, polyaminoborane, polyphosphazene, etc., for which, often for the first time, an accurate estimate of the polymeric bond length alternation is given. The variations induced either by chemical substitution of the backbone atoms or conformational modifications are discussed. Only three polymers present a large bond length alternation (>0.03 A). Systematic basis set effects have been unravelled, i.e., MP2/6-311G(2d) always overshoots the bond length alternation. Best estimates of the bond length alternation are provided for more than a dozen of polymers.     

硝酰阳离子和二氧化氮分子的弯曲变形研究

采用密度泛函理论的B3LYP方法(6-311＋G*基组)计算了、NO2以及其它与硝化反应机理研究相关的分子、离子和激发态的结构与性质.进而研究了当键角在90～180°之间变化时，这些相关物质能量的变化规律，由此探讨了不同硝化机理发生的可能性，为以后进一步研究不同结构与活性的芳香化合物的硝化反应机理提供依据.     

On the spectroscopic and thermochemical properties of ClO, BrO, IO, and their anions

A coupled cluster composite approach has been used to accurately determine the spectroscopic constants, bond dissociation energies, and heats of formation for the X1(2)II(3/2) states of the halogen oxides ClO, BrO, and IO, as well as their negative ions ClO-, BrO-, and IO-. After determining the frozen core, complete basis set (CBS) limit CCSD(T) values, corrections were added for core-valence correlation, relativistic effects (scalar and spin-orbit), the pseudopotential approximation (BrO and IO), iterative connected triple excitations (CCSDT), and iterative quadruples (CCSDTQ). The final ab initio equilibrium bond lengths and harmonic frequencies for ClO and BrO differ from their accurate experimental values by an average of just 0.0005 A and 0.8 cm-1, respectively. The bond length of IO is overestimated by 0.0047 A, presumably due to an underestimation of molecular spin-orbit coupling effects. Spectroscopic constants for the spin-orbit excited X2(2)III(1/2) states are also reported for each species. The predicted bond lengths and harmonic frequencies for the closed-shell anions are expected to be accurate to within about 0.001 A and 2 cm-1, respectively. The dissociation energies of the radicals have been determined by both direct calculation and through use of negative ion thermochemical cycles, which made use of a small amount of accurate experimental data. The resulting values of D0, 63.5, 55.8, and 54.2 kcal/mol for ClO, BrO, and IO, respectively, are the most accurate ab initio values to date, and those for ClO and BrO differ from their experimental values by just 0.1 kcal/mol. These dissociation energies lead to heats of formation, DeltaH(f) (298 K), of 24.2 +/- 0.3, 29.6 +/- 0.4, and 29.9 +/- 0.6 kcal/mol for ClO, BrO, and IO, respectively. Also, the final calculated electron affinities are all within 0.2 kcal/mol of their experimental values. Improved pseudopotential parameters for the iodine atom are also reported, together with revised correlation consistent basis sets for this atom.     

NH3…H2O体系氢键团簇结构的从头计算方案比较

对H2O，NH3单分子以及反式线性NH3…H2O双分子团簇应用HF，DFT，MR2，CCD ，QCISD等从头计算方法在不同的基组水平上进行几何结构优化和氨—水分子间相 互作用能计算。比较实验值和计算结果表明：对氨—水体系，MP2／6-31+G^**方法 能够满足氢键N-0键长误差为0．004nm，键角∠NOH误差为1°，NH3…H2O相互作用 能△E与CCD和QCISD偏差2．1kJ／mol计算精度的要求，并有较合理的计算代价。     

Theoretical calculations of hyperfine coupling constants for muoniated butyl radicals

The hyperfine coupling constants (HFCCs) of all the butyl radicals that can be produced by muonium (Mu) addition to butene isomers (1- and 2-butene and isobutene) have been calculated, to compare with the experimental results for the muon and proton HFFCs for these radicals reported in paper II (Fleming, D. G.; et al. J. Phys. Chem. A 2011, 10.1021/jp109676b) that follows. The equilibrium geometries and HFCCs of these muoniated butyl radicals as well as their unsubstituted isotopomers were treated at both the spin-unrestricted MP2/EPR-III and B3LYP/EPR-III levels of theory. Comparisons with calculations carried out for the EPR-II basis set have also been made. All calculations were carried out in vacuo at 0 K only. A C-Mu bond elongation scheme that lengthens the equilibrium C-H bond by a factor of 1.076, on the basis of recent quantum calculations of the muon HFCCs of the ethyl radical, has been exploited to determine the vibrationally corrected muon HFCCs. The sensitivity of the results to small variations around this scale factor was also investigated. The computational methodology employed was "benchmarked" in comparisons with the ethyl radical, both with higher level calculations and with experiment. For the β-HFCCs of interest, compared to B3LYP, the MP2 calculations agree better with higher level theories and with experiment in the case of the eclipsed C-Mu bond and are generally deemed to be more reliable in predicting the equilibrium conformations and muon HFCCs near 0 K, in the absence of environmental effects. In some cases though, the experimental results in paper II demonstrate that environmental effects enhance the muon HFCC in the solid phase, where much better agreement with the experimental muon HFCCs near 0 K is found from B3LYP than from MP2. This seemingly better level of agreement is probably fortuitous, due to error cancellations in the DFT calculations, which appear to mimic these environmental effects. For the staggered proton HFCCs of the butyl radicals exhibiting no environmental effect in paper II, the best agreement with experiment is consistently found from the B3LYP calculations, in agreement also with benchmark calculations carried out for the ethyl radical.     

A crystal structure survey of the geometry of the methoxyphenyl group

The Cambridge Structural Database has been used to retrieve the geometry of the methoxyphenyl group as determined in 212 crystal structure analyses by X-ray diffraction. The experimental data are in accord with recent STO-3G basis MO calculations in that the preferred conformation is planar. However, one bond length, that from oxygen to phenyl carbon and several bond angles show significant differences from the MO calculation.     

An ab initio (RHF) and DFT-B3LYP level spectroscopic studies of BrCCCN and the analysis of atomic polar tensors

Conventional ab initio (RHF) and DFT-B3LYP level calculations in conjunction with a variety of basis sets have been used to investigate the variations in the bond lengths, dipole moment, rotational constant, quadruple coupling constants, infrared frequencies, IR intensities and rotational invariants of BrCCCN. Satisfactory agreements between the B3LYP and experimental values were found for bond lengths, rotational constant, dipole moment and all other parameters. All the calculated bond lengths are in good agreement with each other for a given method having the average standard deviations varying between ±0.005 Å at the B3LYP level. Harmonic vibrational frequencies obtained from the B3LYP calculations show good agreement with the available experimental data. The global atomic polar tensor charges, used for interpreting the IR intensities, of all the atoms of BrCCCN have been calculated at the RHF and B3LYP levels in conjunction with the 6-311g(d) and 6-311++g(d,p) basis sets. Linear regression analysis between calculated and experimental infrared frequencies as well as between IR intensities in a series of 15 similar type of nitrile compounds have been achieved at the B3LYP/6-311++g(d,p) level and gives linear regression coefficients 0.983 and 0.970 respectively. Finally, a number of linear relations were found between r(CN) bond lengths and GAPT charges, and GAPT charges on CHELPG and MK charges at the nitrogen atom for these molecules and proved to be producing satisfactory results at the B3LYP/6-311++g(d,p) level of calculations.