Accurate prediction of norbornadiene cycle enthalpies by DLPNO-CCSD(T1)/CBS method

The DLPNO-CCSD(T₁)/CBS method combined with simple reactions containing small reference species leads to an improvement in the accuracy of theoretically evaluated enthalpies of formation of medium-sized polyalicyclic hydrocarbons when compared with the widely used composite approach. The efficiency of the DLPNO-CCSD(T₁)/CBS method is most vividly demonstrated by comparing with the results of G4 calculations for adamantane. The most important factor in choosing appropriate working reaction is the same number of species on both sides of the equation. Among these reactions, the reactions with small enthalpy change usually provide a better cancellation of errors. The DLPNO-CCSD(T₁)/CBS method was used to calculate the enthalpies of formation of compounds belonging to the norbornadiene cycle (norbornadiene, quadricyclane, norbornene, nortricyclane, and norbornane). The most reliable experimental enthalpies of formation are recommended for these compounds by comparing calculated values with conflicting experimental data.     

DFT,DLPNO-CCSD(T), and NEVPT2 benchmark study of the reaction between ferrocenium and trimethylphosphine

The reaction between ferrocenium and trimethylphosphine was studied using density functional theory (DFT), domain-based local pair natural orbital coupled cluster theory with single-, double-, and perturbative triple excitations (DLPNO-CCSD(T)), and N-electron valence state perturbation theory (NEVPT2). The accuracy of the DFT functionals decreases compared to the DLPNO-CCSD(T) level in the following order: M06-L > TPSS > M06, BLYP > PBE, PBE0, B3LYP > > PWPB95 > > DSD-BLYP. The roles of thermochemical, continuum solvation (SMD), and counterpoise corrections were evaluated. Grimme's D3 empirical dispersion correction is essential for all functionals studied except M06 and M06-L. The reliability of the frequency calculations performed directly within the SMD was confirmed. The systems showed no significant multireference character according to T₁ and T₂ diagnostics and the fractional occupation number (FOD) weighted electron density analysis. The multireference NEVPT2 calculations gave qualitatively valid conclusions about the reaction mechanism. However, a multireference approach is generally not recommended because it requires arbitrary chosen active spaces.     

Ab Initio (GIAO) Calculations of Absolute Nuclear Shieldings for Representative Compounds Containing 1(2)H, 6(7)Li, 11B, 13C, 14(15)N, 17O, 19F, 29Si, 31P, 33S,and 35Cl Nuclei

Two kinds of ab initio calculations (B3LYP and HF) using the GIAO approach have been carried out for fifteen H, three Li, three B, eleven C, seven N, nine O, four F, three Si, four P, six S and five Cl containing derivatives. The calculated absolute nuclear shieldings have been compared with experimental absolute values (either measured or estimated from relative chemical shifts) when available or with relative chemical shifts (¹¹B, ³⁵Cl). The correlations range from good to excellent and only three compounds (PN, P₂H₂, SO₂) deviate significantly.     

Some Regularities of Standard Enthalpies of Formation (SEF) for Relative Inorganic Compounds

The empirical regularities of the SEF for relative inorganic substances in binary and quasibinary systems (energetic and dimensional rules of linear approximation - ELAR and DLAR) are described. This revised version was published online in August 2006 with corrections to the Cover Date.     

Scaled Quantum Mechanical Force Fields for the CF3SX Molecules (X = H,F, Cl,Br, I)

Density functional theory calculations at different levels of theory were performed on the molecules of the series CF₃SX (X = H, F, Cl, Br, I) in order to obtain their optimized geometric parameters and conformations, the wavenumbers corresponding to the normal modes of vibrations and the associated force constants. The obtained force fields were transformed to local symmetry coordinates and scaled to reproduce the experimental wavenumbers.     

B−Hb←:X (X= N,O, P,S, F,Cl, Br) interactions: A density functional study

Density functional theory calculation on B H_b←:X interaction (X= N, O, P, S, F, Cl, Br) is performed. HOMO energy predicts the feasibility of such complexation. Steric and electronic effects play significant role on geometry of the complexes. Interaction energy suggests that the interaction is moderately strong (< 5.00 kcal mol⁻¹) in nature and the complexes are stable in both gas and solvent phase. Electron donating group on: X facilitates the interaction whereas electron withdrawing group impedes the same. MP2 and CCSD(T) calculations further confirm the suitability of ωB97X‐D and M06‐2X functional for studying such interactions. Dispersive interaction is the primary mode of interaction in stabilizing the complexes. ¹H NMR and IR study are also performed. Thermochemical analysis advocates exothermic nature of complexation.     

Ab initio and DFT energetics of silylenic X–CNSi (X=H, F, Cl, and Br)

Singlet–triplet energy splitting for 24 silylenic reactive intermediates, X–CNSi (where X=H, F, Cl and Br), are compared and contrasted at 11 levels of theory: B1LYP/6-31++G**, B3LYP/6-31++G**, B1LYP/6-311++G**, B3LYP/6-311++G**, MP3/6-31G*, MP3/6-311++G**, MP2/6-31+G**, MP2/6-311++G**, MP4 (SDTQ)/6-311++G**, QCISD(T)/6-311++G** and CCSD(T)/6-311++G**. Each X-substituted silylenic species may either be singlet (s) or triplet (t), with one of the following three structures: 3-X-2-aza-1-silacyclopropenylidene (1_s-X, 1_t-X); [(X-imino)methylene]silylene (2_s-X, 2_t-X); and X-cyanosilylene (3_s-X, 3_t-X). For all X–CNSi species studied, orders of singlet–triplet energy separations (ΔE_s-t,X), appear as a function of electro-negativity (F>Cl>Br>H). For the six H–CNSi isomers (X=H), stability order is: 3_s-H>1_s-H>2_t-H>3_t-H>2_s-H>1_t-H. Likewise, stability order for the six isomers with X=F, is: 3_s-F>3_t-F>1_s-F>1_t-F>2_s-F>2_t-F. For X=Cl, the order of stability is: 3_s-Cl>1_s-Cl>3_t-Cl>2_t-Cl>1_t-Cl>2_t-Cl. Finally, the order of stability for six isomers of Br–CNSi is: 3_s-Br>3_t-Br>1_s-Br>2_s-Br>2_t-Br>1_t-Br. The lowest energy minimum, among all 24 species scrutinized, appears to be the singlet acyclic 3_s-X. Triplet silylene 2_t-H is suggested to be more stable than its corresponding 2_s-H at MP3, MP2 and DFT levels of theory. Comparisons between relative stabilities; multiplicities and geometrical parameters of 1–3 are discussed.     

PuX~ (X=H,O,N,C)的结构与势能函数

用密度泛函B3LYP方法对PuX＋(X=H,O,N,C)分子离子体系进行了理论研究.结果表明,这些分子离子的基态电子状态分别是X 7Σ－(PuH＋)、X 6Σ－(PuO＋)、X 5Σ＋(PuN＋)和X 8Σ－(PuC＋);势能函数为Murrell-Sorbie势函数.并得到了相应的几何性质、力学性质和光谱数据.     

Ab Initio calculations of the stabilization energies of the conformational and the structural isomers of C(3)H(7)X where X = F,Cl, and Br

HF, MP2, and B3LYP calculations with different basis sets have been used in the computation of the stabilization energies of C(3)H(7)X isomers, where X is F, Cl, and Br. The experimental stabilization energies of the structural isomers of C(3)H(7)Cl and C(3)H(7)Br have been reproduced via B3LYP calculations. However, the calculated stabilization energies of fluoropropane isomers from their reported enthalpies of formation have been reproduced in all methods of calculations in present work. The experimental relative stabilities of the gauche conformers of 1-fluoro-, 1-chloro-, and 1-bromopropanes have been also reproduced via some of the used calculations in the present work. The effect of the geminal interactions on X atomic charges and on the C-X and C-C bond lengths in halopropane isomers are also discussed.     

A density functional theory study of the dimers of HX (X = F,Cl, and Br)

The geometries, interaction energies, and vibrational properties of (HF)₂, (HCl)₂, and (HBr)₂ have been investigated using a variety of hybrid density functional methods and the 6‐311+G(2df,p) basis set. Although most of the density functional methods predict geometries in reasonable agreement with experiment, methods containing the LYP correlation functional yield geometrical parameters in slightly better agreement. The (HF)₂ interaction energy, predicted by the hybrid density functional methods, is in reasonable agreement with experiment, but the (HCl)₂ and (HBr)₂ interaction energies are underestimated substantially. The frequency shift for the X? H donor bond correlates linearly with the elongation of the X? H bond upon complexation, and is predicted reasonably well by methods containing the LYP functional. Overall, the hybrid density functional methods adequately predict the properties of the halide dimers. It is interesting to note that the BHandHLYP and B1LYP density functional methods offer a competitive alternative to the popular B3LYP method. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1590–1597, 2001     

稀土脯氨酸配合物[RE_2(L-Pro)_6(H_2O)_4](ClO_4)_6的标准生成焓测定

合成了两种稀土高氯酸盐与Ｌ－脯氨酸配合物的晶体．经热重、差热、化学分析及对比有关文献,知其组成 是［Ｐｒ２（Ｌ－Ｐｒｏ）６（Ｈ２Ｏ）４］（ＣｌＯ４）６和［Ｅｒ２（Ｌ－ＰｒＯ）６（Ｈ２Ｏ）４］（ＣｌＯ４）６,质量分数为９９．２４％和９８．２０％．选用ＲＥ（ＮＯ３）· ６Ｈ２Ｏ（ＲＥ＝Ｐｒ,Ｅｒ）、ＬＰｒｏ、ＮａＣｌＯ４·Ｈ２Ｏ和 ＮａＮＯ３作辅助物,使用具有恒温环境的反应热量计,以 ２ ｍｏｌ·Ｌ－１ＨＣｌ 作溶剂,分别测定了［２ＲＥ（ＮＯ３）３·６Ｈ２Ｏ＋６Ｌ－ＰｒＯ＋６ＮａＣｌＯ４·Ｈ２Ｏ］和｛ ［ＲＥ２（Ｌ－ＰｒＯ）６（Ｈ２Ｏ）４］（ＣｌＯ４）６＋６ＮａＮＯ３｝在 ２９８．１５ Ｋ时的溶解热．设计一热化学循环求得化学反应的反应焓ｒＨ分别是：６３．９０４ ｋＪ·ｍｏｌ－１和 ９１．０１７ ｋＪ·ｍｏｌ－１,经计算得配合物［ＲＥ２（Ｌ－Ｐｒｏ）６（Ｈ２Ｏ）４］（ＣｌＯ４）６（ｓ）在 ２９８．１５ Ｋ时的标准生成焓（２９８．１５ Ｋ）分别 是－６ ５９４．７８ ｋＪ·ｍｏｌ－１和－６ ５３２．８７ ｋＪ·ｍｏｌ－１。     

Kristallstruktur-Untersuchungen von Bis(pentafluorphenyl)tellurdihalogeniden (C6F5)2TeHal2 (Hal = Cl,Br)

Crystal Structure Determinations of Bis(pentafluorophenyl)tellurium Dihalides (C₆F₅)₂TeHal₂ (Hal = Cl, Br) Bis(pentafluorophenyl)telluriumdichloride and bis(pentafluorophenyl)telluriumdibromide crystallize at 10°C or 20°C from CH₂Cl₂ or CHCl₃ solution in the monoclinic space group P2₁/c with a = 649.5(1) pm, b = 1 275.6(2) pm, c = 1 816.2(5) pm, β = 92.89(2)° for (C₆F₅)₂TeCl₂ and a = 694.4(1) pm, b = 1 579.1(2) pm, c = 1 423.4(1) pm, β = 90.22(2)° for (C₆F₅)₂TeBr₂ with four formula units per each unit cell.     

Ab initio study of hydrated potassium halides KX(H2O)1-6 (X=F,Cl,Br,I)

The ionic dissociation of salts was examined with a theoretical study of KX (X=F,Cl,Br,I) hydrated by up to six water molecules KX(H2O)n (n=1-6). Calculations were done using the density functional theory and second order M?ller-Plesset (MP2) perturbational theory. To provide more conclusive results, single point energy calculations using the coupled cluster theory with single, double, and perturbative triple excitations were performed on the MP2 optimized geometries. The dissociation feature of the salts was examined in terms of K-X bond lengths and K-X stretch frequencies. In general, the successive incorporation of water molecules to the cluster lengthens the K-X distance, and consequently the corresponding frequency decreases. Near 0 K, the KX salt ion pairs can be partly separated by more than five water molecules. The pentahydrated KX salt is partly dissociated, though these partly dissociated structures are almost isoenergetic to the undissociated ones for KFKCl. For the hexahydrated complexes, KF is undissociated, KClKBr is partly dissociated, and KI is dissociated (though this dissociated structure is nearly isoenergetic to a partly dissociated one). On the other hand, at room temperature, the penta- and hexahydrated undissociated structures which have less hydrogen bonds are likely to be more stable than the partly dissociated ones because of the entropy effect. Therefore, the dissociation at room temperature could take place for higher clusters than the hexahydrated ones.     

RM1: a reparameterization of AM1 for H, C, N, O, P, S, F, Cl, Br, and I

Twenty years ago, the landmark AM1 was introduced, and has since had an increasingly wide following among chemists due to its consistently good results and time-tested reliability--being presently available in countless computational quantum chemistry programs. However, semiempirical molecular orbital models still are of limited accuracy and need to be improved if the full potential of new linear scaling techniques, such as MOZYME and LocalSCF, is to be realized. Accordingly, in this article we present RM1 (Recife Model 1): a reparameterization of AM1. As before, the properties used in the parameterization procedure were: heats of formation, dipole moments, ionization potentials and geometric variables (bond lengths and angles). Considering that the vast majority of molecules of importance to life can be assembled by using only six elements: C, H, N, O, P, and S, and that by adding the halogens we can now build most molecules of importance to pharmaceutical research, our training set consisted of 1736 molecules, representative of organic and biochemistry, containing C, H, N, O, P, S, F, Cl, Br, and I atoms. Unlike AM1, and similar to PM3, all RM1 parameters have been optimized. For enthalpies of formation, dipole moments, ionization potentials, and interatomic distances, the average errors in RM1, for the 1736 molecules, are less than those for AM1, PM3, and PM5. Indeed, the average errors in kcal x mol(-1) of the enthalpies of formation for AM1, PM3, and PM5 are 11.15, 7.98, and 6.03, whereas for RM1 this value is 5.77. The errors, in Debye, of the dipole moments for AM1, PM3, PM5, and RM1 are, respectively, 0.37, 0.38, 0.50, and 0.34. Likewise, the respective errors for the ionization potentials, in eV, are 0.60, 0.55, 0.48, and 0.45, and the respective errors, in angstroms, for the interatomic distances are 0.036, 0.029, 0.037, and 0.027. The RM1 average error in bond angles of 6.82 degrees is only slightly higher than the AM1 figure of 5.88 degrees, and both are much smaller than the PM3 and PM5 figures of 6.98 degrees and 9.83 degrees, respectively. Moreover, a known error in PM3 nitrogen charges is corrected in RM1. Therefore, RM1 represents an improvement over AM1 and its similar successor PM3, and is probably very competitive with PM5, which is a somewhat different model, and not fully disclosed. RM1 possesses the same analytical construct and the same number of parameters for each atom as AM1, and, therefore, can be easily implemented in any software that already has AM1, not requiring any change in any line of code, with the sole exception of the values of the parameters themselves.     

RE(C5H8NS2)3(C12H8N2)(RE=La,Pr,Nd,Sm)的标准摩尔生成焓测定研究

在无水乙醇中,使低水合氯化稀土(RE=La, Pr, Nd, Sm)与吡咯烷二硫代氨基甲酸铵(APDC)和1,10-邻二氮菲(σ-phen·H₂O)反应,制得其三元固态配合物.用化学分析和元素分析确定它们的组成为RE (C₅H₈NS₂)₃(C₁₂H₈N₂) (RE= La, Pr, Nd, Sm).IR光谱说明RE³⁺分别与3个PDC-的6个硫原子双齿配位,同时与σ-phen的2个氮原子双齿配位,配位数为8.用精密转动弹热量计测定了它们的恒容燃烧热Δ_cU,分别为-17776.94±7.72, -17810.41±7.93, -17762.71±7.91和-17482.42±9.35 kJ·mol^-1;并计算了它们的标准摩尔燃烧焓和标准摩尔生成焓,分别为-17792.43±7.72, -17825.90±7.93, -17778.20±7.91, -17497.91±9.35 kJ*mol^-1和-83.05±8.60, -64.70±9.40, -104.77±8.78, -388.70±10.13 kJ·mol^-1.估算出未研究的同类配合物Ce(C₅H₈NS₂)₃(C₁₂H₈N₂)和Pm(C₅H₈NS₂)₃(C₁₂H₈N₂)的和分别为-17815, -17660 kJ·mol^-1和-60, -217 kJ·mol^-1.     

Conformational Stability of Propenoyl Bromide from Temperature-Dependent Infrared Spectra of Krypton Solutions,Ab Initio Calculations,and r 0 Structural Parameters of the Propenoyl Halides (F,Cl, Br)

Variable temperature (–100 to –150°C) studies of the infrared spectra (3500–400 cm^–1) of propenoyl bromide, CH₂=CHCBrO, dissolved in liquid krypton, have been carried out. Utilizing six different conformer pairs, an enthalpy difference of 204 ± 20 cm^–1 (2.44 ± 0.24 kJ/mol) was obtained, with the anti conformer (carbonyl bond trans to C=C bond) the more stable form. At ambient temperature, there is approximately 28 ± 2% of the syn conformer present. The anti conformer also remains in the infrared and Raman spectra of the polycrystalline solid. The optimal geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios, and vibrational frequencies, are reported for both conformers from MP2/6-31G(d) ab initio calculations. The potential function governing the conformational interchange has been obtained from the MP2/6-31G(d) ab initio calculations. The conformational stabilities were calculated from a variety of basis sets and at the highest level of calculations, MP2/6-311 + (2df,2pd), the anti conformer is predicted to be more stable by 178 cm^–1, which is in excellent agreement with the experimental results. The r ₀ adjusted structural parameters have been obtained for propenoyl fluoride and chloride from a combination of the previously reported microwave rotational constants and ab initio predicted parameters. Several of the parameters for the chloride are significantly different than those proposed from an electron diffraction investigation. The results of these spectroscopic, structural, and theoretical studies are discussed and compared to the corresponding results for some similar molecules.     

HNCO与CX（X=F，Cl，Br）自由基反应机理的密度泛函理论研究

用量子化学密度泛函理论的B3LYP方法,在6-31+G~*水平上按BERNY能量梯度解 析全参数优化了HNCO与CX（X=F,Cl,Br）反应势能面上各驻点的几何构型,通过 振动频率分析确认了中间体和过渡态,内禀反应坐标（IRC）对反应物、中间体、 过渡态和产物的相关性予以证实,对各驻点进行了零点能校正（ZPE）在此基础上 计算了反应能垒。研究结果表明,与HNCO和其它小分子自由基反应不同,HNCO与 CX自由基反应首先发生分子间H原子迁移,随后N与CX的C（1）原子相互靠近成键并 生成较稳定的中间体,再发生N-C（2）键的断裂,完成N向C（1）上的迁移并进一 步解离为产物。反应按反应物→TS1→IM→TS2→产物通道进行。反应为放热反应。     

PuX＋(X=H,O,N,C)的结构与势能函数

用密度泛函B3LYP方法对PuX＋(X=H,O,N,C)分子离子体系进行了理论研究.结果表 明,这些分子离子的基态电子状态分别是X 7Σ-(PuH＋)、X 6Σ-(PuO＋)、X 5Σ＋(P uN＋)和X 8Σ-(PuC＋);势能函数为Murrell-Sorbie势函数.并得到了相应的几何性质、 力学性质和光谱数据.     

氯化钐与甘氨酸配合物Sm(Gly)2Cl3·3H2O热化学研究

A complex of samarium with glymine， [Sm(Gly)₂Cl₃·3H₂O]， was synthesized and characterized by DSC， TG and DTG. A possible mechanism of thermal decomposition of this complex was suggested. The heat capacities of the complex were measured by a precision adiabatic calorimeter over the temperature range from 82 to 375 K. The solution enthalpies of reactants [SmCl₃·6H₂O+2Gly] and the products [Sm(Gly)₂Cl₃·3H₂O+3H₂O] were determined by an isoperibel solution- reaction calorimeter at 298.15 K， respectively; the standard molar enthalpy of formation of [Sm(Gly)₂Cl₃·3H₂O] was calculated through a designed thermochemical cycle.