Electronic Absorption Spectroscopy of H2X （X=O,Te, Po）： Theoretical Treatment of Spin-Orbit Effects

The electronic spectroscopy of H2X （X=O, Te, Po） was investigated by means of spinorbit configuration interaction （EPCISO） and restricted active space state interaction （SORASSI）. The transition energies to the low-lying singlet and triplet states of H2O, in which the SO interaction is zero, compare rather well with the experimental data as well as to other theoretical values. The theoretical electronic absorption spectrum is characterized by three allowed transitions A^1B1 （2px（O）→σ^＊g/3s（O））, B^1A1（σg→σ^＊g/3s（O）） and A^1S2（σg→σ^＊u） calculated at 7.68, 9.94, and 11.72 eV, respectively. The theoretical absorption spectra of H2X （X=Te, Po） are shifted to the red with the A^1B1 （npx（X）→σ^＊g） states calculated at 5.06 eV （H2Te） and 4.40 eV （H2Po） and the A^1B2 （σg→σ^＊u） states calculated at 7.89 eV （H2Te） and 7.77 eV （H2Po）. The largest SO splitting amounts to 0.34 eV and is found for the lowest a^3A1 of H2Po. In H2Te the SO effects are still negligible with a maximum splitting of 0.04 eV for the lowest a^3B2. The two methods lead to comparable results but the EPCISO approach depends strongly on the reference wavefunction.     

Molecular assembly of dithiaparacyclophanes mediated by non-covalent X…X,X…Y and C–H…X (X,Y=Br,S, N) interactions

Regioselectivity for the 5,8,15,18-substituted isomer over the 5,8,14,17-isomer was observed in a series of mercaptan–bromide coupling reactions leading to the formation of 2,11-dithia[3.3]paracyclophanes. Their molecular assembly was established by X-ray crystallographic studies. In the crystal packing of these paracyclophanes, several types of non-covalent interactions including halogen–halogen interaction, halogen-bonding interaction, weak hydrogen-bonding interaction, etc. are observed in crystals 3a, 3b and 3c. There is evidence to indicate that weak non-covalent Br…Br, Br…S, Br…N, C–H…S, S…S and C–H…N interactions play an important role in governing their molecular assembly assumed in the solid state. The attractive interactions of Br…Br, Br…S and Br…N are also rationalised and supported in terms of the density functional theory calculations.

     

Theoretical study of aluminide clusters Al13X, Al13X−, and Al13X 2 − (X=H, Hal, OH, NH2, CH3, and C6H5)

The structural, electronic, energy, and vibrational characteristics of the Al₁₃X^? and Al₁₃X ₂ ^? clusters, with an aluminum-centered (Al_c) icosahedral cage Al₁₃ and with one or two outer-sphere ligands X=H, F, Cl, Br, OH, NH₂, CH₃, C₆H₅, have been calculated within the B3LYP approximation of the density functional theory using the 6-31G* and 6-311+G* basis sets. In all Al₁₃X^? radicals, the unpaired electron is localized at the cage atom Al* located opposite the Al-X bond. This Al* atom is the most favorable site for attaching the second X ligand of any nature (trans-addition rule). According to the previously suggested molecular model of the valence state of the [Al ₁₃ ^? ] “superatom,” the calculated energies D ₁(Al ₁₃ ^? -X) of addition of the first ligand to the Al ₁₃ ^? anion are about 1 eV lower than the corresponding energies of addition of the second ligand D ₂(XAl ₁₃ ^? -X). The structure of the Al₁₃ cage depends on the nature of the nature of the substituent X and can radically change in going from anions to their neutral congeners. In the lowest-lying Al₁₃X isomer with electronegative substituents X (Hal, OH, NH₂, CH₃, etc.), the aluminum cage has a marquee structure (1, symmetry C _s) with a hexagonal base and a pentagonal “roof.” For Al₁₃X analogues with electropositive ligands X (Al, Li, Na), a tridentate isomer (T, C _3v ) with the X substituent coordinated to a face of the Al₁₃ icosahedron is preferable. In the case of moderately electronegative X ligands (of the H type), the marquee (1) and icosahedral (T) isomers are close in energy. The stretching vibration frequencies of isomers 1 and T differ significantly in magnitude and intensity so that vibrational spectroscopy methods can be especially applicable to their experimental identification.     

Intramolecular vibrational energy redistribution in aromatic molecules of type C₆H₅X (X = H, D, F, Cl, CH₃, CF₃)

Femtosecond IR pump UV probe spectroscopy was employed in the gas phase to study intramolecular vibrational energy redistribution (IVR) in benzene and five monosubstituted derivatives thereof. After selective excitation of the first overtone of the ring CH-stretch vibration, all molecules showed the same two-step redistribution dynamics characteristic for nonstatistical IVR. The nature of the substituent influences mainly the second, slower IVR component. The presence of an internal rotor does not alter the redistribution rate or pathway compared to that of a monatomic substituent of equal mass. Coupling order model calculations reflect the experimental trends well if the polyatomic substituents are regarded as decoupled from the intra-ring dynamics and modeled as point masses.     

Structures and bonding situation of Pb2X2 (X?=?H, F, Cl, Br and I)

Quantum chemical calculations using DFT (BP86) and ab initio methods (MP2, MP4 and CCSD(T)) have been carried out for the title compounds. The nature of the Pb?CPb interactions has been investigated with an energy decomposition analysis. The energy minimum structures of the halogen substituted Pb₂X₂ molecules possess a doubly bridged butterfly geometry A like the parent system Pb₂H₂. The unusual geometry can be explained with the interactions between PbX fragments in the X ²?? ground state which leads to one Pb?CPb electron-sharing ?? bond and two donor?Cacceptor bonds between the Pb?CX bonds as donor and vacant p(??) AOs of Pb. The energy difference between the equilibrium form A and the linear structure XPb??PbX (E) which is a second-order saddle point is much higher when X is a halogen atom than for X?=?H. This is because the a ⁴??^?????X ²?? excitation energies of PbX (X?=?F?CI) are higher than for PbH. The structural isomers B, D1, D2, E, F1, F2 and G of Pb₂X₂ are no minima on the potential energy surface.     

Assessment of the intramolecular C–H⋯X (X=F,Cl, Br) hydrogen bonding of 1,4-diphenyl-1,2,3-triazoles

The intramolecular six-membered C–H?X (X=F, Cl, Br) hydrogen bonding motif of halogen-substituted 1,4-diphenyl-1,2,3-triazole compounds has been assessed. Twelve triazole derivatives have been designed and prepared, which bear fluorine, chlorine or bromine atoms on the ortho- and/or para-positions of the benzene rings. ¹H NMR, X-ray crystallography, and DFT calculation investigations revealed that the ortho-fluorine, chlorine, and bromine atoms of the benzene ring on the C-4 of the triazole unit all can form six-membered C–H?X hydrogen bonding. In contrast, only fluorine forms similar, relatively stable intramolecular hydrogen bonding on the N-1 side of the triazole unit.     

C28X4（X=H,Cl）,CX4（X=H,Cl）的结构和电子光谱的理论研究

用ＩＮＤＯ法对Ｃ２８Ｘ４（Ｘ＝Ｈ，Ｃｌ）和ＣＸ４（Ｘ＝Ｈ，Ｃｌ）进行几何构型优化，得到Ｔｄ对称性的构型Ｃ２８Ｘ４有４种键、４种不等同原子，基态为稳定的闭壳层分子，以此构型为基础计算了上述分子的电子光谱，并预测Ｃ２８Ｘ４的电子光谱。     

Theoretical study of X + H2 → XH + H and reverse reactions (X = F,Cl, Br,I) using a new empirical potential energy surface

A method for constructing empirical potential surfaces is proposed which is based on the BSBL (bond-strength-bond-length) treatment originally developed to predict kinetic parameters for atom transfer reactions. Quasiclassical trajectory results for X + H₂ → HX + H (X = F, Cl, Br, I) and the reverse reactions were used to demonstrate the utility of the new PES for the study of the dynamics and kinetics of metathesis reactions.     

C70X2(X=H,F, Cl)的稳定性和电子光谱

用INDO方法研究C70H2四种异构体的稳定性, 表明其最稳定异构体为1, 9-C70H2和7, 8-C70H2, 两者能量差为16.3KJ.mol^-^1, 与实验值及ab initio计算值接近; 光谱计算表明, 其特征吸收峰与实验值一致。在此基础上预测C70F2和C70Cl2的稳定性和电子光谱, 表明C70F2四种异构体的稳定性顺序与C70H2一致, 而C70Cl2则以21, 42-异构体最为稳定。二者的电子光谱与C70H2极其相似只是在500nm以上有细微差别。     

Structures, energies, bonding, and NMR properties of pnicogen complexes H2XP:NXH2 (X ═ H, CH3, NH2, OH, F, Cl)

Ab initio calculations have been carried out in a systematic investigation of P···N pnicogen complexes H(2)XP:NXH(2) for X ═ H, CH(3), NH(2), OH, F, and Cl, as well as selected complexes with different substituents X bonded to P and N. Binding energies for complexes H(2)XP:NXH(2) range from 8 to 27 kJ mol(-1) and increase to 39 kJ mol(-1) for H(2)FP:N(CH(3))H(2). Equilibrium structures have a nearly linear A-P-N arrangement, with A being the atom directly bonded to P. Binding energies correlate with intermolecular N-P distances as well as with bonding parameters obtained from AIM and SAPT analyses. Complexation increases (31)P chemical shieldings in complexes with binding energies greater than 19 kJ mol(-1). One-bond spin-spin coupling constants (1p)J(N-P) across the pnicogen interaction exhibit a quadratic dependence on the N-P distance for complexes H(2)XP:NXH(2), similar to the dependence of (2h)J(X-Y) on the X-Y distance for complexes with X-H···Y hydrogen bonds. However, when the mixed complexes H(2)XP:NX'H(2) are included, the curvature of the trendline changes and the good correlation between (1p)J(N-P) and the N-P distance is lost.     

Comparison of the crystal structures of Co2(X 2O7)·2H2O,X=P and As

Summary Crystals of Co₂(X ₂O₇)·2H₂O,X=P/As were synthesized under hydrothermal conditions. Their crystal structures were determined by single crystal X-ray diffraction:a=6.334(1)/6.531(2),b=13.997(2)/14.206(4),c=7.637(1)/7.615(2)Å, =94.77(2)/94.74(2)°, space group P2₁/n,R=0.032/0.046,R _w=0.028/0.034 for 2423/2042 reflections and 131/119 variables. Within the twoXO₄ tetrahedra connected via a common corner to anX ₂O₇ group the average P-O bond lengths are approximately equal (1.540 and 1.543 Å), but As-O differs significantly (1.685 and 1.696 Å). A comparison with the isotypic Mn and Mg pyrophosphates shows a correlation between the ratio Me-O/X-O and the angle O-X-O.

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Vergleich der Kristallstrukturen von Co₂(X ₂O₇)·2H₂O,X=P und As

Zusammenfassung Kristalle von Co₂(X ₂O₇)·2H₂O,X=P/As wurden unter Hydrothermalbedingungen synthetisiert. Ihre Kristallstrukturen wurden mittels Röntgenbeugung an Einkristallen bestimmt:a=6.334(1)/6.531(2),b=13.997(2)/14.206(4),c=7.637(1)/7.615(2) Å, =94.77(2)/97.74(2)°, Raumgruppe P2₁/n,R=0.032/0.046,R _w=0.028/0.034 für 2423/2042 Reflexe und 131/119 Variable. In den beiden über eine gemeinsame Ecke zuX ₂O₇-Gruppen verknüpftenXO₄-Tetraedern sind die mittleren P-O-Abstände ungefähr gleich (1.540 und 1.543 Å), hingegen differiert As-O signifikant (1.685 und 1.696 Å). Ein Vergleich mit den isotypen Mn- und Mg-Pyrophosphaten zeigt eine Korrelation zwischen dem Quotienten Me-O/X-O und dem WinkelX-O-X.

     

Reactivity of the Ge–H,Sn–H,P–H,and Se–H Bonds in Radical Abstraction Reactions

The experimental data for the liquid- and gas-phase reactions of atoms and radicals with organoelement compounds R _{n – 1}E–H

Comparative study of the photoassociation reaction of He + X+→ HeX+ (X = H,D): Including multiphoton transitions and dissociations

Using the time-dependent quantum wave packet method, the photoassociation (PA) processes of He + H ⁺→ HeH⁺ and He + D ⁺→ HeD⁺, driven by the sin²-shaped femtosecond laser pulse in the electronic ground state, including multiphoton transitions and dissociations, are investigated for a wide range of initial collision momenta spanning from 1 to 4 a.u. (or for the collision energy roughly in the ranges of 0.009∼0.148 eV and 0.006∼0.089 eV for HeH⁺ and HeD⁺ systems, respectively). It is found that, at some collision momenta, multiphoton transitions to deeply bound states are inevitable to occur and can greatly decrease the PA probability of the target state that selected is the vibrational state v = 6. For the dissociation process, the higher-order (two- and three-photon) dissociations, measured from the target state, tend to be significant at relative high collision energies, which implies that above-threshold dissociations may also be an important loss mechanism in the PA process. In addition, it is also shown that the higher-order dissociation is much stronger for HeH⁺ systems than that for HeD⁺ systems at a given collision momentum, and could be enhanced by the strong transitions among deeply bound states.     

Reactions of SiH2(X̄1A1) with H2, CH4, C2H4, SiH4 and Si2H6 at 298 K

Reaction rate constants of SiH₂(X̄¹A₁) have been directly measured for the first time using the laser photolysis—laser-induced fluorescence method. The preparation of SiH₂ radical in the laser photolysis (193 nm) of phenylsilane and the concentration of the radical is demonstrated by a dye laser at 580.1 nm (X̄¹A₁-Ā¹B₁). The reaction rate constants of SiH₂(X̄¹A₁) with H₂, CH₄, C₂H₄, SiH₄ and Si₂H₆, are 0.001, 0.01, 0.97, 1.1 and 5.7×10⁻¹⁰ cm³ molecule⁻¹ s⁻¹, respectively. For SiH₂(Ā¹B₁(0.2,0)), the collision-free lifetime is 0.6 μs and the quenching rate constant for He is 3.8×10⁻¹⁰ cm³ molecule⁻¹ s⁻¹.     

CH2X(X=H,F,Cl)与臭氧反应机理的量子化学研究

用量子化学UMP2方法,在6-311++G**基组水平上研究了CH2X(X=H,F,Cl)与臭氧反应机理,全参数优化了反应过程中反应物、中间体、过渡态和产物的几何构型,在UQCISD(T)/6-311++G**水平上计算了它们的能量,并对它们进行了振动分析,以确定中间体和过渡态的真实性.从CH2X(X=H,F,Cl)与O3的反应机理的研究结果看,它们与O3反应的活性都比较强,相对而言,活性大小顺序为CH2F＞CH3＞CH2Cl,也就是说,CH2F自由基与臭氧间的反应活性最强,对大气臭氧的损耗将是最大的.同时研究还发现CH2X(X=H,F,Cl)系列自由基与O3的反应都是强放热反应.     

11B-11B cosy NMR studies of derivatives of the octahydrotriborate anion, [B3H7(X)]− and [B3H6(X)2]−

2-D ¹¹B-¹¹B correlation (COSY) spectra have been obtained on the series of monosubstituted and disubstituted octahydrotriborate anions, [B₃H₇(X)]⁻ (X = Cl, NCS, NCSe, NCBH₃, NCBH₂Cl, NCBPh₃, NCBH₂CN, NCB₃H₇ or CNB₃H₆Cl) and [B₃H₆(Cl)(X)]⁻ (X = Cl, NCS, NCBH₂Cl or NCB₃H₇). All monosubstituted derivatives and [B₃H₆(Cl)₂]⁻ showed a coupling correlation between the substituted and unsubstituted borons. The unsymmetrically disubstituted derivatives showed only one coupling correlation, between the borons carrying the substituents. The absence of other correlations is attributed to relaxation phenomena. The correlations are independent of the solid-state structural type.     

On the infrared spectra of libratory modes of H2O molecules in SrX2 · 6H2 O (X = Cl,Br)

A detailed study of the libratory modes of H₂O molecules in the i.r. spectra of SrX₂ · 6H₂O (X = Cl, Br) is reported. The rocking, wagging and twisting libratory modes of (H₂O)_b (bridging type bonding) and (H₂O)_t (terminal type bonding) molecules are assigned at 705, 552, 658 and 460, 400, 438 cm⁻¹ and at 687, 532, 625 and 448, 370, 405 cm⁻¹ in the respective spectra. Using a semi-empirical relation reported by the authors in an earlier communication, the barrier height for (H₂O)_b is estimated to be 22.16 and 20.04 kcal/mole and that for (H₂O)_t to be 10.04 and 8.64 kcal/mole in the respective salts. The value of the force constants K_H and K_H′ for H₂O molecules are also reported.     

Heats of reaction of HMo(CO)3C5H5 with CCl4 and CBr4 and of NaMo(CO)3C5H5 with I2 and CH3. Solution thermochemical study of the MoX bond for X = H,Cl, Br,I and CH3

The heats of reaction of HMo(CO)₃C₅H₅ with CX₄ (X = Cl, Br) producing XMo(CO)₃C₅H₅ have been measured by solution calorimetry and are −31.8±0.9 and −34.4±2.0 kcal/mole, respectively. The heats of reaction of NaMo(CO)₃C₅H₅ with I₂ and CH₃I producing IMo(CO)₃C₅H₅ and H₃CMo(CO)₃C₅H₅ are −32.3± 1.3 and −7.7± 0.3 kcal/mole. Oxidation with Br₂CCl₄ yielding Br₃Mo(CO)₂C₅H₅ was measured for the following complexes: (C₅H₅(CO)₃Mo)₂, (−92.0±1.0 kcal/mole), BrMo(CO)₃C₅H₅ (−24.9± 2.0 kcal/mole) and HMo(CO)₃C₅H₅ (−60.7± 2.0 kcal/mole). These and other data are used to calculate the Mo–X bond strength for X = H, Cl, Br, I, and CH₃. These bond strength estimates are compared to those reported for X₂Mo(C₅H₅)₂. Iodination of H₃CMo(CO)₃C₅H₅, reported in the literature to yield CH₃I and IMo(CO)₃C₅H₅, actually produces CH₃C(O)I and I₃Mo(CO)₂C₅H₅.     

Substituent effects on the compounds CX1X2•− (X1, X2 = H, F, Cl, Br, I) from theoretical investigation

The electronic and molecular structures of mono- and dihalocarbene anions constructed by model CX¹X^2?? (X¹, X² = H, F, Cl, Br, I), as well as the corresponding carbenes CX¹X² and analogous silicon-anions SiX¹X^2??, have been studied in detail using the B3LYP, MP2, and QCISD(T) levels of theory. Our calculated findings suggest that stabilization of the compounds is associated with the size of the halogen substituent X, which is further confirmed by ionization energies, the spin density (S _d), and the second-order perturbative energies (E(2)). Besides, we have also explored the source of the anions’ proton affinity difference.