Mechanism of the addition of nonenolizable aldehydes and ketones to (Di)metallenes (R(2)X=YR(2), X = Si,Ge Y = C,Si, Ge): a density functional and multiconfigurational perturbation theory study

The mechanism of the addition of nonenolizable aldehydes and ketones to group 14 (di)metallenes has been examined through a theoretical study of the addition of formaldehyde to Si=C, Ge=C, Si=Si, Si=Ge, and Ge=Ge bonds at the B3LYP/6-311++G(d,p) and CAS-MCQDPT2/6-31++G(d,p) levels of theory. The reaction pathways located can be grouped as either involving the formation of singlet diradical or zwitterionic intermediates or as concerted processes. Within each group of reaction pathways, several different mechanisms have been located, with not all mechanisms being available to all of the (di)metallenes. It was found that for reactions in which a Si-O bond results (i.e., addition to Si=C, Si=Si, and Si=Ge) both diradical and zwitterionic intermediates are possible; however, the formation of diradical intermediates was not found for reactions that result in the formation of a Ge-O bond (addition to Ge=C and Ge=Ge). The underlying cause of this pathway selectivity is examined, as well as the effect of solvent on the relative energies of the pathways. The results of the study shed light on the cause of experimentally obtained results regarding the mechanism of the reaction of (di)metallenes with nonenolizable ketones and aldehydes.     

Structural and electronic properties of Al12X+ (X=C, Si, Ge, Sn, and Pb) clusters

Using the first-principles method with the generalized gradient approximation, the authors have studied the structural and electronic properties of Al(12)X(+) (X=C, Si, Ge, Sn, and Pb) clusters in detail. The ground state of Al(12)C(+) is a low symmetry C(s) structure instead of an icosahedron. However, the Si, Ge, Sn, and Pb atom doped cationic clusters favor icosahedral structures. The ground states for Al(12)Si(+) and Al(12)Ge(+) are icosahedra, while the C(5nu) structures optimized from an icosahedron with a vertex capped by a tetravalent atom have the highest binding energy for Al(12)Sn(+) and Al(12)Pb(+) clusters. The I(h) structure and the C(5nu) structure are almost degenerate for Al(12)Ge(+), whose binding energy difference is only 0.03 eV. The electronic properties are altered much by removing an electron from the neutral cluster. The binding strength of a valence electron is enhanced, while the binding energy of the cluster is reduced much. Due to the open electronic shell, the band gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital are approximately 0.3 eV for the studied cationic clusters.     

杂硼原子簇XB6+ (X=C,Si, Ge,Sn, Pb)的稳定性和芳香性

利用从头算MP2方法和密度泛函理论B3LYP和B3PW91方法, 研究了杂硼原子簇XB₆⁺ (X=C, Si, Ge, Sn, Pb)的结构、稳定性及化学键合情况. 对C, Si, Ge, B使用6-311+G(d)基组, 对Sn和Pb使用LANL2DZ赝势基组. 研究结果表明, 具有C_s对称性的假平面XB₆⁺ (X=C, Si, Ge, Sn, Pb)结构是势能面上的全域极小点, 其稳定性要高于C_6v对称性的锥形结构和C₂对称性的假锥形结构. 在B3LYP水平上, 对这些异构体的势能面的极小点进行了自然键轨道(NBO)的分析; 对最稳定构型的最高占据分子轨道(HOMO)和最低空轨道(LUMO)能级差、分子轨道(MO)和核独立化学位移(NICS)进行了计算和讨论. 分析了杂原子和硼原子间、相邻硼原子间的键合情况, 讨论了最稳定构型的芳香性质.     

Zur Strukturchemie der Verbindungsreihe BaMg2X2 (X  Si,Ge, Sn,Pb)

On the Structural Chemistry of BaMg₂X₂ (X ? Si, Ge, sn, Pb) The new compounds BaMg₂X₂ (X ? Si, Ge, Sn, Pb) have been prepared and their structures have been determined. BaMg₂Si₂ and BaMg₂Ge₂ crystallize in the ThCr₂Si₂-type, BaMg₂Sn₂ and BaMg₂Pb₂ show two new atomic arrangements, which are layer variants of the former type.     

Theoretical studies on the band structures of superconducting solid compounds: Nb3X (X=Si, Ge, Sn, Pb)

The band structures of several analogous superconducting A-15 type solid compounds, Nb3X (X=Si, Ge, Sn, Pb), have been calculated by use of the tight-binding method within the Extended Huckel approximation (EHT). By analysis of their energy bands, densities of states and crystal orbital overlap populations, the dependence of the superconducting transition temperatures (Tc) on the electronic structures and bondings is qualitatively elucidated.     

LCGTO MP LSD calculations for the diatomics PdX (X = C,Si, Ge,Sn)

Results are presented of a theoretical study of RhC, PdC, PdSi, PdGe and PdSn metal-alloy diatomics performed with the LCGTO MP LSD method. For the RhC molecule the computed electronic structure and spectroscpic constants are in good agreement with experimental data. The ground state of RhC is found to be ²Σ⁺ withe the lowest-lying excited state, ²II, at 10654 cm⁻¹ above the ground state, in good agreement with experiment and with ab initio CI calculations. For PdC and the other Pd-group IV A dimers the ground state is predicted to be ¹Σ and the two lowest-lying excited state are ³II (at 2718 cm⁻¹ for PdC) and ³gS (at 12164 cm⁻¹ for PdC). Our results are in disagreement with ab initio CI studies for PdC, which found a ³Σ ground state with a ³II lowest-lying excited state, and for PdGe, which found a ³II ground state followed by ³Σ⁻ and ¹Σ⁺.     

Spektroskopische Untersuchungen an R3MF-Verbindungen (M = Si,Ge, Sn)

Spectroscopical Investigations on R₃MF Compounds (M = Si, Ge, Sn) The IR and RAMAN spectra of a number of R₃MF compounds (M? Si, Ge, Sn) have been recorded. The frequencies of the vibrational spectra were almost completely assigned. The measurements of the IR-spectra were investigated (as for as possible) in all states of aggregations. The force of the intermolecular interactions were discussed by means of the spectroscopic data.     

Mechanism and regioselectivity for the reactions of propylene oxide with X(100)-2x1 surfaces (X = C, Si, Ge): a density functional cluster model investigation

We have performed density functional cluster model calculations to explore the mechanism and regioselectivity for the reactions of propylene oxide with X(100)-2x1 surfaces (X = C, Si, and Ge). The computations reveal the following: (i) the reactions on Si(100) and Ge(100) are barrierless and highly exothermic; (ii) the reactions on X(100) (X = Si and Ge) are initiated by the formation of a dative-bonded precursor state followed by regioselective cleavage of the C2-O bond (C2 directly connected to the methyl-substituent) in propylene oxide, giving rise to a five-membered ring surface species; and (iii) the reaction on C(100), although highly exothermic, requires a large activation energy and would be kinetically forbidden at room temperature.     

Electronic structure and vibrational spectra of X20H20 (X=C, Si, Ge, Sn): A theoretical study

Optimized geometries, HOMO–LUMO gaps, vertical ionization potentials and electron affinities are obtained using HF, and B3LYP methods with 6-311G** basis set for C₂₀H₂₀, Si₂₀H₂₀ and Ge₂₀H₂₀. For germanium and tin analogues, B3LYP calculations are performed with LANL2DZ effective core potential. Electron correlation is included by doing MP2 calculation. The harmonic frequencies of all the compounds are obtained using B3LYP with 6-311G** and/or LANL2DZ basis sets. The force field and vibrational spectra are analyzed and 74 symmetry unique non-redundant local force constants are evaluated. Probable assignments are proposed for all the fundamentals based on the potential energy distribution.     

Sandwich-shaped silver(I) metallomacrocycles encapsulating a XF6(2-) (X = Si, Ge and Sn) anion

A series of sandwich-shaped complexes based on two square tetranuclear Ag(I) metallomacrocycles, [[Ag4(pprd)4]2(XF6)]-(BF4)6.8MeNO2 (pprd = 4-(2-pyridyl)pyrimidine; X = Si, Ge and Sn), in which a XF6(2-) anion is encapsulated, were prepared and their structures were characterized both in the solid state and solution.     

Synthesis and multinuclear NMR data of the ferrocenes (Me3Ecp)2Fe (E = C,Si, Ge,Sn, Pb)

The substituted cyclopentadienyl anions Me₃Ecp⁻ with E = C, Si, Ge, Sn, Pb have been prepared from either the mono- or disubstituted cyclopentadienes, including the hitherto unknown (Me₃Pb)₂C₅H₄. Representative examples have been characterized by ¹³C NMR spectroscopy. Treatment with iron(II) chloride yielded the ferrocenes (Me₃Ecp)₂Fe, which have been investigated by ¹H, ¹³C, ²⁹Si, ¹¹⁹Sn, and ²⁰⁷Pb NMR spectroscopy. ¹³C¹³C coupling and selective proton decoupling were used for the assignment of the ¹³C and ¹H signals. The shifts δ(¹³C) reflect the electron-releasing or -withdrawing power of the substituents Me₃E, but the isotope shifts ¹Δ¹³C(i)(¹³C(j)) do not show a similar trend. There is evidence that δ(¹¹⁹Sn) and δ(²⁰⁷Pb) are influenced by the coordination. The analysis of the coupling constants reveals that ¹J(¹³C(1)¹³C(2/5)) varies with the electronegativity of E. Because of the small range (4.5–5.0 Hz) of ¹J(⁵⁷Fe¹³C) the effect of E is apparent only when E = C is replaced by E = Si. As for the coupling between E and ¹³C or ¹H, the square root of the reduced coupling constant K is related linearly to the atomic number of E; exceptions are ¹K(²⁰⁷Pb¹³C).     

Infrared band intensities and bond polarities: Part 5 - XCl4 molecules (X = C,Si, Ge,Sn)

Gas phase band intensities of v₃ and v₄ of SiCl₄, GeCl₄ and SnCl₄ have been derived from dispersion curves measured using a Michelson interferometer in the range 1000 to 10 cm^?1. The results obtained are discussed in relation to the corresponding liquid phase band intensities. Bond polar properties are derived from the observed intensities using a modified Gribov method, the moments obtained being 0.9 D for SiCl, 1.5 D for GeCl and 2.7 D for SnCl.     

Geometries,vibrational frequencies,and electron affinities of X2Cl (X=C,Si,Ge) clusters

Ab initio quantum chemical calculations have been performed on X₂Cl^? and X₂Cl (X = C, Si, Ge) clusters. The geometrical structures, vibrational frequencies, electronic properties and dissociation energies are investigated at the Hartree–Fock (HF), Møller–Plesset second‐ and fourth‐order (MP2, MP4), CCSD(T) level with the 6‐311+G(d) basis set. The X₂Cl (X = C, Si, Ge) and X₂Cl^? (X = Si, Ge) take a bent shape obtained at the ground state, while C₂Cl^? has a linear structure. The impact on internal electron transfer between the X₂Cl and the corresponding anional clusters is studied. The three different types of electron affinities (EAs) at the CCSD(T) are reported. The most reliable adiabatic electronic affinities, obtained at the CCSD(T)/cc‐pvqz level of theory, are predicted to be 3.30, 2.62, and 1.98 eV for C₂Cl, Si₂Cl, and Ge₂Cl, respectively. The calculated EAs of C₂Cl and Ge₂Cl are in good agreement with theoretical results reported. The correlation effects and basis sets effects on the geometrical structures and dissociation energies are discussed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Gas‐phase reactions of XH3+ (X = C,Si, Ge) with NF3: a comparative investigation on the detailed mechanistic aspects

The gas‐phase reaction of CH₃⁺ with NF₃ was investigated by ion trap mass spectrometry (ITMS). The observed products include NF₂⁺ and CH₂F⁺. Under the same experimental conditions, SiH₃⁺ reacts with NF₃ and forms up to six ionic products, namely (in order of decreasing efficiency) NF₂⁺, SiH₂F⁺, SiHF₂⁺, SiF⁺, SiHF⁺, and NHF⁺. The GeH₃⁺ cation is instead totally unreactive toward NF₃. The different reactivity of XH₃⁺ (X = C, Si, Ge) toward NF₃ has been rationalized by ab initio calculations performed at the MP2 and coupled cluster level of theory. In the reaction of both CH₃⁺ and SiH₃⁺, the kinetically relevant intermediate is the fluorine‐coordinated isomer H₃X‐F‐NF₂⁺ (X = C, Si). This species forms from the exoergic attack of XH₃⁺ to one of the F atoms of NF₃ and undergoes dissociation and isomerization processes which eventually result in the experimentally observed products. The nitrogen‐coordinated isomers H₃X‐NF₃⁺ (X = C, Si) were located as minimum‐energy structures but do not play an active role in the reaction mechanism. The inertness of GeH₃⁺ toward NF₃ is also explained by the endoergic character of the dissociation processes involving the H₃Ge‐F‐NF₂⁺ isomer. Copyright © 2009 John Wiley & Sons, Ltd.     

Spin-orbit corrections to the indirect nuclear spin-spin coupling constants in XH4 (X = C, Si, Ge, and Sn)

Summary Using the quadratic response function at theab initio SCF level of approximation we have calculated the relativistic corrections from the spin-orbit Hamiltonian,H ^SO, to the indirect nuclear spin-spin coupling constants of XH₄ (X = C, Si, Ge, and Sn). We find that the spin-orbit contributions toJ _X-H are small, amounting only to about 1% forJ _Sn-H. For the geminal H-H coupling constants the relativistic corrections are numerically smaller than forJ _X-H, but in some cases relatively larger compared to the actual magnitude ofJ _H-H. We also investigate the use of an effective one-electron spin-orbit Hamiltonian rather than the fullH ^SO in the calculation of these corrections.