Mechanism of abstraction reactions of dimetallenes (R2X=XR2; X = C, Si, Ge, Sn, Pb) with halocarbons: a theoretical study

Potential energy surfaces for the abstraction reactions of dimetallenes with halocarbons have been studied using density functional theory (B3LYP). Five dimetallene species, (SiH(3))(2)X=X(SiH(3))(2), where X = C, Si, Ge, Sn, and Pb, have been chosen in this work as model reactants. The present theoretical investigations suggest that the relative dimetallenic reactivity increases in the order C=C < Si=Si < Ge=Ge < Sn=Sn < Pb=Pb. That is to say, for halocarbon abstractions there is a very clear trend toward lower activation barriers and more exothermic reactions on going from C to Pb. Moreover, for a given dimetallene, the overall barrier heights are determined to be in the order CF(4) > CCl(4) > CBr(4) > CI(4). That is, the heavier the halogen atom (Y), the more facile its abstraction from CY(4). Halogen abstraction is always predicted to be much faster than the abstraction of a CY(3) group irrespective of the dimetallene or halocarbon involved. Our model conclusions are consistent with some available experimental findings. Furthermore, both a configuration mixing model based on the work of Pross and Shaik and bonding dissociation energies can be used to rationalize the computational results. These results allow a number of predictions to be made.     

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.     

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.     

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.     

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.     

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.     

Electronic Structure of Fe+X Alloys (X = Si, Ge, Co)

The electronic structure of Fe–Ge, Fe–Si, and Fe–Co alloys has been investigated by X-ray photoelectron spectroscopy. In Fe–Ge alloys with less than 10 at.% Ge, the Fe–Ge bond is mainly formed by the Fe 4sp- and Ge 4p-electrons. The results obtained for this system are identical to those for the Fe–Si system. The form of the valence band reflects the density distribution of both iron d-electronic states the and p-electronic states of the second component, having more extended density distribution of valence electrons. In FeCo alloys, strong spatial localization of d-electron density takes place in the vicinity of the corresponding atoms, which is stronger on the iron atoms compared to pure iron; the valence band has a two-band structure reflecting the density distribution of the d-states of each component. X-ray photoelectron spectroscopy data are in good agreement with kinetic data for the alloys.     

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.     

Vibrational assignment of some X3MCo(CO)4 molecules (M = Si,Ge, Sn and X = Cl,Br, I)

The infrared and Raman vibrational spectra of X₃MCo(CO)₄ compounds (M = Si, Ge, Sn and X = Cl, Br, I) including depolarization measurements are presented. These spectra result in complete vibrational assignments which are different from those reported previously.     

Darstellung von Germanium-Mangan-, Germanium-Rhenium- und Zinn-Rhenium-Clustern des Typs M2(CO)8[μ-EXM(CO)5]2, (M = Mn,E = Ge,X = Br,I; M = Re,E = Ge bzw. Sn,X = I bzw. Cl,Br, I)

Preparation of Germanium-Manganese-, Germanium-Rhenium- and Tin-Rhenium-Clusters of the Type M₂(CO)₈[μ-EXM(CO)₅]₂ (M = Mn, E = Ge, X = Br, I; M = Re, E = Ge or Sn, X = I or Cl, Br, I) The clusters Re₂(CO)₈[μ-SnXRe(CO)₅]₂ are prepared by reaction of Re₂(CO)₁₀ and SnX₂ in a Schlenk-tube under release of pressure (X = Cl, Br, I) or in a sealed glass tube (X = Br, I). As central structural unit a four-membered Re₂Sn₂ ring has to be assumed. This unit can be opened again by reaction with CO under pressure. X₂Sn[Re(CO)₅]₂, which is also formed during the preparation of the clusters in dependance of the CO-pressure, indicates insertion of SnX₂ into the Re—Re bond to be the primary step. The corresponding clusters M₂(CO)₈[μ-GeXM(CO)₅]₂ (M = Mn, X = Br, I; M = Re, X = I) are prepared by reaction of GeI₂ and M₂(CO)₁₀ or of I₂Ge[Mn(CO)₅]₂ and Mn₂(CO)₁₀ or of Br₃GeMn(CO)₅ and BrMn(CO)₅. Ir frequencies of the new clusters are assigned.     

Magnetic Susceptibilities of ThM2X2 Compounds (M = Cr,Mn, Fe,Co, Ni and Cu; X = Si and Ge)

Magnetic susceptibilities of a series of ternary intermetallic compounds of the general composition ThM₂X₂(M = Cr, Mn, Fe, Co, Ni and Cu; X = Si and Ge) were determined by means of FARADAY method in the temperature interval 100–570°K. The results confirm the previously proposed magnetic behaviour of these compounds, based on the observation of the basic crystallographic parameters as a function of the atomic number of the transition metal element. The compounds were found to be alternatively ferromagnetics and antiferromagnetics depending on the atomic number of the transition metal atom.     

Nickel(O)-Komplexe mit anionischen Liganden des Typs E(C6H5) (E = Si,Ge, Sn)

Nickel(O) Complexes with the Anionic Ligands E (C₆H₅)^?₃ (E = Si, Ge, Sn) Complexes of the type Me^I_XNi(EPH₃)_X(THF)_Y are formed from Ni(COD)₂ by substitution with Me^IEPh₃ (E = Si, Ge, Sn) in THF (COD = Cyclooctadiene-1,5). In the case of the ligands GePh^?₃ and SnPh^?₃ nickel(O) is fourfold coordinated, but in the case of SiPh^?₃ it is only two-fold or threefold coordinated. Products of the reaction between Ni(COD)₂ and LiPbPh₃ are Li₂Ni(COD)Ph₂(THF)₅ and Ph₃PbPbPh₃. The ¹H-n.m.r., ²⁹Si-n.m.r., and ¹¹⁹Sn-Mössbauer spectra of the complexes Me^I_XNi(EPh₃)_X(THF)_Y are compared with the spectra of the corresponding alkali compounds Me^IEPh₃. The magnetic anisotropy effects of the atomes Ge, Sn, Pb and Ni are of high importance for ¹H- and ²⁹Si-chemical shifts. The donor action of SnPh^?₃ is shown by the Mössbauer spectrum of Na₄Ni(SnPh₃)₄(THF)₄. But there is no direct evidence of π-back donation in the compound.     

The ruthenium(II)-supported heteropolytungstates [Ru(dmso)3(H2O)-XW11O39]6- (X = Ge, Si)

The novel Ru(II)-supported heteropolytungstates [Ru(dmso)(3)(H(2)O)XW(11)O(39)](6-)(X = Ge, Si) have been synthesized and characterized by single-crystal X-ray diffraction, multinuclear NMR ((183)W, (13)C, (1)H, (29)Si) and IR spectroscopy, elemental analysis and electrochemistry. The novel polyanion structure consists of a Ru(dmso)(3)(H(2)O) unit linked to a monolacunary [XW(11)O(39)](8-) Keggin fragment via two Ru-O-W bonds resulting in an assembly with C(1) symmetry. Polyanions 1 and 2 were synthesized by reaction of cis-Ru(dmso)(4)Cl(2) with [A-alpha-XW(9)O(34)](10-) in aqueous, acidic medium (pH 4.8). Tungsten-183 NMR of 1 leads to a spectrum with 11 peaks of equal intensity, indicating that the solid-state structure is preserved in solution. Electrochemistry studies revealed that 1 and 2 are stable in solution at least from pH 0 to 7, even in the presence of dioxygen. Their cyclic voltammetry patterns show mainly two two-electron reversible W-waves, those of the Si derivative 2 being located at slightly more negative potentials than those of the Ge derivative 1. The observed stability of 1 and 2 might be attributed to a stabilization of the Ru-center both by the strongly bound dmso ligands and the Keggin moiety. This stabilization drives the redox waves of Ru outside the accessible potential range. However, conditions were found to reveal, at least partially, the redox behavior of Ru in 1 and 2.     

Interaction between cobaltocenium and decamethylcobaltocenium salts and Ph3ELi (E = Si,Ge, Sn)

Reactions of cobaltocenium salts [(C₅R₅)₂Co]PF₆ (R = H, Me) with Ph3ELi (E = Si, Ge, Sn) and with Ph₂SbLi mainly follow two pathways (nucleophilic addition and one-electron reduction), yielding cobalt cyclopentadiene-cyclope ntadienyl complexes (⁴-Ph₃EC₅R₅)(⁵-C₅R₅)Co (R = H, E = Si, Ge, Sn; R = Me, E = Si) and cobaltocenes (C₅R₅)₂Co (R = H, Me), respectively. The contribution of nucleophilic addition of Ph₃ELi decreases in the order of elements Si > Ge > Sn and when hydrogen atoms are replaced by methyl groups in the initial cobaltocenium salt. Thermal decomposition of cobalt cyclopentadiene-cyclopentadienyl complexes results in substituted cobaltocenes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 10, pp. 2557–2560, October, 1996.     

Magnetische Messungen anHeusler-Phasen (Co,Mn)2 XY (X=Ti,Zr,Hf und Mn;Y=Ge und Sn)

Magnetic measurements onHeusler alloys (Co,Mn)₂ XY have been performed. With a few exceptions there is no enhancement of ferromagnetism while substituting cobalt by manganese. The results can be explained by a partially antiferromagnetic ordering of the manganese atoms.     

X-ray crystal structures of [XF(6)][Sb(2)F(11)] (X = Cl, Br, I); (35,37)Cl, (79,81)Br, and (127)I NMR studies and electronic structure calculations of the XF(6)(+) cations

The single-crystal X-ray structures of [XF(6)][Sb(2)F(11)] (X = Cl, Br, I) have been determined and represent the first detailed crystallographic study of salts containing the XF(6)(+) cations. The three salts are isomorphous and crystallize in the monoclinic space group P2(1)/n with Z = 4: [ClF(6)][Sb(2)F(11)], a = 11.824(2) A, b = 8.434(2) A, c = 12.088(2) A, beta = 97.783(6) degrees , V = 1194.3(4) A(3), R(1) = 0.0488 at -130 degrees C; [BrF(6)][Sb(2)F(11)], a = 11.931(2) A, b = 8.492(2) A, c = 12.103(2) A, beta = 97.558(4) degrees , V = 1215.5(4) A(3), R(1) = 0.0707 at -130 degrees C; [IF(6)][Sb(2)F(11)], a = 11.844(1) A, b = 8.617(1) A, c = 11.979(2) A, beta = 98.915(2) degrees , V = 1207.8(3) A(3), R(1) = 0.0219 at -173 degrees C. The crystal structure of [IF(6)][Sb(2)F(11)] was also determined at -100 degrees C and was found to crystallize in the monoclinic space group P2(1)/m with Z = 4, a = 11.885(1) A, b = 8.626(1) A, c = 12.000(1) A, beta = 98.44(1), V = 1216.9(2) A(3), R(1) = 0.0635. The XF(6)(+) cations have octahedral geometries with average Cl-F, Br-F, and I-F bond lengths of 1.550(4), 1.666(11) and 1.779(6) [-173 degrees C]/1.774(8) [-100 degrees C] A, respectively. The chemical shifts of the central quadrupolar nuclei, (35,37)Cl, (79,81)Br, and (127)I, were determined for [ClF(6)][AsF(6)] (814 ppm), [BrF(6)][AsF(6)] (2080 ppm), and [IF(6)][Sb(3)F(16)] (3381 ppm) in anhydrous HF solution at 27 degrees C, and spin-inversion-recovery experiments were used to determine the T(1)-relaxation times of (35)Cl (1.32(3) s), (37)Cl (2.58(6) s), (79)Br (24.6(4) ms), (81)Br (35.4(5) ms), and (127)I (6.53(1) ms). Trends among the central halogen chemical shifts and T(1)-relaxation times of XF(6)(+), XO(4)(-), and X(-) are discussed. The isotropic (1)J-coupling constants and reduced coupling constants for the XF(6)(+) cations and isoelectronic hexafluoro species of rows 3-6 are empirically assessed in terms of the relative contributions of the Fermi-contact, spin-dipolar, and spin-orbit mechanisms. Electronic structure calculations using Hartree-Fock, MP2, and local density functional methods were used to determine the energy-minimized gas-phase geometries, atomic charges, and Mayer bond orders of the XF(6)(+) cations. The calculated vibrational frequencies are in accord with the previously published assignments and experimental vibrational frequencies of the XF(6)(+) cations. Bonding trends within the XF(6)(+) cation series have been discussed in terms of natural bond orbital (NBO) analyses, the ligand close-packed (LCP) model, and the electron localization function (ELF).     

Highly luminescent complexes [Mo6X8(n-C3F7COO)6]2- (X=Br, I)

New complexes (Bu(4)N)(2)[Mo(6)X(8)(n-C(3)F(7)COO)(6)] (X = Br, I) display extraordinarily bright long-lived red phosphorescence both in solution and solid phases, with the highest emission quantum yields and the longest emission lifetimes among hexanuclear metal cluster complexes of Mo, W and Re, hitherto reported.