Les phases Na4XO4 (X = Si,Ti, Cr,Mn, Co,Ge, Sn,Pb) et K4XO4 (X = Ti,Cr, Mn,Ge, Zr,Sn, Hf,Pb)

The isotypic Na₄XO₄ (X = Si, Ti, Cr, Mn, Co, Ge, Sn, Pb) and K₄XO₄ (X = Ti, Cr, Mn, Ge, Zr, Sn, Hf, Pb) phases crystallize in the triclinic system. Optical and magnetic properties of the chromium, manganese, and cobalt compounds show that the transition element has a tetrahedral surrounding.     

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.     

Verbindungsbildung in den quasi-binären Systemen AcX4?MX2 (Ac = Th,U; M = Ca,Sr, Ba,Eu, Ge,Sn, Pb; X = Br,I)

Formation of Compounds in the Quasi-binary Systems AcX₄? MX₂ (Ac = Th, U; M = Ca, Sr, Ba, Eu, Ge, Sn, Pb; X = Br, I) T,x-phase diagrams of the systems ThI₄? SnI₂, ThI₄? PbI₂, ThI₄? CaI₂, and ThI₄? SrI₂ were established using thermoanalysis and x-ray methods. The only ternary compounds have a 1:1 composition. Further AcMX₆ compounds (Ac: Th, U; M: Ca, Sr, Ba, Eu, Ge, Sn, Pb; X: Br, I) were synthesized and their structures investigated. Four structure types are found depending on the temperature and the Ac/M combinations. The structures of γ-ThSnI₆ and β-ThSnI₆ were determined with single crystal methods as representatives of a whole series of isotypic compounds.     

Zur Kenntnis der inversen Perowskite M3TO (M = Ca,Sr, Yb; T = Si,Ge, Sn,Pb)

On the Inverse Perovskites M₃TO (M = Ca, Sr, Yb; T = Si, Ge, Sn, Pb) Ca₃SiO and seven further inverse perovskites M₃TO (M = Ca, Sr, Yb; T = Si, Ge, Sn, Pb) were prepared in iron crucibles under argon by the reactions 6 M + TO₂ + T = 2 M₃TO, and 3 M+ TO = M₃TO for Yb₃PbO, respectively, at temperatures between 1123 to 1173 K. The crystal structures of all compounds were solved and refined using X—ray powder diffraction methods. Ca₃SiO, Ca₃GeO, Sr₃SiO, Sr₃GeO, Yb₃SiO and Yb₃GeO are orthorhombic perovskites (anti—GdFeO₃—type, space group Pbnm, No. 62, Z = 4). They show slightly distorted corner—sharing OM₆ octahedra that are tilted with respect to their positions in the ideal perovskite structure. The effective radii of the T^4— vary significantly with M²⁺. Thus, these perovskites can no longer be discussed in terms of the hard—sphere model, and Goldschmidt's tolerance factor does not apply. The ideal cubic representatives Yb₃SnO and Yb₃PbO were refined in space group Pm3¯m (anti—SrTiO₃ type, Z = 1).     

Studies on ABX6 Compounds. V. Thermodynamics and kinetics of the high pressure transformations on ABX6 compounds (A = Ca,Dy, Ge,Sn, Pb; B = Th,U; X = I)

The results of high pressure experiments with ternary iodides of the general formula ABI₆ with A = Ca, Dy, Ge, Sn, Pb and B = Th, U are described. These compounds transform from a β- to a γ-SnThI₆-type structure, both variants of known trihalide structures (BiI₃- and PuBr₃-type). Trends and pecularities in the values for the minimal transformation pressures and in the velocities of transition are pointed out, and they are discussed in terms of geometric and electronic factors.     

Central‐Atom Size Effects on the Methyl Torsions of Group XIV Tetratolyls

The Group XIV tetratolyl series X(C₆H₄‐CH₃)₄ (X=C, Si, Ge, Sn, Pb) were studied by using inelastic neutron scattering to measure the low‐energy phonon spectra to directly access the methyl‐group torsional modes. The effect of increased molecular radius as a function of the size of the central atom was shown to have direct influence on the methyl dynamics, reinforced with the findings of molecular dynamics and contact surface calculations, based upon the solid‐state structures. The torsional modes in the lightest analogue were found to be predominantly intramolecular: the Si and Ge analogues have a high degree of intermolecular methyl–methyl group interactions, whilst the heaviest analogues (Sn and Pb) showed pronounced intermolecular methyl interactions with the whole phonon bath of the lattice modes.     

Gd5-xYxTt4 (Tt = Si or Ge): effect of metal substitution on structure, bonding, and magnetism

A crystallographic study and theoretical assessment of the Gd/Y site preferences in the Gd 5- x Y x Tt 4 ( Tt = Si, Ge) series prepared by high-temperature methods is presented. All structures for the Gd 5- x Y x Si 4 system belong to the orthorhombic, Gd 5Si 4-type (space group Pnma). For the Gd 5- x Y x Ge 4 system, phases with x < 3.6 and x >or= 4.4 adopt the orthorhombic, Sm 5Ge 4-type structure. For the composition range of 3.6 相似文献   

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.     

Order–disorder phenomena in crystalline phases of compounds E(XMe3)4 where E = C,Si, Ge and X = Si,Sn

We discuss the dynamic solid‐state properties of crystalline phases E(XMe₃)₄ as seen by solid‐state NMR and powder X‐ray diffraction. In the first part we will qualitatively describe some of the NMR tools suitable for such investigations. In the second part we will give examples from the group of solid compounds E(XMe₃)₄ with E = C, Si, Ge and X = Si, Sn. Copyright © 2002 John Wiley & Sons, Ltd.     

First-principle studies of Ca-X (X=Si,Ge,Sn,Pb) intermetallic compounds

The structural properties, elastic properties, heats of formation, electronic structures, and densities of states of 20 intermetallic compounds in the Ca-X (X=Si, Ge, Sn, Pb) systems have been systematically investigated by using first-principle calculations. Our computational results indicated that with increasing atomic weight of X, the bulk modulus of Ca-X intermetallic compounds decreases gradually. It was also found that Ca₃₆Sn₂₃ and CaPb are mechanically unstable phases. Results on the electronic energy band and densities of states also indicated that Ca₃Si₄ is an indirect band gap semiconductor with a band gap of 0.598 eV, and Ca₂Si, Ca₂Ge, Ca₂Sn, and Ca₂Pb are direct band gap semiconductors with band gaps of 0.324, 0.265, 0.06, and 0.07 eV, respectively. In addition, it is found that the absolute values of heats of formation for all Ca-X intermetallics are larger than 30 kJ/mol atom.     

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.     

New heteroorganic betaines containing the (+)E15—C—E14—X(–) and (+)E15—C—E14(–) structural fragments (E15 = P,As; E14 = Si,Ge, Sn; X = C,S, O,NR)

The review surveys the data on the reactions of phosphorus and arsenic ylides with compounds containing E=X bonds (E = C, Si, Ge, or Sn; X = C or S), cyclic oligomers (R₂ES)_n (n = 2 or 3), and heavier analogs of carbenes. These reactions give rise to two new classes of heteroorganic betaines containing the ⁽⁺⁾E¹⁵—C—E¹⁴—X^(–) (I) and ⁽⁺⁾E¹⁵—C—E^14(–) (II) (E¹⁵ = P or As; E¹⁴ = Si, Ge, or Sn; X = C or S) structural fragments. Procedures for the synthesis of these compounds, their reactivities, the X-ray diffraction structures, and the electronic structures established by high-level quantum-chemical calculations are considered in detail. The carbon analogs of betaines of type I, viz., compounds bearing the ⁽⁺⁾P—C—C—X^(–) fragment (III), are also discussed. The latter were long considered as possible intermediates in the reactions of compounds containing the polar C=X bond (X = C, O, S, NR, etc.) with phosphorus ylides (classical Wittig and Corey—Chaykovsky reactions and related processes).     

Neue ternäre Phasen von Platinmetallen mit Lithium und Elementen der 4. Hauptgruppe

Novel Ternary Phases of Platinum Metals with Lithium and Main Group IV Elements The elements palladium, platinum, and iridium (Me) form ternary compounds with lithium and the elements germanium, tin or lead (X) of the formulas Li₂MeX and/or LiMe₂X. The lattice constants of the cubic fc. crystallizing compounds see ?Inhaltsübersicht”?. Besides the cubic form of LiPd₂Ge there exists a tetragonal structure with a = 6.25₄ and c = 6.41₀ Å. X-ray investigations on single crystals showed that LiPd₂Ge crystallizes in a Heusler lattice (L2₁A type), Li₂PdSn has a modified Li₃Bi structure (L2₁C type). The homogeneity range between the compositions Li₂PdX and LiPd₂X was investigated.     

通过核独立化学位移(NICS)计算研究二价三、五、七元环C2H2M, C4H4M and C6H6M(M=C, Si, Ge, Sn and Pb)的芳香族特性

The aromatic character of divalent three, five and seven-membered rings C₂H₂M, C₄H₄M and C₆H₆M(M=C, Si, Ge, Sn and Pb) is investigated through magnetic and geometric criteria by Density Functional Theory (DFT)method using 6^-311++G(3df,2p) basis set of the GAUSSIAN 98 program. The result of Nucleus-independent Chemical Shifts (NICS)(0.5) calculations show an aromatic character for singlet state of C₂H₂M(M=C, Si, Ge, Sn and Sn) and nonaromatic character for triplet states of C₂H₂M(except M=Ge and Pb). NICS (0.5) calculations show nonaromatic character for the singlet state of C₄H₄C and antiaromatic character for C₄H₄M(M=Si, Ge, Sn and Pb). In contrast, NICS (0.5) calculations indicate antiaromatic character for the triplet state of C₄H₄C and nonaromatic character to C₄H₄M(M=Si, Ge, Sn and Pb). NICS (0.5) calculations show a slightly homoaromatic character for the singlet state of C₆H₆M and anti-aromatic character for triplet state of C₆H₆M.     

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.     

Chemical Tricks To Stabilize Silanones and Their Heavier Homologues with EO Bonds (E=Si–Pb): From Elusive Species to Isolable Building Blocks

In contrast to the well‐established chemistry of ketones (R₂C?O), the reactivity of the elusive heavier congeners R₂E?O (E=Si, Ge, Sn, Pb) is far less explored because of the high polarity of the E?O bonds and hence their tendency to oligomerize with no activation barrier. Very recently, great advances have been achieved in the synthesis of isolable compounds with E?O bonds, including the investigation of donor‐stabilized isolable silanones and the first stable “genuine” germanone. These compounds show drastically different reactivities compared to ketones and represent versatile building blocks in silicon–oxygen and germanium–oxygen chemistry. This and other exciting achievements are described in this Minireview.     

Infrarot-und Raman-Spektren von unvollständig und vollständig deuterierten Tetramethyl-Verbindungen (CH3) n M(CD3)4-n der ElementeM=Si,Ge, Sn und Pb

The infrared andRaman spectra of theM(CH₃)₄ andM(CD₃)₄ species,M=Si, Ge, Sn and Pb, have been reinvestigated. The spectra of the mixed tetramethyl compounds (CH₃)₃ MCD₃,M=Si, Ge, Sn and Pb, and of (CH₃)₂Si(CD₃)₂ and CH₃Si(CD₃)₃ have been recorded in the gaseous (i.r.) and liquid states (Raman). The proposed assignment is supported by a normal coordinate analysis.

     

Kristallchemische Aspekte ternärer Phasen des Lithiums mit 3B- und 4B-Elementen in elektrovalenter und nicht elektrovalenter Zusammensetzung

Crystallographic Aspects of Ternary Phases of Lithium with Main Group III and IV Elements in “Ionic” and “Nonionic” Composition Some new ternary phases in the systems Li? Me^III? X^IV (Me^III = Al, Ga, In; X = Si, Ge, Sn) were prepared by melting element mixtures in Ta crucibles. The resulting phases were characterized by X-ray investigation and some chemical reactions. A region of the ternary system Li? Ga? Si was investigated by X-ray phase analysis and the results were compared with the results which we obtained in the Li? Ga? Ge-System. A chemical characterization was realized by thermal decomposition of the gaseous products which were developped by the reaction of the phases with diluted sulphuric acid.     

Low-Valent Group 14 Phosphinidenide Complexes [({SIDipp}P)2M] Exhibit P–M pπ–pπ Interaction (M=Ge,Sn, Pb)

Herein, the synthesis of new low-valent Group 14 phosphinidenide complexes [({SIDipp}P)₂M ] exhibiting P–M pπ–pπ interactions (SIDipp=1,3-bis(2,6-diisopropylphenyl)-imidazolidin-2-ylidene, M=Ge, Sn, Pb), is presented. These compounds were investigated by means of structural, spectroscopic, and quantum-chemical methods. Furthermore, the monosubstituted compounds [(SIDippP)MX]₂ (M=Sn, X=Cl; M=Pb, X=Br) are presented, which show dimeric structures instead of multiple bonding interaction.     

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.