Straightforward synthesis and structure of a new starting material for niobium cluster phases: [Nb6Cl(i)12(CH3OH)a4Cla2].6CH3OH

A new, fast, and straightforward synthetic route for the new cluster compound [Nb(6)Cl(i)(12)(CH(3)OH)(a)(4)Cl(a)(2)].6CH(3)OH, taking advantage of the special solubility properties of tetracyanoborate salts has been established, and the single-crystal X-ray structure of this compound, which is a promising starting material for new cluster phases, has been determined.     

Schwingungsspektren und Kraftkonstanten von Cl3SiP(CH3)2 und Cl3SiAs(CH3)2

Vibrational Spectra and Force Constants of Cl₃SiP(CH₃)₂ and Cl₃SiAs (CH₃)₂ The i.r. and Raman spectra of Cl₃SiP(CH₃)₂ and Cl₃SiAs (CH₃)₂ have been recorded and assigned. A normal coordinate analysis has been made using a modified valence force field. The SiP force constant is slightly higher than those of alkylsilylphosphines, whereas a similar effect is not found for the SiAs bond.     

Electronic structure and bonding of the metal cluster compound Au55(PPh3)12Cl6

We discuss the electronic structure, bonding and physical properties of the gold cluster compound Au₅₅(PPh₃)₁₂Cl₆. Results from our experimental measurements, including EXAFS, specific heat, Mössbauer, UV-visible and photoelectron spectroscopy, are combined with those of other work to form a consistent physical picture of the system. The bonding in Au₅₅(PPh₃)₁₂Cl₆ is much more delocalised and non-directional than in smaller gold cluster molecules. The Au₅₅ cluster exhibits a substantial degree of metallic bonding, while displaying some of the characteristics of a discrete energy level spectrum.     

Superfine and hyperfine structures in the v3 band of 32SF6

We present a first detailed account of our theoretical approach to reproduce observed superfine and hyperfine structures in the ν₃ band of SF₆ and we display various observed and calculated patterns of superfine clusters exhibiting hyperfine effects. The main operators of the hamiltonian are derived and the associated constants are related to molecular parameters. We show that, owing to the off-diagonal terms in the hyperfine hamiltonian, a mixing occurs between vibration—rotation states with different point-group symmetry species. As a consequence, superfine and hyperfine structures have to be considered simultaneously and hyperfine hamiltonian matrices connecting several vibration—rotation states need to be diagonalized to reproduce the spectra. We analyse in greater detail a few typical examples from which several molecular constants have been determined (e.g. t₀₄₄, c_d). For the first time, the sign c_d is obtained. Also an effective change, Δc_d, is found between upper and lower levels which can be readily interpreted as a manifestation of the tensor spin—vibration interaction.     

[(CH3)Al(CH2)]12: Methylaluminomethylene (MAM-12)

The molecular structure of enigmatic “poly(aluminium-methyl-methylene)” (first reported in 1968) has been unraveled in a transmetalation reaction with gallium methylene [Ga₈(CH₂)₁₂] and AlMe₃. The existence of cage-like methylaluminomethylene moieties was initially suggested by the reaction of rare-earth-metallocene complex [Cp*₂Lu{(μ-Me)₂AlMe₂}] with excess AlMe₃ affording the deca-aluminium cluster [Cp*₄Lu₂(μ₃-CH₂)₁₂Al₁₀(CH₃)₈] in low yield (Cp*=C₅Me₅). Treatment of [Ga₈(CH₂)₁₂] with excess AlMe₃ reproducibly gave the crystalline dodeca-aluminium complex [(CH₃)₁₂Al₁₂(μ₃-CH₂)₁₂] (MAM-12). Revisiting a previous approach to “poly(aluminium-methyl-methylene” by using a (C₅H₅)₂TiCl₂/AlMe₃ (1 : 100) mixture led to amorphous solids displaying solubility behavior and spectroscopic features similar to those of crystalline MAM-12. The gallium methylene-derived MAM-12 was used as an efficient methylene transfer reagent for ketones.     

Dissociative electron attachment to CH2Cl2, CHCH3Cl2, and C(CH3)2Cl2

We perform theoretical studies of dissociative electron attachment (DEA) for the compounds CH(2-n)(CH(3))(n)Cl(2), n = 0, 1, 2, by combining the finite-element discrete model with the resonance R-matrix theory. An unexpectedly low DEA cross section for CH(2)Cl(2) is likely due to the relatively large resonance width for this compound that confirms experimental observations. However, there are some quantitative discrepancies with the experimental results. Since DEA cross sections are very sensitive to the resonance width, a slight adjustment of its value can significantly improve agreement between theory and experiment. Our calculation of the thermal rate coefficients show that there are some inconsistencies between beam and swarm measurements and between different swarm measurements of the rate coefficients for DEA to CH(2)Cl(2). Further experimental and theoretical studies are warranted.     

Crystal structure of the new compound Co6(TeO3)2(TeO6)Cl2

The new compound Co₆(TeO₃)₂(TeO₆)Cl₂ has been isolated during an investigation of the system CoO:CoCl₂:TeO₂. The new compound is deep purple in color and crystallizes in the tetragonal system, space group P4₂/mbc, a=8.3871(7) Å, c=18.5634(19) Å, Z=4. The Co(II) ions have octahedral [Co1O₆] and tetrahedral [Co2O₃Cl] coordinations. Tellurium is present both as Te(IV) with a tetrahedral [Te1O₃E] coordination, where E is the 5s² lone-pair and as Te(VI) with an octahedral [Te2O₆] coordination. The structure is made up of intersecting layers of tetrahedra forming channels comprising octahedra chains that run along the c-axis. The new compound is the first cobalt tellurium oxochloride described.     

Anion-controlled redistribution reactions in the system C3Cl3+A−/(CH3)3SiN(CH3)2

Transmination reactions of the 4z-exchange type between C₃Cl₃⁺A^? and (CH₃)₃SiN(CH₃)₂ are introduced as a novel mode of aromatic substitution at the C₃⁺-core. The extent of transamination can be controlled by appropriate choice of counterion A^?.     

Crystal structure and dynamics of Mg(ND3)6Cl2

The crystal structure and dynamics of Mg(ND(3))(6)Cl(2) have been investigated by powder neutron diffraction and molecular dynamics. The powder diffraction data can be well described by 4 partly occupied deuterium sites in a square arrangement around the N atoms, which is seemingly inconsistent with the 3-fold symmetry of the ND(3) molecule. Molecular dynamics show highly correlated rotational and translational motion of the ND(3) molecules which explains the apparent 4-fold symmetry of the deuterium arrangement. A more disordered structure model based on the molecular dynamics results gives a better fit to the experimental data and is in agreement with the 3-fold symmetry of ND(3).     

Attempted Abstraction of the Halogenides in (HNEt3)[Re(CH3CN)2Cl4] and Crystal Structures of cis‐[Re(CH3CN)2Cl4]·CH3CN and cis‐[Re(NHC(OCH3)CH3)2Cl4]

The abstraction of the halogenide ligands in [Re(CH₃CN)₂Cl₄]^? should result in a solvent‐only stabilized Re^III complex. The reactions of salts of [Re(CH₃CN)₂Cl₄]^? with silver(I) and thallium(I) salts were investigated and the solid‐state structures of cis‐[Re(CH₃CN)₂Cl₄]·CH₃CN and cis‐[Re(NHC(OCH₃)CH₃)₂Cl₄] are described.     

Low-temperature specific heat of the cluster compound Au55 (P(C6H5)3)12Cl6

Specific-heat measurements on the cluster compound Au₅₅(P(C₆H₅)₃)₁₂Cl₆ at temperatures 0.06 K ≤T≤3 K and in magnetic fields 0≤B≤6 T are reported. While above 0.6 K the specific heatC is dominated by the inter-cluster vibrational contribution observed previously, an anomalous increase ofC towards lowT is observed below 0.3 K, withC ～T ^?2. This contribution develops into a Schottky-like anomaly forB≥0.4 T, indicating that it might be attributed to local moments which are also observed in ESR measurements. From the height of the anomaly one can infer that approximately one tenth of the Au₅₅ clusters carry a magnetic moment. For 0.6 K≤T≤1 K andB=0 our data indicate the absence of a linear electronic specific-heat contribution expected for bulk Au. This possibly constitutes the first direct observation of the quantum-size effect on electronic energy levels in the specific heat.