Der Gaskomplex MnAlF5 und sein Einfluß auf die sublimative Reinigung von AlF3

The Gas Complex MnAlF₅ and its Influence on the Purification of AlF₃ by Sublimation The gas complex MnAlF₅ has been determined mass spectroscopically by the ions MnAlF₅⁺ and MnAlF₄⁺. The gas complex MnAlF₅ is formed above 973 K by heating up mixtures of AlF₃/MnF₂ or AlF₃ · 3 H₂O endowed with Mn²⁺ or by heating up solid MnAlF₅ too. At 1 008 K the enthalpie of dissociation is 197 kJ/mole. The equilibrium structures of the high spin molecule MnAlF₅ (S = 5/2) were examined with ab initio calculations at the HF-level by comlete gradient optimizing. Two minimum structures were found on the potential energy surface. A bidentate fluorine bridged structure was found to be the most stable at the HF-level. Vibrational frequencies and thermodynamic functions of complex formation were estimated for both minimum structures. The importance of the formation of the gas complex for the separation of MnF₂ and AlF₃ by sublimation is discussed.     

Acyl- und Alkylidenphosphane. XXIII [1]. Synthese und Struktur der [Bis(trimethylsilylsulfano)methyliden]phosphane

Acyl- and Alkylidenephosphines. XXIII. Synthesis and Structure of [Bis(trimethylsilylsulfano)methylidene]phosphines Analogous to the phenyl derivative 1a [2] tert-butyl- 1b , mesityl- 1c and methylbis-(trimethylsilyl)phosphine 1 d react with carbon disulfide to give the corresponding [bis(trimethylsilylsulfano)methylidene]phosphines 4 . Only in case of the mesitylphosphine 1 c the intermediate compounds 2 and 3 could be detected by n.m.r. spectroscopic methods; thermally unstable [bis(trimethylsilylsulfano)methylidene]methylphosphine 4 d dimerizes rapidly [1]. [Bis(trimethylsilylsulfano)methylidene]phenylphosphine 4 a crystallizes in the monoclinic centrosymmetric space group P2₁/c with following dimensions of the unit cell determined at ?95 ± 3°C: a = 1386.4(8); b = 1036.0(7); c = 1281.7(8) pm; ß = 101.23(4)°; Z = 4. An X-ray structure determination (R = 0.032) proves the constitution of this compound as already derived from its nmr spectra. Characteristic bond lengths and angles are: P?C 170; P? C(phenyl) 183; C? S 176; S? Si 219 pm; C? P?C 107; P?C? S 124 and 120; S? C? S 116 and C? S? Si 111°.     

Acyl- und Alkylidenphosphane. XXII [1]. Synthese und Struktur des 1, 3-Dimethyl-2,2,4,4-tetrakis-(trimethylsilylsulfano)-1,3-diphosphetans

Acyl- and Alkylidenephosphines. XXII. Synthesis and Structure of 1, 3-Dimethyl-2,2,4,4-tetrakis(trimethylsilylsulfano)-1,3-diphosphetane At ?30°C methylbis(trimethylsilyl)phosphine reacts with carbon disulfide to give a red adduct first which rearranges to [bis(trimethylsilylsulfano)methylidene]methylphosphine 1a . In contrast to the thermally stable phenyl derivative 1b [2], this compound with its insufficiently shielded P?C group dimerizes fast with increasing temperature. 1,3-Dimethyl-2,2,4,4-tetrakis(trimethylsilylsulfano)-1,3-diphosphetane 2a formed by this reaction, crystallizes in the triclinic space group P1 with following dimensions of the unit cell, determined at a temperature of measurement of ?80 ± 3°C: a = 1024.7(3); b = 1360.2(5); c = 1326.3(6)pm; α = 117.85(4); ß = 111.05(3); γ = 72.09(3)°; Z = 2. Due to ring folding at the P1? P2 axis of 149.1°, the molecule shows pseudosymmetry C_s. Characteristic averaged bond lengths and angles obtained at an R_w-value of 0.030, are: P? C(endocyclic) 188 and 191; P? CH₃ 184; C? S 183; S? Si 216 pm; C? P? CH₃ 105; P? C? S 113; S? C? S 114; C? S? Si 108; P? C? P 90 and C? P? C 86°.     

Molekül- und Kristallstruktur des 1,4-Bis[tris(tetrahydrofuran)lithium]-octaphenyltetrasilans

Molecular and Crystal Structure of 1,4-Bis[tris(tetrahydrofuran)lithium]-octaphenyltetrasilane 1,4-Dilithium-octaphenyltetrasilane prepared from octaphenyl-cyclo-tetrasilane and lithium in tetrahydrofuran (THF) [4], can be isolated from tetrahydrofuran/n-pentane as an adduct with six molecules of tetrahydrofuran per formula unit. The orange-red compound crystallizes in the triclinic space group P1 {a = 1159.6(3); b = 1268.4(2); c = 1367.8(3) pm; α = 92,23(2)° β = 113.79(2)° γ = 111.62(2)° at ?5 ± 3°C; Z = 1}. An x-ray structure determination (R_w = 0.046) shows the existence of a centrosymmetric molecule with an extended planar Li? Si₄? Li unit; either lithium atom is bound to silicon and to the oxygen atoms of three molecules of tetrahydrofuran. Characteristic bond lengths and angles are: Li? Si 271; Si? Si 241 and 243; Si? C 190 to 192 pm; Li? Si? Si 126°; Si? Si? Si 127°. ²⁹Si and ⁷Li n.m.r. measurements at low temperatures indicate the presence of three different adducts.     

Electrochemical oxidation of alkyl-substituted allenes in methanol

Mono-, di- and tri-alkyl-substituted allenes were potentiostatically oxidized in methanol at graphite and Pt anodes. At the former electrode, α-methoxylated ketones (due to 4F/mole electricity consumption) and esters (6F/mole) were the major products. At a Pt anode, intermediate products such as vinyl-ether derivatives (2F/mole) were characterised too. Unlike the anodic oxidation of alkenes and alkynes previously reproted in the literature, dimerisation is not a typical process in the allenes' oxidation, since of all the products obtained only a sole dimer has been observed. The mechanism for the formation of most products is discussed.     

Formation of Zn(1-x)MnxS nanowires within mesoporous silica of different pore sizes

Arrays of highly ordered Zn(1-x)MnxS quantum wires with x ranging from 0.01 to 0.3 and with lateral dimensions of 3, 6, and 9 nm were synthesized within mesoporous SiO2 host structures of the MCM-41 and SBA-15 type. The hexagonal symmetry of these arrays (space group p6m) and the high degree of order was confirmed by X-ray diffraction and transmission electron microscopy (TEM) studies. Physisorption measurements show the progressive filling of the pores of the SiO2 host structures, while TEM and Raman studies reveal the wire-like character of the incorporated Zn(1-x)MnxS nanostructures. X-ray absorption near-edge structure, extended X-ray absorption fine structure, photoluminescence excitation (PLE), and electron paramagnetic resonance studies confirm the good crystalline quality of the incorporated Zn(1-x)MnxS guest species and, in particular, that the Mn2+ ions are randomly distributed and are situated on tetrahedrally coordinated cation sites of the Zn(1-x)MnxS wires for all x up to 0.3. The amount of Mn2+ ions loosely bound to the surface of the Zn(1-x)MnxS nanowires is less than 4% of the total Mn content even for the 3 nm nanostructures up to the highest Mn content of x = 0.3. The effects of the reduction of the lateral dimensions on electronic properties of the diluted magnetic semiconductor were studied by PLE spectroscopy. Due to the quantum confinement of the excitons in the wires an increase of the direct band gap with decreasing particle size is observed.     

Single-molecule fluorescence detection in microfluidic channels—the Holy Grail in μTAS?

Both single-molecule detection (SMD) methods and miniaturization technologies have developed very rapidly over the last ten years. By merging these two techniques, it may be possible to achieve the optimal requirements for the analysis and manipulation of samples on a single molecule scale. While miniaturized structures and channels provide the interface required to handle small particles and molecules, SMD permits the discovery, localization, counting and identification of compounds. Widespread applications, across various bioscience/analytical science fields, such as DNA-analysis, cytometry and drug screening, are envisaged. In this review, the unique benefits of single fluorescent molecule detection in microfluidic channels are presented. Recent and possible future applications are discussed.Dedicated to the memory of Wilhelm Fresenius     

Electrode processes in the oxidation of tetrahydroisoquinoline derivatives

The electrochemical oxidation of the alkaloid laudanosine (Ia) to O-methylflavinantine (II) has been studied in acetonitrile solvent. Using cyclic voltammetry, rotating disc voltammetry and preparative electrolyses on several alkaloids, simple aliphatic amines and aromatic compounds, some aspects of the mechanism of this coupling reaction are elucidated. The first anodic wave for laudanosine at platinum has E_p=0.55 V vs. Ag/Ag⁺. The electrode rapidly becomes partially passivated at potentials above 0.5 V. This is due to a film which “dissolves” below 0.5 V, at a rate independent of the potential. It is shown that the reaction (Ia)→(II) proceeds at 0.5 V by initial oxidation of the amine moiety. If acids such as sodium bicarbonate are added to the anolyte the amine is protonated causing the first wave to disappear. Oxidation at 1.1 V under these acidic conditions produces the same product, but more rapidly and in significantly higher yield because electrode filming and side reactions resulting from the amine oxidation are abrogated.     

Internal energy effects in collision induced dissociation spectra

The effect of the precursor ion internal energy on the branching ratios obtained from collision induced dissociation fragmentation patterns was examined for [NH₃]⁺ and [C₂H₄N]⁺. The ion internal energy was changed by varying both the chemical ionization reagent gas and the ion source pressure. Effects observed in the collision induced dissociation fragmentation patterns as a function of the ion source pressure are explained by the reaction exothermicities and by collisional deactivation of internally excited ions (at high pressure).     

Synthese und thermische Eigenschaften von molekularen Clusterverbindungen zusammengesetzt aus Elementen der Gruppen 11‐13‐16

Syntheses and Thermal Properties of Cluster Molecules, formed from Groups 11‐13‐16 Elements In the presence of PPh₃, CuX (X = Cl, CH₃COO) or AgOC(O)C₆H₅ and GaCl₃ react in THF with S(SiMe₃)₂ or Se(SiMe₃)₂ to yield [Cu₆Ga₈Cl₄S₁₃(PPh₃)₆] ( 1 ), [Cu₆Ga₈Cl₄Se₁₃(PPh₃)₆] ( 2 ), [Ag₆Ga₈Cl₄S₁₃(PPh₃)₆] ( 4 ) and [Ag₆Ga₈Cl₄Se₁₃(PPh₃)₆] ( 5 ). The use of PⁿPr₂Ph instead of PPh₃ and subsequent layering with n‐hexane leads to the formation of the cluster [Cu₆Ga₈Cl₄Se₁₃(PⁿPr₂Ph)₁₂] ( 3a , 3b ). Reaction of CuCl, GaCl₃ and PⁿPr₃ with Se(SiMe₃)₂ in THF results in the crystallisation of the ionic cluster (HPⁿPr₃)₂[Cu₂Ga₄Cl₄Se₆(PⁿPr₃)₄] ( 6 ). The structures of 1 — 6 were determined by X‐ray single crystal structure analysis. Thermogravimetric measurements of the cluster molecules and powder diffraction patterns of the remaining powders reveal the potential use of them as single source precursor compounds for the synthesis of the related ternary solid state materials.