Gas-chromatographic and mass-spectrometric determination of impurity hydrocarbons in organochlorine compounds and dichlorosilane

A procedure was proposed for the gas-chromatographic determination of impurity organic compounds in high-purity dichlorosilane with a detection limit of 0.1–0.2 ppm, which allows metrological control in the production of high-purity dichlorosilane according to the current requirements of microelectronics.     

Structure and bonding in cluster compounds of gold

Recently a number of high nuclearity gold cluster compounds of the type [Au(AuPR₃)_n]^x+ have been synthesised and structurally characterised using single crystal X-ray crystallographic measurements. The structures and properties of these compounds are contrasted with those of comparable high nuclearity metal carbonyl cluster compounds. In order to account for the structures of [Au(AuPR₃)_n]^x+ in the solid state and in solution it has proved necessary to develop a flexible bonding model which emphasises the topologies of the clusters rather than their detailed geometries. In this fashion the observed stereochemical non-rigidity of these compounds in solution is readily accounted for. In the solid state the structures of the higher nuclearity cluster cations can be derived either from the centred chair [Au(AuPR₃)₆], or the centred crown [Au(AuPR₃)₈] by adding edge or face capping AuPR₃ fragments. The bonding in heterometallic clusters containing the AuPR₃ fragment is also considered.     

An EXAFS study of some gold and palladium cluster compounds

Gold L₃-edge EXAFS measurements at 80 K on Au₅₅(PPh₃)₁₂Cl₆ confirm that the Au-Au distances in this amorphous metal cluster compound are significantly shorter than in bulk gold. The nearest-neighbour Au-Au distances are all equal within experimental uncertainty. Outer-shell Au-Au distances have also been resolved. The results are consistent with the cuboctahedral structure originally proposed for this cluster, but not the polyicosahedral one recently suggested. Very similar results have been obtained from the sulphonated water-soluble derivative Au₅₅(PPh₂C₆H₄SO₃Na)₁₂Cl₆. In contrast, EXAFS of Au₁₁{PPh₂(p-ClC₆H₄)}₇I₃ has clearly resolved the two nearest-neighbour Au-Au distances associated with its icosahedral structure.Palladium K-edge EXAFS has been used to study the cluster Pd₅₆₁(phen)₃₆O₂₀₀. The Pd-Pd distance is nearly equal to that in bulk palladium. The results show a cubic close-packed cluster structure for this material, in contrast to the icosahedral structure reported for Pd₅₆₁(phen)₆₀(OAc)₁₈₀.     

Recent developments in the homo- and hetero-metallic cluster compounds of gold

TMC Literature Highlights-26,Transition Met. Chem.,16, 136 (1991).     

杂环生物碱类化合物的分离及结构鉴定

首次报道从中国南海西沙群岛海绵spongiaobligue中分离得到3个新的含氮生物碱杂环化合物,通过MS,1DNMR,20NMR等波谱数据及元素分析确定它们的结构。     

Gold cluster carbonyls: saturated adsorption of CO on gold cluster cations, vibrational spectroscopy, and implications for their structures

We report on the interaction of carbon monoxide with cationic gold clusters in the gas phase. Successive adsorption of CO molecules on the Au(n)(+) clusters proceeds until a cluster size specific saturation coverage is reached. Structural information for the bare gold clusters is obtained by comparing the saturation stoichiometry with the number of available equivalent sites presented by candidate structures of Au(n)(+). Our findings are in agreement with the planar structures of the Au(n)(+) cluster cations with n < or = 7 that are suggested by ion mobility experiments [Gilb, S.; Weis, P.; Furche, F.; Ahlrichs, R.; Kappes, M. M. J. Chem. Phys. 2001, 116, 4094]. By inference we also establish the structure of the saturated Au(n)(CO)(m)(+) complexes. In certain cases we find evidence suggesting that successive adsorption of CO can distort the metal cluster framework. In addition, the vibrational spectra of the Au(n)(CO)(m)(+) complexes in both the CO stretching region and in the region of the Au-C stretch and the Au-C-O bend are measured using infrared photodepletion spectroscopy. The spectra further aid in the structure determination of Au(n)(+), provide information on the structure of the Au(n)(+)-CO complexes, and can be compared with spectra of CO adsorbates on deposited clusters or surfaces.     

Trends in the electronic structure of extended gold compounds: implications for use of gold in heterogeneous catalysis

First-principles electronic structure calculations are presented on a variety of Au compounds and species--encompassing a wide range of formal oxidation states, coordination geometries, and chemical environments--in order to understand the potentially systematic behavior in the nature and energetics of d states that are implicated in catalytic activity. In particular, we monitor the position of the d-band center, which has been suggested to signal catalytic activity for reactions such as CO oxidation. We find a surprising absence of any kind of correlation between the formal oxidation state of Au and the position of the d-band center. Instead, we find that the center of the d band displays a nearly linear dependence on the degree of its filling, and this is a general relationship for Au irrespective of the chemistry or geometry of the particular Au compound. Across the compounds examined we find that even small calculated changes in the d-band filling result in a relatively large effect on the position of the d-band center. The results presented here have some important implications for the question of the catalytic activity of Au and indicate that the formal oxidation state is not a determining factor.     

Syntheses and molecular structures of new ferrocenylacetylide-bridged binuclear cobalt carbonyl cluster compounds

The reaction of ferrocenylacetylide compounds with Co₂(CO)₈ at room temperature affords four complexes bearing ferrocenyl units with approximately tetrahedral (μ-alkyne)dicobalt moieties [R–(C≡C) _n –R′] [Co₂(CO)₆] _{n ′} [R?=?C₅H₅FeC₅H₄-C(CH₃)₂-C₅H₄FeC₅H₄, R′?=?H, n?=?1, n′?=?1 (1); R?=?C₅H₅FeC₅H₄ [ferrocenyl (Fc)], R′?=?–CH=CHCl, n?=?1, n′?=?1 (2); R?=?Fc, R′?=?Fc, n?=?2, n′?=?1 (3), n′?=?2 (4)]. The compounds were characterized by elemental analysis, IR, ¹H(¹³C) NMR, MS and single-crystal X-ray diffraction analysis. The X-ray analyses show that coordination of the carbon–carbon triple bond and the dicobalt unit result in the formation of a Co₂C₂ tetrahedral core, and the substituents on the acetylenic units show a distortion from linearity that reflects this coordination mode.     

钼铁硫原子簇化合物的合成与结构化学IV: 双类立方烷化合物与酰氯的反应

报导了双类立方烷簇状化合物(Et4N)4[Mo2Fe7S8(SC6H5)12]与乙酰氯在乙腈中的反应, 结果获得不含Fe(SC6H5)3桥的双类立方烷化合物(Et4N)4[Mo2Fe6S8(SC6H5)9]. 反应用^1H NMR和元素分析表征. 这种类型的结构转换为首次所见, 从而对化合物中桥的松散结构提供了新的实验证据.     

Inkjet deposition of alkanethiolate monolayers and DNA oligonucleotides on gold: evaluation of spot uniformity by wet etching

Inkjet printing allows localized, contact-free deposition of liquids onto arbitrary substrates. In this article we demonstrate the fast formation of high-quality self-assembled monolayers (SAMs) on gold surfaces. Using a selective etch process, we verify the uniformity of the deposited spots. A direct comparison with microcontact-printed SAMs on Au revealed similar resist quality as inkjet-deposited alkanethiolate SAMs. Likewise, inkjet printing of thiol-functionalized and non-thiolated single-stranded DNA oligomers formed molecular layers protecting Au from etchants. For all compounds used, we achieved etched patterns that were homogeneous and free of defects. These results indicate that an inkjet is a convenient tool for surface functionalization and the direct writing of molecular films and resists.     

Metalloid group 14 cluster compounds: an introduction and perspectives to this novel group of cluster compounds

Metalloid cluster compounds of group 14 of the general formulae E(n)R(m) with n > m (E = Si, Ge, Sn and Pb, tetrel elements; R = ligand), where "naked" tetrel atoms are present as well as ligand-bound tetrel atoms, represent a novel class of cluster compounds in group 14 chemistry. Since the "naked" tetrel atoms in these clusters exhibit an oxidation state of 0, the average oxidation state of the tetrel atoms in such metalloid group 14 cluster compounds is between 0 and 1. Thus, these cluster compounds may be seen as intermediates on the way to the elemental state. Therefore, interesting properties maybe expected for these compounds which might complement results from nanotechnology. During the last years many different syntheses of such novel cluster compounds have been introduced, leading to several metalloid group 14 cluster compounds which exhibit new and unusual structure and bonding properties. In this tutorial review an account is given of the first steps in this novel field of group 14 chemistry. Special attention is focused on structural features and bonding properties.     

Localized molecular orbital study on chemical bonding and reactivities of certain Mo-Cu-S cluster compounds

The localized molecular orbitals (LMOs) and Mulliken bond orders for the cluster anions of [Et₄N]₂[Mo₂S₄(edt)₂] (1), [(CH₃CH₂)₄N][Mo₂CuS₄(PPh₃)(edt)₂] (2) and the cluster molecule [Mo₂Cu₂S₄(PPh₃)₂(edt)₂] (3) have been calculated by means of the Edmiston-Ruedenberg energy localization technique under the CNDO/2 approximation. The results of the LMOs calculations show that there are two pairs of (S₁ Mo) bonds each pair of the Mo atoms and the terminal S₁ atoms in the anion of (1). In the addition reactions of the cluster compound (1) with one or two Cu atoms these (S₁ Mo) bonds are sequentially opened and form correspondently the cluster compounds (2) and (3) with the three-centered or four-centered bonds among the copper, sulfur, and molybdenum atoms, accounting for the stronger bonding of the Cu atom to the Mo-S cluster compounds such as (1). This also gives the explanation of chemical bonding for the [2+1] and [2+2x1] synthetic reaction schemes of the compounds (2) and (3). The structural features for the cluster compounds studies are briefly discussed as well.     

Syntheses and structural characterizations of Fe4S4 cubane-like cluster compounds containing cycloalkylthiolate ligands

In a reaction system consisting of FeCl₂, tetrathiometallate and cycloalkylthiolate, two Fe₄S₄ cubanelike cluster compounds were obtained with the following crystallographic data: (PhCH₂NMe₃)₂ [ Fe₄S₄ (SC₅H₉)₄] (I), monoclinic space groupP2₁/c,a = 1.632 7(4),b=1.122 9(3),c = 2. 802 5(10) nm, β= 94.63(2)°, Z=4, andR= 0.074; (Et₄N)₂[F₄S4(SC₆H_lI)₄] (II), tetragod space group ,a = l.167 05(9),b = 1.167 06(2),c = 2.063 26(5) nm,Z = 2, D_obs = 1. 28 g/cm³, andR = 0. 078. The participation of cycloalkylthiolate ligand does not obviously arouse the change of the Fe₄S₄ core structure. Meanwhile, the influence of the cation on the structural symmetry of the Fe₄S₄ cluster dianion is also discussed. Project supported by the National Natural Science Foundation of China and the Climbing Program Foundation of China.     

Syntheses and structural characterizations of Fe_4S_4 cubane-like cluster compounds containing cycloalkylthiolate ligands

In a reaction system consisting of FeCl2,tetrathiometallate and cycloalkylthiolate,two Fe4S4 cubane-like cluster compounds were obtained with the following crystallographic data:(PhCH2NMe32[Fe4S4 (SC5H9)4](Ⅰ),monoclinic space group P21/c,a=1.6327(4),6=1.1229(3),c=2.802 5( 10) nm,β=94.63(2)°,Z=4,and R=0.074; (Et4N)2[Fe4S4(SC6H11)4](Ⅱ),tetragonal space group I42m,a=1.16705(9),b=1.167 06(2),c=2.063 26(5) nm,Z=2,Dabs=1.28 g/cm3,and R=0.078 The participation of cy-cloalkylthiolate ligand does not obviously arouse the change of the Fe4S4 core structure.Meanwhile,the influence of the cation on the structural symmetry of the Fe4S4 cluster dianion is also discussed.     

Precise and accurate determination of halogens in organic compounds using an amalgamated gold electrode

Precise and accurate titration of halogens in organic and inorganic materials has been studied. The halogen was titrated with coulometrically generated silver and determined potentiometrically by using an amalgamated gold indicator electrode. An argentometric titration curve using the amalgamated gold indicator electrode showed a large jump in potential at the endpoint as well as in mercurometric determination. Sodium carboxymethyl cellulose (CMC) and aluminum nitrate were added as they are most effective for clarifying the sample solution and eliminating adsorption of the halide ion on the silver halide generated. The electrolytes used were 0.5 M nitric acid containing 0.1% CMC and 0.2 M aluminum nitrate. Approximately 0.2 mmol of chloride, bromide, and iodide ions were titrated with high precision and accuracy. Their standard deviations were 0.03, 0.02, and 0.02%, respectively, with no apparent systematic error. The precise determination of halogens, employing oxygen flask combustion and dissolution of the halide salts in the electrolyte, was carried out with ±0.1% absolute error using samples weighing between 20 and 30 mg.     

Solution state structure determination of silicate oligomers by 29SI NMR spectroscopy and molecular modeling

Evidence for nine new solution state silicate oligomers has been discovered by (29)Si NMR homonuclear correlation experiments of (29)Si-enriched samples. In addition to enhancing signal sensitivity, the isotopic enrichment increases the probability of the (29)Si-(29)Si two-bond scalar couplings that are necessary for the observation of internuclear correlations in 2-D experiments. The proposed assignments are validated by comparisons of experimental and simulated cross-peaks obtained with high digital resolution. The internuclear connectivity indicated by the NMR data suggests that several of these oligomers can have multiple stereoisomers, including conformers and/or diastereomers. The stabilities of these oligomers and their possible stereoisomers have been investigated by electronic structure calculations.     

Synthesis and comparative structural investigation of crystalline and liquid-crystalline phases of low molecular mass compounds and side group polymers I. Low molecular mass compounds

Low molecular mass compounds and analogous side group polymers with a thermotropic phase behaviour crystalline-smectic liquid-crystalline-isotropic have been synthesized for a comparative structural study. As characteristic features of the compounds a biphenyl group has been chosen for the mesogenic core and alkoxy parts of various lengths as terminal and spacer groups. The phase behaviour has been studied with differential calorimetric (DSC) measurements and polarization microscopic observations. The low molecular mass compounds form crystalline phases at room temperature and exhibit predominantly mosaic textures in the polarization microscope at elevated temperatures indicating high order of the packing of the molecules. The arrangements of the molecules in the crystalline and liquid-crystalline phase can best be described as layered structures according to X-ray diffraction measurements. A structural analysis of a solution grown single crystal provides valuable information on the conformation and packing of the compounds investigated in this study.     

Determination of molecular formulas and structural regularities of low molecular weight fulvic acids by size-exclusion chromatography with electrospray ionization quadrupole time-of-flight mass spectrometry

Size-exclusion chromatography was coupled to a quadrupole time-of-flight mass spectrometer using electrospray ionization in the negative ion mode to analyze Suwannee River fulvic acid. About 220 exact masses of low molecular weight fulvic acids (FAs) were measured in the range from m/z 190 to 350, and molecular formulas could be deduced for all these molecular masses. All molecular formulas can be described by the superimposition of three homologous series in the FA mixture: (a) a series of hydrogen homologs constituted of five to six members for a given number of carbons and oxygens; (b) a series of alkyl chain homologs with stepwise addition of one methylene group; and (c) isobaric compounds that differ by the formal replacement of an oxygen atom by a methane group. Product ion spectra of the FA species reflect the repeated parallel losses of carbon dioxide and water. The minimum number of carboxylate groups and the maximum number of hydroxy moieties could be determined from the product ion spectra. Furthermore, it was obvious that the structural differences between homologs in the three series are located in the carbon backbone of the FA rather than in its extremities that are expelled as neutral fragments. These structural regularities reduce the complexity of FA mixtures to a certain set of yet unknown basic structures.