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1.
A combined experimental and theoretical approach has been employed to establish the basicity and proton affinity of SiF4 and the structure of SiF4H+. The kinetics and energetics for the transfer of a proton between SiF4, N2, and Xe have been explored experimentally in helium at 0.35±0.02 torr and 297±3 K with a selected-ion flow tube apparatus. The results of equilibrium constant measurements are reported that provide a basicity and proton affinity for SiF4 at 297±3 K of 111.4±1.0 and 117.7±1.2 kcal mol?1, respectively. These values are more than 2.5 kcal mol?1 lower than currently recommended values. The basicity order was determined to be GB(Xe)>GB(SiF4)>GB(N2), while the proton-affinity order was shown to be PA(Xe)>PA(N2)>PA (SiF4). Ab initio molecular orbital computations at MP4SDTQ(fc)/6-311++G(3df,3pd) using geometries from B3LYP/6-31+G(d,p) indicate a value for PA(SiF4)=118.7 kcal mol?1 that is in good agreement with experiment. Also, the most stable structure of SiF4H+ is shown to correspond to a core SiF 3 + cation solvated by HF with a binding energy of 43. 9 kcal mol?1. Support for this structure is found in separate SIFT collision induced dissociation (CID) measurements that indicate exclusive loss of HF.  相似文献   

2.
The free electron concentration in hydrogen and chemically active plasmas in H2 + SiF4 and H2 + GeF4 mixtures was measured by microwave interferometry. The investigations were carried out under conditions of a RF capacitive-coupled discharge at a pressure of 1 Torr. In hydrogen plasma the concentration of free plasma electrons is 1.5 ± 0.03 × 1012 cm?3. When the fluoride is added to the hydrogen plasma, the electron concentration is reduced to 1.1 ± 0.05 × 1012 cm?3 for SiF4 and 9.8 ± 0.05 × 1011 cm?3 for GeF4. It is suggested that the main mechanism responsible for reducing the concentration of free electrons is the mechanism of dissociative attachment of electrons to SiF4 and GeF4 molecules. The difference in the electron concentration for these mixtures is due to the difference in the electron-acceptor ability of the SiF4 and GeF4 molecules determined by the affinity for the electron.  相似文献   

3.
《Solid State Sciences》2012,14(7):952-963
Recently we established the existence of an entire class of salts of amino acids with hexafluorosilicate anions. Three types of salts with singly charged cations are formed: 2A+·SiF62−, A+·(A⋯A+)·SiF62−, 2(A⋯A+)·SiF62−, where A and A+ are amino acids in zwitterionic and singly charged state and (A⋯A+) is dimeric cation with short hydrogen bond. In present work we investigated the system sarcosine + H2SiF6 + H2O. Salts of all three mentioned types are formed in this system: 2Sar·H2SiF6 (2Sar+·SiF62−) (I), 3Sar·H2SiF6·2H2O (Sar+·(Sar⋯Sar+)·SiF62−·2H2O) (II), 4Sar·H2SiF6 (2(Sar⋯Sar+)·SiF62−) (III). The crystal and molecular structures at room temperature as well as thermal expansion of all three crystals are determined. A phase transition near 180 K was found in (II) and the structure below phase transition point (at 150 K) is determined. In addition to (I) a hydrated sample (Ia) is identified by the infrared spectrum. Infrared and Raman spectra of (I, II, III) are discussed on the basis of their structures.  相似文献   

4.
Quantumchemical Investigations on the Stability of Si? F Species Semiempirical MO calculations (EHT, CNDO/2) have been used to examine the stability of Si—F-species (SiF62?, SiF4 planar and tetrahedral, SiF3+ planar and pyramidal, and SiF2 (SiF22+) linear and angled). The calculations showed, that the appearance of planar structures is possible from the energetical point in solid state reactions. In the case of SiF2 (SiF22+) it was not possible to find an energetic difference between linear and not linear forms. The neutral form is energetic more stable than SiF22+. A comparison of investigated species shows, that with growing bonding angle and in this way with decreasing number of fluorine atoms in the molecule the bond lengths are decreased. The EHT-bond energies become more negative in the same way.  相似文献   

5.
《Analytical letters》2012,45(6):1010-1021
Abstract

A carbon paste electrode modified with cobalt phthalocyanine (CPECoPc) was developed and applied to the determination of hydrazine [N2H4] in industrial boiler feed water. The CPECoPc exhibited good electrocatalytical activity for hydrazine oxidation at pH 13. A linear correlation was obtained between anodic peak current (Iap) and hydrazine concentration in the range of 1.25 × 10?4 to 9.80 × 10?4 mol L?1, fit by the equation Iap = 1.47 + 4.90 × 105 [N2H4] with a correlation coefficient of 0.9967. A detection limit of 7.35 × 10?5 mol L?1 was obtained. Recovery of hydrazine from three samples ranged between 99.0% and 102.9%. The modified electrode showed no interference by cations commonly present in boiler water, such as K+, Na+, Ca2+, Mg2+, Al3+, Pb2+, and Zn2+. The results obtained for hydrazine in boiler water using the proposed modified electrode are in agreement with the data obtained by a standard spectrophotometric method, at the 95% confidence level.  相似文献   

6.
A new sandwich-type polyoxometalate, Na5H[N(CH3)4]2[Co(C3N2H4)2(H2O)4][Co4(H2O)2(PW9O34)2]·21H2O (1), has been synthesized. 1 is composed of a Weakley-type polyanion, [Co4(H2O)2(PW9O34)2]10?, four kinds of cations (five Na+, two [N(CH3)4]+, one [Co(C3N2H4)2(H2O)4]2+, and one H+), and 21 crystalline H2O molecules. The surface oxygen of the polyanion in 1, the crystalline water, and coordinated water molecules make an extended 3-D hydrogen-bonding network. Alternating current (AC) impedance experiments of 1 reveal good proton conductivity for 1 of 5.03 × 10??4 S cm?1 at 25 °C under 98% relative humidity (RH). Activation energy of 1 calculated from Arrhenius plots is 0.358 eV, indicating Grotthuss mechanism is dominant in the proton transfer. Thermal decomposition behavior of 1 was examined by thermogravimetry/mass spectrometry (TG/MS) measurements.  相似文献   

7.
The gas‐phase reaction of CH3+ with NF3 was investigated by ion trap mass spectrometry (ITMS). The observed products include NF2+ and CH2F+. Under the same experimental conditions, SiH3+ reacts with NF3 and forms up to six ionic products, namely (in order of decreasing efficiency) NF2+, SiH2F+, SiHF2+, SiF+, SiHF+, and NHF+. The GeH3+ cation is instead totally unreactive toward NF3. The different reactivity of XH3+ (X = C, Si, Ge) toward NF3 has been rationalized by ab initio calculations performed at the MP2 and coupled cluster level of theory. In the reaction of both CH3+ and SiH3+, the kinetically relevant intermediate is the fluorine‐coordinated isomer H3X‐F‐NF2+ (X = C, Si). This species forms from the exoergic attack of XH3+ to one of the F atoms of NF3 and undergoes dissociation and isomerization processes which eventually result in the experimentally observed products. The nitrogen‐coordinated isomers H3X‐NF3+ (X = C, Si) were located as minimum‐energy structures but do not play an active role in the reaction mechanism. The inertness of GeH3+ toward NF3 is also explained by the endoergic character of the dissociation processes involving the H3Ge‐F‐NF2+ isomer. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

8.
Three water-soluble ruthenium(III) compounds, Y[cis-RuCl2(pic)2]?nH2O (where pic = picolinate anion, Y = H(Hpic)2+ (1), H2pic+ (2) or K+ (3), n = 2, 1.5, and 2.5, respectively), were synthesized and their X-ray structures determined. Compound 1 was fully characterized both as solid and in aqueous solution by elemental analysis, magnetic susceptibility measurements, EPR, IR and UV-visible spectroscopy, cyclic voltammetry, microwave plasma atomic emission, and mass spectrometry, capillary electrophoresis and chromatographic methods. It was shown that the coordination geometry around the low spin (S = ½) RuIII center is distorted octahedral with the chlorido ligands in a cis configuration. Furthermore, all the measurements showed that the structures in the solid state and solution are absolutely identical with the cis-[RuCl2(pic)2]? anion being inert in aqueous solution. Microbial studies showed that 1 exerts a strong inhibition on the growth and increased mortality level of the bacterial strains – Escherichia coli, Pseudomonas sp., Sarcina sp., Micrococcus sp., Serratia sp., Bacillus cereus, Bacillus subtilis and yeast – Saccharomyces cerevisiae.  相似文献   

9.
《Analytical letters》2012,45(5):973-983
Abstract

A rapid and sensitive flow‐injection chemiluminescence (FI‐CL) method, which is based on the CL intensity that generated from the redox reaction of Ce(IV)‐rhodamine B in H2SO4 medium, for the determination of acyclovir and gancyclovir is described. For acyclovir, the determination range is 3×10?8 g mL?1–7×10?5 g mL?1, with 1.56×10?8 g mL?1 as its determination limit. During 11 repeated measurements for 1×10?6 g mL?1 acyclovir, the relative standard deviation was 2.08%. For gancyclovir, the determination range was 5×10?8 g mL?1–7×10?5 g mL?1, with 2.35×10?8 g mL?1 as its determination limit. The relative standard deviation is 2.83% with 11 repeated measurements of 1×10?6 g mL?1 gancyclovir. This method can be successfully used to determine the content of acyclovir and gancyclovir in injections, acyclovir in eye drops, and, maybe, also for other ciclovirs.  相似文献   

10.
Ab initio calculations at 6–31G**, 6–31++G**, and MP2/6–31G** levels were performed on disilyl–fluoronium, (SiH3)2F+, with the SiH3 group eclipsed or staggered. Optimized geometries, total energies, dipole moments, atomic charges, electronic density, and vibrational frequencies were computed. The results were compared with calculated structural parameters and vibrational frequencies of H3SiF, H2SiF+, H2SiF?, and H4SiF+ ions. The basis-set effects were studied. Several thermochemistry parameters—ZPE, thermal energy, rotational constants, and entropies—were also calculated. © 1994 John Wiley & Sons, Inc.  相似文献   

11.
Two constitutional isomers of dibenzo-18-crown-6 derivatives (6 and 7) were synthesised and their binding behaviours towards trivalent lanthanoid cations (La3 + , Ce3 + , Pr3 + , Nd3 + , Sm3 + , Eu3 + , Gd3 +  and Tb3 + ) were investigated. Both isomers expressed better binding affinities towards Sm3 +  and Tb3 +  than a group of other lanthanoids, as measured by the ligand-to-metal charge-transfer (LMCT) band intensity at ca. 425 nm using UV–vis spectroscopic method. Additionally, the trans isomer 7 was shown to have a higher binding ability than the cis isomer 6 towards Tb3 + .

  相似文献   

12.
The mechanism of the gas‐phase reactions of SiHn+ (n = 1,2) with NF3 were investigated by ab initio calculations at the MP2 and CAS‐MCSCF level of theory. In the reaction of SiH+, the kinetically relevant intermediates are the two isomeric forms of fluorine‐coordinated intermediate HSi‐F‐NF2+. These species arise from the exoergic attack of SiH+ to one of the F atoms of NF3 and undergo two competitive processes, namely an isomerization and subsequent dissociation into SiF+ + HNF2, and a singlet‐triplet crossing so to form the spin‐forbidden products HSiF+ + NF2. The reaction of SiH2+ with NF3 involves instead the concomitant formation of the nitrogen‐coordinated complex H2Si‐NF3+ and of the fluorine‐coordinated complex H2Si‐F‐NF2+. The latter isomer directly dissociates into NF2+ + H2SiF, whereas the former species preferably undergoes the passage through a conical intersection point so to form a H2SiF‐NF2+ isomer, which eventually dissociates into H2SiF+ and NF2. © 2012 Wiley Periodicals, Inc.  相似文献   

13.
Beibei Zhou  Jian Pan 《Chromatographia》2009,70(5-6):739-745
Cichoric acid is a water-soluble phenolic acid in Echinacea purpurea and has a high medicinal value. A rapid and novel argentation complex liquid chromatography method has been developed and validated for determination of cichoric acid in E. purpurea extract. The determination of cichoric acid was carried out on a Restek Pinnacle 11 C18 column (250 mm × 4.6 mm, 5 μm), using acetonitrile-deionized water (38:62, v/v, with 6 mmol L?1 AgNO3 and 0.8% acetic acid) as the mobile phase at a flow rate of 1.0 mL min?1 within 10 min. The wavelength was set at 326 nm. It improved the effect of determination by adding AgNO3 in the mobile phase while cichoric acid coordinated with Ag+. The mechanism of coordination between cichoric acid and Ag+ has been studied by Fourier transform infrared spectroscopy, electrospray ionization mass spectrometry. The mechanism which improved the effect of determination of cichoric acid is analyzed and applied in the rapid determination of salvianolic acid B (Sal B) in Danshen extract solution which has been stored for half a year. The possible structures of the complex and complex ratio are all provided in this article. The experiments have facilitated the study of cichoric acid–Ag+ and Sal B–Ag+ complex and provide a theoretical basis for industrialized extraction of cichoric acid and Sal B in the future.  相似文献   

14.
A novel, simple, efficient and environmentally friendly closed-microwave-assisted extraction (MAE) method of silicon and boron from a variety of industrial and environmental samples using ammonium fluoride as an extractant was developed. This method avoids handling the corrosive and toxic HF and prevents the potential risk of analyte loss due to the creation of volatile SiF4 and BF3 in the presence of HF. Atomic absorption spectrometry and inductively coupled plasma optical emission spectrometry were employed for the subsequent analysis of the resulting supernatant for determination of Si and B, respectively. Certified reference material BCR®-032 Natural Moroccan Phosphate Rock (phosphate fertiliser) was taken to optimise the extraction parameters such as the sample amount, extraction temperature and time and the volume of the extractant. The optimum extraction parameters evaluated using a fractional factorial design were as follows: 50 mg of the sample extracted with 5 mL of 100 g L?1 NH4 F for 15 min at 180°C. The optimised MAE procedure was successfully applied to nine different matrix reference materials intended primarily for validation of methods for determination of components in fertilisers, sludge, plants and fly ash. The obtained results were in a good agreement with the certified or comparative values with an overall precision better than 10% in all cases. The proposed method is recommended for fast and reliable preparation of samples with silicon content <8.2% (w/w). However, further decreasing the sample mass to 10 mg enabled the quantitative extraction of silicon from fly ashes at levels of 23% (w/w).  相似文献   

15.
Two new doubly methoxido-bridged MnIII dinuclear complexes, [MnIII(mphp)(μ-OCH3)(CH3OH)]2·2CH3OH (1) and ([MnIII(ahbz)(μ-OCH3)(CH3OH)]2·2CH3OH (2), have been synthesized by using the tridentate ligands H2mphp (H2mphp = 2-methyl-6-(pyrimidin-2-yl-hydrazonomethyl)-phenol) and H2ahbz (H2ahbz = N-(2-amino-propyl)-2-hydroxy-benzamide). The complexes have been characterized by single-crystal X-ray diffraction analysis and magnetic measurements. Complexes 1 and 2 have a similar dimeric molecular structure. Two [Mn(L)(CH3OH)]+ moieties (L2? = mphp2? or ahbz2?) are bridged by two μ-OCH3? groups in the axial-equatorial asymmetric manner. The coordination geometry of MnIII is an axially elongated octahedron with two oxygens of a methanol ligand and a methoxido ligand situated at the axial positions. Magnetic measurements indicate that 1 and 2 exhibit antiferromagnetic behavior with the fitting parameter of J = ?1.49(3) cm?1, D = ?1.3(1) cm?1, g = 1.98(1) and zJ′ = ?0.18(4) cm?1 for 1, and J = ?1.6(2) cm?1, D = 4.5(3) cm?1, g = 2.06(1) and zJ′ = 1.4(1) cm?1 for 2 on the basis of the spin Hamiltonian ? = ?2J?Mn1?Mn2.  相似文献   

16.
In bis(2‐carboxypyridinium) hexafluorosilicate, 2C6H6NO2+·SiF62−, (I), and bis(2‐carboxyquinolinium) hexafluorosilicate dihydrate, 2C10H8NO2+·SiF62−·2H2O, (II), the Si atoms of the anions reside on crystallographic centres of inversion. Primary inter‐ion interactions in (I) occur via strong N—H...F and O—H...F hydrogen bonds, generating corrugated layers incorporating [SiF6]2− anions as four‐connected net nodes and organic cations as simple links in between. In (II), a set of strong N—H...F, O—H...O and O—H...F hydrogen bonds, involving water molecules, gives a three‐dimensional heterocoordinated rutile‐like framework that integrates [SiF6]2− anions as six‐connected and water molecules as three‐connected nodes. The carboxyl groups of the cation are hydrogen bonded to the water molecule [O...O = 2.5533 (13) Å], while the N—H group supports direct bonding to the anion [N...F = 2.7061 (12) Å].  相似文献   

17.
A novel compound Salvialactomine (1) along with two other unusual occurring natural products Pentatriacontanoic acid 1, 3-dihydroxypropyl ester (2) and 5-Methylflavone (3) were isolated from the callus of Salvia santolinifolia Boiss. Callus was initiated on MS medium containing NAA (0.5 mg/L) and further sub-cultured on MS medium supplemented with NAA with BA (0.5 + 1.5 mg/L). The structures of isolated compounds were determined by using mass spectrometry, 1D, and 2D–NMR techniques. Compounds 1, and 3 were tested for two different cancer cell lines, i.e. Hela (Cervical cancer cell) and PC-3 (Prostate cancer cells). IC50 was found as > 30 using Doxorobicin (0.912 ± 0.12 μmol L?1) as a standard.  相似文献   

18.
At beginning thermal decomposition K2[SiF6] loses SiF4-planes from [SiF6]2?-octahedrons, which has been proved by x-ray-diffraction [1], [2]. Analogous disorder structures are supposed to be present with all solids having complex ions including carbonates, sulfates and others. The result is a high reactivity at this spots. Another reactive form in hexefluorosilicates is represented by mobile SiF-species, perhaps SiF3+. The reactivity is shown by heterogenous reactions with CHCl3 and by solid-solid reactions for instance with halides, oxides etc. As an example corundum (α-Al2O3) reacts at 600°C giving K3 AlF6 and KAlSiO4 [3].  相似文献   

19.
From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M+(aq) + 1·Cs+(nb) ? M+(nb) + Cs+(aq) taking place in the two-phase water–nitrobenzene system (M+ = Li+, Na+, H+, NH4 +, Ag+, K+, Rb+, Tl+; 1 = dibenzo-30-crown-10; aq = aqueous phase, nb = nitrobenzene phase) were determined. Furthermore, the stability constants of the 1·M+ complexes in water-saturated nitrobenzene were calculated; they were found to increase in the series of Cs+ < H+, Ag+ < NH4 + < Na+ < Rb+ < Li+ < K+, Tl+.  相似文献   

20.
The coordination compounds of group 12 halides with 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen), 2[CdF2(bpy)2]·7H2O (1), [ZnI(bpy)2]+·I3? (2), [CdI2(bpy)2] (3), [Cd(SiF6)H2O(phen)2]·[Cd(H2O)2(phen)2]2+·F·0.5(SiF6)2–·9H2O (4), [Hg(phen)3]2+·(SiF6)2–·5H2O (5), [ZnBr2(phen)2] (6), 6[Zn(phen)3]2+·12Br·26H2O (7) and [ZnI(phen)2]+·I (8), have been synthesized and characterized by X-ray crystallography, IR spectroscopy, elemental and thermal analysis. Structural investigations revealed that metal?:?ligand stoichiometry in the inner coordination sphere is 1?:?2 or 1?:?3. A diversity of intra- and intermolecular interactions exists in structures of 18, including the rare halogen?halogen and halogen?π interactions. The thermal and spectroscopic properties were correlated with the molecular structures of 18. Structural review of all currently known coordination compounds of group 12 halides with bpy and phen is presented.  相似文献   

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