Stretching vibrations and structure of (HF) n (n=4–8) clusters

IR spectra of 24 structural isomers of (HF) _n (n=4–8) clusters were calculated in the framework of semiempirical theory of polyatomic molecule vibrations. Based on the results obtained and available experimental data it is proposed that (HF) _n associates comprising 3–5-membered cycles with attached monomeric HF units are present in molecular beams and gas phase.Ab initio calculations performed by the SCF method show the existence of local minima corresponding to such structures on the potential energy surface of (HF) _n clusters (n=4–6). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 435–443, March, 1997.     

Gas-Sensing Property of TM-MoTe2 Monolayer towards SO2, SOF2, and HF Gases

Detecting the characteristic decomposition products (SO₂, SOF₂, and HF) of SF₆ is an effective way to diagnose the electric discharge in SF₆-insulated equipment. Based on first-principles calculations, Au, Ag, and Cu were chosen as the surface modification transition metal to improve the adsorption and gas-sensing properties of MoTe₂ monolayer towards SO₂, SOF₂, and HF gases. The results show that Au, Ag, and Cu atoms tend to be trapped by T_H sites on the MoTe₂ monolayer, and the binding strength increases in the order of Ag < Au < Cu. In gas adsorption, the moderate adsorption energy provides the basis that the TM-MoTe₂ monolayer can be used as gas-sensing material for SO₂, SOF₂, and HF. The conductivity of the adsorption system changes significantly. The conductivity decreases upon gases adsorption on TM-MoTe₂ monolayer, except the conductivity of Ag-MoTe₂ monolayer increases after interacting with SOF₂ gas.     

Coordination compounds with XeF2, AsF3 and HF as ligands to metal ions: a review of reaction systematics, Raman spectra and metal, fluoro-ligand polyhedra

The reactions between Ln(AsF₆)₃ (Ln: lanthanide) and excess of XeF₂ in anhydrous HF (aHF) as a solvent yield coordination compounds [Ln(XeF₂)₃](AsF₆)₃ or LnF₃ together with Xe₂F₃AsF₆ or mixtures of all mentioned products depending on the fluorobasicity of XeF₂ and LnF₃ along the series. XeF₂ in a basic aHF is able to oxidize Pr³⁺ to Pr⁴⁺ besides Ce³⁺ to Ce⁴⁺ and Tb³⁺ to Tb⁴⁺. The tetrafluorides obtained are weaker fluorobases as XeF₂ and are immediately exchanged with XeF₂ yielding Xe₂F₃AsF₆ and LnF₄. The analogous reaction between Ln(BiF₆)₃ and XeF₂ in aHF yields [Ln(XeF₂)₃](BiF₆)₃, Ln: La, Nd. Raman spectra of the compounds [Ln(XeF₂)_n](AF₆)₃ (A: As, Bi) show that no XeF⁺ salts are formed. The interaction of XeF₂ with metal ion is covalent over the fluorine bridge. Analogous reactions of Ln(AsF₆)₃ with AsF₃ in aHF yield [Ln(AsF₃)₃](AsF₆)₃ which are stable in a dynamic vacuum at temperatures lower than 233 K. In reactions between M(AF₆)₂ (M: alkaline earth metal and Pb, A: As, Sb) and XeF₂ in aHF as a solvent, compounds of the type [M(XeF₂)_n](AF₆)₂ were synthesized. Analogous reactions with AsF₃ yield coordination compounds of the type [M(AsF₃)_n](AsF₆)₂. During the preparation of M^x(AsF₆)_x (M: metal in oxidation state x+) by the reaction between metal fluoride and excess of AsF₅ in aHF it was found that HF could also act as a ligand to the metal ions (e.g. Ca(HF)(AsF₆)₂).     

基于TiO2纳米管阵列的高效正面透光型染料敏化太阳能电池的制备及其光电性能

报道了一种基于TiO2纳米管(TNT)阵列正面透光型光阳极的高效染料敏化太阳能电池.将TNTs在450°C烧结后能避免其有序结构在HF处理过程中被破坏,使膜内高速电子传输通道被保留,有利于染料敏化太阳能电池(DSSC)实现高速电荷传输.再用HF、TiCl4、HF和TiCl4混合等溶剂对TNTs进行处理,提高其表面粗糙度以吸附更多染料.染料吸附量的增加能提高光阳极在300-570 nm波段光子捕获效率,该波段是染料吸收光子的主要区域.然而,在染料吸收光子较弱的长波段区域(570-800 nm)光子捕获效率的增加主要源于光阳极光散射率的提高.光阳极光子捕获效率的提高使DSSC的内外量子效率在全波段(300-800 nm)均有所增加,从而使短路电流明显提高.从电化学阻抗数据可知,与电子传输性能密切相关的电化学参数如电荷传输电阻、界面电荷复合电阻、电容、电子寿命、电子扩散长度和电子收集效率等在含处理过的TNTs光阳极DSSC中均有所改善,从而提高电池光电转换效率.含HF和TiCl4混合溶剂处理TNTs光阳极的DSSC最高光电转换效率能达到7.30%,比未处理的DSSC(5.38%)提高35.69%.     

Synthesis of novel salts with HF, AsF3 and XeF2 as ligands to metal cations

A review of all known compounds of the type [Mⁿ(L)_m](AF₆)_n (M is a metal in the oxidation state n; A = P, As, Sb and Bi; L = HF, AsF₃ and XeF₂) is given with the emphasis on the compounds isolated and characterized by our group. The synthetic routes for the preparation of these compounds are given together with a brief analysis of their structures. In the case of L = XeF₂ the influence of the properties of the cation and the anion on the structural diversity of these coordination compounds is discussed. A brief analysis of their Raman spectra is also given.     

Correlation of the position of the bond functions in H-X with electronegativity

S type Gaussian bond functions are optimized for HF, H₂O, NH₃, and CH₄. The optimization is carried out with respect to the exponent and position in the H-X bond. The position is found to correlate well with the electronegativity of Pauling and Allred-Rochow.     

Synthesis and structural investigation of the compounds containing HF2 anions: Ca(HF2)2, Ba4F4(HF2)(PF6)3 and Pb2F2(HF2)(PF6)

Three new compounds Ca(HF₂)₂, Ba₄F₄(HF₂)(PF₆)₃ and Pb₂F₂(HF₂)(PF₆) were obtained in the system metal(II) fluoride and anhydrous HF (aHF) acidified with excessive PF₅. The obtained polymeric solids are slightly soluble in aHF and they crystallize out of their aHF solutions. Ca(HF₂)₂ was prepared by simply dissolving CaF₂ in a neutral aHF. It represents the second known compound with homoleptic HF environment of the central atom besides Ba(H₃F₄)₂. The compounds Ba₄F₄(HF₂)(PF₆)₃ and Pb₂F₂(HF₂)(PF₆) represent two additional examples of the formation of a polymeric zigzag ladder or ribbon composed of metal cation and fluoride anion (MF⁺)_n besides PbF(AsF₆), the first isolated compound with such zigzag ladder. The obtained new compounds were characterized by X-ray single crystal diffraction method and partly by Raman spectroscopy. Ba₄F₄(HF₂)(PF₆)₃ crystallizes in a triclinic space group P1¯ with a=4.5870(2) Å, b=8.8327(3) Å, c=11.2489(3) Å, α=67.758(9)°, β=84.722(12), γ=78.283(12)°, V=413.00(3) Å³ at 200 K, Z=1 and R=0.0588. Pb₂F₂(HF₂)(PF₆) at 200 K: space group P1¯, a=4.5722(19) Å, b=4.763(2) Å, c=8.818(4) Å, α=86.967(10)°, β=76.774(10)°, γ=83.230(12)°, V=185.55(14) ų, Z=1 and R=0.0937. Pb₂F₂(HF₂)(PF₆) at 293 K: space group P1¯, a=4.586(2) Å, b=4.781(3) Å, c=8.831(5) Å, α=87.106(13)°, β=76.830(13)°, γ=83.531(11)°, V=187.27(18) Å³, Z=1 and R=0.072. Ca(HF₂)₂ crystallizes in an orthorhombic Fddd space group with a=5.5709(6) Å, b=10.1111(9) Å, c=10.5945(10) Å, V=596.77(10) Å³ at 200 K, Z=8 and R=0.028.     

Facile Preparation of Indolyl-2/3-methylsulfoxides Using HF/H2O2

A variety of indolyl-2/3-methylsulfides tethered with sensitive functionalities were oxidized to the corresponding sulfoxides using a hitherto unexplored HF/H₂O₂ system.     

The C2H 3 + cation and its interaction with HF

The structure and stability of classical and bridged C₂H ₃ ⁺ is reinvestigated. The SCF and CEPA-PNO computations performed with flexibles andp basis sets including twod-sets on carbon confirm our previous results. We find the protonated acetylene structure to be more stable than the vinyl cation by 3.5–4 kcal/mol. The energy barrier for the interconversion of these two structures is at most a few tenths of a kcal/mol. The equilibrium SCF geometries of Weberet al. [15] are affected insignificantly by further optimization at the CEPA-PNO level. Several structures for the interaction of C₂H ₃ ⁺ with HF have been investigated at the SCF level. With our largest basis set which includes a complete set of polarization functions we find a remarkable levelling of the stabilities of most of the structures. In these cases the stabilization energy ΔE ranges from −10 to −13 kcal/mol.     

Exploratory study of the reaction of bis(2-methoxyethyl)aminosulfur trifluoride (Deoxofluor™ reagent) with diaryl sulfoxides: novel routes to Ar2SF2 and Ar2SF(OTf) via sulfoxide activation

Neither bis(2-methoxyethyl)aminosulfur trifluoride (Deoxofluor™ reagent) nor HF/pyridine alone can fluorinate diaryl sulfoxides. S-fluorination can be effected by activating the sulfoxide via protonation with HF/pyridine (70:30) to form sulfoxonium ions in equilibrium which are then S-fluorinated in situ with Deoxofluor™ to give Ar₂SF₂ compounds. Conversions depend strongly on steric factors and the reactions require the use of excess Deoxofluor™ and HF/pyridine. NMR data for the resulting diarylsulfur difluorides are gathered and discussed. Sulfoxide activation via diaryl (trifloxy) sulfonium triflate generated in situ from Ar₂SO with triflic anhydride at low temperature represents another strategy for S-fluorination with Deoxofluor™ to generate Ar₂S(OTf)F.     

The effect of substituents and operating conditions on the electrochemical fluorination of alkyl phenylacetates in Et3N·4HF medium

Selective electrochemical fluorination of alkyl phenylacetates (Ph-CH₂-COOR, where R is methyl, ethyl, n-propyl, n-butyl, i-propyl and sec-butyl) under galvanostatic conditions were reported in Et₃N·4HF medium. Preparative electrolysis experiments were carried out both in pre-electrolysed dry Et₃N·4HF and the same electrolyte medium without pre-electrolysis. Very little hydrolysed fluorinated products were obtained in pre-electrolysed medium where as significant quantities of hydrolysed products leading to fluorinated phenylacetic acid were obtained from Et₃N·4HF without pre-electrolysis. Under optimum experimental conditions up to 87% selectivity of monofluoro ester could be achieved. Difluoro alkyl phenylacetate, monofluoro and difluoro phenylacetic acids were the other predominant side products obtained. The hydrolysis appears to be initiated by tautomeric transformation of proton after the initial electro oxidative formation of the cation radical. ¹⁹F as well as ¹H NMR spectroscopy have been employed to identify the minor constituents formed during the electro oxidative process.     

HF在α-AlF3(0001)表面吸附的密度泛函理论研究

利用密度泛函理论系统研究了不同覆盖度下HF在3F、2F、1F与Al 终端的α-AlF₃(0001)表面的吸附行为, 分析了HF与不同终端表面相互作用的电子机制. 计算结果表明: HF在3F终端的α-AlF₃(0001)表面物理吸附; 在2F及1F终端表面化学吸附, 形成Al-F键和FHF结构, 使HF分子活化, 可以参加下一步的氟化反应; 在Al 终端表面解离吸附形成Al-F与Al-H键. 3F、2F、1F及Al 终端表面配位不饱和数目分别为0、1、2与3配位.不同覆盖度研究表明, 在2F终端表面上, 吸附一个HF分子使表面Al 配位达到饱和, 后续吸附的HF为物理吸附; 而在1F与Al 终端表面仍可化学吸附. 因此, 推测α-AlF₃暴露不同终端表面中Al 原子配位不饱和数越高, 其对HF吸附与活化能力越强, 可能的氟化催化反应活性越高. 差分电荷密度与电子态密度分析表明, HF与3F终端α-AlF₃(0001)表面发生弱相互作用, 而与2F、1F与Al 终端表面形成较强的电子相互作用.     

CC bond formation using allylic organozirconium compounds. Nucleophilic additions on to isolated and in situ generated η-pentadienyl-Fe(CO)3/Fe(CO)2PPh3(+1) cations

Two nucleophilic allylic organozirconium compounds 9-10 (R⁵: Me and tBu) have been reacted with acyclic isolated η⁵-pentadienyl-Fe(CO)₃/Fe(CO)₂PPh₃(+1) cations or with these intermediates generated in situ (Uemura-like conditions). Depending on reaction conditions, iron-complexed η⁴-dienyl-Fe(CO)₃/Fe(CO)₂PPh₃ and σ,η³-π-allyl-Fe(CO)₃/Fe(CO)₂PPh₃ condensation products have been selectively isolated and fully characterized.     

氢氟酸腐蚀对α-Fe2O3薄膜光解水电极光电化学性质的影响

使用溶胶-凝胶法制备了α-Fe₂O₃薄膜,研究了氢氟酸腐蚀薄膜表面对其光电化学性质的影响. 实验发现,薄膜表面的孔洞和间隙随着氢氟酸浸蚀时间的增长而发生变化. 氢氟酸浸蚀5 min,α-Fe₂O₃电极的光电流降低;随后随浸蚀时间增加而迅速增加;当浸蚀时间大于15 min时,其光电流再次下降,但对浸蚀过的样品再次退火可以使光电流大幅增加. 通过电化学交流阻抗谱、拉曼和X射线光电子能谱分析,提出了两个影响光电流的因素：氢氟酸表面浸蚀造成薄膜表面的多孔性和结晶度降低. 为此,通过示意图解释了结合浸蚀和退火后处理两个步骤来增强α-Fe₂O₃薄膜光解水电极光电活性的原理. 相对于初始的α-Fe₂O₃电极,浸蚀并且再退火处理后,其光电性质更加稳定.     

Raman spectra and structural features of ClOF2 + cation in a solution of anhydrous HF

The Raman spectra of ClOF₂ ⁺ cation in solutions of anhydrous HF were studied. In the ClOF₂ ⁺HF₂ ⁻ and ClOF₂ ⁺BF₄ ⁻−HF systems, this cation exists as a pyramidal structure (C _s symmetry), while in the ClOF₂ ⁺AuF₆ ⁻−HF system, it exists as a planar structure (C _2v symmetry). Based on nonempirical calculations by the Hartree-Fock-Roothaan method, an explanation for the dependence of the structure of the ClOF₂ ⁺ cation on the nature of the anion was proposed. For the Cl−O bond vibrations, the correlation functions of vibrational and rotational relaxations were calculated, and the characteristic times of these processes were determined. The main contribution to the formation of the band contours corresponding to the above-mentioned modes is made by the vibrational dephasing. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 432–437, March, 1998.     

Phenoxide-assisted P-C bond cleavage in PdCl2(PPh3)2 under very mild conditions

PdCl₂(PPh₃)₂ reacted with NaOAr (Ar = Ph, p-tolyl) at 0 °C to afford PdCl(Ph)(PPh₃)₂, instead of PdCl(OAr)(PPh₃)₂, in 12-16% isolated yields based on Pd. The structure was confirmed by NMR and X-ray crystallography. GC-MS analysis of the reaction solution revealed that OPPh₂(OAr), OPPh(OAr)₂, and OP(OAr)₃ are formed, while NMR studies indicated that PdCl(Ph)(PPh₃)₂ is produced when PdCl(OAr)(PPh₃)₂ decomposes. The reaction of PdCl₂(PPh₃)₂ with Bu₃Sn(OC₆H₄-p-OMe) also gave PdCl(Ph)(PPh₃)₂ in 8% isolated yield. These results suggest that PdCl(OAr)(PPh₃)₂ is highly labile and the aryloxy ligand exchanges with the phenyl groups in triphenylphosphine even under very mild conditions.     

Untersuchungen der Hydroxylammonium-Fluorozirconate(IV)

Summary Hydroxylammonium fluorozirconates have been investigated. Two new microcristalline phases have been isolated from aqueous solutions: (NH₃OH)₂ZrF₆ (1) and (NH₃OH)₃ZrF₇ (2). The crystals were prepared by slow evaporation of the solution of NH₂OH, Zr, and HF. Different compositions of the crystals were achieved by varying the molar ratios of the components. They were characterized by thermal analysis, vibrational spectroscopy, and structure (single crystal x-ray methods). (NH₃OH)₂ZrF₆ (1) crystallizes triclinic, P (No.: 2),a=7.400(2),b=7.609(2),c=7.887(2) Å, =57.29(3)°, =62.16(3)°, =67.83(2)°. (NH₃OH)₃ZrF₇ (2) crystallizes triclinic, P (No.: 2),a=7.128(1),b=7.989(1),c=8.888(1) Å, =109.72(1)°, =91.01(1)°, =104.27(1)°.

     

Chemical analysis of acidic silicon etch solutions: II. Determination of HNO3, HF, and H2SiF6 by ion chromatography

The processing of silicon in microelectronics and photovoltaics involves the isotropic chemical etching using HF-HNO₃ mixtures to clean the surface from contaminations, to remove the saw damage, as well as to polish or to texture the wafer surface. Key element of an effective etch process control is the knowledge of the actual etch bath composition in order to maintain a certain etch rate by replenishment of the consumed acids. The present paper describes a methods for the total analysis of the etch bath constituents HF, HNO₃, and H₂SiF₆ by ion chromatography. First step is the measurement of the total fluoride and nitrate content in the analyte. In a second step, H₂SiF₆ is precipitated as K₂SiF₆. After careful filtration of the precipitate, the fluoride concentration in the filtrate is measured and the content of free HF is calculated therefrom. The K₂SiF₆ is dissolved again and the fluoride content measured and recalculated as H₂SiF₆. The results obtained with the presented method are discussed with respect to the results from two other, previously published methods, based on a titration using methanolic cyclohexylamine solution as titrant and based on a method using a fluoride ion selective electrode (F-ISE). An evaluation with respect to the needs for an industrial application is given.     

Spectroscopic properties of guanidinium zinc sulphate [C(NH2)3]2Zn(SO4)2 and ab initio calculations of [C(NH2)3]2 and HC(NH2)3

Raman and FTIR spectra of guanidinium zinc sulphate [C(NH₂)₃]₂Zn(SO₄)₂ are recorded and the spectral bands assignment is carried out in terms of the fundamental modes of vibration of the guanidinium cations and sulphate anions. The analysis of the spectrum reveals distorted SO₄²⁻ tetrahedra with distinct S–O bonds. The distortion of the sulphate tetrahedra is attributed to Zn–O–S–O–Zn bridging in the structure as well as hydrogen bonding. The CN₃ group is planar which is expressed in the twofold symmetry along the C–N (1) vector. Spectral studies also reveal the presence of hydrogen bonds in the sample. The vibrational frequencies of [C(NH₂)₃]₂ and HC(NH₂)₃ are computed using Gaussian 03 with HF/6-31G* as basis set.     

A density functional theory study of the dimers of HX (X = F,Cl, and Br)

The geometries, interaction energies, and vibrational properties of (HF)₂, (HCl)₂, and (HBr)₂ have been investigated using a variety of hybrid density functional methods and the 6‐311+G(2df,p) basis set. Although most of the density functional methods predict geometries in reasonable agreement with experiment, methods containing the LYP correlation functional yield geometrical parameters in slightly better agreement. The (HF)₂ interaction energy, predicted by the hybrid density functional methods, is in reasonable agreement with experiment, but the (HCl)₂ and (HBr)₂ interaction energies are underestimated substantially. The frequency shift for the X? H donor bond correlates linearly with the elongation of the X? H bond upon complexation, and is predicted reasonably well by methods containing the LYP functional. Overall, the hybrid density functional methods adequately predict the properties of the halide dimers. It is interesting to note that the BHandHLYP and B1LYP density functional methods offer a competitive alternative to the popular B3LYP method. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1590–1597, 2001