Theoretical study of binding interactions and vibrational Raman spectra of water in hydrogen-bonded anionic complexes: (H2O)n- (n = 2 and 3), H2O...X- (X = F, Cl, Br, and I), and H2O...M- (M = Cu, Ag, and Au)

Binding interactions and Raman spectra of water in hydrogen-bonded anionic complexes have been studied by using the hybrid density functional theory method (B3LYP) and ab initio (MP2) method. In order to explore the influence of hydrogen bond interactions and the anionic effect on the Raman intensities of water, model complexes, such as the negatively charged water clusters ((H2O)n-, n = 2 and 3), the water...halide anions (H2O...X-, X = F, Cl, Br, and I), and the water-metal atom anionic complexes (H2O...M-, M = Cu, Ag, and Au), have been employed in the present calculations. These model complexes contained different types of hydrogen bonds, such as O-H...X-, O-H...M-, O-H...O, and O-H...e-. In particular, the last one is a dipole-bound electron involved in the anionic water clusters. Our results showed that there exists a large enhancement in the off-resonance Raman intensities of both the H-O-H bending mode and the hydrogen-bonded O-H stretching mode, and the enhancement factor is more significant for the former than for the latter. The reasons for these spectral properties can be attributed to the strong polarization effect of the proton acceptors (X-, M-, O, and e-) in these hydrogen-bonded complexes. We proposed that the strong Raman signal of the H-O-H bending mode may be used as a fingerprint to address the local microstructures of water molecules in the chemical and biological systems.     

Microhydration of X2 gas (X = Cl, Br, and I): a theoretical study on X2.nH2O clusters (n = 1-8)

Structure and properties of hydrated clusters of halogen gas, X2.nH2O (X = Cl, Br, and I; n = 1-8) are presented following first principle based electronic structure theory, namely, BHHLYP density functional and second-order Moller-Plesset perturbation (MP2) methods. Several geometrical arrangements are considered as initial guess structures to look for the minimum energy equilibrium structures by applying the 6-311++G(d,p) set of the basis function. Results on X2-water clusters (X = Br and I) suggest that X2 exists as a charge separated ion pair, X+delta-X-delta in the hydrated clusters, X2.nH2O (n > or = 2). Though the optimized structures of Cl2.nH2O clusters look like X2.nH2O (X = Br and I) clusters, Cl2 does not exist as a charge separated ion pair in the presence of solvent water molecules. The calculated interaction energy between X2 and solvent water cluster increases from Cl2.nH2O to I2.nH2O clusters, suggesting solubility of gas-phase I2 in water to be a maximum among these three systems. Static and dynamic polarizabilities of hydrated X2 clusters, X2.nH2O, are calculated and observed to vary linearly with the size (n) of these water clusters with correlation coefficient >0.999. This suggests that the polarizability of the larger size hydrated clusters can be reliably predicted. Static and dynamic polarizabilities of these hydrated clusters grow exponentially with the frequency of an external applied field for a particular size (n) of hydrated cluster.     

Ionization energies of LinX (n = 2, 3; X = Cl, Br, I) molecules

Molecules of Li(n)X (n = 2, 3; X = Cl, Br, I) were examined with a magnetic sector mass spectrometer by surface ionization using a triple rhenium filament impregnated with fullerene (C60). The ionization energies obtained for Li(2)Cl, Li(2)Br and Li(2)I molecules are 3.8 +/- 0.1, 3.9 +/- 0.1 and 4.0 +/- 0.1 eV, respectively. The first ionization energy of Li(2)Cl is documented, while there are no literature data for the ionization energies of Li(2)Br and Li(2)I. The molecules of Li(3)Cl, Li(3)Br and Li(3)I were detected experimentally for the first time with ionization energies of 4.0 +/- 0.1, 4.1 +/- 0.1 and 4.1 +/- 0.1 eV, respectively. The ionization energies of Li(n)X (n = 2, 3; X = Cl, Br, I) are in correlation with the theoretical prediction of their hyperlithiated configurations.     

Infrared spectra of X-.CO(2).Ar cluster anions (X=Cl,Br,I)

Ion-molecule clusters of the heavier halide anions X-.CO(2) (X=Cl-,Br-,I-) with CO2 have been studied by gas phase infrared photodissociation spectroscopy, using Ar evaporation from the complexes X-.CO2.Ar upon infrared excitation. We observe that the asymmetric stretch vibrational mode of the CO(2) molecule is red-shifted from the frequency of free CO2, with the red-shift increasing toward the lighter halide ions. A similar trend is repeated in the region of the Fermi resonance of the combination bands of the asymmetric stretch vibration with two quanta of the bending vibration and the symmetric stretch vibration. We discuss our findings in the framework of ab initio and density functional theory calculations.     

Systematic DFT study of gas phase and solvated uranyl and neptunyl complexes [AnO2X4]n (An = U, Np; X = F, Cl, OH, n = -2; X = H2O, n = +2)

The six-valent uranyl and neptunyl complexes [An(VI)O2X4]n (An = U, Np; X = F, Cl, OH, n = -2; X = H2O, n = +2) have been studied within the framework of density functional theory. The relative stabilities of the cis and trans isomers, structural properties, charge distribution, and ligand binding energies have been determined using the modified Perdew-Burke-Ernzerhof functional at the all-electron scalar relativistic level. Uranyl and neptunyl complexes with different ligands have been compared in a systematic fashion, demonstrating close similarity of these actinides in oxidation state VI. In addition, the effect of an aqueous solution has been taken into account with the polarizable continuum model COSMO. Computed averaged ligand binding energies permit one to rationalize the observed different stabilities of the title species in aqueous media.     

Schwingungsspektren und Normalkoordinatenanalyse von (CF3)2SbX-Verbindungen (X = H,Cl, Br,I)

The gas phase i.r. and liquid phase Raman spectra of (CF₃)₂SbX (X = H, Cl, Br, I) have been investigated. The spectra are assigned on the basis of C_s local symmetry and a normal coordinate analysis making use of a transferred force field.     

Ag(PPh3)nX(n=1,2,3；X=Cl,Br,I)的电化学合成

银配合物;;三苯基膦;电合成;Ag(PPh3)nX(n=1;2;3；X=Cl;Br;I)的电化学合成     

Ab initio molecular dynamics simulations of an excited state of X(-)(H(2)O)(3) (X = Cl, I) complex

Upon excitation of Cl(-)(H(2)O)(3) and I(-)(H(2)O)(3) clusters, the electron transfers from the anionic precursor to the solvent, and then the excess electron is stabilized by polar solvent molecules. This process has been investigated using ab initio molecular dynamics (AIMD) simulations of excited states of Cl(-)(H(2)O)(3) and I(-)(H(2)O)(3) clusters. The AIMD simulation results of Cl(-)(H(2)O)(3) and I(-)(H(2)O)(3) are compared, and they are found to be similar. Because the role of the halogen atom in the photoexcitation mechanism is controversial, we also carried out AIMD simulations for the ground-state bare excess electron -- water trimer [e(-)(H(2)O)(3)] at 300 K, the results of which are similar to those for the excited state of X(-)(H(2)O)(3) with zero kinetic energy at the initial excitation. This indicates that the rearrangement of the complex is closely related to that of e(-)(H(2)O)(3), whereas the role of the halide anion is not as important.     

Schwingungsspektren der Vinylmethylhalosilane H2C = CH(CH3)3−nSiXn (n = 1,2; X = F,Cl)

Ohne Zusammenfassung     

The Coordination Polyhedra PdX n (X = Cl,Br, I) in Crystal Structures

The Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres were used to perform crystal-chemical analysis of 106 compounds containing palladium atoms surrounded by halogen atoms. Depending on the oxidation number (2 or 4), Pd atoms can bind 4 to 6 X atoms (X = Cl, Br, I) and form PdX _n coordination polyhedra shaped like octahedra or square pyramids (n = 6), square pyramids (n = 5), or squares (n = 4). A lone electron pair on Pd(II) was found on the basis of X-ray diffraction data. The influence of the palladium valence state on the key stereochemical features of palladium halide complexes is considered in terms of the 18-electron rule. The tendency of palladium atoms to Pd···H aghostic interactions was noted.     

Ab initio study of hydrated potassium halides KX(H2O)1-6 (X=F,Cl,Br,I)

The ionic dissociation of salts was examined with a theoretical study of KX (X=F,Cl,Br,I) hydrated by up to six water molecules KX(H2O)n (n=1-6). Calculations were done using the density functional theory and second order M?ller-Plesset (MP2) perturbational theory. To provide more conclusive results, single point energy calculations using the coupled cluster theory with single, double, and perturbative triple excitations were performed on the MP2 optimized geometries. The dissociation feature of the salts was examined in terms of K-X bond lengths and K-X stretch frequencies. In general, the successive incorporation of water molecules to the cluster lengthens the K-X distance, and consequently the corresponding frequency decreases. Near 0 K, the KX salt ion pairs can be partly separated by more than five water molecules. The pentahydrated KX salt is partly dissociated, though these partly dissociated structures are almost isoenergetic to the undissociated ones for KFKCl. For the hexahydrated complexes, KF is undissociated, KClKBr is partly dissociated, and KI is dissociated (though this dissociated structure is nearly isoenergetic to a partly dissociated one). On the other hand, at room temperature, the penta- and hexahydrated undissociated structures which have less hydrogen bonds are likely to be more stable than the partly dissociated ones because of the entropy effect. Therefore, the dissociation at room temperature could take place for higher clusters than the hexahydrated ones.     

同核双卤分子X2(X=F,CI,Br,I)与C2H2相互作用本质的量子化学研究

用对称性匹配微扰理论(SAPT)对C2H2与X2(X=F,CI,Br,I)相互作用进行了量子化学研究.优化所得的4个稳定复合物相互作用能在-3.276 8～-10.639 5 kJ/mol之间.自然键轨道(NBO)理论分析表明,形成复合物分子间的电荷转移量都很少,在0.002 3～0.013 2之间.SAPT2能量分析显示,从F到I,静电能和诱导能先增大后减小,交换能和色散能逐渐增强,相互作用能依次增强.复合物稳定构型的相互作用能中静电能占主导作用,对吸引能的贡献比例在C2H2…F2中最大(57.3％),在C2H2…I2中最小(49.7％);其次为色散能,在吸引能中所占的比例在21.9％(C2H2…F2)～31.2％(C2H2…I2)之间;诱导能在吸引能中所占的比例最小,均小于20.7％.     

Structures and Electron Attachment Properties of Halomethanes (CX n Y m,X = H,F; Y = Cl,Br, I; n = 0,4; m = 4n)

Abstract

Theoretical studies of structures of neutral molecules and their anions as well as dissociative electron attachment properties are presented for the halomethanes of general formula CX _n Y _m ; X = H, F; Y = Cl, Br, I; n = 0,4; m = 4 – n. The dissociative electron attachment seems to be the primary process resulting in toxicity of these species. The halomethane anions containing hydrogens are formed as radical-anion adducts. When H is replaced by F, these species become true σ? radicals. The electron affinities are computed using a variety of computational techniques including the four-order M?ller-Plesset (MP4) technique that included 250 basis functions. It is challenging to compare the computed results with experiment due to dearth of experimental data and uncertainties in the existing experimental data. Thus in certain cases larger differences are found between the computed and experimental values.     

Superacidity of Boron Acids H2(B12X12) (X=Cl,Br)

Acid remarks : The anhydrous diprotic boron acids H₂(B₁₂X₁₂) (X=Cl, Br; see picture, B orange, X green) are the first examples of diprotic superacids and may be the strongest acids yet isolated. Both protons protonate benzene to give benzenium ion salts that are stable at room temperature. These acids owe their existence to the stability of the icosahedral B₁₂ cluster with its dinegative charge buried beneath a layer of halide substituents.

     

XAFS spectroscopic study of Tc2(O2CCH3)4X2 (X = Cl,Br)

Technetium dimers Tc₂(O₂CCH₃)₄X₂ (X =?Cl, Br) were synthesized and studied by X-ray Absorption Fine Structure spectroscopy (XAFS). EXAFS analysis gave for Tc₂(O₂CCH₃)₄Cl₂: d Tc-Tc =?2.18(1) Å, d Tc–Cl =?2.43(1) Å and for Tc₂(O₂CCH₃)₄Br₂: d Tc–Tc =?2.19(1) Å, d Tc-Br =?2.63(1) Å. The Tc Tc separations are in agreement with Raman studies while the Tc–X distances are somewhat larger. Comparison with other Tc(III) quadruply bonded dimers indicates that the carboxylate compounds exhibit larger Tc–Tc separations. The effect of the terminal ligand (nature and position) on the Tc–Tc separation is discussed.     

Topological characterization of HXO2 (X = Cl, Br, I) isomerization

The isomerization reactions of HOOX --> HOXO --> HXO2 (X = Cl, Br, I) have been studied by using the density functional theory. The breakage and formation of the chemical bonds of the titled reactions have been discussed by the topological analysis method of electronic density. The calculated results show that there is a transitional structure of a three-membered ring on each of the isomerization reaction paths. The "energy transition state (ETS)" and the "structure transition state (STS)" in all of the studied reactions have been found. In all these reactions, the position of the structure transition state and the scope of the structure transition region correlate well with the reaction energy. The STS appears after the ETS in the exothermic reaction but it appears before the ETS in the endothermic reaction. The less reaction energy there is, the wider scope of the structure transition region.     

CH2X(X=H,F,Cl)与臭氧反应机理的量子化学研究

用量子化学UMP2方法,在6-311++G**基组水平上研究了CH2X(X=H,F,Cl)与臭氧反应机理,全参数优化了反应过程中反应物、中间体、过渡态和产物的几何构型,在UQCISD(T)/6-311++G**水平上计算了它们的能量,并对它们进行了振动分析,以确定中间体和过渡态的真实性.从CH2X(X=H,F,Cl)与O3的反应机理的研究结果看,它们与O3反应的活性都比较强,相对而言,活性大小顺序为CH2F＞CH3＞CH2Cl,也就是说,CH2F自由基与臭氧间的反应活性最强,对大气臭氧的损耗将是最大的.同时研究还发现CH2X(X=H,F,Cl)系列自由基与O3的反应都是强放热反应.