Gas-phase Geometries Research Articles

Molecular structure of ( Z)-6-[(5-chloro-2-hydroxyphenylamino) methylene]-3-(diethylamino)cyclohexa-2,4-dienone: A combined experimental and theoretical study

The crystal structure and spectroscopic properties of ortho-hydroxy Schiff base compound ( Z)-6-[(5-chloro-2-hydroxyphenylamino)methylene]-3-(diethylamino)cyclohexa-2,4-dienone were determined by X-ray diffraction, IR and UV–Vis spectroscopy techniques. Molecules of the compound exist as NH tautomeric form in solid state. The gas phase geometry optimizations of two possible tautomeric forms of the title compound were achieved using DFT calculations at B3LYP/6-31G(d,p) level of theory. In order to describe the potential energy barrier belonging to the intramolecular proton transfer and to observe the effects of transfer on the molecular geometry, a relaxed potential energy surface (PES) scan was performed based on the optimized geometry of the NH tautomeric form by varying the redundant internal coordinate, N–H bond distance. At the same level of theory, the vibrational frequencies were calculated and compared with the experimental frequencies. The electronic absorption spectra of the tautomers were calculated using time-dependent density functional theory (TD-DFT) method started from solution phase optimized geometries and compared with the experimental ones.

Hydrogen Bonding in Water Clusters and Their Ionized Counterparts

Ab initio and DFT computations were carried out on four distinct hydrogen-bonded arrangements of water clusters (H(2)O)(n), n = 2-20, represented as W1D, W2D, W2DH, and W3D. The variation in the strength of hydrogen bond as a function of the chain length is studied. In all the four cases, there is a substantial cooperative interaction, albeit in different degrees. The effect of basis set superposition error (BSSE) on the complexation energy of water clusters has been analyzed. Atoms in molecules (AIM) analysis performed to evaluate the nature of the hydrogen bonding shows a high correlation between hydrogen bond strength and the trends in complexation energy. Solvated water clusters exhibit lower complexation energies compared to corresponding gas-phase geometries on PCM (polarized continuum model) optimization. The feasibility of stripping an electron or addition of an electron increases dramatically as the cluster size increases. Although W3D caged structures are stable for neutral clusters, the helical W2DH arrangement appeared to be an optimal choice for its ionized counterparts.

Comparison of Mass Transfer Efficiency and Energy Consumption in Static Mixers

The aim of this study was to compare the pressure drop (Δp) generated by a static mixer with sieve plates in two-phase downflow (water as a continuous phase), and the mass transfer efficiency (kLa, a) with the performance of other static mixers (Sulzer, Kenics, Karman, etc.). The relationships for Δp, kLa and interfacial area (a) calculation depending on liquid and gas phase velocities and geometry of the plates (sieves) in this static mixer are presented. kLa was found to be strictly proportional to the power consumption (P/V) and its values were quite close to those obtained in Sulzer & Kenics mixers with an 8-element mesh. Enhancement factors for oxygen absorption in the sodium sulphite solution and for ozone absorption in Lake Ülemiste water were calculated and the plausible values of the interfacial area (a) were estimated.

Calculation of dissociation constants and chemical hardness of some biologically important molecules: A theoretical study

The gas-phase geometries of neutral, protonated, and deprotonated forms of some biologically important molecules, alanine (Ala), glycine (Gly), phenylalanine (Phe), and tyrosine (Tyr), were optimized using density functional theory at B3LYP/6-311++G(d) and the ab initio HF/6-311++G(d) level of theories. The neutral and different stable ionic states of Ala, Gly, Phe, and Tyr have also been solvated in aqueous medium using polarizable continuum model for the determination of solvation free energies in the aqueous solution. The gas-phase acidity constants of above four molecules have been also calculated at both levels of theories and found that the values calculated at HF/6-311++G(d) method are in good agreement with experimental results. A thermodynamic cycle was used to determine the solvation free energies for the proton dissociation process in aqueous solution and the corresponding pKa values of these molecules. The pKa values calculated at B3LYP/6-311++G(d) method are well supported by the experimental data with a mean absolute deviation 0.12 pKa units. Additionally, the chemical hardness and the ionization potential (IP) for these molecules have been also explored at both the level of theories. The Tyr has less value of chemical hardness and IP at both levels of theories compared with other three molecules, Ala, Gly, and Phe. The calculated values of chemical hardness and IP are decreasing gradually with the substitution of the various functional groups in the side chain of the amino acids. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

A transferable classical potential for the water molecule

We developed a new model for the water molecule which contains only three Gaussian charges. Using the gas-phase geometry the dipole moment of the molecule matches, the quadrupole moment closely approximates the experimental values. The negative charge is connected by a harmonic spring to its gas-phase position. The polarized state is identified by the equality of the intermolecular electrostatic force and the spring force acting on the negative charge. In each timestep the instantaneous position of the massless negative charge is determined by iteration. Using the technique of Ewald summation, we derived expressions for the potential energy, the forces, and the pressure for Gaussian charges. The only properties to be fitted are the half-width values of the Gaussian charge distributions and the parameters of the nonelectrostatic repulsion-attraction potential. We determined the properties of gas-phase clusters up to six molecules, the internal energy and density of ambient water and hexagonal ice. We calculated the equilibrium density of ice VII as a function of pressure. As an additional test, we calculated the pair-correlation function, the isotherm compressibility, the heat capacity, and the self-diffusion coefficients for ambient water. As far as we know, this is the first classical model of water which is able to estimate both ends of the phase diagram, the high pressure ice VII, and the gas clusters of water with excellent accuracy.

Cooperativity in Al3+Hydrolysis Reactions from Density Functional Theory Calculations

Aqua/hydroxo mononuclear Al(3+) species in aqueous solution are investigated using density functional theory (DFT B3LYP/6-311++G(d,p)) and the polarized continuum model (PCM). Optimized gas-phase geometries have been obtained for the species Al(OH)(n)(H(2)O)(m)((3-n)+) in which n = 0, 1, 2, 3, or 4 while (n + m) = 4, 5, or 6. For Al(OH)(2)(H(2)O)(4)(1+) the cis and trans geometries were considered. The structures were analyzed in terms of water and hydroxide M-O and O-H distances, which are shown to be strongly modulated by water hydrolysis. The atomic charges were computed and the electronic structure of these complexes is discussed. The conversion from one aqua-/hydroxo- species to another follows independent hydrolysis and dehydration reactions for which the aqueous Gibbs free energies have been estimated by means of constructing thermodynamic cycles. Results clearly demonstrate that the dehydration reaction is increasingly favorable as hydrolysis proceeds. Similarly, as the complex coordination number decreases the hydrolysis reaction proceeds increasingly more favorably. The aqueous Gibbs free energy of each species, relative to Al(H(2)O)(6)(3+), has been determined by combining the appropriate Gibbs free energies of the hydrolysis and dehydration reactions demonstrating that the additive effect is quite complex showing a gradual transition from preferring the 6-coordination to 5-coordination to 4-coordination as a function of ligand hydrolysis, in agreement with published experimental and theoretical work. We have also computed the equilibrium constants of each of the above reactions and, using [H(+)] as a parameter, estimated the mole fraction of each species as a function of pH. This offers a clear demonstration that the qualitative hydrolysis behavior, e.g., cooperativity, of aqueous Al(3)+ species is obtained at the B3LYP/IEF-PCM level of theory.

Synthesis, Characterization, and Computational Study of MoSF4

Molybdenum sulfide tetrafluoride was synthesized from MoF(6) and S(Si(CH(3))(3))(2) in CFCl(3) at low temperature and was fully characterized by Raman, infrared, and (19)F NMR spectroscopy and by X-ray crystallography. The crystal structure revealed that MoSF(4) forms infinite fluorine-bridged chains. Quantum-chemical calculations using B3LYP and PBE1PBE methods were used to calculate the gas-phase geometry and vibrational frequencies of monomeric MoSF(4) and (MoSF(4))(3)F(-). The vibrational frequencies of (MoSF(4))(3)F(-) have been used in the assignment of the vibrational spectra of solid MoSF(4). Natural bond order analyses were carried out for monomeric MoSF(4) and, for comparison, for WSF(4).

Syntheses and Multi-NMR Study offac- andmer-OsO3F2(NCCH3) and the X-ray Crystal Structure (n= 2) and Raman Spectrum (n= 0) offac-OsO3F2(NCCH3)·nCH3CN

Dissolution of the infinite chain polymer, (OsO(3)F(2))(infinity), in CH(3)CN solvent at -40 degrees C followed by solvent removal under vacuum at -40 degrees C yielded fac-OsO(3)F(2)(NCCH(3)).nCH(3)CN (n >/= 2). Continued pumping at -40 degrees C with removal of uncoordinated CH(3)CN yielded fac-OsO(3)F(2)(NCCH(3)). Both fac-OsO(3)F(2)(NCCH(3)).nCH(3)CN and fac-OsO(3)F(2)(NCCH(3)) are yellow-brown solids and were characterized by low-temperature (-150 degrees C) Raman spectroscopy. The crystal structure (-173 degrees C) of fac-OsO(3)F(2)(NCCH(3)).2CH(3)CN consists of two co-crystallized CH(3)CN molecules and a pseudo-octahedral OsO(3)F(2).NCCH(3) molecule in which three oxygen atoms are in a facial arrangement and CH(3)CN is coordinated trans to an oxygen atom in an end-on fashion. The Os---N bond length (2.205(3) A) is among the shortest M---N adduct bonds observed for a d(0) transition metal oxide fluoride. The (19)F NMR spectrum of (OsO(3)F(2))(infinity) in CH(3)CN solvent (-40 degrees C) is a singlet (-99.6 ppm) corresponding to fac-OsO(3)F(2)(NCCH(3)). The (1)H, (15)N, (13)C, and (19)F NMR spectra of (15)N-enriched OsO(3)F(2)(NCCH(3)) were recorded in SO(2)ClF solvent (-84 degrees C). Nitrogen-15 enrichment resulted in splitting of the (19)F resonance of fac-OsO(3)F(2)((15)NCCH(3)) into a doublet ((2)J((15)N-(19)F), 21 Hz). In addition, a doublet of doublets ((2)J((19)F(ax)-(19)F(eq)), 134 Hz; (2)J((15)N-(19)F(eq)), 18 Hz) and a doublet ((2)J((19)F(ax)-(19)F(eq)), 134 Hz) were observed in the (19)F NMR spectrum that have been assigned to mer-OsO(3)F(2)((15)NCCH(3)); however, coupling of (15)N to the axial fluorine-on-osmium environment could not be resolved. The nitrogen atom of CH(3)CN is coordinated trans to a fluorine ligand in the mer-isomer. Quantum-chemical calculations at the SVWN and B3LYP levels of theory were used to calculate the energy-minimized gas-phase geometries, vibrational frequencies of fac- and mer-OsO(3)F(2)(NCCH(3)) and of CH(3)CN. The relative stabilities of the mer- and fac-isomers have been determined and are in accordance with the solution NMR assignments.

DFT‐GIAO1H NMR chemical shifts prediction for the spectral assignment and conformational analysis of the anticholinergic drugs (−)‐scopolamine and (−)‐hyoscyamine

The relatively large chemical shift differences observed in the (1)H NMR spectra of the anticholinergic drugs (-)-scopolamine 1 and (-)-hyoscyamine 2 measured in CDCl(3) are explained using a combination of systematic/molecular mechanics force field (MMFF) conformational searches and gas-phase density functional theory (DFT) single point calculations, geometry optimizations and chemical shift calculations within the gauge including/invariant atomic orbital (GIAO) approximation. These calculations show that both molecules prefer a compact conformation in which the phenyl ring of the tropic ester is positioned under the tropane bicycle, clearly suggesting that the chemical shift differences are produced by the anisotropic effect of the aromatic ring. As the calculations fairly well predict these experimental differences, diastereotopic NMR signal assignments for the two studied molecules are proposed. In addition, a cursory inspection of the published (1)H and (13)C NMR spectra of different forms of 1 and 2 in solution reveals that most of them show these diastereotopic chemical shift differences, strongly suggesting a preference for the compact conformation quite independent of the organic or aqueous nature of the solvent.

Analysis of SM8 and Zap TK calculations and their geometric sensitivity

A prospective study of aqueous solvation energies was done using the SM8 and Zap TK models for a variety of geometries. CM4M charges calculated with M06 and M06-2X were found to yield similar results for the SM8 model. Zap TK calculations were primarily done with AM1BCC charges but limited attempts to use charges derived from DFT showed promise. The OMEGA application quickly generated conformations that performed well with both solvation models, while the use of computationally expensive DFT optimized geometries yielded increased RMSE and MSE. It is shown that increasing levels of gas phase geometry optimization yield increasingly unfavorable solvation energy for single conformer models.

The proton transfer process observed in the structure analysis and DFT calculations of (E)-2-ethoxy-6-[(2-methoxyphenylimino)methyl]phenol

The crystal and molecular structures of an o-hydroxy Schiff base derivative, (E)-2-ethoxy-6-[(2-methoxyphenylimino)methyl]phenol, have been determined by single crystal X-ray diffraction analyses at 296 and 100 K. The results from temperature-dependent structural analysis regarding the tautomeric equilibrium of the compound were interpreted with the aid of quantum chemical calculations. To clarify the tautomerization process and its effects on the molecular geometry, the gas-phase geometry optimizations of two possible tautomers of the title molecule, its OH and NH form, were achieved using DFT calculations with B3LYP method by means of 6-31 + G(d,p) basis set. In order to describe the potential barrier belonging to the phenolic proton transfer, nonadiabatic Potential Energy Surface (PES) scan was performed based on the optimized geometry of the OH tautomeric form by varying the redundant internal coordinate, O–H bond distance. The Harmonic Oscillator Model of Aromaticity (HOMA) indices were calculated in every step of the scan process so as to express the deformation in the aromaticities of principal molecular moieties of the compound. The results show that there is a dynamic equilibrium between the aromaticity level of phenol and chelate ring and furthermore π-electron coupling affecting overall molecule of the title compound. Charge transfer from phenol ring to pseudo-aromatic chelate ring increases with increasing temperature, whereas π-electron transfer from chelate ring to anisole ring is decreased as temperature increases. The most strength intramolecular H-bonds are observed for conformers close to transition state.

A computational study of solution equilibria of platinum-based ethylene hydroamination catalytic species including solvation and counterion effects: Proper treatment of the free energy of solvation☆

. A DFT/B3LYP study of the effect of the explicit inclusion of the Me 4 P + cation (as a model of n Bu 4 P + ) on the calculation of solution equilibria involving anionic Pt II complexes is reported. The calculated complexes are models of species that potentially participate in the low-energy portion of the catalytic cycle of the ethylene hydroamination by aniline catalyzed by the PtBr 2 /( n Bu 4 P)Br system, namely ( n Bu 4 P) 2 [PtBr 4 ] ( 1 ), ( n Bu 4 P) 2 [Pt 2 Br 6 ] ( 1′ ), ( n Bu 4 P)[PtBr 3 (C 2 H 4 )] ( 2 ), ( n Bu 4 P)[PtBr 3 (PhNH 2 )] ( 3 ), trans -[PtBr 2 (C 2 H 4 )(PhNH 2 )] ( 4 ), cis -[PtBr 2 (C 2 H 4 )(PhNH 2 )] ( 5 ), cis -[PtBr 2 (PhNH 2 ) 2 ] ( 6 ), trans -[PtBr 2 (C 2 H 4 ) 2 ] ( 7 ), and cis -[PtBr 2 (C 2 H 4 ) 2 ] ( 8 ). The relative energies are based on gas-phase geometry optimizations followed by C-PCM calculations of the solvation effects in dichloromethane and aniline at 25 °C and 150 °C. Three different approaches have been considered to describe the relative energies in solution: Δ E CPCM (Δ E el gas + ΔΔ G solv ), Δ G v CPCM (Δ E el gas + Δ E ZPVE gas + Δ E v gas − T Δ S v gas + ΔΔ G solv ) and Δ G CPCM (Δ H gas − T Δ S gas + ΔΔ G solv ), where Δ E v gas and Δ S v gas includes only the vibrational contribution and ΔΔ G solv for each compound is the solvation free energy resulting from the C-PCM calculation. The cation-anion association was found favourable in both solvents at the Δ E CPCM and Δ G v CPCM levels, but nearly neutral at the Δ G CPCM level. Consideration of the associated salts has a drastic effect on the energy scheme but significantly changes the relative energies only when doubly charged complexes are involved. The energy changes for equilibria that involve only neutral of singly charged species are not greatly affected by the cation inclusion. The Δ G CPCM approach provides results in greater agreement with the available equilibrium data.

Electronic structure modeling of dinuclear copper(II)-methacrylic acid complex by density functional theory

A dinuclear centrosymmetric copper(II) complex with the formula [Cu(2)(mu-maa)(4)(maaH)(2)] has been synthesized and experimentally characterized by IR, electronic spectroscopy, and X-ray single-crystal diffractometry. Starting from experimental X-ray geometry and using antiferromagnetic singlet ground state, gas phase geometry optimization was performed by density functional hybrid (B3LYP) method with 6-31G(d) and LANL2DZ basis sets. Gas-phase vibrational frequencies and single point energy (SPE) calculations have been carried out at the geometry-optimized structure. Molecular electrostatic potential calculated at the optimized geometry and natural bond orbital analysis data have been extracted from SPE output. The gas-phase electronic transitions of the title complex were investigated by the time dependent-density functional theory (TD-DFT) approach with the same theory employing LANL2DZ basis set. Also the calculated UV-Vis based upon TD-DFT results and IR spectra were simulated for comparison with the experimental ones.

Combining ab initio quantum mechanics with a dipole-field model to describe acid dissociation reactions in water: First-principles free energy and entropy calculations

We introduce a novel approach to compute dissociation free energy and entropy values in simulations that employ a density functional theory description of the acidic moiety and of the solvent. The approach consists of utilizing an alchemical transformation of a weak acid A-COOH into the strong acid B-COOH, which makes it practical to employ alchemical free energy perturbation methods in the context of ab initio molecular dynamics simulations. The present alchemical transformation circumvents the need to tackle changes in the total number of electrons and atoms by replacing the chemical residue responsible for the change in acidity with an easily tunable external effective potential. Our investigation demonstrates that (1) a simple but effective class of external potentials that control acidity changes in the acetic/trifluoroacetic acid series can be achieved by replacing the methyl and trifluoromethyl substituents by screened dipoles. Using this dipole-field/quantum-mechanics (DF/QM) approach one can predict gas-phase geometries, proton dissociation energies, total dipole moments, and water binding energies in good agreement with full-QM values. (2) The resulting alchemical perturbation calculations are stable and well converged and allow one to compute absolute pK(a) values whose accuracy is limited primarily by the exchange-correlation functional employed: H-COOH=2.5+/-0.6 (full-QM calculation), 3.7 (exp); F(3)C-COOH=0.4+/-0.6 (DF/QM calculation), 0.5 (exp); H(3)C-COOH=3.1+/-0.7 (DF/QM calculation), 4.7 (exp); 3) Our DF/QM model predicts that the difference in acidity between H-COOH and H(3)C-COOH is dominated by solvent entropy effects, in excellent agreement with experimental observations. The calculated difference between the dissociation energies of these acids is DeltaDelta(d)U=0.0+/-0.26 kcal/mol while the experimental value is 0.0+/-0.1 kcal/mol.

Indazaboles—synthesis and molecular structure

AbstractThe reaction of 1‐trimethylsilyl‐indazole with boranes affords indazaboles accompanied by elimination of trimethysilane. Thus, the two isomers of parent indazabole are formed in a 1:1 ratio using borane in THF (BH3/THF), characterized by NMR spectroscopy in solution (1H, 11B and 13C NMR). In contrast, the analogous reaction with 1,2‐bis(tetramethylene)diborane(6) proceeds to give a single isomer of the B‐alkylated indazabole via symmetric ring cleavage of the diborane(6), as shown by NMR in solution and X‐ray structural analysis in the solid state. The molecular structure is fluxional in solution. In the solid state, the central B2N4 ring adopts a distorted boat conformation. Calculated gas phase geometries of the parent indazaboles and of the B‐alkylated indazabole were optimized by DFT methods at the B3LYP/6‐311 + G(d,p) level of theory. Copyright © 2010 John Wiley & Sons, Ltd.

Does the MgO(100)-Support Facilitate the Reaction of Nitrogen and Hydrogen Molecules Catalyzed by Zr2Pd2 Clusters? A Computational Study

Reactions of the "naked" and MgO(100) supported Zr(2)Pd(2) cluster with nitrogen and four hydrogen molecules were studied at the density functional level using the periodic slab approach (VASP). It was shown that adsorption of the Zr(2)Pd(2) cluster on the MgO(100) surface does not change its gas-phase geometry and electronic structure significantly. In spite of this the N(2) coordination to the MgO(100)-supported Zr(2)Pd(2) cluster, I/MgO, is found to be almost 30 kcal/mol less favorable than for the "naked" one. The addition of the first H(2) molecule to the resulting II/MgO, that is, II/MgO + H(2) --> IV/MgO reaction, proceeds with a relatively small, 9.0 kcal/mol, barrier and is exothermic by 8.3 kcal/mol. The same reaction for the "naked" Zr(2)Pd(2) cluster requires a slightly larger barrier (10.1 kcal/mol) and is highly exothermic (by 23.3 kcal/mol). The interaction of the H(2) molecule with the intermediate IV/MgO (i.e., the second H(2) molecule addition to II/MgO) requires larger energy barrier, 23.3 kcal/mol vs 8.8 kcal/mol for the "naked" cluster, and is exothermic by 20.5 kcal/mol (vs 18.2 kcal/mol reported for the "naked" Zr(2)Pd(2) cluster). The addition of the H(2) molecule to VI/MgO and VI (i.e., the third H(2) molecule addition to II/MgO and II, respectively) requires similar barriers, 12.0 versus 16.8 kcal/mol, respectively, but is highly exothermic for the supported cluster compared to the "naked" one, 13.6 versus 0.1 kcal/mol. The addition of the fourth H(2) molecule occurs with almost twice larger barrier for the "naked" cluster compared to the adsorbed species, 30.7 versus 15.9 kcal/mol. Furthermore, this reaction step is endothermic (by 11.4 kcal/mol) for the gas-phase cluster but exothermic by 7.8 kcal/mol for the adsorbed cluster. Dissociation of the formed hydrazine molecule from the on-surface complex X/MgO and the "naked" complex X requires 19.1 and 26.3 kcal/mol, respectively. Thus, the Zr(2)Pd(2) adsorption on the MgO(100) surface facilitates its reaction with N(2) and four H(2) molecules, as well as formation of hydrazine from the hydrogen and nitrogen molecules. The reported differences in the reactivity of the "naked" and MgO adsorbed Zr(2)Pd(2) clusters were explained by analyzing the nature of the H(2) addition steps in these systems.

Ab Initio and DFT Studies on Methanol−Water Clusters

The gas-phase geometries, binding energies (BEs), vibrational spectra, and electron density topological features of methanol (M), water (W), and methanol-water mixed clusters (M(m)W(n), where m = 0-4 and n = 0-4; m + n < or = 4) have been calculated using Hartree-Fock, second-order Møller-Plesset perturbation, and density functional theory with Becke three-parameter hybrid functional combined with Lee-Yang-Parr correlation functional methods. Bader's "atoms in molecules" theory has been used to analyze the hydrogen bonding network. To understand the effect of cooperativity, we have performed natural bond orbital analysis and reduced variational space decomposition analysis. The results show that BEs of methanol and mixed clusters are higher than those of water clusters due to the electron-donating nature of the methyl group. These findings are in accordance with the role of cooperative polarization and cooperative charge transfer in the methanol and mixed clusters. As the size of the cluster increases, the contribution from the cooperative effects also increases. The cooperativity contributes approximately 14 and 24% of stabilization in trimers and tetramers, respectively. The calculated nu(OH) frequencies at MP2/6-311++G(d,p) are in close agreement with the corresponding experimental values.

Structure and energetics of silicon clusters adsorbed on the Au(111) surface: a first principles study

We report an extensive first-principles investigation of the structure and electronic properties of small Si n (n = 1, 2, 3, 4, and 6) clusters deposited on the Au(111) surface. The calculations were performed using a plane wave based pseudopotential method under the framework of density functional theory. The electron-ion interaction energy has been described using ultrasoft pseudopotentials (USPP) and the spin polarised GGA scheme was used for the exchange correlation energy. The results reveal that Si atom prefers to adsorb on the hcp site of the Au(111) surface with strong binding energy. For Si3, the closed triangle geometry of the bare cluster forms an open triangle by rupturing one of the three Si-Si bonds. Remarkable structural changes in the gas phase geometries were observed from Si4 onwards. For example, while the adsorption of rhombus in parallel and perpendicular orientation to the surface plane remains almost unaltered, the tetrahedral conformation becomes almost flat by the interaction of Au surface. The nature of chemical bonding between Au surface and Si clusters was investigated from the charge distribution analysis and the electronic density of states (EDOS). Based on charge distribution analysis it is found that Si atoms transfer charges to the Au surface. Based on the results it is inferred that Si clusters deposition on the Au surface involves large energy release and would lead to coat the surface by spill over of Si atoms rather than island formation.

Fluoride Ion Donor Properties of cis-OsO2F4: Synthesis, Raman Spectroscopic Study, and X-ray Crystal Structure of [OsO2F3][Sb2F11

The salt, [OsO(2)F(3)][Sb(2)F(11)], has been synthesized by dissolution of cis-OsO(2)F(4) in liquid SbF(5), followed by removal of excess SbF(5) at 0 degrees C to yield orange, crystalline [OsO(2)F(3)][Sb(2)F(11)]. The X-ray crystal structure (-173 degrees C) consists of an OsO(2)F(3)(+) cation fluorine bridged to an Sb(2)F(11)(-) anion. The light atoms of OsO(2)F(3)(+) and the bridging fluorine atom form a distorted octahedron around osmium in which the osmium atom is displaced from its center toward an oxygen atom and away from the trans-fluorine bridge atom. As in other transition metal dioxofluorides, the oxygen ligands are cis to one another and the fluorine bridge atom is trans to an oxygen ligand and cis to the remaining oxygen ligand. The Raman spectrum (-150 degrees C) of solid [OsO(2)F(3)][Sb(2)F(11)] was assigned on the basis of the ion pair observed in the low-temperature crystal structure. Under dynamic vacuum, [OsO(2)F(3)][Sb(2)F(11)] loses SbF(5), yielding the known [mu-F(OsO(2)F(3))(2)][Sb(2)F(11)] salt with no evidence for [OsO(2)F(3)][SbF(6)] formation. Attempts to synthesize [OsO(2)F(3)][SbF(6)] by the reaction of [OsO(2)F(3)][Sb(2)F(11)] with an equimolar amount of cis-OsO(2)F(4) or by a 1:1 stoichiometric reaction of cis-OsO(2)F(4) with SbF(5) in anhydrous HF yielded only [mu-F(OsO(2)F(3))(2)][Sb(2)F(11)]. Quantum-chemical calculations at the SVWN and B3LYP levels of theory and natural bond orbital analyses were used to calculate the gas-phase geometries, vibrational frequencies, natural population analysis charges, bond orders, and valencies of OsO(2)F(3)(+), [OsO(2)F(3)][Sb(2)F(11)], [OsO(2)F(3)][SbF(6)], and Sb(2)F(11)(-). The relative thermochemical stabilities of [OsO(2)F(3)][SbF(6)], [OsO(2)F(3)][Sb(2)F(11)], [OsO(2)F(3)][AsF(6)], [mu-F(OsO(2)F(3))(2)][SbF(6)], [mu-F(OsO(2)F(3))(2)][Sb(2)F(11)], and [mu-F(OsO(2)F(3))(2)][AsF(6)] were assessed using the appropriate Born-Haber cycles to account for the preference for [mu-F(OsO(2)F(3))(2)][Sb(2)F(11)] formation over [OsO(2)F(3)][SbF(6)] formation and for the inability to synthesize [OsO(2)F(3)][SbF(6)].

Benzene−Water (BZWn(n= 1 − 10)) Clusters

The gas-phase geometries, binding energies (BEs), infrared spectra and electron density parameters of benzene (BZ)-water (W) clusters (BZW(n), where n = 1-10) have been calculated using Truhlar's meta hybrid functional, M05-2X, employing 6-31+G** basis set. Both basis set superposition error (BSSE) and zero point energy corrected BEs are in close agreement with the previously reported high level ab initio and experimental values. Among all of the BZW(n) clusters, the same with inverted book conformer of water hexamer has the highest BE when compared to all other water clusters. The Bader's theory of atoms in molecule (AIM) provides evidence for the presence of O-H...pi interactions in all of these clusters. In addition, the roles of C-H...O and lone pair...pi (lp...pi) interactions in the stabilization of BZW(n) clusters are also evident from the AIM analysis. The trend in the electron density at the hydrogen bond critical points varies as O-H...pi < lp...pi < C-H...O. Spectral signatures of these clusters further reinforce the existence of weak H-bond between BZ and W(n) clusters. The red shift in all of these clusters ranges from 13 to 95 cm(-1). The results clearly show that the presence of pi-cloud does not affect the H-bonded network of water clusters except in the case of W(6) ring.