Influence of solid solution formation on polarity: molecular modeling investigation of the system 4-chloro-4'-nitrostilbene/4,4'-dinitrostilbene

Growth-induced polarity formation in solid solutions composed of dipolar 4-chloro-4'-nitrostilbene molecules and nonpolar 4,4'-dinitrostilbene molecules was investigated by means of two molecular modeling procedures. Calculation of the mixing energy in the bulk structures predicted solid solution formation within the whole composition range. Computation of the interaction energies present at growing surfaces allowed the distribution coefficient as well as the fraction of dipoles in either the up or down orientation to be calculated by a mean-field model. Miscibility and polarity were found to vary for the faces (hkl) investigated, leading to crystals composed of sectors with different compositions and polarities. The present study highlights the fact that a solid solution crystal may not be a homogeneous entity and that surface effects arising during slow growth can have an impact on solid state properties.     

Untersuchungen an 1,2-Komplexen der Nickel(II)-halogenide mit N-substituierten Aminoäthylpyridinen-(2)

In the solid state complexes of the type MiL₂X₂ (L = N-substituted β-aminoethyl-pyridine; X = Cl, Br, J) have a cis-octahedral (X = Cl, Br) or a distorted trigonal bipyramidal structure (X = J). In solutions in acetone a partial dissociation occurs with the formation of NiLX₂, L, NiL₂X⁺, and X^?. Using a spectrophotometric method stability constants K_2S of the complexes NiL₂X₂ are determined. A correlation exists between log K_2s and the pK- values of the quarternary ammonium ions derived from the ligands L. Sterical factors cause the exeptional position of the chelates of β-methylaminoethylpyridine-(2).     

SP3-Hybridization Feature of Ag4 Superatom in Superatomic Molecules

Analogous to atoms, superatoms can be used as building blocks to compose molecules and materials. To demonstrate this idea, the possibility of using tetrahedral Ag₄ cluster to form a series of superatomic molecules Ag₄X₄ (X=H, Li, Na, K, Cu, Ag, Au and F, Cl, Br) is discussed. Based on the super valence bond model, a tetrahedral Ag₄ cluster can be viewed as a 4-electron superatom, which can mimic a sp³ hybridization C atom. By comparison of the representative superatomic molecules Ag₄X₄ (X=Au, Cl) with the corresponding simple molecules CX₄ (X=H, Cl), the similarities in terms of chemical bonding patterns and molecular orbitals (MOs) are conspicuous. Energy calculations predict that the Ag₄ superatom can bind with all the involved ligands. Furthermore, the stabilities of superatomic molecules are enhanced by the large gaps of the highest occupied molecular orbital and the lowest unoccupied molecular orbital (HOMO-LUMO gaps) and high aromaticity. Our studies may find applications in assembling materials with superatoms.     

Stabilization Studies on Divalent Five‐Membered Rings C4H4C,C4H4Si,C4H4Ge,C4H4Sn,and C4H4Pb

Energy differences, ΔX_S‐t (X = E, H and G) (ΔX_S‐t = X_(singlet)‐X_(triplet)) between singlet (s) and triplet (t) states are calculated at B3LYP/6‐311++G (3df,2p). The DFT calculations show that the triplet state of C₄H₄C is a ground state with planar conformer respect to its corresponding nonplanar singlet state. Both singlet and triplet states of C₄H₄M (M = Si, Ge, Sn and Pb) have a planar conformer with the singlet ground state. Four isodesmic reactions are presented for determining the stability energies, SE. NICS calculations are carried out for C₄H₄M to determine the aromatic character.     

Noncovalent association phenomena of 2,5-dihydroxybenzoic acid with cyclic and linear oligosaccharides. A matrix-assisted laser desorption/ionization time-of-flight mass spectrometric and X-ray crystallographic study

D-Glucose and 19 glucose derivatives were investigated by positive and negative ion matrix assisted laser desorption/ionization time-of-flight mass spectrometry using 2,5-dihydroxybenzoic acid (DHB) as the matrix. The set of substrates includes oligomers of amylose and cellulose, native alpha-, beta-, and gamma-cyclodextrin, and chemically modified beta- and gamma-cyclodextrins. These analytes were chosen to modulate molecular weight, polarity, and capability of establishing noncovalent interactions with guest molecules. In the negative-ion mode, the DHB matrix gave rise to charged multicomponent adducts of type [M + DHB - H]- (M = oligosaccharide) selectively for those analytes matching the following conditions: (i) underivatized chemical structure and (ii) number of glucose units > or = 4. In the positive-ion polarity, only some amylose and cellulose derivatives and methylated beta-cyclodextrins provided small amount of cationized adducts with the matrix of type [M + DHB + X]+ (X = Na or K), along with ubiquitous [M + X]+ ions. The results are discussed by taking into account analyte-matrix association phenomena, such as hydrogen bond and inclusion phenomena, as a function of the molecular structure of the analyte. The conclusions derived by mass spectrometric data are compared with the X-ray diffraction data obtained on a single crystal of the 1:1 alpha-cyclodextrin - DHB noncovalent adduct.     

Density functional theory study on the reactions of X− with CH3SY (X,Y = F,Cl, Br,I)

Gas‐phase anionic reactions X^? + CH₃SY (X, Y = F, Cl, Br, I) have been investigated at the level of B3LYP/6‐311+G (2df,p). Results show that the potential energy surface (PES) of gas‐phase reactions X^? + CH₃SY (X, Y = Cl, Br, I) has a quadruple‐well structure, indicating an addition–elimination (A–E) pathway. The fluorine behaves differently in many respects from the other halogens and the reactions F^? + CH₃SY (Y = F, Cl, Br, I) correspond to deprotonation instead of substitution. The gas‐phase reactions X^? + CH₃SF (X = Cl, Br, I), however, follow an A–E pathway other than the last two out going steps (COM2 and PR) that proceeds via a deprotonation. The polarizable continuum model (PCM) has been used to evaluate the solvent effects on the energetics of the reactions X^? + CH₃SY (X, Y = Cl, Br, I). The PES is predicted to be unimodal in the solvents of high polarity. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Radical Impurity Mechanisms for Helium Incorporation into Buckminsterfullerene

Radical impurity mechanisms for incorporating He into C₆₀ have been examined by semiempirical (MNDO) and density functional (BLYP/3-21G) calculations. The key step in these mechanisms is the insertion of He into C₆₀X or C₆₀X₂ intermediates generated by adding the impurity X to C₆₀ (X = H, Me in our model study). Contrary to C_60. several window-type structures with one broken C,C bond exist as local minima on the MNDO potential surfaces of C₆₀X and C₆₀X₂, but they are mechanistically irrelevant due to extremely facile ring closure. Effective activation barriers for the penetration of He through intact hexagons and various windows are reported for 65 different pathways in C₆₀X and C₆₀X₂. Window-type transition states are stabilized significantly when there is a C? X bond involving a C-atom from the broken C,C bond. The corresponding barriers in C₆₀X and C₆₀X₂ are much lower than in C₆₀, This provides some theoretical support for the suggested impurity mechanisms even though the computed barriers for X = H, Me are still higher than indicated by the experiment (X unknown).     

Concentration effects and ion properties controlling the fractionation of halides during aerosol formation

During the aerosolization process at the sea surface, halides are incorporated into aerosol droplets, where they may play an important role in tropospheric ozone chemistry. Although this process may significantly contribute to the formation of reactive gas phase molecular halogens, little is known about the environmental factors that control how halides selectively accumulate at the air-water interface. In this study, the production of sea spray aerosol is simulated using electrospray ionization (ESI) of 100 nM equimolar solutions of NaCl, NaBr, NaI, NaNO(2), NaNO(3), NaClO(4), and NaIO(4). The microdroplets generated are analyzed by mass spectrometry to study the comparative enrichment of anions (f(X(-))) and their correlation with ion properties. Although no correlation exists between f(X(-)) and the limiting equivalent ionic conductivity, the correlation coefficient of the linear fit with the size of the anions R(X(-)), dehydration free-energy ΔG(dehyd), and polarizability α, follows the order: R(X(-))(-2) > R(X(-))(-1) > R(X(-)) > ΔG(dehyd) > α. The same pure physical process is observed in H(2)O and D(2)O. The factor f(X(-)) does not change with pH (6.8-8.6), counterion (Li(+), Na(+), K(+), and Cs(+)) substitution effects, or solvent polarity changes in methanol- and ethanol-water mixtures (0 ≤ x(H(2)O) ≤ 1). Sodium polysorbate 20 surfactant is used to modify the structure of the interface. Despite the observed enrichment of I(-) on the air-water interface of equimolar solutions, our results of seawater mimic samples agree with a model in which the interfacial composition is increasingly enriched in I(-) < Br(-) < Cl(-) over the oceanic boundary layer due to concentration effects in sea spray aerosol formation.     

Synthesis and Structure of Solvated Protons Incorporating Weakly Coordinating Anions. Precursors of Superacids

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ChemInform Abstract: Protic Anions [H(B12X12)]‐ (X: F,Cl, Br,I) that Act as Broensted Acids in the Gas Phase.

The protic anions [H(B₁₂X₁₂)]^‐ (X: F, Cl, Br, I) are investigated with respect to their ability to protonate neutral molecules in the gas phase by using a combination of tandem mass spectrometry and quantum‐chemical calculations.     

Phase behavior of polarizable spherocylinders in external fields

Applied electric fields are known to induce significant changes in the properties of systems of polarizable molecules or particles. For rod-shaped molecules, the field-induced behavior can be rather surprising, as in the case of the negative electric birefringence of concentrated solutions of rodlike polyelectrolytes. We have investigated the interplay of shape anisotropy and field-induced anisotropy in molecular dynamics simulations of systems of polarizable soft spherocylinders in an electric field, in the limit of infinitely anisotropic polarizability, taking full account of mutual induction effects. We find a novel crystalline structure (K(2)) in the high-field limit, whose formation is driven by interactions between induced dipoles. For high pressures, the phase diagram exhibits a polar nematic phase between the hexagonal close-packed crystal phase and the K(2) phase. We also compare this system with an analogous system of spherocylinders with permanent electric dipoles and find that qualitatively similar behavior is obtained in the limit of strong coupling of the permanent dipoles to the external field.     

Functionalities of one-dimensional dynamic ultramicropores in nickel(II) coordination polymers

Ni(II) coordination polymers with a 4,4'-azobis(pyridine) (azpy) ligand, {[Ni2(NCX)4(azpy)4].G}n (X = S, G (guest molecule) = MeOH (1.MeOH); X = S, G = EtOH (1.EtOH); X = S, G = H2O (1.H2O); X = S, G = no guest (1); X = Se, G = MeOH (2.MeOH); X = Se, G = H2O (2.H2O); X = Se, G = no guest (2)), have been synthesized and structurally characterized with their porosity. These compounds have one-dimensional periodic ultramicropores that contain the small guest molecules, H2O, MeOH, or EtOH, whose hydroxy groups interact with the S or Se atoms of isothiocyanate or isoselenocyanate, respectively, via -S(Se)...HO- hydrogen bonds. Although the molecular dimensions of the MeOH guest are considerably larger than the window size of the ultramicropore, 1.MeOH and 2.MeOH easily release their guest molecules without decomposition of the framework to form 1 and 2 without any guest molecules. This shows that 1 and 2 have dynamic ultramicropores constructed from the interpenetrating framework. The guest desorption experiments using 1.MeOH and 1.EtOH reveal that the difference in the desorption behavior is due to van der Waals interactions that depend on the molecular shape of the guest molecule in the ultramicropores and/or an entrance blocking effect that depends on the minimum dimensions of the guest molecule for the pore windows. A marked difference in the N2 and CH4 adsorption isotherms was observed and is associated with the strength of the host-guest interaction.     

Relation between alkali ion affinity and ionic radius ratio by means of fast atom bombardment tandem mass spectrometry

Cationization of organic molecules has been studied using fast atom bombardment mass spectrometry and tandem mass spectrometric methods. The order of the A⁺ affinity to G (G ? H + A) and AX was determined by this tandem mass spectrometric approach, where G, A and X represent glycerol, alkali metal element and halogen element, respectively. The affinity orders of most alkali halides are divided into three classes. By analogy with the ionic radius ratio rule in solid ionic crystals, this particular parameter, ionic radius ratio, was introduced to analyse the experimental results. This classification is thought to be caused by the ionic radius ratio (X^?/A⁺). These ratios of the I, II and III classes exist between 0.657 and 1.026, 1.096 and 1.776, and 1.856 and 2.289, respectively. The ionic radius ratio plays an important role for determination of the order of alkali ion affinity.     

Microscopic hydration of the sodium chloride ion pair

Hydration of ion pairs is an essential process in various physicochemical phenomena occurring in solutions. Isolated clusters of an ion pair solvated with finite number of waters have been considered as a model system for the critical evaluation of microscopic interactions involved in the process, and theoretical studies have contributed exclusively to the subject up to now. Here we report the first experimental characterization of structure and internal dynamics of hydrated ion pairs, NaCl-(H2O)n (n = 1-3). The measurements of their rotational spectra have proven that the clusters have cyclic forms, in which Na+ and Cl- ions are strongly interacted with the O and H atoms of the solvent molecules, respectively. The Na-Cl distance shows a pronounced increase with the successive addition of water molecules. The separation for n = 3 approaches the value predicted for the contact ion-pair state in aqueous solution by recent molecular dynamics simulations.     

Phosphoniumsalze mit Hydrogendihalogenidanionen HCl2−, HBr2− Hl2− oder HBrCl−

Phosphonium Salts with Hydrogen Dihalide Anions HCl₂^?, HBr₂^?, HI₂^?, or HBrCl^? Phosphonium hydrogen dihalides [R₃PR′][XHY] (X = Y = Cl, Br, I; X = Br, Y = Cl) resp. [R₃PH]HBr₂ are obtained as extremely hydrolyzable crystals by reaction of phosphonium halides or tertiary phosphanes with hydrogen halide. According to IR spectroscopic results the solid compounds mostly contain anions [XHX]^? with symmetric hydrogen bonds. In solution ¹H NMR measurements show a slight (X = Cl, Br) or considerable (X = I) dissociation according to HX₂^? ? X^? + HX. On heating the solid compounds decompose with formation of hydrogen halide and [R₃PR′]X or [R₃PH]X. In this process the hydrogen bromidechlorides [R₃PR′][BrHCl] exclusively eliminate HCl. NMR studies (¹H und ³¹P) with solutions containing [R₃PH]HBr₂ (R = phenyl, 1-naphtyl) or HBr and Ph₃P in varying molar ratios show that a fast proton exchange between the competing Lewis bases R₃P and Br^? exists.     

Quantum chemical studies on the conformational behaviour of substituted banana‐shaped mesogens with a central 1,3‐phenylene unit

Ab initio and DFT calculations on the HF/STO‐3G and B3LYP/6‐31G(d) level were performed on the conformational behaviour of isolated banana‐shaped molecules of 1,3‐phenylene bis[4‐(4‐n‐hexyloxyphenyliminomethyl)benzoate] systems (P‐6‐O‐PIMB). The influence of small substituents in both the central phenyl ring and the external phenyl rings on the shape, polarity and flexibility of these molecules was investigated by one‐ and two‐fold relaxed potential energy scans in a systematic way. The effect of substituents on the global polarity of banana‐shaped mesogens was analysed by the magnitude and direction of the dipole moment and its components in relation to the long axis of the molecules. Moreover, a simple model for the calculation of the bending angle was tested for banana‐shaped molecules with a central 1,3‐phenylene unit. The findings for the isolated banana‐shaped molecules are correlated with solid state X‐ray and liquid crystalline state NMR results. Banana‐shaped molecules with both hexyloxy (P‐6‐O‐PIMB) and hexyl (P‐6‐PIMB) terminal chains are included to study the effect of substituents in the external phenyl rings on the flexibility of these chains. An attempt will be made to correlate the results with experimental findings on banana‐shaped mesogens.     

3D-RISM-KH molecular theory of solvation and density functional theory investigation of the role of water in the aggregation of model asphaltenes

We applied a multiscale modeling approach that involves the statistical-mechanical three-dimensional reference interaction site model with the Kovalenko-Hirata closure approximation (3D-RISM-KH molecular theory of solvation) as well as density functional theory (DFT) of electronic structure to study the role of water in aggregation of the asphaltene model compound 4,4'-bis(2-pyren-1-yl-ethyl)-2,2'-bipyridine (PBP) [X. Tan, H. Fenniri and M. R. Gray, Energy Fuels, 2008, 22, 715]. The solvation free energy and potential of mean force predicted by 3D-RISM-KH reveal favorable pathways for disaggregation of PBP dimers in pure versus water-saturated chloroform solvent. The water density distribution functions elucidate hydrogen bonding preferences and water bridge formation between PBP monomers. The ΔG(298) values of -5 to -7 kcal mol(-1) for transfer of water molecules in chloroform to a state interacting with PBP molecules are in agreement with experimental results. Geometry optimization and thermochemistry analysis of PBP dimers with and without water bridges using WB97Xd/6-31G(d,p) predict that both PBP dimerization and dimer stabilization by water bridges are spontaneous (ΔG(298) < 0). The (1)H NMR chemical shifts of PBP monomers and dimers predicted using the gauge-independent atomic orbital method and polarizable continuum model for solvation in chloroform are in an excellent agreement with the experimental results for dilute and concentrated PBP solutions in chloroform, respectively [X. Tan, H. Fenniri and M. R. Gray, Energy Fuels, 2009, 23, 3687]. The DFT calculations of PBP dimers with explicit water show that bridges containing 1-3 water molecules lead to stabilization of PBP dimers. Additional water molecules form hydrogen bonds with these bridges and de-shield the PBP protons, negating the effect of water on the (1)H(C3) NMR chemical shift of PBP, in agreement with experiment. The ΔG(298) results show that hydrogen bonding to water and water-promoted polynuclear assembly bridging is as important as π-π interactions for asphaltene aggregation.     

X-ray Structural Analysis of Liquid Solutions of n-Butanol-1 in Cyclohexane

Abstract

Angular distributions of intensity of X-ray radiation scattered in solutions of n-butanol-1 in cyclohexane have been measured and analyzed. The mean least intermolecular distances in the solution were determined. It was established that in the range of very low concentrations X of the solutions studied the distribution of the intermolecular distances R(X) revealed three extremes. In this concentration range the fluctuations of the distance R are related to the earlier observed fluctuations of the solution density: the minimum in R(X) at X?0.028 mole fraction corresponds to the maximum in d(X) in the range 0.015 ≤X≤ 0.035 mole fraction, while the two maxima in R(X) at X ?0.007 and X?0.05 mole fraction correspond to the minima in d(X) in the mole fraction ranges 0≤ X ≤0.015 and 0.026 ≤ X ≤0.05.

In the range 0.05 ≤X≤ 0.9 mole fraction the main role in ordering of the solution molecules is played by the associated molecules of the alcohol with voids containing individual molecules of the solvent.     

A microscopic model for calculations of chemical processes in aqueous solutions

A new microscopic model for calculations of chemical processes in aqueous solutions is presented. The model, referred to here as the “surface constrained soft sphere dipoles” (SCSSD) model avoids the problems of the continuum models by explicitly including the solvent molecules. Each solvent molecule is represented as a point dipole attached to the center of a soft sphere. The solvation energy is evaluated by minimizing the solute-solvent energy with respect to the orientations and positions of those dipoles while constraining the surface dipoles to have the orientations and positions of the bulk solvent. The model is demonstrated by calculating the energetic of charge separation in aqueous solution and evaluating the corresponding dielectric constant. The SCSSD model can be used for quantitative studies of ionic reactions in solutions. This is demonstrated by calculation of the potential surface for the dissociation of formic acid in aqueous solution.     

Molecular Structure of Phenylphosphine and Its Analogs by Gas-Phase Electron Diffraction and Quantum-Chemical Calculations

The molecular structures of phenylphosphine and its analogs, aniline and phenylarsine, were studied by gas-phase electron diffraction and quantum-chemical methods. The geometry and force constants were calculated at the HF/6-31G and B3LYP/6-31G^* levels of theory. Phenylphosphine and phenylarsine possess a bisector conformation with asymmetric phenyl rings. The main geometric parameters are as follows (r _a): P-C 1.833(6), C-Cav 1.397(1)Å. The structures of molecules like X₂YPh (X = H, F, Cl; Y = N, P, As) were discussed.