Guest and host deuterium effects of the large ZFS parameters D of dimethylbenzaldehydes in durene single crystals

The ZFS parameters D of 2,4-, 2,5- and 3,4-dimethylbenzaldehyde-1h₁ and -1d₁ guests in perhydrogenated and perdeuterated durene single crystals are determined by comparing the experimental and calculated resonance curves. It is found that the deuterium substitution of the guest aldehydic group in a given host leads to the decrease of the D values and to the increase of the energy gaps ΔE_T between the zero-point levels of the ³nπ* and ³ππ* states of the guests. On the other hand, the perdeuteration of the host results in the decrease of ΔE_T with a corresponding increase of the D value of a given guest. The D value of 1 cm⁻¹ determined for 2,5-dimethylbenzaldehyde-1h₁ in perdeuterated durene is the lategest ever found for an aromatic carbonyl compound. Correlations between D and ΔE_T indicate that the ZFS parameters D of the guests are determined by contributions from both spin-spin and spin-orbit interactions between the ³nπ* and ³ππ* states. The large guest and host deuterium effects observed on the D values are attributed to the changes of the gaps ΔE_T of the guests.     

Vibrational spectra and density functional study of propylgermane

Raman and infrared spectra of propylgermane, CH₃CH₂CH₂GeH₃, and its Ge-deuterated analog, CH₃CH₂CH₂GeD₃, were investigated in their gaseous, liquid and solid states. The normal coordinate treatment was carried out by density functional theory (DFT) calculation, using B3LYP/6-31G^* and 6-311++G^** basis sets, and the corresponding fundamental vibrations were assigned. The trans (T) and gauche (G) forms around the central C–C bond coexisted in the gaseous and liquid states and only the T form existed in the solid state. From the temperature dependent measurements of the Raman spectra in the liquid state, the enthalpy difference was found to be ΔH(T−G)=−0.36±0.02 kcalmol⁻¹ with the T form being more stable. The energy differences between the isomers obtained by DFT calculations were ΔE(T−G)=−0.46 kcalmol⁻¹ and ΔE(T−G)=−0.87 kcalmol⁻¹ by the 6-31G^* basis set and 6-311++G^** basis set, respectively.     

The optical properties of polymethylmethacrylate polymer dispersed liquid crystals

The effect of the addition of polymer liquid crystals as dispersed molecules to polymethylmethacrylate (PMMA) on the optical properties in the UV-visible and near infrared regions is investigated. From transmission, absorption and reflection spectra the absorption coefficient (ω) and refractive index (n) at angular frequency of radiation (ω) have been calculated at room temperature. The values of the optical band gap (E_opt) have been obtained from the direct allowed transitions in k-space. The width of the tails of localized states in the band gap (ΔE) was evaluated from Urbach edges. Both the parameters (E_opt) and (ΔE) vary with the mixing ratio of dispersed liquid crystals.     

Crystalline polysilicate magadiite with intercalated n-alkylmonoamine and some correlations involving thermochemical data

Synthesized hydrated lamellar acidic crystalline magadiite (H₂Si₁₄O₂₉·2H₂O) nanocompound was used as host for intercalation of polar n-alkylmonoamine molecules of the general formula H₃C(CH₂)_nNH₂ (n = 1–6) in aqueous solution. The original interlayer distance (d) of 1500 pm, determined by X-ray powder diffraction patterns, increases after intercalation. The values correlated with the number of aliphatic amine carbon (n_c) atoms: d = [(1312 ± 11) + (21 ± 2)]n_c. The amount of intercalated amines (N_s), decreased as n_c increased: N_s = [(5.82 ± 0.04) − (0.45 ± 0.01)]n_c. The acidic layered nanocompound was calorimetrically titrated with the amines and the thermodynamic data gave exothermic values for all guest molecules, as shown by the correlation: Δ_intH = −[(24.45 ± 0.49) − (1.91 ± 0.10)]n_c and d = [(1576 ± 16) − (10.8 ± 1.0)]Δ_intH. The negative values of the Gibbs energies and the positive entropies also presented the correlations: Δ_intG = −[(22.8 ± 0.2) − (0.2 ± 0.1)]n_c and Δ_intS = [(6 ± 1) + (5 ± 1)]n_c, respectively.     

Ab initio calculations of minimum-energy pathways of the nucleophilic addition of the H anion, LiH molecule and Li/H ion pair to acetylene and methylacetylene

Ab initio calculations were performed for special points of the minimal energy pathways (MEP) of the nucleophilic addition reactions of the isolated H⁻ anion, LiH molecule and Li⁺/H⁻ ion pair to acetylene (A) and methylacetylene (MA) molecules, proceeding in accordance (M) and against (aM) the Markovnikov's rule. All structural parameters were optimized using the restricted Hartree–Fock (RHF) method. For the addition of H⁻, the 6-31++G^* basis set was used and for the reactions of LiH and Li⁺/H⁻ the 6-31G^* basis set with the subsequent recalculation of single point energies, taking into account of electron correlation energy by means of the second-order Möller–Plesset perturbation theory at the MP2/6-31++G^** level. The results of calculations demonstrate, that the energy characteristics of both M- and aM-additions with H⁻ do not differ sufficiently (0.1–1.2 kcal/mol for the activation energies (ΔE_a) and the reaction heats (ΔQ)). The substitution of the H atom by the CH₃ group in A molecule results in practically the same values of ΔQ and ΔE_a. On the contrary, for the LiH molecule and Li⁺/H⁻ ionic pair, the M-addition is favorable (charge control). It is found that the presence of electrophile decreases the activation energy by 3–5 kcal/mol as compared with the addition of the isolated hydride ion H⁻.     

Allylstannation V. cis-stereoconvergent sysnthesis of homoallylic alcohols and 4-chloro-2,6-dialkyl-3-methyltetrahydro-pyrans by the addition reaction of 1-buten-3-yldichloro-n-butyltin and aldehydes

1-Buten-3-yl-n-butyldichlorotin, generated in situ by redistribution of (E/Z)-2-butenyltri-n-butyltin and BuSnCl₃, reacts readily with neat RCHO (R = CH₃, C₂H₅, (CH₃)₂CH) at 25°C to give linear alcohols RCH(OH)CH₂CH---CHCH₃ and/or 2,3,4,6-tetrasubstituted tetrahydropyrans, CH₂CH(R)OCH(R)CH(CH₃)CH-(Cl), which are mainly in the cis-configuration with respect to the CH(CH₃)-CH(Cl) bond. When R = (CH₃)₃C and C₆H₅, only the homoallylic alcohols are obtained. These cis-stereoconvergent syntheses are explained in terms of kinetic control of the formation of adducts obtained by insertion of one or two aldehyde molecules into the organotin substrate.     

Pathway dependence of the efficiency of calculating free energy and entropy of solute–solute association in water

In this study we investigate two alternative pathways to compute the free energy and the entropy of small molecule association (ΔF_assoc and ΔS_assoc) in water. The first route (direct pathway) uses thermodynamic integration as function of the distance R between the solutes. The mean force and the mean covariance of the force with the energy in solution are calculated from molecular dynamics simulation followed by integration of these quantities with respect to the reaction coordinate R. The alternative approach examined (solvation pathway) would first remove the solutes from the solution using thermodynamic integration as function of a solvation coupling parameter λ, change the solute–solute distance in vacuo and then solvate back the solute pair at the new separation distance. The system studied was a pair of CH₄ molecules in water. We investigate the influence of the CH₄–water interaction strength on the obtained ΔF_assoc and ΔS_assoc values by changing van der Waals and Coulomb interaction and evaluated the accuracy and efficiency for the two pathways. We find that the direct route seems more suitable for the calculation of free energies of hydrophobic solutes while the solvation pathway performs better when calculating entropy changes for solutes that have a stronger interaction with the solvent.     

Transport phenomenon as a function of counter and co-ions in solution: chronopotentiometric behavior of anion exchange membrane in different aqueous electrolyte solutions

Anion exchange membrane has been investigated in different electrolyte solutions by chronopotentiometry to explore the influence of co-ion and counterion of the exchange group of the membrane, on the transport phenomena. Chloride, nitrate, sulfate and acetate in sodium salts were used as counterions and sodium, potassium, calcium and ammonium in chloride salts were used as co-ions. The membrane showed a potential drop (E₀) in all these electrolytes when a constant current was applied across it, which remained constant for a period less than τ, called the transition time and rose gradually to a maximum (E_max) value. The parameters such as τ, E₀ and E_max and the potential jump (ΔE) and τ and the inflection zone (Δt) along the time axis have been measured and compared at an applied current density (I) of 10 mA cm⁻² in 10 mM solutions. The values of τ^1/2/z_A[A₀] or τ^1/2/z_C[C₀], with or , E₀ and ΔE with or (where r_A and r_C are the ionic radii of counter and co-ions, respectively) have been correlated. Permselectivity (P) and transference number of the membrane with respect to each one of the above electrolytes have been evaluated and discussed.     

Hybrid density functional studies on the EPR parameters of heterosubstituted vinyl radicals: substituent effect on the isotropic hyperfine couplings with H and C nuclei

Isotropic hyperfine parameters of a set of vinyl radicals are investigated using the B1LYP hybrid density functional. The systems studied are RH_βC_β=CH radicals, where R=H, BH₂, CH₃, NH₂, OH and F. Theoretical results indicate that electronegativity of the substituent strongly affects the magnitude of hyperfine coupling with hydrogen nuclei as well as with ¹³C_β. A_iso(¹³C_β) varies from −8.7 (4.9) to 17.4 G (−17.8 G) for Z (E) isomers of the radicals depending on the R group, BH₂ and F, respectively. In the same order, for Z (E) isomeric forms A_iso(¹H_β) diminishes from 40.1 (67.7) to 18.4 G (40.9 G) and A_iso(¹H) – from 25.6 (24.1) to 1.5 G (1.3 G). The effect of the substituents on the spin and electron density distribution is discussed in the framework of natural population analysis and theory of atoms in molecules.     

The Ericksen number and Deborah number cascades in sheared polymeric nematics

Samples of liquid crystalline poly(γ-benzyl-glutamate) solutions are sheared between glass surfaces with gaps, d = 10-500 μ, and shearing velocities, V = 0·05-10 000 μs^-1 so that the Ericksen number E ≡ Vdγ₁/K is varied over a large range, E ≈ 1-10⁷. Here γ₁ is the rotational viscosity and K₁ is the Frank splay constant, with γ₁/K₁ estimated to be approximately 1 s μ^-2 for our samples. We observe by polarizing microscopy a sequence of transitions with increasing Ericksen number analogous to that observed in small molecule tumbling nematics: namely rotation of the director out of the shearing plane and into the vorticity direction at Vd ≈ 25 μ² s^-1, and formation of roll cells at Vd ≈ 50 μ² s^-1. The roll cells become finer with increased Vd in accord with predictions of linear stability theory using the Leslie-Ericksen equations, and at Vd ≳ 500 μ² s^-1, the cells become very irregular, producing director turbulence. The turbulence becomes finer in scale as Vd increases, reaching sub-micron, and possibly molecular scales when Vd ≧ 10⁵ μ² s^-1. At the highest velocities, transitions in orientation and texture are controlled by the Deborah number De≡λV/d, where λ is the molecular relaxation time, and uniform texture-free samples are obtained when De ≳ 5.     

Theoretical and experimental study of the biamperometry for irreversible redox couple in flow system

The biamperometry for the direct determination of irreversible redox analytes in flow system has been proposed based on coupling two independent and irreversible couples to form the biamperometric detection scheme. In this work, the method is studied both theoretically and experimentally. Equations describing the current–voltage characteristics and the current–concentration relationship are presented. The influence of the applied potential difference (ΔE) and the half-wave potential difference (ΔE_1/2) between two irreversible couples on the method are discussed. It shows that small ΔE_1/2 is favorable to construct the biamperometric detection system and to achieve high sensitivity and selectivity. Increasing ΔE leads to an increase in sensitivity. This is, however, accompanied by a decrease in selectivity and signal-to-noise ratio. To construct the biamperometric scheme for the irreversible systems with large ΔE_1/2, two approaches, adjusting acidity of supporting electroyte or adding new irreversible couple, are proposed by taking uric acid/platinum oxide and phenol/permanganate systems as examples. Uric acid and phenol are, respectively, detected in a flow injection system with a biamperometric detector.     

Crystalline calcium phenylphosphonate—thermodynamic data on n-alkylmonoamine intercalations

Lamellar crystalline calcium phenylphosphonate, as anhydrous Ca(HO₃PC₆H₅)₂ and hydrated Ca(HO₃PC₆H₅)₂·2H₂O compounds, were used as hosts for intercalation of polar n-alkylmonoamine molecules of the general formula CH₃(CH₂)_nNH₂ (n=0–4, 7) in water or 1,2-dichloroethane. An increase in the interlayer distance was observed. The exothermic enthalpic values for intercalation increased with the number of carbon atoms and with increasing concentration of the amines. The intercalation followed by a titration procedure in the solid/liquid interface with Ca(HO₃PC₆H₅)₂·2H₂O and Ca(HO₃PC₆H₅)₂ gave the enthalpy/number of carbons correlations: Δ_intH=−(1.74±0.43)–(1.30±0.13)n_c and Δ_intH=−(4.15±0.15)–(1.07±0.03)n_c, for water and 1,2-dichloroethane, respectively. A similar correlation Δ_intH=−(4.27±0.80)–(1.85±0.21)n_c was obtained in water by using the ampoule breaking procedure for Ca(HO₃PC₆H₅)₂·2H₂O. The increase in exothermic enthalpic values with the increase in n-aliphatic carbon atoms is more pronounced for the anhydrous compound and also when using the ampoule breaking procedure. The Gibbs free energies are negative. Positive entropic values favor intercalation in these systems.     

Reaction of diazonium salts with transition metals : IX. Reaction of vinyltrimethylsilane with arenediazonium tetrafluoroborates under palladium(0) catalysis

Arenediazonium tetrafluoroborates (ArN₂BF₄ where Ar=Ph, 4-MeC₆H₄, 4-BrC₆H₄, 4-IC₆H₄ and 4-NO₂C₆H₄) reacted easily with CH₂=CHSiMe₃ at 25 δC to give ArCH=CH₂, (E-ArCH=CHSiMe₃ and Ar(Me₃Si)C=CH₂ in excellent yields under palladium(O) catalysis. (E)-ArCH=CHSiMe₃ compounds were obtained predominantly and isolated in good yields by using an excess of CH₂=CHSiMe₃ over ArN₂BF₄. Protodesilylation of the reaction mixture afforded styrene derivatives.     

1,1,2,2-tetrabromodisilane: gas-phase molecular structure and conformational composition as determined by electron diffraction

The molecular structure of 1,1,2,2-tetrabromodisilane has been investigated using gas-phase electron diffraction data obtained at 110°C. At this temperature the molecules exist as a mixture of about equal parts (X = 0.5 ±0.2) of the two conformers with the H---Si---Si---H torsion angle equal to 180° (anti) or 60° (gauche). Assuming that the two conformers differ in their geometries only in the torsion angle φ, some of the important distance (r_a) and angle () parameters are: r(Si---Si) = 2.349(19) Å, r(Si---Br) = 2.205(5) Å, r(Si---H) = 1.485 Å (assumed), Br---Si---Br = 110.1(1.6)°, Si---Si---Br = 107.1(1.2)° Si---Si---H = 108.6° (assumed). The error limits are 2σ. The observed conformational composition (X_anti = 0.5(0.2)) corresponds to an energy difference between the conformers of ΔE = E(gauche) — E(anti) = 0.5 ± 0.6 kcal mol⁻¹, assuming ΔS = Rln2.     

Asymmetric transfer hydrogenation of ferrocenyl ketones: a new simple route to chiral ferrocenyl alcohols

The asymmetric transfer hydrogenation (ATH) of ferrocenyl ketones, such as FcC(O)CH₂Y [Fc = ferrocenyl, Y = H (1a), CH₃ (1b), Cl (1c) or N₃ (1d)] has been carried out using the Noyori/Ikariya catalysts [(−)-(1R,2S)-ephedrine] or N-tosyl-(1R,2R)-diphenylethylenediamine [(R,R)-TsDPEN] as chiral ligands combined with [RuCl₂(η⁶-benzene)]₂ and 2-PrOH or HCO₂H–Et₃N as the hydrogen sources, respectively. The best results were achieved with the [(R,R)-TsDPEN–Ru^IIHCO₂H–Et₃N] catalytic system, which produced the ferrocenylalcohols (R)-2a, (R)-2c, and (R)-2d in good yields and excellent enantiomeric excesses (>98% ee).     

The electrostatic potential at atomic sites as a reactivity index in the hydrogen bond formation

The paper reviews results from computational studies by molecular orbital and density functional theories on several series of hydrogen bonded complexes. These studies aim at quantifying the reactivity of molecules for the complexation process. Excellent linear relationships are found between the electrostatic potential values at the sites of the electron donor and electron accepting atoms and the energy of hydrogen bond formation (ΔE). The series studied are: (a) complexes of R–CHO and R–CN molecules with hydrogen fluoride; (b) complexes of mono-substituted acetylene derivatives with ammonia; (c) (HCN)_n hydrogen bonded cluster for n=2–7. All 22 studied complexes of carbonyl and nitrile compounds with hydrogen fluoride fall in the same dependence between the energy of hydrogen bond formation and the electrostatic potential at the atomic site of the carbonyl oxygen and nitrile nitrogen atoms, with linear regression correlation coefficient r=0.979. In the case of complexes of mono-substituted acetylene and diacetylene derivatives with NH₃, the correlation coefficient for the dependence between the electrostatic potential at the acidic hydrogen atom and ΔE equals 0.996. For the series of hydrogen bonded (HCN)_n clusters, the correlation coefficient for the relationship between the electrostatic potential at the end nitrogen atom and ΔE is r=0.9996. Similarly, the analogous relationship with the electrostatic potential at the end hydrogen atom has a regression coefficient equal to 0.9994. The dependencies found are theoretically substantiated by applying the Morokuma energy decomposition scheme. The results show that the molecular electrostatic potential at atomic sites can be successfully used to predict the ability of molecules to form hydrogen bonds.     

Supercooling phenomena in binary mixtures of acetamide and inorganic salts

Liquid—solid equilibrium temperatures are measured in binary mixtures of acetamide and inorganic salts [NaClO₄, LiCNS, LiNO₃, CH₃COOLi, Ca(NO₃)₂, (CH₃)₄ NCl, (C₂H ₅)₄ NBr]. In some ranges of concentration all these systems (with the exception of CH₃COOLi, R₄NX) exhibit supercooling phenomena and crystallization occurs only through vigorous agitation and in the presence of crystalline nuclei, or does not occur at all, according to the type of salt. A probable explanation is presented on the basis of the trend of ΔT/νmK vs. m.     

An ab initio and density functional theory study of the dimethylzinc-hydrogen selenide adduct: (CH3)2Zn:SeH2

The molecular structure (equilibrium geometry) and binding energy of the dimethylzinc (DMZn)-hydrogen selenide (H₂Se) adduct, (CH₃)₂Zn:SeH₂, have been computed with ab initio molecular orbital and density functional theory (DFT) methods and, where possible, compared with experimental results. The structure of the precursors DMZn and H₂Se are perturbed to only a small extent upon adduct formation. (CH₃)₂Zn:SeH₂ was found to be 3 kcal mol⁻¹ less stable than the precursors at the B3LYP/6-311 + G(2d,p)//B3LYP/6-311 + G(2d,p) level of computation, indicating that the (CH₃)₂Zn:SeH₂ adduct is unlikely to be a stable gas-phase species under chemical vapour deposition conditions. Further calculations at the B3LYP/6-311 + G(2d,p)//B3LYP/6-311 + G(2d,p) level of computation suggest that the 1:2 adduct species, (CH₃)₂Zn:(SeH₂)₂, is much less stable than the 1:1 adduct and consequently the precursors by 19 kcal mol⁻¹.     

Studies on organolanthanide complexes : LXIII. Synthesis, spectroscopic and X-ray crystallographic characterization of new early organolanthanide, organoyttrium hydride and organoholmium hydroxide complexes

Organolanthanide chloride complexes [(CH₃OCH₂CH₂C₅H₄)₂Ln(μ-Cl)]₂ (Ln = La, Pr, Ho and Y) react with excess NaH in THF at 45°C to give the dimeric hydride complexes [(CH₃OCH₂CH₂C₅H₄)₂Ln(μ-H)]₂, which have been characterized by IR, ¹H NMR, MS and XPS spectroscopy, elemental analyses and X-ray crystallography. [(CH₃OCH₂CH₂C₅H₄)₂Y(μ-H)]₂ crystallizes from THF/n-hexane at −30°C, in the triclinic space group P1 with a = 8.795(2) Å, b = 11.040(1) Å, c = 16.602(2) Å, = 93.73(1)°, β = 91.82(1)°, γ = 94.21(1)°, D_c = 1.393 gcm⁻³ for Z = 2 dimers. However, crystals of [(CH₃OCH₂CH₂C₅H₄)₂Ho(μ-OH)]₂ were obtained by recrystallization of holmium hydride in THF/n-hexane at −30°C, in the orthorhombic space group Pbca with a = 11.217(2) Å, b = 15.865(7) Å, c = 17.608(4) Å, D_c = 1.816 gcm⁻³ for Z = 4 dimers. In the complexes of yttrium and holmium, each Ln atom of the dimers is coordinated by two substituted cyclopentadienyl ligands, one oxygen atom and two hydrogen atoms (for the Y atom) or two hydroxyl groups (for the Ho atom) to form a distorted trigonal bipyramid if the C(η⁵)-bonded cyclopentadienyl is regarded as occupying a single polyhedral vertex.     

Rhenium(I) methoxo carbonyl complexes containing tetraphosphine or triphosphine ligands; facile separation and X-ray crystallographic studies of d/l- and meso-[{Re2(μ-OMe)2(CO)6}2(μ,μ′-1,1,4,7,10,10-hexaphenyl-1,4,7,10-tetra-phosphadecane)]

Reaction of the activated mixture of Re₂(CO)_10, Me₃NO and MeOH with a 1:1 mixture of rac (d/l)- and meso-1,1,4,7,10,10-hexaphenyl-1,4,7,10-tetraphosphadecane (hptpd) yields a mixture of (d/l)- and meso-[{Re₂(μ-OMe)₂(CO)₆}₂(μ,μ′-hptpd)] 1. The diastereomers can be easily separated by selective dissolution of d/l-1 in benzene, and give clearly distinguishable ¹H- and ³¹P-NMR spectra. The fluxional behavior of d/l-1 in solution has been studied by variable-temperature ¹H- and ³¹P-{¹H}-NMR spectroscopy. The crystal structures of both d/l- and meso-1 have been determined. Both molecules consist of two {Re₂(μ-OMe)₂(CO)₆} moieties which are bridged by the two P---CH₂---CH₂---P moieties of the hptpd ligand. Whilst the molecules of meso-1 possess crystallographic i-symmetry, those of d/l-1 do not have any crystallographic symmetry. These diastereomers therefore give clearly distinguishable Raman spectra in the solid state. Reaction of tris[2-(diphenylphosphino)ethyl]phosphine (tdppep) with the activated mixture affords the complex [{Re₂(μ-OMe)₂(CO)₆}(μ,η²-tdppep)] 2, and the analogous reaction involving bis[2-diphenylphospinoethyl)phenylphosphine (triphos) gives [{Re₂(μ-OMe)₂(CO)₆}(μ,μ′,η³-triphos){Re₂(CO)₉}] 3 and [{Re₂(μ-OMe)₂(CO)₆}(μ,η²-triphos)] 4.