Molecular orientation in poly(vinyl chloride) studied by Raman spectroscopy and birefringence measurements

The ratios of the intensities of Raman scattering in the C? CI stretching region for eight combinations of sample orientation and directions of polarization of incident and scattered light have been measured for 15 samples of poly(vinyl chloride) (PVC) containing 0, 5, 10, 15 or 20 pph dioctyl sebacate (DOS) plasticizer which had been drawn uniaxially at 22, 70, 75, 80, or 90°C to draw ratios in the range 1–4.5. The birefringences of the samples were also measured. The Raman data were analyzed to give 〈P₂(cosθ)〉_cryst and 〈P₄(cosθ)〉_cryst, the values of the second- and fourth-order Legendre polynomials in cosθ averaged over the distribution of orientations of the crystallites, where θ is the angle between the c axis of a typical crystallite and the draw direction. Comparison of 〈P₂(cosθ)〉_cryst with the birefrigence showed that the crystallites are more highly oriented than the noncrystalline material in samples containing the higher amounts of plasticizer drawn at the higher temperatures. A value of 13.0 × 10^?3 was deduced for the birefringence of fully oriented PVC. The values of 〈P₄(cosθ)〉_cryst for a given 〈P₂(cosθ)〉_cryst were found to be higher than predicted by calculations based on two simple models, the pseudoaffine rigid-rod rotation model and the affine rubber elasticity model.     

Interpretation of the vibrational spectra of methylglyoxal and biacetyl in their first singlet excited electronic states

Laser-induced fluorescence spectra for the first allowed electronic transition (22125 cm^?1) of methylglyoxal (CH₃COCHO) and its perdeutero analog (CD₃COCDO) in a supersonic nozzle beam are quantitatively represented assuming that the potential function governing the CH₃(CD₃) rotation is changed during the transition. In the excited state the potential function is ternary (V₁ = 95 (1 + cos 3θ)cm^?1) as in the fundamental state (V₀ = 134.5 (1 - cos 3θ)cm^?1), but the minima are shifted by an angle of π/3. The spectrum of biacetyl (CH₃COCH₃CO) can be reproduced assuming two uncoupled methyl groups undergoing similar conformational changes during the electronic transition (the estimated potential function is V₁ = 117.5 (1 + cos 3θ) cm^?1 for each methyl group), in perfect agreement with the most recent assignment of the 0-0 transition. These results are consistent with ab initio calculations for the fundamental and first excited singlet states.     

Behavior of Halogen Bonds of the Y−X⋅⋅⋅π Type (X,Y=F,Cl, Br,I) in the Benzene π System,Elucidated by Using a Quantum Theory of Atoms in Molecules Dual‐Functional Analysis

The nature of halogen bonds of the Y?X‐?‐π(C₆H₆) type (X, Y=F, Cl, Br, and I) have been elucidated by using the quantum theory of atoms in molecules (QTAIM) dual‐functional analysis (QTAIM‐DFA), which we proposed recently. Asterisks (?) emphasize the presence of bond‐critical points (BCPs) in the interactions in question. Total electron energy densities, H_b( r _c), are plotted versus H_b( r _c)?V_b( r _c)/2 [=(?²/8m)?²ρ_b( r _c)] for the interactions in QTAIM‐DFA, in which V_b( r _c) are potential energy densities at the BCPs. Data for perturbed structures around fully optimized structures were used for the plots, in addition to those of the fully optimized ones. The plots were analyzed by using the polar (R, θ) coordinate for the data of fully optimized structures with (θ_p, κ_p) for those that contained the perturbed structures; θ_p corresponds to the tangent line of the plot and κ_p is the curvature. Whereas (R, θ) corresponds to the static nature, (θ_p, κ_p) represents the dynamic nature of the interactions. All interactions in Y?X‐?‐π(C₆H₆) are classified by pure closed‐shell interactions and characterized to have vdW nature, except for Y?I‐?‐π(C₆H₆) (Y=F, Cl, Br) and F?Br‐?‐π(C₆H₆), which have typical hydrogen‐bond nature without covalency. I?I‐?‐π(C₆H₆) has a borderline nature between the two. Y?F‐?‐π(C₆H₆) (Y=Br, I) were optimized as bent forms, in which Y‐?‐π interactions were detected. The Y‐?‐π interactions in the bent forms are predicted to be substantially weaker than those in the linear F?Y‐?‐π(C₆H₆) forms.     

Production of electronically excited atoms. H + Br2 → HBr + Hb(*), H + HBr → H2 + Br(*)

By measurement of infrared chemiluminescence we have obtained for the branching ratio of the room temperature reaction H + Br₂ (1), k*₁/k₁ = 0.015 ± 0.004 and for H + HBr (2), k*₂/k₂ ? 0.013. For H + Br₂ → HBr(υ^· ? 6) + Br (1), the detailed rate constant k(υ^* = 6) = 0.014 ± 0.003 relative to k(υ^· = 4) = 100.     

Synthesis, crystal structure and characterization of a 2-D network organic-inorganic hybrid polymer with [α-BW12O40]5− as building blocks

A two-dimensional network compound [Ce(DMF)₄(H₂O)][α-BW₁₂O₄₀]·H₂O·(HDMA)₂ (HDMA = protoned dimethylamine, DMF = N,N-dimethylformamide) was synthesized from α-H₅BW₁₂O₄₀·nH₂O, Ce(NO₃)₃·6H₂O and DMF and characterized by IR, UV spectra and TG-DTA. The result of the X-ray single crystal diffraction indicates that the crystal is monoclinic, space group P2₁/n, with unit cell dimensional: a = 1.1983(3), b = 2.4216(5), c = 1.9517(4) nm, β = 92.91(3)°, Z = 4, R ₁ = 0.07710, wR ₂ = 0.1416. Structural analysis indicates that every [Ce(DMF)₄(H₂O)]³⁺ building block is surrounded by three adjacent [α-BW₁₂O₄₀]^5? polyanions, meanwhile, every [α-BW₁₂O₄₀]^5? polyanion interconnects with three neighboring [Ce(DMF)₄(H₂O)]³⁺ subunits, by making use of which two-dimensional network structure can be constructed. The result of thermogravimetric analysis manifests that the title compound has two-stage weight loss and the decomposition temperature of the title polyanionic framework is 560°C. The electrochemical analysis shows the title polyanion has three-step redox processes in the pH = 4–7 media.     

Analysis and physical significancy of the kinetic parameters associated with albumin adsorption onto glassy carbon obtained by electrochemical impedance measurements

The kinetics of albumin adsorption onto a glassy carbon rotating disk electrode in a phosphate buffer, is reported from the time variations of the double-layer capacitance C_d, of the charge transfer resistance R_t and of the Tafel coefficient of the electrochemical reaction b; these three electrical quantities are determined by electrochemical impedance and faradaic current I measurements. The variations of C_d, 1/R_t, b  (R_tI)⁻¹ and I can be written under the form: α₀ + α₁ e^−t/τ1 + α₂ e^−t/τ2, where α₀, α₁, α₂, τ₁, τ₂ characterize a given electrical quantity. We demonstrate that this type of variation validates a two-step adsorption mechanism already proposed, starting from simply taking into account C_d(t). We analyze and discuss comprehensively various possibilities of interpreting the shifts between the time-constants associated with thevarious quantities as well as the correlations between these constants and those associated with physical adsorption phenomena.     

Magnesium sulphate complexes with hexamethylenetetramine and 1,10-phenanthroline

The magnesium sulphate complex compounds of general formulae [Mg(H₂O)₆]²⁺·2(C₆H₁₂N₄)·SO₄ ^2?·5(H₂O) (1) and Mg(C₁₂H₈N₂)(H₂O)₃SO₄ (2) have been synthesized, characterised by elemental and thermal analysis, IR, UV?CVIS and fluorescence spectroscopy, and X-ray crystallography. The obtained compounds are air stable at room temperature and well soluble in water. In the structures of the investigated complex compounds the O?CH?O, O?CH?N, and C?CH?O hydrogen bonds exist, and they create N₂C ₂ ² (8), R ₂ ² (8) (compound 1) and N₁C ₁ ¹ (6), N₁R ₂ ² (12) (compound 2) patterns. Their thermal decomposition processes in the investigated atmospheres (air and helium) are different. After the slightly similar dehydratation, the observed transitions and the obtained final products are different (in helium atmosphere the sulphate ion of studied compounds undergoes decomposing what does not take place in air atmosphere). The UV?CVIS spectrum of 2 shows maxima that are typical for ????????* and n??????* transitions, and fluorescence spectrum of the same compound displays its great fluoresce properties. The 1 does not exhibit absorption in the investigated region of electromagnetic spectrum due to the absence of respect chromophore groups. The IR spectrum of 2 shows typical vibrations for chelating amine molecule. An interesting fact is that in 1 the SO stretching vibrations (existing at 1119 and 1182?cm^?1) are doubled in comparison to the magnesium sulphate whilst in 2 these vibrations are absent.     

Development of dissociative force field for all-atomistic molecular dynamics calculation of fracture of polymers

A dissociative force field for all-atomistic molecular dynamics calculations has been developed to investigate impact fracture of polymers accompanying dissociation of chemical bonds of polymer main chain. Energy of dimer molecules was evaluated as a function of both bond-length b and bond-angle θ by CASPT2 calculations, whose quality is enough to describe dissociation of chemical bonds. Because we found that the bond dissociation energy D decreases with increasing bond-angle, we employed the Morse-type function V_Bond(b, θ) = {D − V_Angle(θ)}[1 − exp{−α(b − b₀) − β(b − b₀)²}] where a quartic function V_Angle(θ) = k₁(θ − θ₀) + k₂(θ − θ₀)² + k₃(θ − θ₀)³ + k₄(θ − θ₀)⁴ . This function reproduced well the CASPT2 potential energy surface in a wide range of b and θ. The parameters have been obtained for four popular glassy polymers, polyethylene, poly(methyl methacrylate), poly(styrene), and polycarbonate. © 2019 Wiley Periodicals, Inc.     

Studies on werner clathrates. Part 131. Selective criteria in werner clathrates. Six crystal structures with bis(isothiocyanato)tetra(4-vinylpyridine)nickel(II) as host

This paper addresses the general question: what are the significant guest properties selected by this host when interacting with guest molecules in the liquid phase, resulting in cocrystallization of the host and guest? In particular, to what extent do π electrons in a guest molecule effect its potential as a guest? Werner clathrates of the host [Ni(NCS)₂(4-ViPy)₄] with mixtures of tetrahydrofuran (THF) and cyclic hydrocarbons as guests have been synthesised and their structures elucidated. Clathrate (1): [Ni(NCS)₂(4-ViPy)₄](1.78 THF)(0.22 cyclohexane), crystallizes in the orthorhombic space groupP _bcn a=9.976(6),b=20.630(25),c=19.861 (4) Å,V=4087ų,Z=4,R=0.087 for 1461 reflections; (2): [Ni(NCS)₂(4-ViPy)₄](1.76 THF)(0.24 cyclohexene),P _bcn ,a=9.987(7),b=20.614(4),c=19.898(4)Å,V=4096ų,Z=4,R=0.084 for 1304 reflections; (3): [Ni(NCS)₂(4-ViPy)₄](0.48 THF)(0.52 1,3-cyclohexadiene), tetragonalI4₁/a,a=16.898(3),b=16.898(3),c=26.463(6)Å,V=7556ų,Z=8,R=0.120 for 1698 reflections; (4): [Ni(NCS)₂(4-ViPy)₄](0.36 THF)(1.04 1,4-cyclohexadiene),I4₁/a,a=16.986(4),b=16.986(4),c=25.896(15)Å,V=7472ų,Z=8,R=0.103 for 2025 reflections; (5): [Ni(NCS)₂(4-ViPy)₄](0.35 THF)(1.05 benzene),I4₁/a,a=17.102(10),b=17.102(10),c=25.498(8)Å,V=7458ų,Z=8,R=0.118 for 2200 reflections; (6): [Ni(NCS)₂(4-ViPy)₄](3 benzene), triclinicP1,a=10.432(24),b=11.155(9),c=21.581(7)Å, α=78.70(5), β=82.60(7), γ=74.09(13)°,V=2361ų,Z=2,R=0.078 for 3427 reflections. Host-guest ratios and, for mixtures of guests, guest1/guest2 ratios, were elucidated by density and NMR. We show that the conformational freedom of the substituted pyridines is not the primary reason for the clathrating ability of Werner hosts. All six structures show no host-guest interaction at the level of van der Waals interactions. As non-bonding interactions are not observed between the host and guest, this study shows that the above host's selectivity by enclathration of particular guest molecules cannot be accounted for by solid state structural analysis.     

Quenching of the Ba + Cl2 chemiluminescence: Estimate of BaCl*2 radiative lifetime

The chemiluminescence produced by the Ba + Cl₂ reaction was recorded as a function of He and N₂ pressure. A modified Stern-Volmer treatment of competitive electronic quenching of BaCl^* and BaCl^*₂ emission yielded upper limits to the half pressures p_{$\text{1}\text{2}$}(He) ? 9.0 ± 3 mtorr and p_{$\text{1}\text{2}$} (N₂) ? 1.1 ± 0.2 mtorr for quenching of BaCl^*₂ by helium and nitrogen, respectively. A lower limit of the BaCl^*₂ radiative lifetime is placed at τ_R ? 100 μ.     

Formation of five-connected three-dimensional coordination polymers through the bridging function of the anions

New coordination polymers based on 3,3′,5,5′-tetramethyl-4,4′-bipyrazole (L) with the composition [M₂(L)₄A(NCS)₂] (M²⁺ = Co²⁺, Zn²⁺, Cd²⁺; A^2? = SiF ₆ ^2? , SeO ₄ ^2? ) have been synthesized and characterized by IR spectroscopy and X-ray diffraction. According to X-ray diffraction data, cobalt compounds crystallize in the orthorhombic system with the following unit cell parameters, [Co₂(L)₄SiF₆(NCS)₂] · 3CHCl₃ · CH₃OH: a = 20.568(4), b = 14.568(3), c = 22.929(5) Å, α = β = γ = 90°, V = 6870(2) ų, space group Pbca (no. 61), R(I > 2σ(I)) = 0.0514; [Co₂(L)₄SeO₄(NCS)₂] · 2CHCl₃ · 2CH₃OH · H₂O: a = 13.721(2), b = 21.539(3), c = 22.417(3) Å, α = β = γ = 90°, V = 6625(2) ų, space group P2₁2₁2₁ (no. 19), R(I > 2σ(I)) = 0.0452. The 3D structure of the coordination polymers is composed of wavelike two-dimensional coordination layers [ML₂]_n connected by bridging anions SiF ₆ ^2? , or Se O ₄ ^2? . The complexes have the same five-bonded topology but different symmetry.     

The fluorescence of all-trans diphenyl polyenes

The temperature dependence of the fluorescence and fluorescence excitation spectra of all-trans diphenyl hexathene (DPH) and octatetraene (DPO) in six solvents confirms the S₁(¹A_g*) and S₂(¹B_u*) state assignment, and determines their energy difference ΔE. The S₁ fluorescence rate parameter k_F depends on ΔE, the solvent refractive index n, the S₂ (n = 1) fluorescence rate parameter k_F20 (2.23 × 10⁸ s^?1 for DPH, 2.33 × 10⁸ s^?1 for DPO), and the S₂-S₁ coupling matrix element V (745 cm^?1 for DPH, 500 cm^?1 for DPO). The S₁ fluorescence is induced by ¹B_u*-¹A_g* potential interaction (PI), via a b_u vibrational mode (≈ 900 cm^?1), and not by vibronic coupling. The main S₁ radiationless transition, rate parameter k_R, is thermally-activated internal rotation through an angle θ about the central ethylenic bond(s). The PI distorts the S₁ (θ) potential surface and thus influences k_R.     

Graphite-furnace atomization of phosphorus

The slopes of the ln (absorbance) vs. T^?1 dependences for platform/graphite furnace atomization of phosphorus in the presence of Ni²⁺ or La³⁺ modifiers are measured, and found to be similar to the theoretical slope calculated for isothermal atomization. It is concluded that in both cases the atomization mechanism is the same and is expressed by P_2(gas) ? 2P_(gas); P_(gas) ? P^*_(gas). The atomic absorption signal for phosphorus appears and reaches its maximum later when the atomization is carried out from the platform in the presence of modifiers. Hence atomization takes place under nearly isothermal conditions and is much more efficient, thus providing the best conditions for the determination of phosphorus. Treatment of a deteriorated graphite surface with ZrOCl₂ solution repairs any defects and improves the sensitivity of phosphorus determination.     

Scattering of low energy He2+ ions by Ne,Ar, and Kr atoms

Experimental studies of collisions of He²⁺ ions with Ne, Ar, and Kr atoms have been carried out at laboratory kinetic energies in the range 8 ? E₁ ? 10 eV. For each collision pair, relative differential cross sections for elastic scattering, and for the formation of He⁺ by single charge transfer [e.g., He²⁺ + R = He⁺ + (R⁺)^*] were measured. Information concerning the initial states of the charge transfer products was also obtained, from measurements of the kinetic energy distributions of the He⁺ + He = Ne⁺(2s 2p⁶²S) ± He⁺(²S), whereas for the other systems, transfer proceeds via a number of channels. The He⁺-ion kinetic energy measurements indicated that for He²⁺. Ar both Ar⁺ both Ar⁺ and Ar²⁺ are formed in transfer, and that for He²⁺, Kr only Kr²⁺ (and no Kr⁺) was formed.The differential elastic scattering patterns were analyzed by means of cross section calculations based on an approximate form of the optical model. These calculations indicated that the pronounced shoulders observed in the σ_el(θ) versus θ curves arose from scattering from an attractive potential well, in the presence of concurrent inelastic scattering. Using parametrized Morse potentials to represent the ground electronic states of (HeNe)²⁺, (HeAr)²⁺, and (HeKr)²⁺, the corresponding well-depth are estimated to be, respectively: 1.0 eV, 2.1 eV and 2.6 eV.     

Control over the chirality of (R)-1,1'-bi-2-naphthol dibenzoate in nanoparticles

Nanoparticles of (R)-1,1′-bi-2-naphthol dibenzoate (R-BND) ranging from 40 to 170 nm were prepared by using the reprecipitation method. The nanoparticles exhibit size-dependent exciton chirality, where the coupling potential V₁₂ of ¹B_b transitions increases as nanoparticles grow and simultaneously the exciton chirality peaks exhibit the bathochromic shift. Such size-dependent optical properties can be attributed to the lattice hardening with increased particle size, which leads to a decreased dihedral angel θ between the two naphthyl planes in a R-BND molecule.     

Measurement of state-to-state rotational transfer rates in collision of I2*(B 0u+, υ = 15, j) with 3He, 4He,Ne, Ar,H2, D2 and I2

The selective laser excitation and induced fluorescence observation technique has been used to study rotationally inelastic collisions of I₂^*(B 0_u⁺, υ = 15,j) with I₂, ³He, ⁴He, Ne, Ar, H₂ and D₂. For each collision partner, several initial rotational levels ranging from j_i = 12 up to j_i = 146 have been excited. For purely rotational transfer within the υ = 15 level, our data are perfectly consistent with energy sudden (eventually corrected) scaling laws. Thus, any thermally averaged rate constant, k(j_i → j_f), can be expressed as a function of the basis rate constants k(l → 0). Furthermore, these k(l → 0) are found to follow simple empirical fitting laws. Consequently any k(j_i → j_f) can be predicted given a set of two or three fitting parameters. Collisions with relatively heavy particles (I₂, Ar and Ne) are well described by using the inverse power fitting law k(l → 0) = b[l(l+1)]^?γ, where b = 1.7, 1.2 and 1.2×10^?10 cm³ s^?1 and γ = 1.08, 1.02 and 1.17 for I₂^*-Ne, I₂^*-Ar and I₂^*-I₂ collisions respectively. For collisions with light particles (³He, ⁴He, H₂ and D₂), k(l → 0) shows a sharp decrease with l which can be accounted for by a hybrid power-exponential fitting law k(l → 0) = b[l(l+1)]^?γ exp[-l(l+1)/l^* (l^*+1)], where b = 0.84, 0.71, 2.77 and 2.78×10^?10 cm³ s^?1l⁺ = 20.6, 23.1, 18.8 and 31.4, and γ = 0.66, 0.66, 0.78 and 0.91 for I₂^*-³He, I₂^*-He, I₂^*-H₂ and I₂^*-D₂ collisions, respectively. We confirm that the rotational transfer dynamics in heavy molecules is mainly governed by angular momentum exchange.     

The reduction of triosmium dodecacarbonyl by sodium borohydride. The preparation and X-ray structure of the cluster anion [H2Os4(CO)12]2−

The reduction of Os₃(CO)₁₂ by NaBH₄ in tetrahydrofuran has been studied, and the formation of the anionic clusters [HOs₃(CO)₁₁]^?, [H₃Os₄(CO)₁₂]^? and [H₂Os₄(CO)₁₂]^2? observed. The previously unreported dianion [H₂Os₄(CO)₁₂]^2? was prepared in satisfactory yield, and characterised as the bis(triphenylphosphine)iminium salt. This compound crystallizes in the space group P$\text{1}$, with Z = 1, and cell dimensions of a 11.014(2), b 14.751(3), c 15.168(3) Å, α 123.95(2)°, β 95.77(2)°, γ 98.73(2)°. The structure was solved by a combination of multisolution sign expansion and Fourier methods, and final residuals were R 0.067 and R_W 0.066 for 5972 observed intensity data. The dianion comprises a distorted tetrahedron of osmium atoms, each metal also bonding to three terminal carbonyl ligands, which as staggered with respect to the metalmetal bonds. Unlike the cation, the cluster anion is statistically disordered between two centrosymmetrically related sites.     

Synthesis and circular dichroism studies of steroidal schiff bases of biogenic amines

A number of imines (Schiff bases) have been prepared from ketosteroids (estrone, estrone-3-methyl ether, androsterone, epiandrosterone, 5α-cholestan-3-one, 6-ketocholestanol and testosterone) and primary amines (phenethylamine, tyramine and hexanamine). The CD spectra of these compounds have been measured in methanol. Except for the testosterone imines, the azomethine n-π^* band (~ 235 nm) exhibited the same sign (but not as high an ellipticity) as the parent ketone's n - π^* band (~295 nm). The imines of the estrogens (estrone and estrone 3-methyl ether) gave CD spectra characterized by a negative ¹L_b Cotton effect ([θ] ? -1000) near 280 nm and a band near 230 nm ([θ] ? +19,000) which is considered the sum of a positive azomethine n - π^* Cotton effect and positive aromatic ¹L_a Cotton effect(s). The ¹L_a band originating in the amine moiety was prominent in the CD of 5α-cholestan-3-one and 6-ketocholestanol phenethylamine imines. When aromatic Cotton effects originating in the amine moiety were detected, they were of the same sign as the n - π^* Cotton effect.     

Two Modifications of Y2Piv6(Hpiv)6 crystals: Synthesis and structures

Crystals of two modifications of yttrium pivalate solvate Y₂Piv₆(HPiv )₆(HPiv = (CH₃)₃CCOOH) are synthesized and studied by single-crystal X-ray diffraction analysis. The 3α-modification crystallizes in the monoclinic system, a = 16.394(2) Å, b = 11.948(4) Å, c = 20.352(3) Å, β = 108.73(3)°, Z = 4, space group P2₁/n, R ₁ = 0.105. Crystals of the β-modifications are also monoclinic, a = 21.617(4) Å, b = 36.559(4) Å, c = 29.930(4) Å, β = 104.40(2)°, Z = 12, space group P2₁/c, R ₁ = 0.050. The molecular structures of crystals of the α-and β-modifications consist of the Y₂(μ₂-Piv)₄(Piv)₂(HPiv)₆ dimers. The Y atoms with a distorted antiprismatic coordination surrounding of the O atoms (Y-O 2.23–2.53 Å) are linked by four bridging bidentate pivalate anions and form the structural fragment shaped into a distorted lantern. Monodentate Hpiv molecules participate in the formation of intramolecular hydrogen bonds with Piv ligands. Crystal structures of the α-and β-modifications differ in packing of the Y₂Piv₆(HPiv)₆ dimers and in centrosymmetric nature of the dimers in the structure of the α-modification.