C(methyl)–H ⋅ ⋅ ⋅ π(aryl) Interaction Stabilizing Molecular Conformation. X-Ray Crystal Structure of an Inclusion Compound of a Nonprotic Host with Nitromethane Guest

In the cocrystal formation of a nonprotic polar (host) molecule (1) with nitromethane (guest) several weak, but directional, intermolecular interactions have vital importance. The endo conformation of the (N)-xylene group of the polycyclic succinimide-based host 1 is stabilized by a C_methyl $---$ H ??? π interaction [C ??? π /H ??? π distances are 3.554(7)/2.57 Å, the C $---$ H ??? π angle is 159^○], and the crystal packing is governed by dipole–dipole type interhost (C $ =$ )O ??? C( $ =$ O) connection [C ??? O $ =$ 3.000(5) Å and <C $ =$ O ??? C $ =$ 159.8(3)^○] in conjunction with possible C $---$ H ??? O interactions [with C ??? O distances ranging between 3.20 and 3.50 Å] involving the polar groups of both host and guest. Crystal data: 1 ??? nitromethane (1:1), C₂₆H₂₁O₂ N ? CH₃NO₂, M _w = 440.50, P2 ₁/n, a = 14.143(1), b = 7.973(1), c = 20.291(2) Å, β = 95.183(9)^○, Z = 4, D _c = 1.2840(2) g cm^?3, R = 0.055 for 1709 reflections.     

Volumetric properties of a stoichiometric mixture of K+ and Br− ions in H/D isotope-substituted aqueous methanol at 278.15–318.15 K: I. The H2O-CH3OH-KBr system

The densities of potassium bromide solutions in aqueous methanol mixtures have been measured with an error of at most ±(1 × 10^?5) g/cm³ for methanol mole fractions x ₂ of 0.06, 0.1, 0.3, or 0.6 and for the potassium bromide mole fractions up to about 2.65 × 10^?2 at 278.15, 288.15, 298.15, 308.15, and 318.15 K. Limiting partial molar volumes $\overline V _3^\infty $ , excess molar volumes $\overline V _3^{E, \infty } $ , and expansibilities $\overline E _{p, 3}^\infty $ have been calculated for a stoichiometric mixture of solvated K⁺ and Br^? ions in the mixed solvents. In the region of x ₂ ≈ 0.25, $\overline E _{p, 3}^\infty $ changes its sign from positive to negative. The $\overline V _3^{E, \infty } $ (x ₂) trend, on the whole, reflects the topologic features of the molecular structure of aqueous methanol associated through H-bonding.     

The thermodynamic parameters of oxygen nonstoichiometry defects in lanthanum cobaltite doped with acceptor impurities (Sr and Ni)

The oxygen nonstoichiometry δ of lanthanum cobaltite doped with acceptor impurities (Sr and Ni), La_{1 ? x} Sr_xCo_0.9Ni_0.1O_{3 ? δ} (x = 0.1, 0.3), was studied by high-temperature thermogravimetry over the temperature and pressure ranges 723 K ≤ T ≤ 1373 K and 10^?3 atm ≤ $p_{O_2 } $ ≤ 1 atm. The partial replacement of cobalt with nickel and lanthanum with strontium increased the oxygen nonstoichiometry δ. The partial molar enthalpies $\Delta \bar H^\circ _O $ and entropies $\Delta \bar S^\circ _O $ of solution of oxygen in the solid phase were calculated. Models of point defect formation were suggested and analyzed. The equilibrium constants of formation and concentrations of predominant point defects, ionized oxygen vacancies V _o ^.. , holes Me _Co ^. (Co _Co ^. and Ni _Co ^. ), and electrons Me _Co ^′ (Co _Co ^′ and Ni _Co ^′ ) localized on 3d transition metals, were determined by nonlinear regression from the experimental and theoretical logp $p_{O_2 } $ ?δ dependences.     

Exact transient solutions of kinetics of first‐order reactions with end effects

The finite set of rate equations C _m,n ^' =α _n,n-1 C _m,n-1 (t)+α _n,n C _m,n (t)+α _n,n+1 C _m,n+1 (t), $$0 \leqslant m \leqslant N,0 \leqslant n \leqslant N,$$ where $$\alpha _{i,j}$$ are $\alpha _{j,j - 1} = A,\alpha _{j,j} = - \left( {A + B} \right),\alpha _{j,j + 1} = B$ , with $\alpha _{0,0} = - \alpha _{1,0} = - \alpha$ and $\alpha _{N,N} = - \alpha _{N - 1,N} = - b,\alpha _{0, - 1} = \alpha _{N,N + 1} = 0$ , subject to the initial condition $C_{m,n} \left( 0 \right) = \delta _{n,m}$ (Kronecker delta) for some $m$ , arises in a number of applications of mathematics and mathematical physics. We show that there are five sets of values of $a$ and $b$ for which the above system admits exact transient solutions.     

Thermodynamic properties of alkaloids lappaconitine and glaucine

Calorimetric methods were used to study the enthalpy of solution of the alkaloids glaucine C₂₁H₂₅NO₄ and lappaconitine C₃₂H₄₄N₂O₈ in 96% ethanol and their heat capacity in the temperature ranges 173–298.15 and 173–423 K. Equations describing the dependences ΔH _sol ^m ～ f( $\sqrt m $ ) (m is molal concentration) and C _p ⁰ ～ f( $\sqrt T $ ) for the compounds under study were derived. The enthalpies of combustion, melting, and formation of C₂₁H₂₅NO₄ and C₃₂H₄₄N₂O₈ were estimated by means of theoretical calculations.     

Acid Co(II) and Ni(II) trifluoroacetate complexes: Synthesis and crystal structure

Anhydrous and partially hydrated acid trinuclear trifluoroacetates of divalent transition metals of the composition [M₃(CF₃COO)₆(CF₃COOH)₆)](CF₃COOH) and [M₃(CF₃COO)₆(CF₃COOH)₂(H₂O)₄)](CF₃COOH)₂, respectively, where M = Co (I, III) Ni (II, IV), were synthesized and studied by X-ray diffraction. Complexes I and II were obtained by crystallization from solutions of M(CF₃COO)₂ · 4H₂O in trifluoroacetic anhydride; complexes III and IV were synthesized under the same conditions with the use of 99% trifluoroacetic acid as a solvent. Crystals I are triclinic: space group $P\bar 1$ , a = 13.199(6) Å, b = 14.649(6) Å, c = 15.818(6) Å, α = 90.04(4)°, β = 114.32(4)°, γ = 108.55(4)°, V = 2611.3(19) ų, Z = 2, R = 0.0480. Crystals II are trigonal: space group $R\bar 3$ , a = 13.307(2) Å, c = 53.13(1) Å, V = 8148(2) ų, Z = 6, R = 0.1112. Crystals III are triclinic: space group $P\bar 1$ , a = 9.001(8) Å, b = 10.379(9) Å, c = 12.119(9) Å, α = 83.67(5)°, β = 72.33(5)°, γ = 83.44(5)°, V = 1068.3(15) ų, Z = 1 Å, R = 0.1031. Crystals IV are triclinic: space group $P\bar 1$ , a = 9.121(18) Å, b = 10.379(2) Å, c = 12.109(2) Å, α = 84.59(3)°, β = 72.20(3)°, γ = 82.80(3)°, V = 1080.94(40) ų, Z = 1, R = 0.0334.     

Synthesis and reactivity of(\mu - H)(\mu _3 - \eta ^2 - H_2 )_4 )Os_3 (CO)_9 : An unusually reactive triosmium cluster

The synthesis of $(\mu - H)(\mu - \eta ^2 - H_2 )_4 )Os_3 (CO)_{10} $ (4) from piperidine and Os₃(CO)₁₀(CH₃CN)₂ and its solid state structure are reported. The room temperature reactions of the decarbonylation product of4, $(\mu - H)(\mu _3 - \eta ^2 - H_2 )_4 )Os_3 (CO)_9 $ (3), with P(C₆H₅)₃, CNCH₃, HCl and H₂ are reported. Overall, the products obtained closely resemble those obtained from the analogous, $(\mu - H)(\mu _3 - \eta ^2 - H_2 )_3 )Os_3 (CO)_9 $ (1). The isomerizations of the phosphine addition products $(\mu - H)(\mu - \eta ^2 - H_2 )_n )Os_3 (CO)_9 P(C_6 H_5 )_3 $ (n = 3,6a;n = 4,5a) have been studied by¹H-NMR techniques and the initial rearrangement was shown to be an intramolecular process. Slower conversion to the complex $(\mu - H)(\mu _3 - \eta ^2 - H_2 )_4 )Os_3 (CO)_8 P(C_6 H_5 )_3 $ (8) was observed and the solid state structure of this product is reported and compared with a related compound containing an ethyl,n-propylμ ₃-imidoyl ligand. Compound4 crystallizes in the triclinic space group Pl (#2) withZ= 2, and unit cell parametersa = 9.294(3) Å,b = 15.758(5) Å,c = 7.406(2) Å,a = 81.10(2)°,β=76.47(2)°,y =74.88(2)°, andV =1013(l) ų. Least-squares refinement of 2677 reflections gave a final discrepancy factor ofR = 0.054 (R _w = 0.066). Compound8 crystallizes in the space group C2/c with unit cell parametersa = 24.818(3) Å,b = 16.389(3) Å,c = 18.111(3) Å,β= 120.94(2)°,V = 6318(4) ų, andZ = 8. Least squares refinement of 3439 reflections gave a final discrepancy factor ofR = 0.039 (R _w =0.047).     

Fragmentation of doubly charged ammonia cations NH 3 ++ studied by the photoion-photoion coincidence (PIPICO) method

Doubly charged NH ₃ ⁺⁺ cations were produced by double photoionization of neutral ammonia molecules by using the synchrotron radiation from ACO as a photon source of variable energy in the 35–49 eV energy range. The fragmentation of NH ₃ ⁺⁺ was studied by the photoion-photoion coincidence (PIPICO) method. NH ₃ ⁺⁺ cations were produced in the \(\tilde X^1 \) A ₁ and \(\tilde B^1 \) electronic states of which the onset energies were measured at, respectively, 35.4±0.5 eV and 44.5±0.5 eV. It was shown that the NH ₃ ⁺⁺ ions, initially produced in their \(\tilde X^1 \) A ₁ state, rapidly dissociate (in less than 50 ns), into NH ₂ ⁺ + H⁺. Furthermore, the comparison with results obtained by other methods indicates that NH ₃ ⁺⁺ ions can either be long-lived (τ>10 µs) or slowly dissociating (1 µs<τ<10 µs) or rapidly dissociating (τ<50 ns), depending on their geometry and/or internal energy in their \(\tilde X^1 \) E A ₁ electronic state.     

Ordering of Cu(II) ions in supported copper-titanium oxide catalysts

Two types of ESR spectrum (A and B) of exchange-coupled Cu²⁺ ions have been found for Cu-Ti-O catalysts at 77 K and 300 K. In associates A and B, the Cu²⁺ ions form a system with orbital ordering. The difference between the spectra is due to the difference between the ground states of adjacent Cu²⁺ ions in the associates: the ground states are $d_{x^2 } $ and $d_{y^2 } $ for A type associates and $d_{x^2 - y^2 } $ and $d_{z^2 - x^2 } $ for B type associates. The copper associates lie on the surface of the TiO₂ (anatase) support microparticles.     

Slow-brittle-fracture transition in polymethylmethacrylate

A slow crack growth was achieved in initially edge-cracked specimens made of a high-molecular weight PMMA by regulating the cross-head speed of loading by a computer-driven testing machine. The strain rate \(\dot \varepsilon \) used during the tests varied between \(\dot \varepsilon \) =1× l0^?6 s^?1 and 1×10^?4 s^?1. It was shown that, in this zone of slow quasi-static loading of brittle polymethylmethacrylate specimens under conditions of plane stress, the crack initiated for a critical value of loading, at some characteristic zone of strain-rate variation at the crack tip. It was established that for strain rate between \(\dot \varepsilon \) =0.18×10^?5 s^?1 and \(\dot \varepsilon \) =0.45×10^?4 s^?1 brittle cracks were propagating always slowly with velocities in the range ofc=3 to 5×10^?2 m/s. For values ofv _s outside this transition zone fracture was typically brittle with high crack-propagation velocities. As the strain rate was varying beyond the stable low-velocity region, a two-step crack velocity pattern was operative, where the one step took always low values, and the other step corresponded to crack-propagation velocities significantly higher than these limits, tending to typical brittle-fracture velocities of the material. Oscillations of the velocityc at the transition zones, or, in many cases all over the zone of slow propagation of the crack, indicated the unstable character of crack propagation, influenced by different stress raisers and especially by the opposite longitudinal boundary of the specimen. Stress intensity factor values during crack propagation, evaluated from the front (cuspoid) and the rear (external) caustic, which remained alwaysk _g-dominant, were following similar trends as the variation of the crack propagation velocity.     

Synthesis and crystal structure of copper(II) bis-chelate comprising a nitrile derivative of 3-imidazoline nitroxide

Syntheses of a nitroxide radical 2-(1-oxyl-2,2,5,5-tetramethyl-imidazolin-4-yliden)-3-oxo-5-phenylpentannitrile $(HL^{CH_2 CH_2 Ph} )$ and its copper(II) complex are reported. The coordination compound is characterized by the single crystal X-ray diffraction analysis (a = 11.647(2) Å, b = 13.269(3) Å, c = 13.844(3) Å, α = 61.83(2)°, β = 88.13(2)°, γ = 74.12(2)°, space group $P\bar 1$ ). The $Cu(L^{CH_2 CH_2 Ph} )_2 (H_2 O)$ complex has a molecular structure.     

Measurement of hyperfine structure of sodium 3P 1/2,3/2 states using optical spectroscopy

The hyperfine levels of the sodium 3P _1/2,3/2 states were resolved using a narrow linewidth laser to excite the ground state. The laser frequency was scanned while fluorescence resulting from the radiative decay of the excited state was detected. The frequency was calibrated using the known hyperfine splitting of the ground state. The magnetic dipoleA and electric quadrupoleB hyperfine coupling constants of the excited states were determined to be $A_{3P_{1/2} } = 94.44 \pm 0.13$ , $A_{3P_{3/2} } = 18.62 \pm 0.21$ and $B_{3P_{1/2} } = 2.11 \pm 0.52MHz$ . The uncertainty of $A_{3P_{1/2} } $ is less than results previously reported while the data for the 3P _3/2 state are consistent with those existing in the literature.     

The thermodynamic properties and solvation of lithium halides in N-methylpyrrolidone at 298.15 K

The heat capacity and density of solutions of lithium chloride, bromide, and iodide in N-methylpyrrolidone (I) were determined by calorimetry and densimetry techniques. The standard partial molar heat capacities and volumes ( $\overline {C^\circ _{p2} } $ and $\overline {V^\circ _2 } $ ) of lithium halides in I were calculated. The $\overline {C^\circ _{pi} } $ and $\overline {V^\circ _i } $ values for halogen and lithium ions in I were determined. The coordination numbers of the Li⁺, Cl^?, Br^?, and I^? ions in solutions in I at 298.15 K were calculated.     

Limiting partial molar volumes of solutions of oleic, linoleic, and linolenic acids in cyclohexane and benzene

High-precision vibration densimetry was used to measure (with an error of less than 5 × 10^?6 g/cm³) the density of dilute solutions (0≤ x ₂ ≤ 0.01 mole fractions) of oleic, linoleic, and linolenic acids in cyclohexane and benzene at 298.15 K. The limiting $\bar V_2^\infty $ and excess V ₂ ^{E, ∞} partial molar volumes of these C_{18: n} fatty acids in the indicated solvents were calculated. Benzene was demonstrated to selectviely influence the volumetric effects of dissolution (V ₂ ^{E, ∞} ) of the linoleic (n _C=C= 2) and linolenic (n _C=C = 3) polyunsaturated acids.     

Electrical conductances of aqueous sodium trifluoromethanesulfonate from 0 to 450°C and pressures to 250 MPa

The electrical conductances of dilute (0.001 to 0.1 mol-kg^?1) aqueous sodium trifluoromethanesulfonate (NaCF₃SO₃) solutions have been measured from 0 to 450°C and pressures to 250 MPa. The limiting molar conductance $\Lambda _0 $ increases with increasing temperature from 0 to 300°C and decreasing density from 0.8 to 0.3 g-cm^?3. Above 300°C, $\Lambda _0 $ is nearly temperature independent, but increases linearly with decreasing density. The logarithm of the molal association constant of NaCF₃SO₃ calculated at temperatures from 372 to 450°C is represented as a function of temperature (Kelvin) and density of water (g-cm^?3) by $$\log K_m = 0.888 - 330.4/T - (12.83 - 5349/T)\log \rho _w $$ The relative strengths of NaCF₃SO₃ and NaCl are similar within the accuracy of the current measurements over the limited range of temperature and pressure that could be investigated here.     

Crystal structure of (C2H7N4O)2[(UO2)2)(OH)2(C2O4)(CHO2)2]

An X-ray diffraction study of the single crystals of (C₂H₇N₄O)₂[(UO₂)₂(OH)₂(C₂O₄)(CHO₂)₂] was carried out. The compound crystallizes in the triclinic system, space group $P\bar 1$ , Z = 2, a = 5.5621(8) Å, b = 8.1489(10) Å, c = 11.8757(16) Å, α = 88.866(7)°, β = 82.204(6)°, γ = 87.378(6)°, V = 532.7(1) ų, ρ_calcd = 2.988 g/cm³. The main structural units in the crystal are the [(UO₂)₂(OH)₂(C₂O₄)(CHO₂)₂)]^2? chains corresponding to the crystal chemical group A₂M ₂ ² K⁰²M ₂ ¹ (A = UO ₂ ²⁺ , M² = OH^?, K⁰² = C₂O ₄ ^2? , M¹ = CHO ₂ ^? ) of uranyl complexes. The chains are united into a three-dimensional framework through the electrostatic interaction and hydrogen bonds involving uranyl, oxalate, and hydroxyl groups, formate ions, and 1-carbamoylguanidinium cations.     

Differential thermal analysis- studies on the crystallization of strontium tungstate from sodium tungstate melts

The kinetics of strontium tungstate crystallization from sodium tungstate melts in platinum crucibles were studied by differential thermal analysis at crystallization temperaturesT ₀=800, 900 and 1000° by continuous cooling at ratesR _T=40, 120 and 200° per hour. Heterogeneous nuclei that first formed on the metal platinate particles in the solution during the induction periods (t) grew to small crystallites (¯l). The main crystal growth started after the development of some excess solute concentration (Δ¯C) at the end of the induction temperatures (¯T). For the first 80% crystallization, the average crystal lengths (l _τ ) varied with the growth time (τ) according to the relation \(l_\tau ^2 = (\bar l)^2 + + 4\bar k_{D_1 } M\Delta \bar C\) where \(\bar k_{D1} \) is the diffusion rate constant at temperatures nearT, andM is the metal salt molecular weight. The initial growth rates and the ratiosl _τ ² /τ depended onΔ¯C instead ofR _T The last 20% growth was controlled only by the rate of development of the excess solute concentration.     

Fragmentation of doubly charged noble metal clusters

The dissociation patterns of doubly charged noble metal clusters (M) _n ⁺⁺ to two singly charged clusters, (M) _m ^Emphasis>1/+ and (M) _m ^Emphasis>2/+ have been investigated using a double focusing mass spectrometer. They are compared with the dissociation patterns from singly charged clusters. The dissociation probabilities to (M) ₃ ⁺ and (M) ₉ ⁺ were large and the odd-even alternations were observed in both patterns.     

Primary processes in the thiacyanine dimer-photosensitized reduction of p-nitroacetophenone in water by

Primary processes in the reduction of p-nitroacetophenone (p-NAP) by ascorbic acid (AA) in water photosensitized by thiacyanine dimers M ₂ ^2? have been considered. For M ₂ ^2? , the quantum yields of fluorescence and intersystem crossing to the triplet state (M ₂ ^2? )_T increases in comparison to the monomers M^?. The dimers (M ₂ ^2? )_T enter into the reactions of both one-electron photoreduction by ascorbic acid to give AA^+· and M ₂ ^3? and one-electron photooxidation by p-nitroacetophenone to give p-NAP^?· and the dimeric radical anion M ₂ ^? which dissociates to M^? and M^· within 25–30 μs. The primary oxidative or reductive photosensitization in the ternary systems containing (M ₂ ^2? )_T, p-NAP, and AA affords p-NAP^?· and AA^+·.