Micromechanical fast quasi‐static detection of α and β relaxations with nanograms of polymer

Micromechanical string resonators are used as a highly sensitive tool for the detection of glass transition (T_g or α relaxation) and sub‐T_g (β relaxation) temperatures of polystyrene (PS) and poly (methyl methacrylate) (PMMA). The characterization technique allows for a fast detection of mechanical relaxations of polymers with only few nanograms of sample in a quasi‐static condition. The polymers are spray coated on one side of silicon nitride (SiN) microstrings. These are pre‐stressed suspended structures clamped on both ends to a silicon frame. The resonance frequency of the microstrings is then monitored as a function of increasing temperature. α and β relaxations in the polymer affect the net static tensile stress of the microstring and result in measureable local frequency slope maxima. T_g of PS and PMMA is detected at 91 ±2°C and 114 ±2°C, respectively. The results match well with the glass transition values of 93.6°C and 114.5°C obtained from differential scanning calorimetry of PS and PMMA, respectively. The β relaxation temperatures are detected at 30 ± 2°C and 33 ± 2°C for PS and PMMA which is in accordance with values reported in literature. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1035–1039     

Bis(1,2-dimethoxyethan-O,O′)lithium-phosphanid, -arsanid und -chlorid – drei neue Vertreter des Bis(1,2-dimethoxyethan-O,O′)lithium-bromid-Typs

Metal Derivatives of Molecular Compounds. IX. Bis(1,2-dimethoxyethane- O,O′ )lithium Phosphanide, Arsanide, and Chloride – Three New Representatives of the Bis(1,2-dimethoxyethane- O,O′ )lithium Bromide Type Experiments to obtain thermally unstable lithium silylphosphanide at –60 °C from a 1,2-dimethoxyethane solution resulted in the isolation of its dismutation product bis(1,2-dimethoxyethane-O,O′)lithium phosphanide ( 1 ). The homologous arsanide 2 precipitated after a frozen solution of arsane in the same solvent had been treated with lithium n-butanide at –78 °C. Unexpectedly, too, the analogous chloride 3 and bromide 4 were formed in reactions of 1-chloro-2,2-bis(trimethylsilyl)-1λ³-phosphaethene with (1,2-dimethoxyethane-O,O′)lithium bis(trimethylsilyl)stibanide and of lithium 1,2,3,4,5-pentaphenyl-2,3-dihydro-1λ³-phosphol-3-ide with ω-bromostyrene, respectively. The monomeric complexes 1 {–100 ± 3 °C; a = 1391.1(4); b = 809.8(2); c = 1249.1(3) pm; β = 102.84(2)°}, 2 {–100 ± 3 °C; a = 1398.3(4); b = 819.8(3); c = 1258.5(4) pm; β = 103.35(2)°} and 3 {–100 ± 3 °C; a = 1308.4(2); b = 788.2(1); c = 1195.6(1) pm; β = 95.35(1)°} crystallize in the monoclinic space group C2/c with four solvated ion pairs in the unit cell; they are isotypic with bis(1,2-dimethoxyethane-O,O′)lithium bromide ( 4 ) {–73 ± 2 °C; a = 1319.0(2); b = 794.1(1); c = 1214.3(2) pm; β = 96.22(1)°}, already studied by Rogers et al. [13] at room temperature. The neutral complexes show a trigonal bipyramidal configuration of symmetry C₂, pnicogenanide or halide anions occupying equatorial sites {Li–P 260.4(4); Li–As 269.8(6); Li–Cl 238.6(7); Li–Br 256.3(10) pm} and the chelate ligands spanning equatorial and axial positions {Li–O_eq 205.4(4) to 207.4(4); Li–O_ax 208.9(3) to 215.5(2) pm}. The coordination within the (dme)₂Li fragment, the Li–X distances (X = P, As, Cl, Br), the structure of the chelate rings, and the packing of the neutral complexes are discussed in detail.     

Untersuchungen am Chlordiphenyl‐ und Tribenzylstiban sowie am Tribenzyldibromstiboran – Molekülstrukturen und Isotypie

Element–Element Bonds. X. Studies of Chloro(diphenyl)stibane, Tribenzylstibane and Tribenzyldibromostiborane – Molecular Structures and Isotypism Chlorodiphenylstibane ( 1 d ) {P2₁/c; Z = 4; a = 1191.8(1); b = 853.4(1); c = 1112.0(1) pm; β = 93.60(1)°; –100 ± 2 °C} crystallizes isotypically with a series of homologous (H₅C₆)₂E–X compounds (E = As, X = Cl, Br, I; E = Sb, X = Br, I); the structure type of tribenzylstibane ( 5 d ) {Pbca; Z = 8; a = 832.1(2); b = 2681.3(5) pm; c = 1600.9(3); –100 ± 3 °C} is already known from tribenzylmethanol, ‐silanol and ‐silane. Tribenzyldibromostiborane ( 6 ) {P2₁/n; Z = 4; a = 938.4(2); b = 2292.4(5); c = 1019.7(2) pm; β = 112.71(1)°; –100 ± 3 °C} does not show an analogous relationship to known structure types. Characteristic mean bond lengths and angles are { 1 d , Sb–Cl 240.9(1), Sb–C 214.0 pm, Cl–Sb–C 93.8°, C–Sb–C 98.6(1)°; 5 d , Sb–C 217.5(3) pm, C–Sb–C 94.9(6)°; 6 , Sb–Br 264.6; Sb–C 217.0(8) pm, Br–Sb–Br 179.4(1)°; C–Sb–C 120°; Br–Sb–C 84.8(2)° to 94.7(2)°}. Stiborane 6 exhibits very weak intermolecular Sb‥Br interactions of 417 pm which, however, affect the molecular conformation in a striking way.     

Potentiometric measurements of the first hydrolysis quotient of magnesium(II) to 250°C and 5 molal ionic strength (NaCl)

The first molal hydrolysis quotient, Q_1.1, of Mg²⁺ was measured potentiometrically from 1 to 250°C at ionic strengths of 0.11, 0.31, 1.01, and 5.0 mol-kg^-1 in an aqueous NaCl medium using a hydrogen-electrode, concentration cell. Only hydrolysis of the first four percent of the magnesium in solution could be followed before precipitation of brucite, Mg(OH)₂(cr), occurred. The log Q_1.1 values were fitted as a function of temperature and ionic strength using four adjustable parameters. The resulting constants are compared with the limited existing low temperature data. At infinite dilution and 25°C the following quantities are reported: logK _1.1 = -11.68±0.05, †H_so = 70.1±1.2 kJ-mol^-1, †S^o = 11±4 J-K^-1-mol^-1, and †C _p ^o = 0 J-K^-1-mor^-1. At each ionic strength, including the values extrapolated to infinite dilution, the heat capacity change for the hydrolysis reaction was zero,i.e., logQ _1.1 was found to be a linear function of the reciprocal temperature in Kelvin, at least over the measured range of l-250°C. The hydrolysis constants at infinite dilution were modeled to 550°C and two kbar pressure with a function incorporating solvent density using published results obtained at these extreme conditions.     

2,4-Bis{[6-(2,2-dimethylpropyl)-3-ethyl-1,3-benzothiazol-2(3H)-yl­idene]methyl}cyclobutenediylium-1,3-­diolate

The title compound, C₃₄H₄₀N₂O₂S₂, adopts a trans conformation. The four conjugated Csp²—Csp² single and double bonds of the polymethinic moiety, which bridges both heterocyclic end groups and the central four-membered ring, display nearly equal bond lengths. The mol­ecule is nearly planar, with interplanar angles between the benzo­thia­zole end groups and the central four-membered ring of 6.9 (1) and 7.7 (1)°; the angle between the heterocyclic systems is 1.8 (1)°. The crystal packing involves π-stacking effects, with intermolecular C⃛C distances varying from 3.755 (3) to 3.991 (3) Å.     

Thermally induced polymerization of isobutylene in the presence of SnCl4: Kinetic study of the polymerization and NMR structural investigation of low molecular weight products

The polymerization reactivity of isobutylene/SnCl₄ mixtures in the absence of polar solvent, was investigated in a temperature interval from −78 to 60 °C. The mixture is nonreactive below −20 °C but slow polymerization proceeds from −20 to 20 °C with the initial rate r₀ of the order 10⁻⁵ mol · l⁻¹ · s⁻¹. The rate of the process increases with increasing temperature up to ∼10⁻² mol · l⁻¹ · s⁻¹ at 60 °C. Logarithmic plots of r₀ and M̄_n versus 1/T exhibit a break in the range from 20 to 35 °C. Activation energy is positive with values E = 21.7 ± 4.2 kJ/mol in the temperature interval from −20 to 35 °C and E = 159.5 ± 4.2 kJ/mol in the interval from 35 to 60 °C. The values of activation enthalpy difference of molecular weights in these temperature intervals are ΔH_Mn = −12.7 ± 4.2 kJ/mol and −38.3 ± 4.2 kJ/mol, respectively. The polymerization proceeds quantitatively, the molecular weights of products are relatively high, M̄_n = 1500–2500 at 35 °C and about 600 at 60 °C. It is assumed that initiation proceeds via [isobutylene · SnCl₄] charge transfer complex which is thermally excited and gives isobutylene radical‐cations. Oxygen inhibits the polymerization from −20 to 20 °C. Possible role of traces of water at temperatures above 20 °C is discussed. It was verified by NMR analysis that only low molecular weight polyisobutylenes are formed with high contents of exo‐ terminal unsaturated structures. In addition to standard unsaturated groups, new structures were detected in the products. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1568–1579, 2000     

Region of homogeneity for Lu2 ? xMnxO3 ± δ solid solution in air

The solubility boundaries for Lu₂O₃ and Mn₃O₄ oxides and LuMn₂O₅ manganate in LuMnO_{3 ± δ} are determined on the basis of an X-ray phase analysis of homogeneous solid solutions and heterogeneous compositions with molecular formula Lu_{2 − x} Mn _x O_{3 ± δ} (0.90 ≤ x ≤ 1.16; Δx = 0.02) obtained by ceramic synthesis in air in a temperature range of 900–1400°C. It is found that the solubility of Lu₂O₃ in LuMnO_{3 ± δ} corresponds to the composition of Lu_1.03Mn_0.97O_{3 ± δ} and remains invariable over the investigated range of temperatures, while the solubility of Mn₃O₄ (which corresponds to the composition of Lu_0.91Mn_1.09O_{3 ± δ}) remains invariable in the temperature range of 995–1400°C. It is shown that lutetium manganate LuMn₂O₅ coexists with lutetium manganate LuMnO_{3 ± δ} at temperatures of less than 995°C in air, and its solubility in LuMnO_{3 ± δ} decreases as the temperature of 995°C (corresponding to the composition Lu_0.91Mn_1.09O_{3 ± δ}) falls to 900°C for Lu_0.97Mn_1.03O_{3 ± δ}.     

The kinetics and equilibrium of the gas-phase reaction CH3CF2Br + I2 = CH3CF2I + IBr the C-Br bond dissociation energy in 1,1-difluorobromoethane

The kinetics and equilibrium of the gas-phase reaction of CH₃CF₂Br with I₂ were studied spectrophotometrically from 581 to 662°K and determined to be consistent with the following mechanism: A least squares analysis of the kinetic data taken in the initial stages of reaction resulted in log k₁ (M^?1 · sec^?1) = (11.0 ± 0.3) - (27.7 ± 0.8)/θ where θ = 2.303 RT kcal/mol. The error represents one standard deviation. The equilibrium data were subjected to a “third-law” analysis using entropies and heat capacities estimated from group additivity to derive ΔH_r° (623°K) = 10.3 ± 0.2 kcal/mol and ΔH_rr (298°K) = 10.2 ± 0.2 kcal/mol. The enthalpy change at 298°K was combined with relevant bond dissociation energies to yield DH°(CH₃CF₂ - Br) = 68.6 ± 1 kcal/mol which is in excellent agreement with the kinetic data assuming that E₂ = 0 ± 1 kcal/mol, namely; DH°(CH₃CF₂ - Br) = 68.6 ± 1.3 kcal/mol. These data also lead to ΔH_f°(CH₃CF₂Br, g, 298°K) = -119.7 ± 1.5 kcal/mol.     

THE REACTION BETWEEN π-CYCLOPENTADIENYLDI-CARBONYLCOBALT AND PHENYLETHYNYLSILANE,AND AN X-RAY CRYSTALLOGRAPHIC INVESTIGATION OF ONE OF THE PRODUCTS, (π-CYCLOPENTADIENYL)-[trans-DIPHENYL-DI(TRIMETHYLSILYL)-CYCLOBUTADIENE]-COBALT

Abstract

This is a report of the broad range of reactions and products that occur in refluxing xylene when π-cyclopentadienylcobalt or (π-cyclopentadienyl)-dicarbonylcobalt react with either symmetric or unsymmetrical acetylenes, specially when one of the substituents of the acetylene is an aromatic moeity. Since these reactions produce a variety of products, several of which are cis- and trans- tetrasubstituted cyclobutadiene-cobalt isomers, mnr and mass spectral methods were used to distinguish between them. In order to obtain an independent and indisputable structure assignment for the structural isomers investigated by spectral techniques, the crystal structure of the title compound was investigated by x-ray crystallographic techniques. The compound crystallizes in space group Pbca with the following cell dimensions: a = 29.622(7), b = 9.967(2) and c = 17.140(3) Å; V = 5060.46 ų; D(exp) = 1.23(2) gm-cm^?3, D(calc) = 1.24 gm-cm^?3 for Z = 8 molecules/unit cell. The intensity data were collected with MoKα radiation (Λ = 0.71069 Å) using a computer-controlled diffractometer equipped with a graphite monochromator. In all 6331 reflections were collected of which 3173 were independent and had F ₀ ² ± 3[sgrave] (F ₀ ²). The data were corrected for absorption and the transmission coefficients ranged from 0.72 to 0.79. The (π-cyclopentadienyl) ring is planar and has normal Co–C and C–C distances which average 2.049(7) and 1.389(17) Å, respectively. The Co–(Cp ring centroid) distance is 1.67 Å and the ring librates about this axis to a small degree which is not, however, large enough to affect the C–C distances. The average value of the C–C–C angle in the π-cyclopentadienyl ring is 108° indicating that it is planar and, in fact, the largest deviation of any carbon from the least-squares plane is 0.006 Å. In the Co-cyclobutadiene moiety, the Co–C and C–C distances are 1.982(15) and 1.467(3) Å and the Co–(cyclobutadiene ring centroid) distance is 1.69 Å. The angle between the normals of the five- and four-membered rings is 1.6°. The phenyl rings and trimethylsilyl fragments have normal distances and angles and the phenyl rings are planar. The two silicon and two carbon atoms of the phenyl rings linked to the π-cyclobutadiene moeity are out of the mean plane of the ring and bend away from the Co atom.

Finally, and most important, the four-membered ring is planar (the largest deviation from planarity is 0.003 Å) and the four C–C distances are the same length; however, the internal angles are not 90.0°. Instead, the two angles at carbons bonded to phenyl rings have values of 88.1(2)° and 88.4(2)° while those at carbon atoms bonded by silicons have values of 91.6(2)° and 91.8(2)°. The final discrepancy indices for this structural analysis were R ₁ = 0.038 and R ₂(F) = 0.044.     

Substituenteneffekte auf die C–C-Bindungsstärke, 8. Standardbildungsenthalpien und Spannungsenthalpien von 1,1,2,2-Tetraethylethylenglykol-dimethylether und D,L-1,2-Dimethyl-1,2-diphenylethylenglykol-dimethylether

Effects of Substituents on the Strength of C - C Bonds, 8¹. - Heats of Formation and Strain of 1,1,2,2-Tetraethylethylene Glycol Dimethyl Ether and D,L .-1,2-Dimethyl-l,2-diphenylethylene Glycol Dimethyl Ether The heats of combustion of the title compounds 1 and 2 were measured calorimetrically with the result (kcal mol ^-1, s. d. in parentheses) ΔH°_c = − 1880.1 (± 0.6) and − 2373.3 (± 1.4). The heat of vaporisation of 1 ΔH^v = 14.3 (± 0.3) and the heat of sublimation of 2 ΔH^sub = 27.2 (± 0.5) were derived from their temperature dependance of the vapor pressure. The latter were determined between 30 and 80°C using a flow method. The resulting standard heats of formation ΔH°_t(g) = −122.4 (± 0.7) and −43.8 (±1.5) for 1 and 2 correspond to a strain enthalpy (_s) of 15.9 and 8.0 kcal mol^-1, respectively. The steric strain of the dimethoxyethanes 1 and 2 is about one fourth lower than the strain of the corresponding dimethylethanes 3 and 4 bearing the same substituents. Thus, a methoxy group causes less steric stress than a methyl group.     

Common Features in the Crystal Structures of the Compounds Bis(dimethylstibanyl)oxane and ‐sulfane,and the Minerals Valentinite and Stibnite (Grauspießglanz)

Bis(dimethylstibanyl)oxane ( 1 ) and ‐sulfane ( 2 ), the two simplest organoelement species with an Sb–E–Sb fragment (E = O, S), were prepared by alkaline hydrolysis of bromodimethylstibane and by oxidation of tetramethyldistibane with sulfur [18], respectively. As shown by an x‐ray structure analysis of compound 1 (m. p. < –20 °C; P2₁2₁2₁, a = 675.9(2), b = 803.1(2), c = 1666.8(4) pm at –70 ± 2 °C; Z = 4; R1 = 0.042), the molecules (O–Sb 198.8 and 209.9 pm, Sb–O–Sb 123.0°) adopt a syn‐anti conformation in the solid state and are arranged in zigzag chains along [010] via weak intermolecular O‥Sb interactions (258.5 pm, Sb–O‥Sb 117.8°, O‥Sb–O 173.5°) making use, however, of only one Me₂Sb moiety. Primary and secondary bond lengths and angles agree very well with corresponding values published for valentinite, the orthorhombic modification of antimony(III) oxide [3]. Bis(dimethylstibanyl)sulfane ( 2 ) (m. p. 29 to 31 °C) crystallizes in the uncommon space group P6₅22 (a = 927.8(3), c = 1940.9(7) pm at –100 ± 2 °C; Z = 6; R1 = 0.021). Owing to coordination numbers of (1 + 1) and (2 + 2) for both Me₂Sb groups and the sulfur atom, respectively, molecules with an approximate syn‐syn conformation (S–Sb 249.8 pm, Sb–S–Sb 92.35°) build up a three‐dimensional net of double helices which are linked together by Sb‥S contacts (316.4 pm). These parameters shed more light onto the rather complicated structure and bonding situation in stibnite (antimony(III) sulfide [4]). The molecular packing of compound 2 is compared with the structures of relevant inorganic solids, especially with that of β‐quartz [37].     

Bond dissociation energies and radical heats of formation in CH3Cl,CH2Cl2, CH3Br,CH2Br2, CH2FCl,and CHFCl2

An analysis of thermochemical and kinetic data on the bromination of the halomethanes CH_4–nX_n (X = F, Cl, Br; n = 1–3), the two chlorofluoromethanes, CH₂FCl and CHFCl₂, and CH₄, shows that the recently reported heats of formation of the radicals CH₂Cl, CHCl₂, CHBr₂, and CFCl₂, and the C? H bond dissociation energies in the matching halomethanes are not compatible with the activation energies for the corresponding reverse reactions. From the observed trends in CH₄ and the other halomethanes, the following revised ΔH°_f,298 (R) values have been derived: ΔH°_f(CH₂Cl) = 29.1 ± 1.0, ΔH°_f(CHCl₂) = 23.5 ± 1.2, ΔH_f(CH₂Br) = 40.4 ± 1.0, ΔH°_f(CHBr₂) = 45.0 ± 2.2, and ΔH°_f(CFCl₂) = ?21.3 ± 2.4 kcal mol^?1. The previously unavailable radical heat of formation, ΔH°_f(CHFCl) = ?14.5 ± 2.4 kcal mol^?1 has also been deduced. These values are used with the heats of formation of the parent compounds from the literature to evaluate C? H and C? X bond dissociation energies in CH₃Cl, CH₂Cl₂, CH₃Br, CH₂Br₂, CH₂FCl, and CHFCl₂.     

The Crystal Structure of (1, 1′-ferrocenediyl)diphenylsilane

The crystal structure of (1,1′-ferrocenediyl)diphenylsilane has been determined from analysis of photographic X-ray data. The crystal system is orthorhombic, a = 14.18(2), b = 12.54(2), c = 9.28(1) Å, space group Pnma with four formula units. The molecule has crystallographic m (C_s) symmetry with atoms Fe and Si lying in the mirror plane, which bisects the two phenyl groups. The planar cyclopentadienyl rings are bridged by a single silicon atom, and are tilted 19.2° with respect to one another. The Fe—C(Cp) distances vary from 2.01(1) to 2.11(1) Å. The bridging angle C(1)—Si—C(1′) is 99.1°, while the Si—C(sp²) bond lengths range from 1.86 to 1.88 Å. The exocyclic C(1)—Si bond makes an angle of 40° with respect to the plane of the cyclopentadienyl ring.     

Very low-pressure pyrolysis (VLPP) of 3,3-dimethylbut-1-yne (tert-butyl acetylene). The heat of formation and stabilization energy of the dimethylpropargyl radical

The unimolecular decomposition of 3,3-dimethylbut-1-yne has been investigated over the temperature range of 933°-1182°K using the technique of very low-pressure pyrolysis (VLPP). The primary process is C? C bond fission yielding the resonance stabilized dimethylpropargyl radical. Application of RRKM theory shows that the experimental unimolecular rate constants are consistent with the high-pressure Arrhenius parameters given by log (k/sec^?1) = (15.8 ± 0.3) - (70.8 ± 1.5)/θ where θ = 2.303RT kcal/mol. The activation energy leads to DH⁰[(CH₃)₂C(CCH)? CH₃] = 70.7 ± 1.5, θH⁰_f((CH₃)₂?CCH,g) = 61.5 ± 2.0, and DH⁰[(CH₃)₂C(CCH)? H] = 81.0 ± 2.3, all in kcal/mol at 298°K. The stabilization energy of the dimethylpropargyl radical has been found to be 11.0±2.5 kcal/mol.     

Conformational Flexibility of the Methoxyphenyl Group Studied by Statistical Analysis of Crystal Structure Data

In a large sample of observed methoxyphenyl groups, the twist angle τ about the MeO-C_Ph bond measuring internal rotation of the MeO group shows a continuous distribution with maxima at (0°) (coplanar conformation) and (～90°) (perpendicular conformation). The preferred conformation of methoxyphenyl depends on the nature of the ortho--substituents: In general, it is coplanar in the case of one or two ortho-hydrogens, and perpendicular in the case of two substituents. The internal rotation of the MeO group is accompained by systematic variations in bond angles and bond distances: 1 if MeO is twisted out of plane, the bond angle CH₃? O? C_Ph decreases from 117.7°, until it reaches a minimum of 114.9° at τ = ±90°. The O? C? C angle which is syn to CH₃ for τ = 0° decreases from 124.6° to a minimum of 115.4° at τ = ±180°. These angles changes keep the nonbonded distance CH₃ …? ortho substituent maximal during internal rotation of MeO and tend to minimize the corresponding strain energy. (2) In the perpendicular conformation, the O-atom is ～ 0. 06 Å displaced from the Ph plane, O and CH₃ and being on opposite sides of this plane. In addition, small but systematic increases of bond lengths MeO? C_Ph and CH₃? O are observed. These variations indicate a decrease in conjugation with increasing twist angle. Their interdependence during twisting and the magnitudes of the changes are close values obtained by ab initio calculations.     

Host/Guest Simulation of Fluorescent Probes Adsorbed into Low‐Density Polyethylene, 1. Excimer Formation of 1,3‐Di(1‐pyrenyl)propane

Molecular dynamics and Rotational Isomer State/Monte Carlo techniques with a Dreiding 1.01 Force Field are employed to study the excimer formation of isolated 1,3‐di(1‐pyrenyl)propane and the probe adsorbed into a low‐density polyethylene (LDPE) matrix model. The probability of formation of each molecular conformer at several temperatures was calculated using these theoretical techniques. Conformational statistical analysis of the four torsion angles (ϕ₁, ϕ₂, θ₁, θ₂) of Py3MPy showed that the angles —C—C^ar— (ϕ₁, ϕ₂) present two states c ^± = ±90°; and the angles —C—C— (θ₁, θ₂), the three trans states = 180°, g ^± = ±60°. The correlation of θ₁–θ₂ torsion angles showed that the most probable pairs were g⁺g^– and g^–g⁺ for the excimer‐like specimens, although these angles are distorted because of interactions with the polymer matrix. The temperature dependence of the excimer‐formation probability revealed that this process was thermodynamically controlled in the isolated case. When the probe was adsorbed into the LDPE matrix, the excimer formation process was reversed at T = 375 K. At T >  375 K, the behavior was similar to the isolated case but, at T < 375 K, excimer formation probability increased with temperature as found experimentally by steady‐state fluorescence spectroscopy. This temperature was coincident with the onset of the LDPE melting process, determined experimentally by thermal analysis.     

Phase equilibria in the GeSe2–SnSe system

The phase diagram of the system GeSe₂–SnSe is studied by means of X-ray diffraction, differential thermal analysis and measurements of the density and the microhardness of the material. There are no intermediate compounds in it, as well as regions of range of solid solutions at room temperature on the base of GeSe₂ and SnSe. There are two non-variant equilibria in the system: eutectic (where T _e=530±5°C and x _e= 40 mol% SnSe) and metaeutectic (where T _m=550±5°C and x _m=98 mol% SnSe).     

The Temperature-Composition Phase Equilibria in the HgTe–HgI2 Pseudobinary System

The temperature-composition phase diagram of the HgTe—HgI₂ pseudobinary system was determined between 25 and 670°C using differential scanning calorimetry, differential thermal analysis, Debye-Scherrer powder X-ray diffraction techniques, and metallographic analysis methods. Solid solutions of HgTe and HgI₂ with the cubic, zinc blende-type structure exist above 300°C, having a maximum solubility of 11.7±0.8 Mol-% HgI₂ in HgTe at 501±5°C. The monoclinic intermediate phase Hg₃Te₂I₂ is formed by a peritectic reaction upon cooling at 501±5°C, with the peritectic point at approximately 37±4 Mol-% HgI₂. The previously unknown cubic phase Hg₃TeI₄ (a = 6.240±0.003 Å) is formed by a eutectoid reaction at 238±3°C and is stable up to 273±3°C, where it melts by a peritectic reaction with the peritectic point at approximately 79±3 Mol-% HgI₂. Between Hg₃TeI₄ and HgI₂ is a eutectic point at 82±3 Mol-% HgI₂ and 250±3°C. The α to β transition of HgI₂ at 133±3°C is independent of sample composition between 33.3 and 100 Mol-% HgI₂.     

Supramolecular structures of bis‐thionooxalamic acid esters derived from (±)‐cyclohexane‐1,2‐diamine and (±)‐1,2‐diphenylethylenediamine

The bis‐thionooxalamic acid esters trans‐(±)‐diethyl N,N′‐(cyclohexane‐1,2‐diyl)bis(2‐thiooxamate), C₁₄H₂₂N₂O₄S₂, and (±)‐N,N′‐diethyl (1,2‐diphenylethane‐1,2‐diyl)bis(2‐thiooxamate), C₂₂H₂₄N₂O₄S₂, both consist of conformationally flexible molecules which adopt similar conformations with approximate C₂ rotational symmetry. The thioamide and ester parts of the thiooxamate group are significantly twisted along the central C—C bond, with the S=C—C=O torsion angles in the range 30.94 (19)–44.77 (19)°. The twisted s‐cis conformation of the thionooxamide groups facilitates assembly of molecules into a one‐dimensional polymeric structure via intermolecular three‐center C=S...NH...O=C hydrogen bonds and C—H...O interactions formed between molecules of the opposite chirality.     

Kinetics and mechanism of the aquation of pentaaqua (trichloroacetato-O)-chromium(2+) ion

The kinetics of the aquation of (H₂O)₅Cr(O₂CCCl₃)²⁺ have been examined at 35–55°C and 1.00M ionic strength with [H⁺] = 0.01?1.00M. The reaction follows the rate equation -d ln [Cr_total]/dt = (a[H⁺]^?1 + b + c[H⁺])/(1 + d[H⁺]), where [Cr_total] is the stoichiometric concentration of the complex. At 45°C a = (1.41 ± 0.03) × 10^?7M/s, b = (1.66 ± 0.02) × 10^?5 s^?1, c = (7.0 ± 0.8) × 10^?5M^?1·S^?1 and d = 2.3 ± 0.3M^?1. Two mechanisms consistent with this rate law are discussed, with evidence being presented in favor of an ester hydrolysis mechanism involving steady-state intermediates. Equilibrium and activation parameters were determined.