“Normal” and “cine” substitution in the thioalkoxy-dehalogenation of halogenobenzofurazans—III: Investigation on the solvent effect

The reaction of 4-chloro- and 4-chloro-7-deuteriobenzofurazan with MeS^-, isopropyl-S^-, and t-Butyl-S^- in different alcohols as solvents has been investigated. In going from methanol through isopropanol to t-butanol, a progressive decrease of the contribution of the cine-substitution as compared with the normal substitution pathway has been found. By proceeding in the same order, a decrease of the ratio and $\text{k}\text{MeS}{}^{\mathrm{?}}\text{k}{}_{\mathrm{<mtext>t</mtext>}}$-ButylS^? has also been observed.     

Cryogenic luminescence studies of Eu3+ in LiEuCl4

The luminescence associated with the Eu³⁺ ion in LiEuCl₄ has been studied at cryogenic temperatures under conditions of high resolution. Emission was observed to originate from both the ⁵D₀ and ⁵D₁ excited states, and transitions to the ${}^7\text{F}{}_0\text{,}{}^7\text{F}{}_1\text{,}{}^7\text{F}{}_2\text{,}{}^7\text{F}{}_3$, and ⁷F₄ ground levels were observed. The fine structure observed within these emission bands was found to be consistent with the existence of an effective D₄ site symmetry for the emitting Eu³⁺ species, even though the europium polyhedron was found to be that of a bisdisphenoid.     

Dependence of polymer specific volume on molecular characteristics

Linear and branched bisphenol A polycarbonate (PC) samples were characterized by their average molecular weights, $\text{M}{}_{\mathrm{<mtext>n</mtext>}}$ and $\text{M}{}_{\mathrm{<mtext>w</mtext>}}$, polydispersity degree $\text{q =}\text{M}{}_{\mathrm{<mtext>w</mtext>}}\text{/}\text{M}{}_{\mathrm{<mtext>n</mtext>}}$, and branching degree g_v. The weight fraction of microgel was also determined for branched samples. The samples were amorphized and densities were measured at 23°C to obtain the values of specific volume, v_sp. The dependence of v_sp on molecular characteristics is described by the multivariable power function $\text{Δv}{}_{\mathrm{<mtext>sp</mtext>}}\text{=}\text{A}{}_{\mathrm{sp}}\text{M}{}_{\mathrm{<mtext>x</mtext>}}{}^{\mathrm{<mtext>a</mtext>}}\text{q}{}^{\mathrm{<mtext>apx</mtext>}}\text{g}{}_{\mathrm{<mtext>v</mtext>}}{}^{\mathrm{<mtext>ab</mtext>}}$, where Δv_sp = v_sp ? v_sp,∞, and A_sp, a, a_px and a_b are constants. It has been confirmed that a = ?1, a_pn = 0 and a_pw = 1. It has also been found that the branching exponent a_b significantly depends on microgel content. The relationships found for PC should, in principle, be valid for other polymers. Examples based on literature data are given for linear polyethylene and polydimethylsiloxane.     

Energy transfer between Gd3+ and Sm3+ the effect of Gd3+ on quenching of Sm3+ and intensity parameters of Sm3+ in borate glasses

Intensity parameters of Sm³⁺ in borate glasses were obtained by fitting the oscillator strengths to the Judd-Ofelt formula and a study of energy transfer from gadolinium to samarium was performed. An increase of samarium fluorescence originating from the ${}^4\text{G}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ level was observed in the presence of gadolinium, in the concentration range of 0.1–3 wt% samarium with gadolinium constant at 3 wt%. The intensity of samarium fluorescence on excitation at 273 nm increased by one order of magnitude in the presence of gadolinium. From the excitation spectrum of the double-doped glasses (Gd + Sm), it was deduced that energy absorbed by gadolinium is transferred from ${}^6\text{P}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ gadolinium levels to the ${}^4\text{P}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and ${}^4\text{P}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ samarium levels.The mechanism of this energy transfer was obtained by plotting the energy transfer probabilities as a function of samarium concentration. A linear dependence of $\text{η}{}_0\text{η}$ (η intensity of gadolinium in the presence of samarium) versus square of concentration of Sm + Gd is obtained. From this it is concluded that the transfer is of electric-multipolar type, mainly dipole-dipole. A small increase (about 10%) of fluorescence of samarium in the presence of gadolinium excited at levels where no energy transfer can take place is attributed to the fact that the quenching of samarium occurring by the cross relaxation $\text{(}{}^4\text{G}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{→}{}^6\text{F}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{) (}{}^6\text{H}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{→}{}^6\text{F}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{)}$ is suppressed by the presence of gadolinium as seen from concentration dependence of samarium doped glasses compared to double-doped glasses.     

Nonstoichiometry and defect structure of the perovskite-type oxides La1−xSrxFeO3−°

In order to elucidate the defect structure of the perovskite-type oxide solid solution La_1?xSr_xFeO_3?δ (x = 0.0, 0.1, 0.25, 0.4, and 0.6), the nonstoichiometry, δ, was measured as a function of oxygen partial pressure, P_O2, at temperatures up to 1200°C by means of the thermogravimetric method. Below 200°C and in an atmosphere of P_O2 ≥ 0.13 atm, δ in La_1?xSr_xFeO_3?δ was found to be close to 0. With decreasing log P_O2, δ increased and asymptotically reached $\text{x}\text{2}$. The value corresponding to $\text{δ =}\text{x}\text{2}$ was about ?10 at 1000°C. With further decrease in log P_O2, δ slightly increased. For LaFeO_3?δ, the observed δ values were as small as <0.015. It was found that the relation between δ and log P_O2 is interpreted on the basis of the defect equilibrium among Sr′_La (or V?_La for the case of LaFeO_3?δ), V^··_O, Fe′_Fe, and Fe^·_Fe. Calculations were made for the equilibrium constants K_ox of the reaction

$\text{1}\text{2}\text{O}{}_2\text{(g) + V}{}^{\mathrm{··}}{}_{\mathrm{o}}\text{+ 2Fe}{}^{\mathrm{x}}{}_{\mathrm{Fe}}\text{= O}{}^{\mathrm{x}}{}_{\mathrm{o}}\text{+ 2Fe}{}^{\mathrm{·}}{}_{\mathrm{Fe}}$

and K_i for the reaction

$\text{2Fe}{}^{\mathrm{x}}{}_{\mathrm{Fe}}\text{= Fe}{}^{\mathrm{\prime }}{}_{\mathrm{Fe}}\text{+ Fe}{}^{\mathrm{·}}{}_{\mathrm{Fe·}}$

Using these constants, the defect concentrations were calculated as functions of P_O2, temperature, and composition x. The present results are discussed with respect to previously reported results of conductivity measurements.     

Low-temperature luminescence of Eu3+ in K2EuCl5

The luminescence associated with the Eu³⁺ ion in K₂EuCl₅ has been studied at cryogenic temperatures under conditions of high resolution. Emission was observed to originate from both the ⁵D₀ and ⁵D₁ excited states, and transitions to the ${}^7\text{F}{}_0\text{,}{}^7\text{F}{}_1\text{,}{}^7\text{F}{}_2\text{,}{}^7\text{F}{}_3$, and ⁷F₄ ground levels were observed. The fine structure observed within these emission bands was found to be consistent with the existence of an effective C₄ site symmetry for the emitting Eu(III) species, even though the crystal structure does not indicate the presence of a true or pseudo C₄ axis.     

Electrical conductivity in strontium titanate with nonideal cationic ratio

The electrical conductivity of polycrystalline strontium titanate with ($\text{Sr}\text{Ti}\text{= 0.996, 0.99,}\text{and}\text{0.98}$ was determined for the oxygen partial pressure range of 10⁰ to 10^?22 atm and the temperature range of 850–1050°C. These data were found to be similar to that obtained for the sample with ideal cationic ratio. The observed data were proportional to the $\text{?}\text{1}\text{6}$ power of oxygen partial pressure for P_O2 < 10^?15atm, proportional to for the pressure range 10^?8–10^?15 atm, and proportional to for P_O2 > 10^?4atm. The deviation from the ideal Sr-to-Ti ratio was found to be accommodated by neutral vacancy pairs, (V″_Sr V″₀. The results indicate that the single-phase field of strontium titanate extends beyond 50.505 mole% TiO₂ at elevated temperatures.     

Electrical conductivity in strontium titanate

The electrical conductivity of polycrystalline SrTiO₃ was determined for the oxygen partial pressure range of 10° to 10^?22 atm and temperature range of 800 to 1050°C. The data were found to be proportional to the $\text{?1}\text{6}\text{th}$ power of the oxygen partial pressure for the oxygen pressure range 10^?15–10^?22 atm, proportional to for the oxygen pressure range 10^?8–10^?15 atm, and proportional to for the oxygen pressure range 10⁰–10^?3 atm. These data are consistent with the presence of very small amounts of acceptor impurities in SrTiO₃.     

Transition metalcarbon bonds: LV. Cyclometallation and other reactions of PBut2Bui and PPh2Bui with platinum(II) and palladium(II)

The new phosphine, PBu^t₂Buⁱ (L), was prepared from Bu^t₂PCl and LiBuⁱ. PPh₂Buⁱ (L′) was prepared from Ph₂PCl and LiBuⁱ. Treatment of [PtCl₂(NCBu^t)₂] with L′ gives [PtCl₂L′₂] which does not cyclometallate even on prolonged boiling in 2-methoxyethanol. In contrast, [PtCl₂(NCBu^t)₂] reacts with PBu^t₂Buⁱ in boiling 2-methoxyethanol to give the cyclometallated complex [$\text{Pt}{}_2\text{Cl}{}_2\text{(PBu}{}^{\mathrm{t}}{}_2\text{CH}{}_2\text{-CHMeCH}$₂)₂] (II, X = Cl). The corresponding bromide, iodide and acetylacetonate were prepared. With PPh₃ II (X = Cl) gives [$\text{PtCl(PBu}{}^{\mathrm{t}}{}_2\text{CH}{}_2\text{CHMeCH}$₂)(PPh₃)] which with NaBH₄ gives [$\text{PtH(PBu}{}^{\mathrm{t}}{}_2\text{CH}{}_2\text{CHMeC}$H₂)(PPh₃)]. Na₂PdCl₄ with L (2 mol equivalents) gave trans-[PdCl₂L₂], which was converted into trans-[Pd(NCS)₂-L₂] by metathesis with KSCN. Treatment of Na₂PdCl₄ with L (1 mol equivalent) gave [Pd₂Cl₄L₂], which on heating in 2-methoxyethanol gave [$\text{Pd}{}_2\text{Cl}{}_2\text{(PBu}{}^{\mathrm{t}}{}_2\text{CH}{}_2\text{-CHMeCH}$₂)₂], as a mixture of syn- and anti-isomers. The complexes trans-[PdCl₂-L′₂] and [Pd₂Cl₄L′₂] were also prepared. ¹H- and ³¹P NMR data are given.     

Electrical conductivity in calcium titanate

The electrical conductivity of polycrystalline CaTiO₃ was measured over the temperature range 800–1100°C while in thermodynamic equilibrium with oxygen partial pressures from 10^?22 to 10⁰ atm. The data were found to be proportional to the $\text{?}\text{1}\text{6}\text{th}$ power of the oxygen partial pressure for the oxygen pressure range 10^?16 – 10^?22 atm, proportional to for the oxygen pressure range 10^?8 – 10^?15 atm, and proportional to for the oxygen pressure range greater than 10^?4 atm. The region of linearity where the electrical conductivity varies as $\text{?}\text{1}\text{4}\text{th}$ power of P_O2 increased as the temperature was decreased. The observed data are consistent with the presence of small amounts of acceptor impurities in CaTiO₃. The band-gap energy (extrapolated to zero temperature) was estimated to be 3.46 eV.     

Thermodynamic properties of two metal-rich tantalum sulfides: Ta2S and Ta6S

The incongruent vaporization reactions of Ta₂S and Ta₆S have been investigated by mass-loss effusion in the temperature range 1576 to 1902 K. By extrapolation of P_S(obs) to equilibrium the enthalpies of the reactions $\text{3}\text{2}\text{Ta}{}_2\text{S(s)}\text{=}\text{1}\text{2}\text{Ta}{}_6\text{S(s) + S(g)}$ and Ta₆S = 6 Ta(s) + S(g) were found to be $\text{ΔH}{}^0{}_{298}\text{R}\text{= 53.0(0.3) · 10}{}^3\text{K}$ and $\text{ΔH}{}^0{}_{298}\text{R}\text{= 58.1(0.4) · 10}{}^3\text{K}$, respectively. Comparison between the above values, determined by a 2nd law treatment, and 3rd law values was used to derive fef (“free energy function”) values for Ta and S in the compounds. These postulated fef's, which apply only to the elements as present in the compounds measured, are compared to tabulated quantities for the pure solid elements to provide a criterion for 2nd and 3rd law evaluation.     

Polymerization in liquid crystals—IV: The polymerization of cholesteryl-vinyl-succinate

The solid-, cholesteric- and liquid-state polymerizations of cholesteryl-vinyl-succinate (CVS) are studied. Only one of the three polymorphic modifications of CVS oligomerizes in the solid state into oligomers of degree $\text{P}\text{= 2}\text{to}\text{6}$ in a homogeneous topochemical reaction. The rate of polymerization in the cholesteric state is lower than that in the liquid state at the same temperature. Kinetic constants were measured at 85° using benzoyl peroxide as initiator and the Banfield radical, giving E_overall = 15.4, 36.4 kcal/mole^?1; $\text{f = 0.52, 0.19; k}{}_{\mathrm{p}}\text{/k}{}_{\mathrm{t}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 0.0167, 0.0192}$, (1/mole sec)^{$\text{1}\text{2}$}, ($\text{E}{}_{\mathrm{p}}\text{?}\text{1}\text{2}\text{E}{}_{\mathrm{t}}\text{) = 0.40, 21.4}$ kcal mole^?1. The values refer to the liquid- and the cholesteric-state reactions, respectively. The average degree of polymerization is low in both cases ($\text{P}\text{= 20}\text{and}\text{22}$). It was concluded that the molecular weights are controlled by chain transfer and that the initiation reaction is mostly dependent on the phase where the reaction takes place.     

PVC chlorination using fluorine as initiator

The chlorination of PVC has been studied in a fluidized bed reactor, initiating the reaction with elementary fluorine. The reaction has been carried out at temperatures between 20° and 60° for various concentrations of chlorine and fluorine. The rate of reaction is given by the equation:

(1)$\text{x=}\text{k[}\text{Cl}{}_2\text{]}{}^{\mathrm{0·5}}\text{[}\text{F}{}_2\text{]t}\text{1+k[}\text{Cl}{}_2\text{]}{}^{\mathrm{0·5}}\text{[}\text{F}{}_2\text{]t}$

, temperature is given by

$\text{log}\text{k=}\text{3500}\text{4·57}\text{1}\text{T}\text{+0·707}$

.Equation (1) is satisfied also by data obtained from a small scale plant reactor. A reaction mechanism is proposed.     

Evaluation of the type of polymer property average

A method for evaluation of the type of average, which is experimentally obtained for a given property of polydisperse polymer, is described. A multivariable power function

where P is the polymer property, $\text{M}{}_{\mathrm{x}}$ is the x-average molecular weight, q is the polydispersity degree, A_p, a and a_px are constants, and the a_px = 0 criterion (a_px being the polydispersity exponent) is used for this purpose.     

Intramolecular metalation of PBut2Ph and PBut3 in palladium acetate complexes

Reaction of [PdCl₂(PBu^t₂Ph)]₂ with silver acetate gives the internally metalated complex [P$\text{dCH}{}_2\text{CMe}{}_2\text{P}$Bu^tPh]₂(μ-Cl)₂. This reacts with TlC₅H₅ and LiC₅Me₅ with chloride-bridge cleavage to yield C₅R₅P$\text{dCH}{}_2$PBu^tPh (R = H, Me). The complex [P$\text{dCH}{}_2\text{CMe}{}_2\text{P}$Bu^t₂]₂(μ-Cl)₂,prepared from [PdCl₂(PBu^t₃)]₂ and CH₃COOAg, is analogously converted into C₅R₅$\text{PdCH}{}_2\text{CMe}{}_2\text{P}$Bu^t₂. The chloride complex C₅H₅Pd(PBu^t₅Ph)CI does not eliminate HCl to form C₅H₅P$\text{dCH}{}_2\text{CMe}{}_2\text{P}$Bu^tPh.     

Tracer diffusion coefficient of oxide ions in LaCoO3 single crystal

The tracer diffusion coefficient, $\text{D1}{}_{\mathrm{<mtext>O</mtext>}}$, of oxide ions in LaCoO₃ single crystal was determined over the temperature range of 700–1000°C by a gas-solid isotopic exchange technique using ¹⁸O tracer. For the determination, two methods, the gas phase analysis and the depth profile measurement, were employed. Under an oxygen pressure of 34 Torr, the temperature dependence of $\text{D1}{}_{\mathrm{<mtext>O</mtext>}}$ in LaCoO₃ was expressed by

$\text{D1}{}_{\mathrm{<mtext>O</mtext>}}\text{(}\text{cm}{}^2\text{·}\text{sec}{}^{\mathrm{?1}}\text{) = 3.63 × 10}{}^4\text{exp}\text{?}\text{(74 ± 5)}\text{kcal}\text{·}\text{mole}{}^{\mathrm{?1}}\text{RT}$

$\text{D1}{}_{\mathrm{<mtext>O</mtext>}}$ at 950°C was found to be proportional to P^?0.35_O2. The diffusion of oxide ions occurs through a vacancy mechanism. The activation energy for the migration of oxide ion vacancies was estimated as 18 kcal · mole^?1.