THE MASS SPECTRA AND THE STEREOCHEMISTRY OF N,N'-BIS-(SALICYLIDENE)-1,1-(DIMETHYL)-ETHYLENEDIAMINO-OXOVANADIUM(IV)

Abstract

The oxovanadium(IV) complex of the ligand, N,N'-bis-(salicylidene)-1,1-(dimethyl)ethylenediamine, has been prepared. It has a magnetic moment of 1.76 B.M., which is almost invariant over a range of temperature. The electron paramagnetic resonance spectrum of the powder has been measured at 296° and 80°K, while that of the solution was measured at 296°K (g_o ≈ 1.97 and A₀ ≈ 90 × 10^?4 cm^?1). The magnetic moment of the complex agrees with that calculated from the paramagnetic resonance g values taken at 80°K. Furthermore, the complex has been characterized by mass spectra, infra-red, ultra-violet and visible spectra, conductivity, osmometry and polarimetry.

All evidence suggests that the complex is a tetragonal-pyramid.     

Interaction potential for He/H2 including the region of the van der waals minimum

The energy of He/H₂ in its ground state is calculated in an ab-initio way using the IEPA PNO method for three different H-H distances, three different angles and for distances between He and the midpoint of H₂ ranging from 3 to 20a₀.A van der Waals minimum of ≈21°K is found for the linear arrangement and a saddle point of ≈14°K for the C_2v geometry. The computed hypersurface is compared with experiment and with the R^?6 term known from perturbation theory. The anisotropy of the potential is much larger than what is predicted asymptotically.     

Fluorescent states of exciplex and charge-transfer complexes: experimental evidence for an identical fluorescent state

The exciplex (above ≈ 170°K) and the charge-transfer (CT) complex (below ≈ 130°K) fluorescences were observed in a nonpolar solution of 9,10-dicyanoanthracene and 2-methylnaphthalene. The fluorescence maxima, lifetimes and quantum yields of the exciplex and the CT complex show continuous changes from room temperature to 77°K suggesting an identical fluorescent state of the exciplex and CT complex.     

Luminescence and nonradiative relaxation of Pb2+, Sn2+, Sb3+, and Bi3+ in oxide glasses

Absorption and fluorescence spectra of Sn²⁺ and Sb³⁺ in borax, phosphate, and germanate glasses were measured in the temperature range 87–295°K. Fluorescence decay times of these ions in borax glass at 87°K was a single exponent with τ ≈ 6–11 μsec. At 293°K, two decay times were resolved in the range of 50–2000 nsec. The nonexponential behavior is interpreted by the repopulation of the ³P₁ level from the ³P₀ level. The temperature dependence of fluorescence and the low values of quantum efficiencies of fluorescence are explained by means of the configurational coordinate diagram model.     

Thermodynamics of the lanthanum-hydrogen system at 917°K

The binary system lanthanum-hydrogen has been studied at pressures up to 1 atm at 917°K by a calorimetric-equilibrium method. From the calorimetric measurements we found the enthalpy of formation of LaH₂ at 917°K to be ?45.7 kcal mole^?1 with an estimated uncertainty at ±0.3 kcal mole^?1. This result is about 4 kcal mole^?1 less negative than the values derived indirectly from plateau pressure equilibrium measurements by Mulford and Halley and by Korst and Warf. A comparison between the calorimetric and equilibrium measurements at 917°K provides information on the partial entropy of hydrogen in lanthanum and in the dihydride LaH_2±δ. The excess entropy of hydrogen in lanthanum is about 6 cal K^?1 mole^?1 at 917°K: this value is essentially fully accounted for by the estimated vibrational entropy contribution of the hydrogen atoms. In LaH_2±δ the partial entropy of hydrogen changes from small negative values at X ≈ 1.95 to positive values for X > 2. This entropy change is explained by an assumed intrinsic disorder of hydrogen in LaH₂ of about 0.02.     

Thermal decomposition kinetics of bisthiourea cadmuim(II) tetrathiocyanato diammine chromate(III)

Cadmium thiourea reinickate undergoes two-stage thermal decomposition on heating. The DTG peak temperatures are 291 and 469°C and the corresponding DTA temperatures are 255 and 490°C. The kinetic parameters for the first stage decomposition are E* ≈ 120kJ mole^?1; Z ≈ 1.2 × 10⁸ cm³ mole^?1 sec^?1 and ΔS* ≈ ?95 J mole^?1 K^?1. For the second stage, E* ≈ 133 kJ mole^?1; Z ≈ 6.1 × 10⁵ cm^?1 mole^?1 sec^?1 and ΔS* ≈ ?142 J mole^?1 K^?1.     

Sorption of Strontium Ions on Potassium-Titanate Nanoparticles of Various Morphology Obtained under Hydrothermal Conditions

The results of the study of the interaction of an aqueous solution of strontium nitrate with potas-sium-titanate nanoparticles of different morphology obtained by the hydrothermal method are reported. Comparative analysis showed the advantage of nanotubes as sorbents over nanolayers and nanowires. As can be seen from the experiment conducted with nanotubes containing aluminum, an amount of strontium sorbed from the solution rises with increasing temperature: at 50°C the absorption by the tubular matrix was ≈ 0.76 × 10^?3 mol g^?1, and at 80°C that was ≈ 2.02 × 10^?3 mol g^?1. Nanotube samples doped with magnesium had the best sorption characteristics: After 5 h of keeping in a solution at 80°С, the content of strontium in them was ≈3.65 × 10^?3 mol g^?1. The results show the promise of using potassium titanate nanoparticles to extract strontium from aqueous solutions.

     

Structural changes in low temperature water

Previous experiments on the neutron structure factor S(q) for heavy water near 11.2°C have been extended so that the next term in the Taylor expansion may be examined. An improved result for the isochoric temperature derivative of S(q) at 11.2°C is obtained. These data and those for the (ΔT)² coefficient in the Taylor expansion may be explained on a simple basis: namely that OH and HH distances between neighbouring molecules vary as (T  t₀)⁻ⁿ where (T  T₀) ≈ 1200n for T ≈ 300 K.     

EPR evidence of possible metastable regions in Mn2+ doped ferroelectric NaNO2

Of the various EPR spectra observed in the ferroelectric phase of NaNO₂, a spectrum designated as spectrum II is observed to have some peculiar properties like dependence of its intensity on growth conditions of the crystal, its disappearance below ≈60°C after heat treatment of the crystal, its reappearance by heating above ≈60°C and also by application of an external dc electric field at ≈30°C. These observations suggest the possible existence, around Mn²⁺-vacancy complex in the ferroelectric phase of NaNO₂, of a metastable structure intermediate to the paraelectric and ferroelectric phase structures.     

Crystal structure and antiferromagnetism of EuSb2

EuSb₂ crystallizes in the monoclinic CaSb₂ type of structure, space group $\text{P2}{}_1\text{m}$, with a = 4.768(2), b = 4.299(2), c = 8.9703(3) Å, β = 103.01(3)°. The structural distortions of the ZrSi₂ type provide the Sb chains required for a Mooser-Pearson phase. EuSb₂ is antiferromagnetic below T_N = 26.2°K. From high-field magnetization measurements a weak anisotropy (H_anis. ≈ 6 kOe at 1.5°K) is deduced. The spins are aligned perpendicular to the (001) planes. Susceptibility measurements between 30 and 1100°K gave no indication of a Eu²⁺ → Eu³⁺ transition.     

Electron-impact excitation of the 3s'3P° and 2s2p53P° autoionizing states of atomic oxygen

The excitation of the 3s''³P° and 2s2p⁵³P° autoionizing states of OI by electron impact on atomic oxygen has been studied. Absolute cross section values from threshold to 300 eV have been obtained for the 3s''³P° state. Limited emission cross section data for the 2s2p⁵³P° and other partially radiating autoionizing states were also obtained at an impact energy of 100 eV. These results suggest that the excitation of the OI autoionizing states account for ≈33% of the total O⁺ total ionization cross section at 40 eV under optically thin conditions and that the cross section ratio, σ(⁴S)/σ(²D + ²P), has been underestimated substantially in earlier theoretical work. Electron-impact excitation of the 3s''³P° and 2s2p⁵³P° states in an optically thick medium enhances the effective total ionization cross section for atomic oxygen by ≈15% and increases the specific O⁺(⁴S) production rate by ≈25% with important implications for O⁺ ion chemistry in gaseous discharges and planetary ionospheres.     

Li6+2x[B10Se18]Sex (x ≈ 2), ein ionenleitendes Doppelsalz

Li_6+2x[B₁₀Se₁₈]Se_x (x ≈ 2), an Ion‐conducting Double Salt Li_6+2x[B₁₀Se₁₈]Se_x (x ≈ 2) was prepared in a solid state reaction from lithium selenide, amorphous boron and selenium in evacuated carbon coated silica tubes at a temperature of 800 °C. Subsequent cooling from 600 °C to 300 °C gave amber colored crystals with the following lattice parameters: space group I2/a (at 173 K); a = 17.411(1) Å, b = 21.900(1) Å, c = 17.820(1) Å, β = 101.6(1)°. The crystal structure contains a well‐defined polymeric selenoborate network of composition ([B₁₀Se₁₆Se_4/2]^6?)_n consisting of a system of edge‐sharing [B₁₀Se₁₆Se_4/2] adamantanoid macro‐tetrahedra forming large channels in which a strongly disorderd system of partial occupied Li⁺ cations and additional disordered Se^2? anions is observed. The crystal structure of the novel selenoborate is isotypic to Li_6+2x[B₁₀S₁₈]S_x (x ≈ 2) [1]. X‐ray and ⁷Li magic‐angle spinning NMR data suggest that the site occupancies of the three crystallographically distinct lithium ions exhibit a significant temperature dependence. The lithium ion mobility has been characterized by detailed temperature dependent NMR lineshape and spin‐lattice relaxation measurements.     

Structural Studies of New Sulfito Mercurates(II) with General Formula xM[XHgSO3]middot;yHgX2·zMX·nH2O (M = NH4, K; X = Cl,Br)

Several solid phases with the general formula xM[XHgSO₃]·yHgX₂·zMX·nH₂O were obtained from aqueous solutions during phase formation studies in the systems M₂SO₃/HgX₂ (M = NH₄, K; X = Cl, Br). All phases were structurally characterized on the basis of single crystal X‐ray diffraction data and adopt new structure types. Compounds with x, y, z = 1 and n = 0 are isostructural (structure type I ) and crystallise with two formula units in space group P2₁/m and lattice parameters of a ≈ 9.7, b ≈ 6.2, c ≈ 10.4Å, β ≈ 111°. Compounds with x, y = 1 and z, n = 0 (structure type II ) crystallize in space group Cmc2₁ with four formula units and lattice parameters of a ≈ 5.9, b ≈ 22.0, c ≈ 6.9Å. The structures with x = 2, y, z = 1 and n = 0 are likewise isostructural (stucture type III ) and consist of four formula units in space group Pnma with lattice parameters of a ≈ 22.2, b ≈ 6.1, c ≈ 12.4Å. K[HgSO₃Cl]·KCl·H₂O is the only representative where x = 1, y = 0, z = 1 and n = 1 (structure type IV ). It is triclinic (space group ) with four formula units and lattice parameters of a = 6.1571(8), b = 7.1342(9), c = 10.6491(14) Å, α = 76.889(2), β = 88.364(2), γ = 69.758(2)°. Characteristic for all structures types is the segregation of the M⁺ cations and the anions and/or HgX₂ molecules into layers. The [XHgSO₃]⁻ anions are present in all structures and have m symmetry, except for K[HgSO₃Cl]·KCl·H₂O with 1 symmetry (but very close to m symmetry). The different [XHgSO₃] units exhibit very similar Hg‐S distances (average 2.372Å) and are more or less bent with ∠(X‐Hg‐S) angles ranging from 159.7 to 173.7°. The molecular HgX₂ entities present in structure types I ‐ III deviate only slightly from linearity with ∠(X‐Hg‐X) angles ranging from 174 to 179°. The structures are stabilised by interaction of the K⁺ or NH₄⁺ cations that are located between the anionic layers or in the vacancies of the framework, by K‐O contacts or, in case of ammonium compounds, by medium to weak hydrogen bonding interactions of the type N‐H···O.     

Origin of the anomalous phosphorescence of aromatic ketones. Xanthone in 3-methylpentane

Based on an emission study of xanthone at ≈2 and 77°K it is concluded that the “dual” phosphorescence at 77°K in a 3-methylpentane glass matrix is due to emission from two n,$\text{π}{}^1$ triplet states of xanthone. The two triplet states and their respective ground states are distinguished by their different molecular geometries.     

The ionic polymerizations of methyl glyoxylate

Methyl glyoxylate has been polymerized in CH₂Cl₂ solution either cationically or anionically to give the corresponding polyacetal. Thermodynamic and kinetic results of the polymerizations initiated by CF₃SO₃H, BF₃OEt₂, and NEt₃ are reported here. Monomer conversion was followed by UV and active centers concentrations were determined through phosphorus end-capping. A ceiling temperature of 26°C was observed for M_eq=l mol.H (T_c = 109°C for bulk) with ΔH°=−29.5 kJ.mo⁻¹ and ΔS°=−99 J.mo⁻¹.K⁻¹. Both initiations were found instantaneous and quantitative, and no termination was observable within the time scale of the reaction (second to hour). Cationic propagation appears to take place essentially on free ions (k_p+ ≈ 60 l.moH.s⁻¹ at −20°C) in equilibrium with a larger amount (K_d ≈ 6.7.10⁻⁶ mol.⁻¹) of much less reactive ion-pairs (k_p± ≈ 0.16 ± 0.03 1.mo⁻¹.s⁻¹). A stopped-flow device was used to follow the much more rapid anionic polymerization (k_p,app ≈ 8 ± 2.10³ 1.mo⁻¹.s⁻¹ at −20°C).     

Der chemische Transport von Platin mit Chlor. Experimentell bearbeitet mit Marita Trenkel

The Chemical Transport of Platinum with Chlorine Experiments show that the chemical transport of platinum by means of chlorine within a temperature gradient at temperatures below ≈ 1000°K goes into the hot temperature region, but at higher temperatures in the reverse direction. From the thermodynamic discussion it can be seen, that the platinum content of the gas phase at low temperatures is governed by the exothermic formation of Pt₆Cl_12,g, and at higher temperatures by the endothermic formation of PtCl_3,g and PtCl_2,g. The platinum content of the gas phase passes a minimum at ≈ 1000°K, if P(Cl₂) = 3.5 atm. This result is in agreement with the observed inversion of the transport direction.     

Pyrolytic production of Se (3P) from carbon diselenide. II. Rate of CSe2 decay

Pyrolytic decay of carbon diselenide was monitored by ultraviolet absorption spectroscopy in reflected shock waves in the temperature range of 1600–2600°K. The temperature dependence of the absorption coefficient of CSe₂ at 2308 Å was determined and was used to provide kinetic information along with a deconvolution procedure which accounted for and removed systematic distortions of the fast time-resolved absorbance profile. For temperatures of 1600–2600°K and argon densities of 1.5–7.0 × 10^?5 mol/cm³ dilute (1.0–9.0 × 10^?9 mol/cm³) CSe₂ pyrolyzed with measured first-order decay rates in the range of log₁₀ k₁ (sec^?1) = 3.0?5.7; at midrange (2100°K and 4.3 × 10^?5 mol/cm³ in Ar) k₁ ≈ 3 × 10⁴ sec^?1. The decay probably occurs via a unimolecular low-pressure process, first order in both CSe₂ and Ar, for which k₂ ± 10⁹ cm³/mol·sec at 2100°K. The deconvoluted data yield Arrhenius activation energies of 53.2 kcal/mol under second-order treatment, but the activation energy is less reliable than the general magnitude of the rate constant. A comparison of CSe₂ with other molecules which are isoelectronic in their valence shells (CO₂, CS₂, OCS, and N₂O) is made.     

Interpretation of the optical dephasing time and lineshape function in the S0 → T1 exciton transitions of 1,4-dibromonaphthalene

The lineshape function for the S₀ → T₁ absorption in 1,4-dibromonaphthalene (DBN) is analyzed in terms of exchange theory. It is shown that the dominant optical dephasing mechanism for the electric dipole transition to the k = 0 state in the band results from the absorption and emission of a low energy optic phonon. This process dephases the optical absorption because of frequency differences of the phonon in the ground and excited state. In addition, it is shown how to extract the energy of the phonon responsible for dephasing, the phonon absorption rate, and the lifetime in the phonon promoted state from the data. The analysis of the data for DBN shows that very little dephasing of the optical transition occurs before ≈ 15 K but from 15 K to ≈ 40 K the singlet-triplet transitions to site I (20192 cm^?1) and site II (20245 cm^?1) are dephased by absorption and emission of an ≈ 38 cm^?1 and 45 cm^?1 phonon respectively. The phonon absorption rates by the k = 0 state in the exciton band are similar for both sites being 5 × 10⁶ s^?1 and 3 × 10⁵ s^?1 at 4 K and 7 × 10¹¹ s^?1 and 4 × 10¹¹ s^?1 at 30 K for site I and II respectively. Finally, the lifetimes in the phonon promoted state for sites I and II are 0.23 and 0.28 ps over the range 15–40 K.     

Completely hydrogen-bonded interpenetrating networks in low-temperature liquid water: Their geometrical possibility and stability

A random tetrahedral network built around linked eight-member rings is denser than an open one described earlier, and has neighbors near in space that are remoter in bond topology. The properties of amorphous ice and liquid water below 0°C correlate with a glass transition in an open network at ≈ 140 K, while linked rings, which increase enthalpy and density, only appear above about ?40°C.     

Measurement of the hall mobility of injected electrons in liquid tetramethylsilane between 22 and 164 °C

We have measured the Hall mobility of excess electrons in liquid tetramethylsilane (TMS) between room temperature and 164°C. The novel result is that, within an experimental error of ≈10%, the Hall mobility μ_h is equal to the drift mobility μ_d; μ_h = 101 ± 7 cm²/V s at 22°C and 53 ± 5 cm²/Vs at 164°C. This indicates that, contrary to what is observed in neopentane, traps are unimportant and, in particular, are not responsible for the mobility drop observed close to the critical point in TMS.