Bernard Weinstock

Electron-Diffraction Investigation of the Hexafluorides of Tungsten, Osmium, Iridium, Uranium, Neptunium, and Plutonium

An electron‐diffraction investigation has been made by the sector–microphotometer method on WF_6, OsF_6, IrF_6, UF_6, NpF_6, and PuF_6. The photographs of all these compounds reflect a phase shift which if not accounted for leads to asymmetric structures for the molecules. It sets in at smaller values of s=4πλ^(−1) sin (θ/2) the heavier the molecule and the greater the electron wavelength. There is good evidence for the symmetrical octahedral structure of all the compounds. The metal–fluorine distances were found to be 1.833 A (W–F), 1.831 A (Os–F), 1.830 A(Ir–F), 1.996 A (U–F), 1.981 A (Np–F), and 1.971 A (Pu–F), with estimated limits of error of ±0.008 A except for ±0.010 A for Pu–F.

PARAMAGNETIC RESONANCE ABSORPTION IN NEPTUNIUM HEXAFLUORIDE

The paramagnetic resonance absorption of crystalline NpF6 has been studied at 3 cm wavelength and at the boiling point of liquid He. The data were fitted to the spin Hamiltonian, H=βH·g·S+I·A·S. The parameters are isotropic within the errors of the measurements, with g = −0.604 and | A/hc | = 0.1100 cm−1. These results are interpreted in terms of the configuration f1 perturbed by spin‐orbit coupling and an octahedral molecular potential. The relationships of the present results to optical data and measurements of magnetic susceptibility for the same substance are discussed. Hyperfine structure due to F is observed and is anisotropic.

THE PROPERTIES OF PLUTONIUM HEXAFLUORIDE

Abstract PuF6 is formed rapidly at 750°C by the reaction between PuF4 and F2, and high yields are obtained if the PuF6 is quickly condensed. AmF6 is not produced under similar conditions. Techniques for the handling, purification, and storage of PuF6 are described. The molecular structure and crystal structure of PuF6 are the same as those of UF6. The melting-point of PuF6 is 50·75°C. Radiation decomposition of PuF6 into PuF4 and F2 occur at the rate of 1·5% per day for the solid phase. The rate of radiation decomposition is much smaller in the vapour phase, and the system may reach a steady state. Solid PuF6 is slightly paramagnetic. The absorption spectrum of PuF6 vapour show six groups of bands between 5000 and 25,000 A, arising from electronic transitions in the molecule. PuF6 is a strong fluorinating agent, and its reactions with BrF3, UF4, and PuF3 are described. Thermal decomposition of PuF6 is not observed at room temperature, but is found to be very rapid at 280°C. The equilibrium constant for the dissociation of PuF6 into F2 and PuF4 is 1·86 × 103 at 220°C; at 25°C, ΔF = −7·6 kcal mole−1, ΔH° = −8·3 kcal mole−1, and ΔS° = − 2·3 cal mole−1 deg− for this dissociation.

Vibrational Spectra of OsF6 and PtF6

Infrared absorption spectra of gaseous OsF6 and PtF6 from 6–50μ and the Raman spectrum of liquid OsF6 are reported. These are interpreted in terms of the octahedral point group Oh, and the six fundamental frequencies are determined. Their values and symmetry species are for OsF6 733 (a1g), 632 (eg), 720 (f1u), 268 (f1u), 252 (f2g), and 230 (f2u); for PtF6 655 (a1g), 601 (eg), 705 (f1u), 273 (f1u), 242 (f2g), and 211 (f2u). Thermodynamic functions, including electronic contributions, are calculated for the ideal gaseous state of both compounds.A comparison of the details of the vibrational spectra of eleven hexafluorides reveals certain characteristic features for OsF6 and ReF6. Since only these two molecules have appropriately degenerate electronic ground states these differences are interpreted as evidence of a Jahn‐Teller effect.

Vibrational Spectra and Thermodynamic Properties of ClF3 and BrF3

The Raman and infrared spectra of ClF3 and BrF3 have been studied. The spectra of ClF3 give strong support for a planar T‐shaped molecular model. The spectra of BrF3 are less complete but are sufficiently similar to that of ClF3 to confirm a like shape for this molecule. The fundamental vibrational frequencies of ClF3 observed for the vapor are 326(a1), 364(b2), 434(b1), 528(a1), 703(b1), and 752(a1) cm‐1. S0 for ClF3, calculated statistically at the boiling point, 11.75°C, is 66.60 cal mole‐1 deg‐1 compared to the value of 67.04 obtained from a revised calculation of this quantity from available thermal data. For BrF3 only two fundamental frequencies were observed in the vapor, 613(b1) and 674(a1) cm‐1; the others were estimated by a normal coordinate calculation. S0 for BrF3 calculated statistically is 70.86 cal mole‐1 deg‐1 at 43.11°C compared to a value of 71.90 calculated from available thermal data. Tables of the thermodynamic functions of ClF3 and BrF3 from 250 to 1000°K are given.

Raman Spectrum of UF6

Two of the 3 Raman‐active fundamentals of UF6 have been observed at 666.6±0.3 (ν1) and 535±5 cm—1 (ν2) for a gaseous sample. The new value for ν2 is in good agreement with the value 532 cm—1 obtained earlier by Gaunt from infrared combinations. The sample of UF6 was contained in a Pyrex Raman tube and was irradiated for many hours with 4358 A light with no visible deterioration. Gaunts thermodynamic functions remain valid.

Jahn‐Teller Effect in the Vibrational Spectra of Hexafluorides

The Jahn-Teller effect in the vibrational spectra of several inorganic hexafluorides is briefly discussed in relation to Raman fundamentals. (C.J. G.) l6833 A relationship between the mean atomic radii and the ionization potentials of the rare gas atoms, based upon the ionization process, is discussed. Values of the radius of collision complex are given. (C.J.G.)

Search for a Jahn-Teller Effect in IrF6

An investigation of the vibrational spectra of IrF6 has failed to reveal the anomalies found for OsF6 that were attributed to a Jahn‐Teller coupling. This is taken to indicate that the Γ8 ground electronic state of IrF6 has a strong spin character. For the vapor in the NaCl range the observed absorption frequencies (cm—1) and their assignments were: 720 (σ3), 852 (σ2+σ6), 921 (σ2+σ4), 979 (σ1+σ4), 1364 (σ2+σ3), and 1425 (σ1+σ3). A Raman shift of 651 cm—1 ascribed to σ2 was obtained for a solution of IrF6 in n‐C7F16.

Magnetic Susceptibility of Neptunium Hexafluoride in Uranium Hexafluoride

The magnetic susceptibilities of solid solutions of NpF6 in UF6 have been measured by the Faraday method. Measurements have been made on solutions with mole fractions 0.0000, 0.0407, 0.0972, 0.1806, 0.340, 0.646, and 1.000 NpF6 and over the temperature range from the boiling point of liquid He to 336.9°K. The susceptibilities χ of Np+6 so determined have been fitted by equations of the form χ=χ0+gs2Nβ2/4kT=χ0+0.09380 gs2/T at the lower concentrations of NpF6, and by χ=χ0+gs2Nβ2/4kT+A/T2 at the higher concentrations of NpF6. The values of | gs | and χ0 extrapolated to infinite dilution are 0.605 and 165×10−6 cm3 mole−1, respectively, using unrationalized Maxwell equations. The standard deviations of these values are 0.004 and 20×10−6, respectively. There is no observable variation of χ0 with concentration of NpF6 in UF6. | gs | is observed to increase from the value 0.641 for pure NpF6 and to pass through a maximum value 0.694 for the 0.340 mole fraction sample as the concentration of NpF6 is decreased. Th...

Heat Capacity, Enthalpy of Fusion, and Thermodynamic Properties of NpF6 from 7 to 350°K

Measurements of the heat capacity of NpF6 from 7 to 350°K by adiabatic calorimetry are reported. No anomalies were observed in the heat‐capacity curve. The triple point is 327.91 ± 0.02°K, and the enthalpy of fusion is 4188.4 ± 4.0 cal mole−1. Thermodynamic functions are tabulated at selected temperatures. At 298.15°K, CP°, S°, H° − H°0, and (G° − H°0) / T for solid NpF6 are 40.02 ± 0.08 cal °K−1·mole−1, 54.76 ± 0.11 cal °K−1·mole−1, 7436 ± 15 cal mole−1, and 29.82 ± 0.06 cal °K−1·mole−1, respectively. At 340°K, S°, for gaseous NpF6 is 94.09 ± 0.38 cal °K−1·mole−1 from the calorimetric and vapor‐pressure data, if Rln2 is added to the entropy obtained by extrapolation of the observed heat‐capacity curve from 7 to 0°K. This value is in excellent agreement with S° calculated from statistical mechanics and molecular data.