A theoretical and experimental study on the Lewis acid-base adducts (P(4)E(3)).(BX(3)) (E = S, Se; X = Br, I) and (P(4)Se(3)).(NbCl(5))

The Lewis acid-base adducts (P(4)E(3)).(BX(3)) (E = S, Se; X = Br, I) and (P(4)Se(3)).(NbCl(5)) have been prepared and characterized by Raman, IR, and solid-state (31)P MAS NMR spectroscopy. Hybrid density functional calculations (B3LYP) have been carried out for both the apical and the basal (P(4)E(3)).(BX(3)) (E = S, Se; X = Br, I) adducts. The thermodynamics of all considered species has been discussed. In accordance with solid-state (31)P MAS NMR and vibrational data, the X-ray powder diffraction structures of (P(4)S(3)).(BBr(3)) [monoclinic, space group P2(1)/m (No. 11), a = 8.8854(1) A, b = 10.6164(2) A, c = 6.3682(1) A, beta = 108.912(1) degrees, V = 568.29(2) A(3), Z = 2] and (P(4)S(3)).(BI(3)) [orthorhombic, space group Pnma (No. 62), a = 12.5039(5) A, b = 11.3388(5) A, c = 8.9298(4) A, V = 1266.09(9) A(3), Z = 4] indicate the formation of an apical P(4)S(3) complex in the reaction of P(4)S(3) with BX(3) (X = Br, I). Basal adducts are formed when P(4)Se(3) is used as the donor species. Vibrational assignment for the normal modes of these adducts has been made on the basis of comparison between theoretically obtained and experimentally observed vibrational data.     

Synthesis and characterization of organogallium-antimony compounds

The simple Lewis acid–base adduct Me₃Ga←Sb(SiMe₃)₃ (1) was prepared by the reaction of Me₃Ga and Sb(SiMe₃)₃. Dehalosilylation reaction between Me₂GaCl and Sb(SiMe₃)₃ in 1:1 mol ratio yields the trimeric [Me₂GaSb(SiMe₃)₂]₃ (2). 1 and 2 were fully characterized by mass and NMR spectroscopy. In addition, the solid state structure of compound 2 was determined by single crystal X-ray diffraction.     

Further studies of the continuous UV emission produced by electron impact on CF4

The intense continuous UV emission which extends from 200 nm to beyond 500 nm produced by electron impact on carbontetrafluoride, CF₄, has been investigated in a crossed electron-beam — gas-beam apparatus as well as in a gas-target apparatus under single collision conditions with special emphasis on the regime of impact energies below 50 eV. Systematic measurements of excitation functions (relative emission cross sections) at various wavelengths between 225 nm and 420 nm revealed the same onset of 23.5±2 eV and the same energy dependence for all excitation functions independent of the selected wavelength indicating that the continuous emission consists of a single fluorescence contribution. Evidence of a second onset around 40 eV, roughly 16 eV above the first onset which is an energy close to the ionization energy of atomic fluorine (17.4 eV), was found — more or less prominent — in all excitation functions. The presence of the second onset lends strong support to the assignment of the excited (CF ₃ ⁺ )* fragment ion as the emitting source of the emission continuum. We identify the lower onset at 23.5 eV with the electron-impact induced breakup of the parent CF₄ molecule into an excited (CF ₃ ⁺ )* ion and a ground state fluorine atom (neutral channel), whereas the second onset around 40 eV indicates the presence of an ionic fragmentation channel in which an excited (CF ₃ ⁺ )* fragment ion is produced together with a fluorine ion, F⁺. Wavelength scans taken at impact energies above and below the second onset revealed no significant difference in the envelope of the observed emission continuum which further supports the notion that the emission continuum consists of a single fluorescence contribution.     

Enthalpies of transfer from water to methanol of cations complexed with 18-crown-6

Enthalpies of transfer from water to methanol have been obtained via a thermochemical cycle for the [M⁺18C6] complexes where M⁺  Na⁺, K⁺, Rb⁺, Cs⁺, and Ag⁺. Variation of the transfer enthalpy with M⁺ is small.