The molecular structure and the conformational composition of fumaryl fluoride were determined by low‐temperature vibrational spectroscopy and single‐crystal X‐ray structure analysis. Three planar rotational isomers, trans‐trans‐, cis‐cis‐ and cis‐trans‐fumaryl fluoride were identified. C4H2F2O2 crystallizes in the monoclinic space group P21/c with four formula units per unit cell. Besides, Lewis acid‐base adducts between fumaryl fluoride and arsenic pentafluoride were synthesized. These adducts, which contain O–As bonding interactions, were found to crystallize as the monoadducts trans‐cis‐C4H2F2O2·AsF5 and cis‐trans‐C4H2F2O2·AsF5. Moreover, the diadduct trans‐trans‐C4H2F2O2·2 AsF5 was determined by X‐ray crystallography. The experimental data are discussed together with quantum chemical calculations of trans‐trans‐, cis‐cis‐, and cis‐trans‐fumaryl fluoride.

Me(4)PF was investigated in the solid state, in the gas phase, and in solutions. Vibrational spectra of the solid and a single-crystal structure show an ionic tetramethylphosphonium fluoride. The compound crystallizes in the space group Pbca with a = 1016.0(1), b = 1018.0(1), c = 1205.8(4) pm, and Z = 8. The fluoride ion is nearly trigonal planar surrounded by three Me(4)P+ cations forming six H...F contacts between 218 and 240 pm. The compound is stable below 120 degrees C and sublimes in a vacuum. It possesses a phosphorane structure in the gas phase that was studied by electron diffraction and vibrational spectra, and additionally by theoretical calculations. The Me(4)PF molecule has a trigonal bipyramidal structure with one methyl group and the fluorine atom in axial positions and bond lengths of d(PC(eq)) = 182.6(4) pm, d(PC(ax)) = 188.4(8) pm, and d(PF) = 175.3(6) pm. The compound is remarkably soluble in acetonitrile, water, and alcohols, and slightly soluble in benzene, dimethyl ether, and diethyl ether. The solutions were studied by (1)H, (13)C, (19)F, and (31)P NMR spectroscopy. The hygroscopic Me(4)PF forms a tetrahydrate which crystallizes in the space group I4(1)/a with a = 1106.1(1) pm, c = 816.3(1) pm, and Z = 4. The fluoride ion in Me(4)PF.4 H(2)O is surrounded by four water molecules. These units form a three-dimensional network in which the Me(4)P+ cations are embedded without any contacts.

Calcium tricyanomethanide reacts with hydrogen fluoride under formation of tricyanomethane and Ca(HF2)2. Tricyanomethane is stable below -40 °C and was characterized by IR, Raman, and NMR spectroscopy. The vibrational spectra were compared to the quantum-chemical frequencies at the PBE1PBE/6-311G(3df,3dp) level of theory and confirm the predicted C(3v) symmetry of the molecule with regular C-H (109.8 pm), C-C (146.7 pm), and C≡N (114.7 pm) bonds.

Structures, relative energies, vibrational spectra, and ESR parameters of the 17emolecule V(CO) 6 in O h , D 3d , D 4h , and D 2h symmetry have been computed with density functional and high-level ab initio methods. At all theoretical levels applied, the same energetic order is obtained, D 3d < D 2h < D 4h < O h , with the D 2h structure as a transition state connecting equivalent D 3d species. At the RCCSD(T)/AE2 level using UBP86/ AE2 geometries, the energies of the D 2h , D 4h and O h species relative to that of D 3d minimum are predicted to be 210, 535, and 731 cm -1 , respectively. According to molecular dynamics simulations on the UBP86/AE1 potential energy surface, the D 3d minimum is preserved at very low temperatures (around 16 K), whereas at 300 K the molecule is highly fluxional with an averaged structure indistinguishable from that of [V(CO) 6 ]with its O h symmetric ground state. Nearly complete IR and Raman spectra of V(CO) 6 and V( 13 CO) 6 have been recorded at 300 K for the first time in the gas phase, in solution, and at cryogenic temperatures in Ne and Ar matrices. The spectra show a pronounced temperature dependence, especially for the Jahn-Teller active modes, E g and T 2g . The observed infrared matrix spectra generally agree well with the calculated spectrum (BP86/AE2 level) for the D 3d structure and much less with that of the D 4h isomer. The A 1g modes in the Raman spectra are reasonably well reproduced computationally in the harmonic approximation, whereas this approximation breaks down for the E g and T 2g bands, as expected. Further evidence for the D 3d symmetry of V(CO) 6 is obtained from a reanalysis of the experimental ESR spectrum that is reported in the literature. The observed ordering of the hyperfine coupling constants A | and A ⊥ is reproduced theoretically only when distortion to D 3d symmetry is assumed. In addition, the bonding properties of V(CO) 6 are compared to those of [V(CO) 6 ]and Cr(CO) 6 .