CONTRIBUTION TO THE CHEMISTRY OF BIS(TRIFLUOROMETHYL)AMINES - PREPARATION OF BIS(TRIFLUOROMETHYL)AMMONIUM HEXAFLUOROMETALATES (CF3)2NH2+MF6- (M = AS, SB) - CRYSTAL-STRUCTURE OF (CF3)2NH2+ASF6- AND GAS-PHASE STRUCTURES OF (CF3)2NX (X = H, CL)

(CF3)2NH2+MF6- (M = As, Sb) were prepared by protonation of (CF3)2NH in superacid media and characterized by infrared, Raman, and NMR spectroscopy. (CF3)2NH2+AsF6- crystallizes in the orthorhombic space group Pmcn, with a = 7.569(5) angstrom, b = 9.031(6) angstrom, c = 13.011(9) angstrom, and Z = 4. In the crystal, cation and anion reside on the mirror planes at x = 0.25 and x = 0.75 of the unit cell, with C-N bond lengths of 1.484(9) and 1.497(9) angstrom, respectively, and an N-H distance of 0.99(7) angstrom. Cation and anion have three short H...F contacts of 2.03(6), 2.26(7), and 2.31(7) angstrom with two anions. The geometric structures of (CF3)2NX with X = H and Cl have been determined in the gas phase by electron diffraction and by ab initio calculations (HF/3-21G*). The N-C bonds in these two compounds (1.416(5) angstrom in (CF3)2NH and 1.455(4) angstrom in (CF3)2NCl) are considerably shorter than those in the (CF3)2NH2+cation (mean value 1.490(9) angstrom). These variations can be rationalized by electrostatic effects.