PROTON TUNNELING IN HYDRAZINIUM CATIONS - VIBRATIONAL-SPECTRA OF (N2H5)(2)HGAF6-CENTER-DOT-2H(2)O AND (N2H5)(2)HFEF6-CENTER-DOT-2H(2)O AND CRYSTAL-STRUCTURE OF (N2H5)(2)HFEF6-CENTER-DOT-2H(2)O AT VARIOUS TEMPERATURES

Infrared spectra of (N2H5)(2)HGaF6 . 2H(2)O and of (N2H5)(2)HFeF6 . 2H (2)O indicate weak to moderate N-H ... N hydrogen bonding. Data are in terpreted in terms of a double minimum symmetrical potential web with a high barrier and statistical distribution of hydrogen in the minima on both sides of the barrier, forming an H3N+H2N ... H+NH2NH3+ hydroge n-bonded cluster with simultaneous presence of N2H5+ and N2H62+ ions. The strong Raman NN stretching band, which is characteristic of the ty pe of cation, is split into two bands when cooled to 77 K and merged a gain when warmed to room temperature. This indicates that H-bridged N2 H5+ ions are spectroscopically indistinguishable at room temperature, presumably because of a high rate of phonon-assisted proton tunnelling through the barrier. This process is inhibited at lower temperature, thus making the N2H5+ and N2H62+ ions distinguishable. H2O is only wea kly hydrogen bonded, not protonated and therefore fairly easily releas ed. Octahedral symmetry of GaF63- and of FeF63- ions is demonstrated. Single-crystal x-ray structure determinations on the Fe compound at th ree different temperatures (296, 200 and 90 K) corroborate the spectro scopic results; in particular, the statistical distribution of one II- atom within the cation was revealed No structural phase transition was observed down to 90 K. The compound crystallizes in space group C2/c (No. 15) with a = 1444.28(13) pm, b = 640.09(6) pm, c = 1048.09(9) pm, beta = 118.942(6)degrees and Z = 4 at 90 K. The octahedron around Fe is slightly compressed with Fe-F distances along the pseudo-fourfold a xis at 193.07 pm shorter than those within the plane (193.86 pm on ave rage). The magnetic moment of the Fe(III) complex was determined as 5. 7 mu(B). (C) 1997 by John Wiley & Sons, Ltd.