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
S. Milicev et al., 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, Journal of Raman spectroscopy, 28(5), 1997, pp. 315-321
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.