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Abstract

F-19 solid-state NMR spectra of the alkali metal fluorosulfites
KSO2F, RbSO2F, alpha -CsSO2F, and beta -CsSO2F show that the
fluorosulfite anion is subjected to dynamical disorder at room
temperature, This disorder can be modeled by 120 degrees
rotational jumps with respect to the C-3-Pseudoaxis of the
anion, The exchange frequency of this disorder decreases with
decreasing temperature. The calculated jump frequencies at room
temperature are 5 x 10(5) Hz for KSO2F, 2 x 10(5) Hz for
RbSO2F, 1 x 10(7) Hz for alpha -CsSO2F, and 5 x 10(5) Hz for
beta -CsSO2F, respectively. The crystal structures of alpha-
and beta -CsSO2F were determined for the First time (alpha:
Pnma; Z = 4; a = 790.98(8), b = 666.07(7), c = 798.93(9) pm; T
= 293 K. beta: R3m; Z = 3 a = 659.22(6), c = 800.50(4) pm; T =
293 K), X-ray single-crystal data of KSO2F, RbSO2F, and alpha -
CsSO2F taken at various temperatures were refined using the
disorder model developed from the NMR results. It is shown that
it is impossible to obtain reliable structural parameters of
the SO2F- ion by refinement of X-ray data as long as rotational
disorder persists, The preference of an ordered structure
increases with decreasing temperature, The degree of disorder
remaining in alpha -CsSO2F at 93 K is small, The structural
parameters of the fluorosulfite anion as obtained by a routine
refinement of this phase (S-F, 169.0(2) pm; S-O, 147.8(1) pm)
are the best lower (S-F) and upper (S-O) limits of the "true"
bond lengths determined experimentally. They comply with the
values obtained from quantum chemical calculations.