Acta Crystallographica Section B

Structural Science

Volume 56, Part 6 (December 2000)

research papers

Acta Cryst. (2000). B56, 1029-1034 [ doi:10.1107/S0108768100010697 ]

Structural characterization of protonated benzeneseleninic acid, the dihydroxyselenonium ion

H. O. Sørensen, N. Stuhr-Hansen, L. Henriksen and S. Larsen

Abstract: The structure of the dihydroxyphenylselenonium ion (C $_{6}$ H $_{7}$ O $_{2}$ Se $^{+}$ ) has been determined in its benzenesulfonate (C $_{6}$ H $_{5}$ O $_{3}$ Se $^{-}$ ) and p-toluenesulfonate (C $_{7}$ H $_{7}$ O $_{3}$ S $^{-}$ ) salts. Whereas the former salt is disordered, the latter less dense salt is well defined. This difference in crystallization behaviour is attributed to a C-HO hydrogen bond involving the methyl group of the p-toluenesulfonate ion. The two salts display very similar hydrogen-bond arrangements and differ only with respect to the stacking of the phenyl groups. The dihydroxyselenonium ion is a strong acid with a pK value of -0.9 determined from the variation of the ⁷⁷Se chemical shift. A comparison with the two deprotonated species reveals a systematic increase in the Se-O bond lengths and the pyramidal configuration around Se with the number of protons attached.

Keywords: Protonation; Hydrogen bonding; Acid-base properties.