Structural characterization of protonated benzeneseleninic acid, the dihydroxyselenonium ion

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-H.O 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 (77)Se 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.