Benzylammonium heptanoate–heptanoic acid (1/1)

Abstract

The title salt, C7H10N+·C7H13O2−·C7H14O2, is an unusual 2:1 stoichiometric combination of two carboxylic acid molecules and one amine. Although there are crystal structures of a number of 1:1 complexes reported in the literature, 2:1 acid amine complexes are rather uncommon. In this case, a proton is transferred between one acid molecule and the amine to give an acid anion and an ammonium cation whilst the other carboxylic acid remains protonated. The species interact strongly via electrostatic forces and hydrogen bonds. In addition we note that the N atom of the ammonium group makes four close contacts to surrounding O atoms. Three of these are hydrogen bonds with neighbouring acid anions while the fourth does not involve a hydrogen atom but is directed towards the carbonyl O atom of the protonated acid. Each of the acid anion O atoms accepts two hydrogen bonds from adjacent N atoms. There is also evidence of short C—H...O contacts. There is disorder (occupancy ratio 0.51:0.49) in the alkyl chain of one of the carboxylic acid molecules.