Benzylammonium hepta­noate–hepta­noic acid (1/1)

The title salt, C(7)H(10)N(+)·C(7)H(13)O(2) (−)·C(7)H(14)O(2), 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.