Benzylammonium hepta­noate–hepta­noic acid (1/1)

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.

Benzyl­ammonium hepta­noate

The title 1:1 stoichiometric salt, C₇H₁₀N⁺·C₇H₁₃O₂⁻, is formed by proton transfer between hepta­noic acid and benzyl­amine. This combination contrasts to the recently published 2:1 acid–amine adduct of cation, anion and neutral acid molecule from the same components [Wood & Clarke (2013). Acta Cryst. E69, o346–o347]. There are N—H...O hydrogen bonds of moderate strength in the structure [the most important graph-set motifs are R²₄(8) and R⁴₄(12)], as well as weak C—H...O inter­actions.