An investigation to elucidate the factors dictating the crystal structure of seven ammonium carboxylate molecular salts

Abstract

The crystal structures of seven ammonium carboxylate salts are reported, namely (RS)-1-phenylethan-1-aminium isonicotinate, C8H12N+·C6H4N1O2 −, (I), (RS)-1-phenylethan-1-aminium flurbiprofenate [or 2-(3-fluoro-4-phenylphenyl)propanoate], C8H12N+·C15H12FO2 −, (II), (RS)-1-phenylethan-1-aminium 2-chloro-4-nitrobenzoate, C8H12N+·C7H3ClNO4 −, (III), (RS)-1-phenylethan-1-aminium 4-iodobenzoate, C8H12N+·C7H4IO2 −, (IV), (S)-1-cyclohexylethan-1-aminium 2-chloro-4-nitrobenzoate, C8H18N+·C7H3ClNO4 −, (V), 2-(cyclohex-1-en-1-yl)ethan-1-aminium 4-bromobenzoate, C8H16N+·C7H4BrO2 −, (VI), and (S)-1-cyclohexylethan-1-aminium 4-bromobenzoate, C8H18N+·C7H4BrO2 −, (VII). Salts (II) to (VII) feature three N+—H...O− hydrogen bonds, which form one-dimensional hydrogen-bonded ladders. Salts (II), (III), (IV), (V) and (VII) have a type II ladder system despite the presence of halogen bonding and other intermolecular interactions, whereas (VI) has a type III ladder system. Salt (I) has a unique hydrogen-bonded system of ladders, featuring both N+—H...O− and N+—H...N hydrogen bonds owing to the presence of the pyridine functional group. The presence of an additional hydrogen-bond acceptor on the carboxylate cation disrupts the formation of the ubiquitous type II and III ladder found predominately in ammonium carboxylate salts. Halogen bonding, however, has no influence on their formation.