Crystal structures of seven molecular salts derived from benzylamine and organic acidic components

Abstract

Cocrystallization of the commonly available organic amine, benzylamine, with a series of organic acids gave a total of seven molecular salts with the compositions: (benzylamine): (p-toluenesulfonic acid) (1) [(HL)+ · (tsa−)], (benzylamine): (o-nitrobenzoic acid) (2) [(HL+) · (onba)−], (benzylamine): (3,4-methylenedioxybenzoic acid) (3) [(HL+) · (mdba−)], (benzylamine): (mandelic acid) (4) [(HL+) · (mda−)], (benzylamine): (5-bromosalicylic acid)2(5) [(HL+) · (bsac−) · (Hbsac)], (benzylamine): (m-phthalic acid) (6) [(HL+) · (Hmpta−)], and (benzylamine)2: (trimesic acid) (7) [(HL+)2 · (Htma2−)]. The seven salts have been characterised by X-ray diffraction technique, IR, and elemental analysis, and the melting points of all the salts were also reported. And their structural and supramolecular aspects are fully analyzed.The result reveals that among the seven investigated crystals the NH2 groups in the benzylamine moieties are protonated when the organic acids are deprotonated, and the crystal packing is interpreted in terms of the strong charge-assisted NH⋯O hydrogen bond formation between the ammonium and the deprotonated acidic groups. Except the NH⋯O hydrogen bond, the OH⋯O hydrogen bonds (charge assisted or neutral) were also found at the salts 4–7.Further analysis of the crystal packing of the salts indicated that a different family of additional CHO/CH2O, CHπ/CH2π, OO, and OCπ associations contribute to the stabilization and expansion of the total high-dimensional (2D-3D) framework structures. For the coexistence of the various weak nonbonding interactions these structures adopted homo or hetero supramolecular synthons or both. Some classical supramolecular synthons, such as R42(8), R43(10) and R44(12), usually observed in organic solids of organic acids with amine, were again shown to be involved in constructing most of these hydrogen bonding networks.