Intermolecular Interactions in the Solid State of Ionic Secondary Mannich Bases

Two new secondary Mannich bases, 4-bromo-2-[(aminopropyl)methyl]-phenol (1) and 4-nitro-2-[(aminopropyl)methyl]-phenol (2), were synthesized. Crystal structures were determined at liquid nitrogen temperature. It was found that in both compounds the proton transfer forms exist in the solid state. In the case of 1, this was unexpected, because of the weak acidity of p-bromophenol being the parent component of this Mannich base. The reason for that was found to be the formation of the O–···H–N+ hydrogen bonded tetramer in the solid state. Two cyclic aggregates R42(8) and R22(12) describe the pattern of hydrogen bonded interactions in the crystals of both compounds. Additionally, C–H···π interactions stabilize the crystal structures. The hydrogen bonds in 1are slightly stronger (N···O distances 2.708 and 2.733 A) than in 2 (2.721 and 2.765 A, respectively) despite the fact that p-nitrophenol participating in 2 is a stronger acid. The influence of permittivity of surroundings and the hydrogen bonding pattern o...