Stoichiometric and polymorphic salts of hexamethylenetetraminium and 2-chloro-4-nitrobenzoate

Four molecular salts made from hexamethylenetetraminium and 2-chloro-4-nitrobenzoate have been synthesized and are reported, namely ammonium hexamethylenetetraminium bis(2-chloro-4-nitrobenzoate), NH 4 + ·C 6 H 13 N 4 + ·2C 7 H 3 ClNO 4 -, (I), hexamethylenetetraminium hydrogen bis(2-chloro-4-nitrobenzoate), 0.5C 6 H 13 N 4 + ·C 7 H 3.50 ClNO 4 -, (II), hexamethylenetetraminium 2-chloro-4-nitrobenzoate, C 6 H 13 N 4 + ·C 7 H 3 ClNO 4 -, (IIIa) and (IIIb). All four molecular salts show N + - H⋯O - hydrogen bonding. Salt (I) crystallized out with an NH 4 + counter-ion which came from decomposition of 50% of the hexamethylenetetraminium cation in solution. (II) shows an unusual asymmetric unit, with both a hexamethylenetetraminium cation and a partially deprotonated 2-chloro-4-nitrobenzoate anion. Salts (IIIa) and (IIIb) are polymorphs of each other. This work shows that hexamethylenetetramine only protonates once, even in the presence of excess acid.