Orthorhombic-to-monoclinic temperature-dependent phase transition of hexamethylenetetraminium-3,5-dinitrobenzoate-3,5-dinitrobenzoic acid monohydrate crystal

The crystal of hexamethylenetetraminium-3,5-dinitrobenzote-3,5-dinitrobenzoic acid monohydrate undergoes a temperature-dependent phase transition from orthorhombic Pbca at temperature higher than 220 K to monoclinic P21/c at temperature lower than 220 K. The crystal structure analyses for data collected at 300 and 203 K show that in both temperature structures, there are two conventional intermolecular hydrogen bonds between the hexamethylenetetraminium and water molecule and between 3,5-dinitrobenzote and 3,5-dinitrobenzoic acid in the asymmetric unit. Another conventional intermolecular O–H⋯N hydrogen bonds link the hexamethylenetetraminium and water molecules into chains parallel to the a-direction and stabilized by the 3,5-dinitrobenzoate-3,5-dinitrobenzoic acids. There are also another six weak intermolecular interactions interconnecting the molecules into a three dimensional network. The shorter donor-acceptor distances of the prevailing hydrogen bonds and the two extra weak intermolecular C–H⋯O interactions interconnecting the hexamethylenetetraminium and 3,5-dinitrobenzoate-3,5-dinitrobenzoic acids in the low temperature monoclinic structure are attributable to the reversible temperature-dependent phase transition.