Polymorphism in n-alkylammonium chlorides: X-ray powder diffraction studies

The n-alkylammonium halides which have thermal transitions above room temperature adopt either a monoclinic or an orthorhombic form when recrystallized at temperatures below the lowest transition. On heating a transition to a tetragonal structure occurs but on subsequent cooling the crystals do not return to their original form but to a different monoclinic structure.