Triethylenetetramine dihydrochloride: interactions and conformations in two anhydrous structures and a hydrate

Triethylenetetramine is a polyamine type chelating ligand for copper(II), which is currently used, mainly in its dihydrochloride form, as an alternative to d-penicillamine against Wilson’s disease. Because knowledge about the solid-state behavior of pharmaceuticals is a prerequisite for the development of an effective dosage form, the crystal structures of two triethylenetetramine dihydrochloride polymorphs have been determined, and the infrared spectra and thermal expansion have been studied. No suitable crystals could be obtained of the two anhydrous forms, for which the structures have been solved from X-ray powder diffraction. Form I is monoclinic P21/n with the cell parameters a = 11.0475(4) A, b = 4.87475(16) A, c = 11.1178(4) A, and β = 106.9826(13)° leading to V = 572.63(3) A3 with Z = 2. Form II is also monoclinic P21/c with cell parameters a = 10.6734(6) A, b = 12.3613(6) A, c = 9.8479(7) A, and β = 115.985(3)° leading to a unit-cell volume of V = 1167.95(12) A3 with Z = 4. A recurring structura...