Crystal Structure of Trimethylammonium Perchlorate in Three Solid Phases Including the Ionic Plastic Phase Obtainable above 480 K

The crystal structures of (CH₃)₃NHC1_O4 in three solid phases were studied by X-ray diffraction techniques. X-ray powder patterns taken at ca. 500 and 445 K revealed that the plastic phase (Phase I) attainable above 480 K crystallizes in a CsCl-type cubic structure with a = 5.845 (1) A, Z = 1, V = 199.7 (2) A³, and D_x= 1.327 gcm⁻³, while Phase II, stable between 480 and 396 K, forms a tetragonal structure with a = 9.912 (4), c = 7.01 (2) A, Z = 4, V = 689 (3) A³, and D_x = 1.54 gcm⁻³. The room temperature phase (Phase III) was studied by single crystal X-ray diffraction and found to form a monoclinic lattice with space group P2₁a = 5.749(1), b = 8.670(1), c = 7.5585 (9) A, β = 102.66(1)°, Z = 2, V = 367.6(2) A³, and D_x= 1.441 gcm⁻³. Thermal measurements, differential thermal analysis and differential scanning calorimetry, were carried out on these solid phases, and the obtained results were compared with those observed for (CH₃)₃NHBF₄.