POLYMORPHIC TRANSITIONS OF TETRAMETHYLAMMONIUMHYDROXIDE-PENTAHYDRATE, NME4OH.5H2O, AND CRYSTAL-STRUCTURE DETERMINATIONS OF THE ROOM-TEMPERATURE AND LOW-TEMPERATURE PHASES

According to the results of thermal analysis and X-ray powder diffraction NMe4OH.5H2O forms three polymorphic phases between -150-degrees-C and the melting point at + 71-degrees-C. Crystal structures of the low temperature phase I, here reported for the first time, and phase II, stable at room temperature, were determined by single crystal X-ray techniques. I-NMe4OH.5H2O: P1BAR; a = 820.6(2), b = 1135.2(5), c = 1764.0(5) pm, a = 105.49(3)-degrees, beta = 93.66(2)-degrees, gamma = 95.52(3)-degrees; -90-degrees-C; MoKa; 7165 diffractometer data; R(w) = 8.9%. II-NMe4OH.5H2O: Cmcm; a = 1248.3(5), b = 1090.0(4), c = 786.2(4) pm; + 20-degrees-C; MoKa; 3240 diffractometer data; R(w) = 4.8%. Hydroxide ions and water molecules form polyhedral sodalithe type host lattices in all three phases which accomodate the cations. With decreasing temperature the three phases differ by decreasing cation disorder leading to an increase of the distortion of the host lattice. DTA/TG and MS measurements prove the loss of crystal water above the melting point and decomposition of the anhydrous hydroxide at about 160-degrees-C.