STRUCTURE OF THE STABLE PHASE OF METHYLHYDRAZINE - 1ST OBSERVATIONS OF PHASE-TRANSITIONS

A study of methylhydrazine, CH3NHNH2, has provided the following data: monoclinic system, P2(1)/C, a = 10.043 (10), b = 3.925 (5), c = 7.670 (8) angstrom, beta 107.28 (10)-degrees, V = 288.7 (1. 1) angstrom3 , Z = 4, M(r) = 46.07, D(x) = 1.06 g cm-3, lambda(Mo Kalpha) = O.7107 an gstrom, mu = 0.81 cm-1, F(000) = 104, T = 179 K, R = 0.039 for 703 ref lexions [I greater-than-or-equal-to 3 sigma(I)]. A single crystal was grown in situ from the liquid by an adapted Bridgman method. The cryst allographic cell contains equimolar proportions of isomers with the ou ter conformation. The internal rotation angle for the NH2 group around the N-C bond is 82-degrees. The molecular volume is estimated to be 4 8.9 angstrom3, Which leads to a relatively high compactness factor (0. 68). The N-C molecular bonds are parallel to the crystallographic a ax is. The structure may be described by planes of molecules, linked by v an der Waals contacts, parallel to the b, c plane and related by a/2 t ranslations. In each plane, one molecule is linked to four neighbours by weak hydrogen bonds. Phase transformations, as observed by DSC (dif ferential scanning calorimetry) and Raman spectroscopy, are detailed. One glassy phase is obtained by quenching the liquid. One metastable p hase appears by rapid cooling. This metastable phase may be simulated from the stable phase as a pseudo-quadratic disordered structure. This allows an analysis of the phase transition.