The low-temperature modification of n-propyl-ammonium chloride

Abstract

The room-temperature structure of n-propylammonium chloride, which shows rotation of the cations, goes over in a second-order transition into a low-temperature form with fixed positions of the cations. In this process, the crystal of the room-temperature form breaks up reversibly into many domains of the low-temperature form, the domains having differing orientations. The space group of the lowtemperature form is C~-C2/m. The transition is produced by the fixing of the positions of the cations in the (li0) planes of the room-temperature structure in a centrosymmetric arrangement, with the result that the angle between the a axes is contracted, and the c axis is tipped in the direction of the axis [110]. The amount of these distortions varies with the temperature. Approximate positions of the a~.oms in the low-temperature form are given.