UNIQUENESS OF THE PROPYL COMPOUND IN THE SERIES (CNH2N+1NH3)2MNCL4 WITH N=1-10

The perovskite-like layer structures of (CnH2n+1NH3)2MnCl4 with n = 1-10 have been investigated by X-ray methods to determine their lattice constants and the temperature of transition to the respective zero-tilt phases. It has been found that the propyl compound is distinctive in that it exhibits the highest temperature of transition to a zero-tilt phase, the longest MnCl bond, and the largest difference between the a and b lattice parameters. Furthermore, it undergoes a large number of phase transitions (five), some of which are accompanied by the formation of commensurable or incommensurable superstructures. The special position of this compound is attributed to geometrical peculiarities related to the terminal methyl groups. The propyl compound is the only member of the series in which coupled movements of terminal methyl groups of neighboring strata do not seem to be important below 400°K. © 1979.