VIBRATIONAL STUDY OF PHASE-TRANSITIONS IN (NH3(CH2)3NH3)MNCL4

Infrared and Raman spectra (10–4000 cm−1) of single crystals and of polycrstalline samples of (NH3(CH2)3NH3)MnCl4 and of its ND3 deuterated derivative have been investigated in the 10–400 K temperature range. An assignment of most of the observed bands is proposed. The first‐order phase transitions at 306 K and 336 K have been characterized. The spectra of the room temperature phase (III) and of the high temperature phase (I) differ mainly in the broadness of the bands and it is concluded that their structures can be similar. A strong perturbation of the chlorine lattice is observed at 306 K and 100 K. A systematic temperature dependence study (10–300 K) of the frequencies, ν, and half‐widths, Δν, of the low frequency Raman bands has been performed; it has been concluded that at about 110 K a large proportion of NH3 groups are jumping and that the activation energy, E0 ≃ 1.0 kcal mol−1, extracted from the curves Δν = f(T), is of the same order of magnitude as the potential barrier, V6 = 1.2 kcal mol−1, calculated from the torsional frequency of NH 3+ (329 cm−1) or of ND 3+ (245 cm−1). The NH3 torsional motions coupled with librations of alkylene chains are believed to be responsible for disorder observed among most of the modes. The low temperature spectra have been interpreted assuming D2h factor group and Z = 2 (i.e. the same as at room temperature) and they can be interpreted as if the sample was ordered, suggesting the possible existence of an ordered low temperature phase IV. Copyright © 1979 Heyden & Son Ltd.