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Vibrational study of phase transitions in (NH 3 (CH 2 ) 3 NH 3 )MnCl 4
Author(s) -
Sourisseau C.,
Lucazeau G.
Publication year - 1979
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1250080604
Subject(s) - chemistry , raman spectroscopy , atmospheric temperature range , analytical chemistry (journal) , spectral line , infrared spectroscopy , phase transition , activation energy , deuterium , lattice (music) , infrared , crystallography , atomic physics , condensed matter physics , physics , thermodynamics , organic chemistry , chromatography , astronomy , acoustics , optics
Infrared and Raman spectra (10–4000 cm −1 ) of single crystals and of polycrstalline samples of (NH 3 (CH 2 ) 3 NH 3 )MnCl 4 and of its ND 3 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 NH 3 groups are jumping and that the activation energy, E 0 ≃ 1.0 kcal mol −1 , extracted from the curves Δν = f ( T ), is of the same order of magnitude as the potential barrier, V 6 = 1.2 kcal mol −1 , calculated from the torsional frequency of NH 3 +(329 cm −1 ) or of ND 3 +(245 cm −1 ). The NH 3 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 D 2 h 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.