RAMAN-SPECTRA AND STRUCTURAL PHASE-TRANSITIONS IN CHAIN COMPOUNDS (CH3)4NMNCL3 AND (CH3)4NCDCL3

The Raman spectra (0 to 1000 cm−1) of the isostructural compounds (CH3)4NMnCl3 (TMMC), (CD3)4NMnCl3 (d‐TMMC) and (CH3)4NCdCl3 (TMCC) are recorded at different temperatures (from 25 to 300 K) and analysed in view of the previously reported structural data and phases transitions. The order‐disorder monoclinic‐hexagonal phase transition occurring at 126 K in TMMC and d‐TMMC is characterized in particular by the appearance, in the hexagonal disordered phase, of a diffuse scattering centered at ω = 0, due to the “rotatory” mode of the MCl3 chains coupled with a (CH3)4N+ ion (TMA) overdamped libration. In TMCC two transitions occur at 118 and 104 K. The mechanism for the monoclinic‐hexagonal transformation at 118 K is probably related to a change in the TMA ion configuration. Furthermore, the observed Raman spectra give some evidence for the existence of a new disordered state of the TMA ions in this intermediate phase. The transition at 104 K is then related to a complete ordering of the TMA ions. Copyright © 1979 WILEY‐VCH Verlag GmbH & Co. KGaA