5 years ago

Phase transitions in tetramethylammonium hexachlorometalate compounds, (TMA)₂MCl₆ (M = U, Np, Pt, Sn, Hf, Zr).

Richard Wilson, Matthieu Autillo
A study of the phase transitions occurring in tetramethylammonium hexachlorometalate compounds with M = UIV, NpIV, ZrIV, SnIV, HfIV and PtIV were performed using single-crystal X-ray diffraction across the temperature range 120 - 400K. When the crystals were cooled, movement of the octahedral [MCl6]2- anions induces a phase transition from Fm¯3 m to Fd¯3 c with a doubling of the unit cell. For the actinide compounds, no correlation between the f-electron configuration and the transition temperature was observed, instead, a correlation between the transition temperatures and both the [MCl6]2- anion and the TMA cation size is highlighted. Two phase transitions were observed and characterized. The first phase transition occurs with the ordering of the TMA cation and the second from a rotation of the [MCl6]2- octahedra. A third phase transition was observed at lower temperatures and was ascribed to a tetragonal distortion of the [MCl6]2- anions. Synthesis and study of their deuterated compounds did not show a significant isotope effect. Raman spectra performed on the protonated and deuterated compounds indicate only weak hydrogen bonding interactions between the TMA cations and the [MCl6]2- octahedra.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/ejic.201700764

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