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Title: Phase Transitions in Tetramethylammonium Hexachlorometalate Compounds (TMA) 2MCl 6 (M = U, Np, Pt, Sn, Hf, Zr)

A study of the phase transitions occurring in tetramethylammonium hexachlorometalate compounds with M = U IV, Np IV, Zr IV, Sn IV, Hf IV and Pt IV were performed using single-crystal X-ray diffraction across the temperature range 120 - 400K. When the crystals were cooled, movement of the octahedral [MCl 6] 2- anions induces a phase transition from Fm3m to Fd3c 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 [MCl 6] 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 [MCl 6] 2- octahedra. A third phase transition was observed at lower temperatures and was ascribed to a tetragonal distortion of the [MCl 6] 2- anions. Synthesis and study of their deuterated compounds did not show a significant isotope effect. As a result, Raman spectra performed on the protonated and deuterated compounds indicate only weak hydrogen bonding interactions between the TMA cations and the [MCl 6] 2- octahedra.
Authors:
 [1] ; ORCiD logo [1]
  1. Argonne National Lab. (ANL), Argonne, IL (United States)
Publication Date:
Grant/Contract Number:
AC02-06CH11357
Type:
Accepted Manuscript
Journal Name:
European Journal of Inorganic Chemistry
Additional Journal Information:
Journal Volume: 2017; Journal Issue: 41; Journal ID: ISSN 1434-1948
Publisher:
ChemPubSoc Europe
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Phase transitions; Actinides; Structure elucidation; Raman spectroscopy
OSTI Identifier:
1422404
Alternate Identifier(s):
OSTI ID: 1408148