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Structure, Phase Transitions, and Isotope Effects in [(CH3)4N]2PuCl6
1Chemical Sciences and Engineering Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
Inorganic Chemistry
|July 31, 2015
Summary
The crystal structure of tetramethylammonium hexachloroplutonate was determined, revealing two phase transitions between 100 and 360 K. An isotopic effect was observed, suggesting cation-anion interactions drive the structural changes.
Area of Science:
- Solid-state chemistry
- Crystallography
- Actinide chemistry
Background:
- The precise crystal structure of tetramethylammonium hexachloroplutonate [(CH3)4N]2PuCl6 has been a subject of long-standing ambiguity.
- Understanding the structural behavior of plutonium compounds is crucial for nuclear materials science.
Purpose of the Study:
- To elucidate the definitive crystal structure of [(CH3)4N]2PuCl6.
- To investigate the temperature-dependent structural transformations and phase transitions of this compound.
- To explore the influence of isotopic substitution on the observed phase transitions.
Main Methods:
- Single-crystal X-ray diffraction was employed to determine the crystal structure.
- Temperature-dependent X-ray diffraction studies were conducted between 100 and 360 K.
- Synthesis and structural analysis of both protonated and deuterated salts, [(CH3)4N]2PuCl6 and [(CD3)4N]2PuCl6, were performed.
Main Results:
- The room temperature crystal structure was determined to be Fd3̅c with a lattice parameter of 26.012(3) Å.
- Two phase transitions were identified between 100 and 360 K, with a transition to space group Fm3̅m at 360 K (a = 13.088(1) Å).
- A significant isotopic effect was observed in the phase transition temperature for the deuterated salt, indicating the involvement of tetramethylammonium cations and hexachloroplutonate anions.
Conclusions:
- The study resolves structural ambiguities for [(CH3)4N]2PuCl6, providing the first definitive crystal structure.
- Temperature-induced rotative displacements of plutonium octahedra and tetramethylammonium cations drive the observed phase transitions.
- Donor-acceptor interactions between the cation and anion are the primary driving force for the phase transformation, as evidenced by the isotopic effect.
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