Actinyl cation-cation interactions in the gas phase: an accurate thermochemical study

Area of Science:

• Computational chemistry
• Actinide chemistry
• Physical chemistry

Background:

• Actinyl cations are key species in actinide chemistry.
• Cation-cation interactions (CCIs) are crucial in condensed phase systems.
• Gas phase CCIs of actinides remain poorly understood.

Purpose of the Study:

• To investigate gas phase actinyl cation-cation interactions (CCIs) for actinide ions (U, Np, Pu, Am).
• To determine the thermodynamic and kinetic stability of these interactions.
• To elucidate the bonding nature and trends in CCIs.

Main Methods:

• Accurate composite coupled cluster thermochemical approach.
• Construction and analysis of CCI dimers from various actinyl monomers.
• Natural bond orbital (NBO) analysis for charge transfer investigation.

Main Results:

• All studied CCI dimers were thermodynamically unstable but exhibited kinetic stability.
• T-shaped geometries were prevalent, with specific orientations favoring stability.
• Stability decreased in the order U > Np > Pu > Am, correlating with experimental condensed phase trends.
• Charge transfer stabilization was identified as a key bonding component.

Conclusions:

• Gas phase actinyl CCIs are kinetically stable despite thermodynamic instability.
• Bonding involves a balance between charge transfer stabilization and Coulombic repulsion.
• The findings provide insights into actinide complexation and correlate with condensed phase behavior.