Dynamics of Cation-Induced Conformational Changes in Nanometer-Sized Uranyl Peroxide Clusters

Area of Science:

• Inorganic Chemistry
• Materials Science
• Nanotechnology

Background:

• Uranyl peroxide nanoclusters are complex structures with potential applications.
• The {U24Pp12} cluster exhibits conformational flexibility.
• Understanding cation-induced structural changes is crucial for controlling nanocluster properties.

Purpose of the Study:

• To investigate the impact of alkali cations on the conformation of the pyrophosphate-functionalized uranyl peroxide nanocluster ({U24Pp12}).
• To elucidate the mechanism of cation-induced conformational transitions using NMR spectroscopy.
• To explore the role of different alkali cations (K+, Rb+, Cs+) in modulating cluster symmetry.

Main Methods:

• One-dimensional and variable-temperature 31P NMR spectroscopy to probe conformational changes and dynamics.
• Two-dimensional exchange spectroscopy (2D-EXSY) 31P NMR to study interconversion mechanisms.
• Single-crystal X-ray diffraction to determine solid-state structures.

Main Results:

• Potassium (K+) and rubidium (Rb+) ions induce an O_h to D_4 conformational change in {U24Pp12}.
• Rb+ leads to slower D_4 to O_h transitions compared to K+, indicated by higher activation enthalpy and entropy.
• 2D-EXSY NMR reveals cation-triggered interconversion of pyrophosphate bridges via conformational rearrangement without bond breaking.
• Cesium (Cs+) ions cause minimal changes, preserving O_h symmetry in solution, while the solid-state structure adopts D_2 symmetry.

Conclusions:

• The actinide-based {U24Pp12} nanocluster exhibits significant conformational flexibility.
• The cluster's symmetry and dynamics are highly sensitive to the type of alkali countercation.
• Cation binding and release within the cluster cavity drive conformational rearrangements, offering a mechanism for dynamic structural control.