U-CN versus Ce-NC coordination in trivalent complexes derived from M[N(SiMe3)2]3 (M = Ce, U)

Area of Science:

• Organometallic Chemistry
• Coordination Chemistry
• Lanthanide and Actinide Chemistry

Background:

• The synthesis and characterization of f-element complexes with cyanide ligands are crucial for understanding their reactivity.
• Investigating the coordination preferences of cyanide in cerium and uranium complexes provides insights into their electronic structures.

Purpose of the Study:

• To synthesize and characterize a series of mononuclear and dinuclear cyanide complexes of cerium and uranium.
• To elucidate the coordination modes of cyanide ligands and their binding affinities towards cerium and uranium.
• To explore the electronic factors governing the preferential coordination of cyanide to uranium over cerium.

Main Methods:

• Reactions of [MN*3] (M = Ce, U; N* = N(SiMe3)2) with various cyanide sources (NR4CN, KCN).
• Isolation and characterization of mononuclear and dinuclear complexes using techniques including X-ray crystallography.
• Thermodynamic studies (formation constants, enthalpy, entropy) of complex formation.
• Density Functional Theory (DFT) calculations to analyze bonding and coordination preferences.

Main Results:

• A series of mononuclear and dinuclear cerium and uranium cyanide complexes were successfully synthesized.
• Crystal structures revealed distinct coordination modes of the cyanide ligand (via C or N) to uranium and cerium centers.
• Equilibrium was observed between mono- and bis(cyanide) complexes.
• DFT calculations and binding energy analysis confirmed the preferential coordination of cyanide to uranium over cerium, linked to orbital interactions.

Conclusions:

• The study successfully synthesized and characterized novel cerium and uranium cyanide complexes.
• Distinct coordination behaviors of cyanide ligands towards U(III) and Ce(III) were observed and explained by electronic factors.
• The preferential binding of cyanide to uranium is attributed to better energy matching between uranium's 6d/5f orbitals and the cyanide ligand.