Mixed-Ligand Uranyl Squarate Coordination Polymers: Structure Regulation and Redox Activity

Area of Science:

• Materials Science
• Inorganic Chemistry
• Coordination Chemistry

Background:

• The electron-rich squarate ion (SA) offers desirable electronic delocalization and redox activity for functionalizing metal-organic complexes.
• Uranyl compounds are of interest due to their unique electronic and redox properties.

Purpose of the Study:

• To construct novel uranyl squarate coordination polymers using a mixed-ligand strategy.
• To explore the structural diversity and redox properties of these new compounds.

Main Methods:

• Hydrothermal synthesis of seven mixed-ligand uranyl squarate compounds.
• Utilizing ancillary ligands such as 4,4'-bipyridine (bpy), 4,4'-bipyridine-N,N'-dioxide (bpydo), 1,10-phenanthroline (phen), 4,4'-vinylenedipyridine (vidpy), and oxalate (OA).
• Characterization of redox properties using cyclic voltammetry.

Main Results:

• Seven novel mixed-ligand uranyl squarate compounds with diverse crystal structures (1D, 2D, and sandwich-like) were synthesized.
• Compounds 1, 4, and 5 demonstrated good redox activity, with distinct anode peaks for squarate oxidation and cathodic peaks for U(VI) reduction.
• The interplay between the redox-active squarate linker and uranyl nodes was confirmed.

Conclusions:

• The mixed-ligand method is effective for synthesizing diverse uranyl squarate coordination polymers.
• These compounds exhibit significant redox activity, highlighting the synergistic effects between organic linkers and metal centers.
• This work expands the library of redox-active uranyl compounds and offers a pathway for designing functional actinide materials.