Single-molecule-magnet behavior in mononuclear homoleptic tetrahedral uranium(III) complexes

Area of Science:

• Coordination chemistry
• Magnetism
• Uranium chemistry

Background:

• Uranium compounds are of interest for their unique magnetic properties.
• Understanding the influence of ligand environments on magnetic behavior is crucial.

Purpose of the Study:

• To investigate and compare the magnetic properties of two uranium(III) coordination compounds with different donor ligands.
• To explore the magnetic relaxation dynamics in these pseudotetrahedral U(III) complexes.

Main Methods:

• Synthesis and characterization of two uranium coordination compounds: [K(18c6)][U(OSi(O(t)Bu)3)4] and [K(18c6)][U(N(SiMe3)2)4].
• Magnetic susceptibility measurements (static and alternating-current) at varying frequencies and temperatures.
• Density functional theory (DFT) calculations to analyze ligand field effects.

Main Results:

• Both compounds feature U(III) ions in similar pseudotetrahedral coordination environments.
• Static magnetic susceptibility and DFT studies indicate distinct ligand fields influenced by O- vs. N-donor ligands.
• Alternating-current susceptibility measurements revealed slow magnetic relaxation in both compounds, even at zero applied magnetic field.
• Similar energy barriers (U ~24 K) for magnetic relaxation were observed in both complexes.

Conclusions:

• The ligand environment significantly impacts the electronic structure and magnetic properties of U(III) complexes.
• Both studied uranium compounds exhibit slow magnetic relaxation, a key characteristic for potential single-molecule magnet applications.
• The observed similar energy barriers suggest a degree of robustness in the magnetic relaxation mechanism despite differing ligand donors.