A Series of Rare-Earth Mesoionic Carbene Complexes

Area of Science:

• Organometallic Chemistry
• Materials Science
• Magnetism

Background:

• Mesoionic carbene (MIC) complexes are valuable in catalysis and materials science.
• The library of f-block MIC complexes remains limited, hindering exploration of their unique properties.
• Understanding metal-carbene bonding in f-block elements is crucial for designing new functional materials.

Purpose of the Study:

• To synthesize and characterize a new series of rare-earth (RE) mesoionic carbene complexes.
• To investigate the electronic structure and bonding characteristics of these f-block MIC complexes.
• To evaluate the magnetic properties, including single-molecule magnet behavior, of the synthesized complexes.

Main Methods:

• Synthesis of rare-earth triamides followed by reaction with an N-heterocyclic olefin (NHO).
• Characterization using static variable-temperature magnetic measurements.
• Quantum chemical calculations to determine metal-carbene bonding interactions.
• Dynamic magnetic measurements to assess single-molecule magnet (SMM) properties.

Main Results:

• Successfully synthesized a series of 12 rare-earth mesoionic carbene complexes, [RE{N(SiMe3)2}3{CN(Me)C(Me)N(Me)CH}] (3RE).
• Quantum chemical calculations indicate only sigma-bonding for RE(III) metals, unlike uranium congeners with pi-back-bonding.
• Dynamic magnetic measurements identified 3Dy and 3Er as field-induced single-molecule magnets with significant energy barriers (35 K and 128 K, respectively).
• Complex 3Er demonstrated unexpectedly high performance as a single-molecule magnet.

Conclusions:

• The study significantly expands the known family of f-block mesoionic carbene complexes.
• The bonding in these RE(III) complexes is primarily sigma-based, differing from some actinide analogues.
• The discovery of potent single-molecule magnet behavior in 3Er opens new avenues for lanthanide-based molecular magnetism research.