Platform for High-Spin Molecules: A Verdazyl-Nitronyl Nitroxide Triradical with Quartet Ground State

Area of Science:

• Organic chemistry
• Materials science
• Quantum chemistry

Background:

• Stable organic high-spin molecules, particularly those with quartet ground states, are rare and highly sought after for advanced applications.
• Designing molecules with multiple unpaired electrons and controlled spin states remains a significant challenge in chemistry.

Purpose of the Study:

• To synthesize and characterize the first thermally resistant and air-stable organic triradical featuring a quartet ground state.
• To investigate the magnetic properties and electronic structure of the novel triradical and its diradical precursor.
• To explore the potential of this new class of compounds for future high-spin system development.

Main Methods:

• Palladium-catalyzed cross-coupling reaction for synthesis.
• Single-crystal X-ray diffraction, EPR spectroscopy, and SQUID magnetometry for characterization.
• Cyclic voltammetry for redox behavior analysis.
• High-level CASSCF/NEVPT2 calculations for magnetic interactions and motifs.

Main Results:

• Successful synthesis of a stable organic triradical comprising oxoverdazyl and nitronyl nitroxide fragments with a quartet ground state.
• Characterization confirmed the structure and magnetic properties of both the diradical precursor and the triradical.
• Electrochemical studies revealed distinct redox behaviors for the diradical and triradical.
• Calculations elucidated magnetic interactions and confirmed moderate singlet-triplet and doublet-quartet energy gaps.

Conclusions:

• The study reports the first stable organic triradical with a quartet ground state, demonstrating a significant advancement in high-spin molecule design.
• The unique stability and synthetic accessibility of this verdazyl-nitronylnitroxide triradical offer promising opportunities for creating novel functional materials.
• This work paves the way for designing more complex high-spin systems with potentially four or more unpaired electrons.