High-spin S = 2 ground state aminyl tetraradicals

Area of Science:

• Organic Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Aminyl tetraradicals are novel organic molecules with potential applications in molecular magnetism.
• Understanding their electronic structure and stability is crucial for their practical use.

Purpose of the Study:

• To investigate the ground and excited spin states of aminyl tetraradicals with tetraazanonacene backbones.
• To determine the stability and decomposition pathways of these tetraradicals in solution.

Main Methods:

• Experimental studies in 2-methyltetrahydrofuran (2-MeTHF) matrix at various temperatures.
• Broken-symmetry density functional theory (DFT) calculations.
• Spectroscopic analysis to identify decomposition products.

Main Results:

• Tetraradicals possess quintet (S = 2) ground states with no detectable population of low-spin excited states up to 100 K.
• The triplet-quintet energy gap (ΔE(TQ)) is greater than 0.3 kcal mol(-1), consistent with DFT calculations.
• Tetraradicals form dimers in concentrated solutions at 133 K with weak antiferromagnetic coupling.
• Sterically shielded tetraradicals exhibit a half-life of 1 hour at room temperature, decomposing to tetraamines via hydrogen atom abstraction from the solvent.

Conclusions:

• Aminyl tetraradicals are stable in their quintet ground state under investigated conditions.
• Dimerization and solvent-mediated decomposition are key factors influencing tetraradical stability.