Metal-Ligand Exchange Coupling Alters the Open-Shell Ligand Electronic Structure in a Bis(semiquinone) Complex

Area of Science:

• Coordination Chemistry
• Materials Science
• Physical Chemistry

Background:

• The electronic structure of bridging ligands like SQTh is sensitive to metal-ligand interactions.
• Understanding magnetic exchange coupling is crucial for designing molecular electronic materials.

Purpose of the Study:

• To investigate the effect of metal-ligand magnetic exchange coupling on the electronic structure of the SQTh ligand.
• To compare the magnetic properties and electronic states of dinuclear Ni(II) and Zn(II) complexes with the SQTh ligand.

Main Methods:

• X-ray diffraction for crystal structure analysis.
• Variable-temperature magnetic susceptibility measurements.
• Analysis of bond lengths and magnetic exchange coupling constants (J_SQ-SQ).

Main Results:

• The (NiSQ)Th complex exhibits an open-shell biradical ground state, unlike the closed-shell quinoidal character of (ZnSQ)Th.
• Reduced SQ-SQ radical-radical magnetic exchange coupling (J_SQ-SQ = -203 cm⁻¹) was observed in (NiSQ)Th compared to (ZnSQ)Th (J_SQ-SQ = -321 cm⁻¹).
• This reduction is attributed to attenuated SQ spin densities due to Ni-SQ antiferromagnetic interactions, effectively lengthening the bridge unit.

Conclusions:

• Metal-radical exchange coupling is a viable mechanism for tuning the electronic structure of organic radicals.
• The modulation of spin populations via Ni-SQ interactions affects electronic coupling in the Th-Th bridge.
• These findings have significant implications for the development of molecular electronics and molecular electron transport devices.