An Ytterbium-Pyrazine Square [(C₅H₄Me)₂Yb^III(pyz^•–)]₄Formed by Reversible Electron Transfer and Concomitant Self-Assembly

Pyrazine (pyz) has been used extensively in coordination chemistry to manifest electron delocalization in mixed-valent compounds and strongly coupled materials. In the current work, using a Yb^IIprecursor, [(C₅H₄Me)₂Yb^II(THF)₂] (1), a molecular square [(C₅H₄Me)₂Yb^III(pyz^•–)]₄·¹/₂(C₇H₅F₃) (2) was synthesized by metal-ligand redox cooperativity. Complex 2 shows evidence of charge transfer from Yb^IIto pyrazine in a range of studies including structural analysis, magnetometry, vibrational spectroscopy, X-ray absorption near-edge structure spectroscopy, and electronic structure calculations. DFT calculations support the assignment of low-energy bands in the UV–vis spectrum as pyrazine-SOMO-to-metal-4f charge transfer. Magnetic studies reveal a Yb-pyz^•–exchange coupling of −3.6 cm^–1and pyz^•–-pyz^•–coupling of −18.6 cm^–1for the radical bridged Yb-square complex.