An Ytterbium-Pyrazine Square [(C 5 H 4 Me) 2 Yb III (pyz •– )] 4 Formed 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 II precursor, [(C 5 H 4 Me) 2 Yb II (THF) 2 ] ( 1 ), a molecular square [(C 5 H 4 Me) 2 Yb III (pyz •– )] 4 · 1 / 2 (C 7 H 5 F 3 ) ( 2 ) was synthesized by metal-ligand redox cooperativity. Complex 2 shows evidence of charge transfer from Yb II to 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 –1 and pyz •– -pyz •– coupling of −18.6 cm –1 for the radical bridged Yb-square complex.