An Ytterbium-Pyrazine Square [(C5H4Me)2YbIII(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 its recent use in strongly coupled materials. In the current work, using a YbII precursor: [(C5H4Me)2YbII(THF)2] (1), a molecular square [(C5H4Me)2YbIII(pyz•–)]4·½(C7H5F3) (2) was synthesized by metal-ligand redox cooperativity. Complex 2 shows evidence of charge transfer from YbII to pyrazine in a range of studies including structural analysis, magnetometry, vibrational spectroscopy, X-ray absorption 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•– cou-pling of -18.6 cm-1 for the radical bridged Yb-square complex.