Dicopper(I,I) and delocalized mixed-valent dicopper(I,II) complexes of a sterically hindered carboxylate ligand

Admixture of the lithium salt of the bulky ligand 2,6-dimesitylbenzoate [ArCO2]– with [Cu(CH3CN)4]O3SCF3 yielded the dicopper(I,I) complex [(ArCO2)2Cu2(THF)2)](1), which upon oxidation with AgX (X = SbF6– or ClO4–) in THF afforded the mixed-valent complexes [(ArCO2)2Cu2(THF) 2]SbF6(2) and [(ArCO2)2Cu2(THF)3]ClO4(3), respectively. Fully delocalized mixed-valent (Cu1.5Cu1.5) formulations for 2 and 3 were determined on the basis of X-ray crystallography and UV-vis, resonance Raman, 1H NMR, and EPR spectroscopy. Notably, solvent dependent UV-vis spectra suggest that THF and/or counter ion coordination influence the intermetal bonding interactions in the mixed-valent cores.