One-Step versus Two-Step Valence Tautomeric Transitions in Tetraoxolene-Bridged Dinuclear Cobalt Compounds

The syntheses of valence tautomeric compounds with multistep transitions using new redox-active ligands are the long-term goal of the field of bistable materials. The redox-active tetraoxolene ligand, 2,7-di-tert-butylpyr-ene-4,5,9,10-tetraone (pyreneQ-Q), is now developed to synthesize a pair of dinuclear compounds {[CoL2]2(pyreneSq-Sq)}[Co(CO)4]2middotxCH2Cl2middot2C6H5CH3(1,x= 2, L = 1,10-phenanthroline, phen;2,x= 1.5, L = 2,2 '-bipyridine, bpy). Variable-temperature magnetic susceptibilities and single-crystal X-ray diffraction measurements indicate a partial one-step valencetautomeric transition for1and a rare two-step valence tautomeric transitionfor2, respectively. DFT calculation results are consistent with the experimental data, revealing the correlation between thermodynamic parameters and the one-step/two-step valence tautomeric behaviors