Testing bridge-mediated differences in dinuclear valence tautomeric behavior

Two structurally characterized dinuclear valence tautomers are described. Cobalt ions are bridged by p- and m-phenylene units connected to 2,2'-bipyridines. X-ray crystal structures show that the molecules are in the [(Co-III)-(Co-III)] forms at ca. 125 K, while spectroscopic studies show that both molecules can achieve the [(Co-II)(Co-II)] form above 400 K and confirm the [(Co-III)(Co-III)] form below 10 K. Magnetic susceptibility studies are also included. Our results highlight the necessity of studying both crystalline and amorphous samples to distinguish the effects of intrinsic electronic structure and intermolecular forces on valence tautomeric behavior.