Influence of Ligand Geometry in Bimetallic Ytterbocene Complexes of Bridging Bis(bipyridyl) Ligands

Two new bimetallic complexes, [Cp*2Yb]2(μ-1,3-(2,2‘-bipyridyl)-5-tBu-C6H3) (1) and [Cp*2Yb]2(μ-1,4-(2,2‘-bipyridyl)-C6H4) (2), and their corresponding two-electron oxidation products [1]2+ and [2]2+ have been synthesized with the aim of determining the impact of the bridging ligand geometry on the electronic and magnetic properties of these materials. Electrochemistry, optical spectroscopy, and bulk susceptibility measurements all support a ground-state electronic configuration of the type [(f)13-(πa*)1-(πb*)1-(f)13]. Density functional theory calculations on the uncomplexed bridging ligands as doubly reduced species also indicate that the diradical electronic configuration is the lowest lying for both meta- and para-bis(bipyridyl) systems. The electrochemical and optical spectroscopic data indicate that the electronic coupling between the metal centers mediated by the diradical bridges is weak, as evidenced by the small separation of the metal-based redox couples and the similarity of the f−f transitions...