Iron Versus Ruthenium: Evidence for the Distinct Differences in the Electronic Structures of Hexa-1,3,5-triyn-1,6-diyl-bridged Complexes [Cp*(dppe)M}{μ-(CC)₃}{M(dppe)Cp*}]⁺ (M = Fe, Ru)

The spectroelectrochemically generated infrared (IR) and near-infrared spectra of the homo-bimetallic, hexa-1,3,5-triyn-1,6-diyl-bridged complex cations [{Cp*­(dppe)­M}­(μ-CCC≡CCC)­{M­(dppe)­Cp*}]⁺ (M = Fe, [1]⁺; Ru, [2]⁺) have been analyzed using density functional theory calculations based on global (BLYP35) and local (LH20t) hybrid functionals. The differences in the number of IR active ν­(CCCCCC) modes in these complexes are attributed to the distinct electronic localization of the Fe­(II)–Fe­(III) mixed-valence cation [1]⁺ on the IR timescale, as opposed to the delocalized electronic character of [2]⁺.