Strong Electronic Couplings between Ferrocenyl Centers Mediated by Bis-Ethynyl/Butadiynyl Diruthenium Bridges

A series of trans-(FcC_2n)Ru₂(Y-DMBA)₄(C_2mFc) with n, m = 1 and 2 and Y-DMBA as N,N‘-dimethylbenzamidinate or N,N‘-dimethyl-(3-methoxy)benzamidinate have been synthesized and characterized. The intramolecular Fc···Fc distances, established through single-crystal X-ray diffraction studies, range from 11.6 to 16.6 Å. Results from both voltammetric and spectroelectrochemical studies indicate that the (−C_2n)Ru₂(Y-DMBA)₄(C_2m−) fragments are among the most efficient mediators of intramolecular hole transfer. Density-functional calculations offer both the insight on the ground-state electronic properties and unambiguous assignment for the observed electronic absorptions.