[Cp*Ru(s-indacene)RuCp*] and [Cp*Ru(s-indacene)RuCp*]⁺: Experimental and theoretical findings concerning the electronic structure of neutral and mixed valence organometallic systems

The reaction of 2,6-diethyl-4,8-dimethyl-s-indacenyl-dilithium (Li₂Ic′) with [Cp*RuCl]₄ gives the organometallic binuclear bis-pentamethylcyclopentadienyl-ruthenium-s-indacene complex, [{Cp*Ru}₂Ic′] (1, Ic′ = 2,4-diethyl-4,8-dimethyl-s-indacene), in high yields. The subsequent oxidation of 1 with a ferricinium salt ([Fc]⁺[BF₄]^-) gives the mixed valence compound [{Cp*Ru}₂Ic′]⁺[BF₄]^- (1⁺). Compound 1 was structurally characterized by X-ray crystallography, finding that both {Cp*Ru} fragments are coordinated to opposite sites of the Ic′ ligand. The structural and electronic features of 1 and 1⁺ have been rationalized by Density Functional Theory (DFT) calculations, which suggest that both metallic centers get closer to the Ic′ and subtle electronic reorganizations occurs when chemical oxidation takes place. Cyclic voltammetry and ESR experiments suggest a high electronic interaction between the metallic centers mediated by the Ic′ bridging ligand. Time dependent DFT (TD-DFT) calculations were carried out to understand and assign the intervalence band present in the mixed-valent specie (1⁺). The main achievement of this article is to feature the relationship of the experimental data with the computational results obtained with the Amsterdam Density Functional package (ADF). Both experimental and theoretical facts demonstrate that the mixed valence system (1⁺) is a delocalized one, and it can be classified as a Class III system according to the Robin & Day classification.