Electron Paramagnetic Resonance and Spectroscopic Characteristics of Electrogenerated Mixed-Valent Systems [(η⁵-C₅Me₅)M(μ-L)M(η⁵-C₅Me₅)]⁺(M = Rh, Ir; L = 2,5-Diiminopyrazines) in Relation to the Radicals [(η⁵-C₅Me₅)ClM(μ-L)MCl(η⁵-C₅Me₅)]⁺and [(η⁵-C₅Me₅)M(μ-L)MCl(η⁵-C₅Me₅)]²⁺

Abstract

Electrochemical reduction of the dinuclear [(eta 5-C5Me5)ClM(mu-L)MCl(eta 5-C5Me5)]2+ ions (M = Rh, Ir; L = 2,5-bis(1-phenyliminoethyl)pyrazine (bpip) and 2,5-bis[1-(2,6-dimethylphenyl)iminoethyl]pyrazine (bxip)) proceeds via the paramagnetic intermediates [(eta 5-C5Me5)ClM(mu-L)MCl(eta 5-C5Me5)]+ (L = bpip) or [(eta 5-C5Me5)M(mu-L)MCl(eta 5-C5Me5)]2+ (L = bxip) and [(eta 5-C5Me5)M(mu-L)M(eta 5-C5Me5)]+. Whereas the first is clearly a radical species with a small g anisotropy, the chloride-free cations are distinguished by structured intervalence charge transfer (IVCT) bands in the near-infrared region and by rhombic electron paramagnetic resonance features between g = 1.9 and g = 2.3, which suggests considerable metal participation at the singly occupied MO. Alternatives for the d configuration assignment and for the role of the bisbidentate-conjugated bridging ligands will be discussed. The main difference between bpip and bxip systems is the destabilization of the chloride-containing forms through the bxip ligand for reasons of steric interference.