Electron Paramagnetic Resonance and Spectroscopic Characteristics of Electrogenerated\nMixed-Valent Systems [(η⁵-C₅Me₅)M(μ-L)M(η⁵-C₅Me₅)]⁺ (M = Rh, Ir; L =\n2,5-Diiminopyrazines) in Relation to the Radicals [(η⁵-C₅Me₅)ClM(μ-L)MCl(η⁵-C₅Me₅)]⁺\nand [(η⁵-C₅Me₅)M(μ-L)MCl(η⁵-C₅Me₅)]²⁺

Abstract

Electrochemical reduction of the dinuclear [(η⁵-C₅Me₅)ClM(μ-L)MCl(η⁵-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\nvia the paramagnetic intermediates [(η⁵-C₅Me₅)ClM(μ-L)MCl(η⁵-C₅Me₅)]⁺ (L = bpip) or [(η⁵-C₅Me₅)M(μ-L)MCl(η⁵-C₅Me₅)]²⁺ (L = bxip) and [(η⁵-C₅Me₅)M(μ-L)M(η⁵-C₅Me₅)]⁺. Whereas the first is clearly a radical species\nwith a small <i>g</i> anisotropy, the chloride-free cations are distinguished by structured intervalence charge transfer\n(IVCT) bands in the near-infrared region and by rhombic electron paramagnetic resonance features between <i>g</i> =\n1.9 and <i>g</i> = 2.3, which suggests considerable metal participation at the singly occupied MO. Alternatives for the\nd configuration assignment and for the role of the bisbidentate-conjugated bridging ligands will be discussed.\nThe main difference between bpip and bxip systems is the destabilization of the chloride-containing forms through\nthe bxip ligand for reasons of steric interference.