Intramolecular Redox-Driven Synthesis of Mono- and Diradical Iridium(III) Complexes: Insights into Molecular and...

Two π-radical complexes containing bisazo-aromatic-centered radical anion (1^⋅-) were synthesized through in-situ electron transfer from metal-to-ligand using [Ir^I] and 2-(2-Pyridylazo)azobenzene (1) in inert hydrocarbon solvent. These are characterized as diradical [Ir^III(1^⋅-)₂]⁺ [2]⁺ and monoradical [Ir^III(1^⋅-)Cl₂(PPh₃)] 3. In contrast, a rare metal-mediated hydrolytic cleavage of the C(sp²)-N bond occurred in protic solvent resulting in quaternary radical complex [Ir^III(1^⋅-)(1')(PPh₃)]⁺ (4)⁺. This provides an easy way to synthesize stable unsubstituted pyridine-2-diazotate (1'), an otherwise unstable organic template. Theoretical scrutiny has been performed at (U)B3LYP/6-31G(d,p)/LANL2DZ level to explore the origin of redox and optical properties in radical complexes. Magnetic study of [2]⁺ reveals that a weak antiferromagnetic (AF) spin-communication (J = -4.39 cm^-1) exists between two radicals, leading to an open-shell singlet ground state. Broken symmetry density functional theory (BS-DFT) calculations were carried out to probe the nature of antiferromagnetic exchange interaction between the two radical centers in species [2]⁺. This method has been employed with different basis functionals (BP86, BLYP, OLYP, TPSS0, TPSSh, ωb97D and B3LYP) to comprehend the nature of the exchange in [2]⁺. The best result is obtained for pure functional OLYP with a J value -8.4 cm^-1.