Intramolecular Redox-driven Synthesis of Mono- and Diradical Iridium(III) Complexes: Insights into Molecular and Electronic Structure, Electrochemistry, and Spin-Communication.

Two π-radical complexes containing bisazo-aromatic-centered radical anion (1•-) were synthesized through in-situ electron transfer from metal-to-ligand using [IrI] and 2-(2-Pyridylazo)azobenzene (1) in inert hydrocarbon solvent. These are characterized as diradical [IrIII(1•-)2]+[2]+ and monoradical [IrIII(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 [IrIII(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.