Direct Synthesis of an Unprecedented Stable Radical of Nickel(II) 3,5-Bis(dimedonyl)azadiisoindomethene with Strong and Narrow Near-Infrared Absorption at λ ∼ 1000 nm.

An unprecedented stable neutral radical nickel(II) complex of 3,5-bis(dimedonyl)azadiisoindomethene (1) was prepared by the direct reaction between 1,3-diiminoisoindoline and dimedone. A new radical complex 1 has an intense and narrow absorption at 1008 nm and can be reduced to a less stable anionic [1] ^- with a typical aza(dibenzo)boron dipyrromethene (aza-BODIPY) UV-vis spectrum. Complex 1, along with two other colored condensation reaction products 2 and 3, was characterized by spectroscopy and X-ray crystallography, while the paramagnetic nature of 1 was probed by EPR and SQUID methods. Complex 1 forms dimers in the solid state with short (∼3.16 Å) Ni---Ni contacts. Redox data on 1 are indicative of a reversible reduction process in this complex; its magnetism suggests a S = ¹ / ₂ state with the spin density delocalized over the aza-BODIPY core. The experimental data 1 and [1] ^- were correlated with the density functional theory (DFT) and time-dependent DFT calculations.