Metal Complex Chromophores Based on o-Iminobenzoquinonato Derivatives of Cobalt(III), Copper(II) and Nickel(II): Molecular Structure, Electronic Absorption Spectra, and Thermal Properties

A series of the 3d-row transition metal complexes was synthesized on the base of o-aminophenol APH₂^p-N_2Ph augmented by azo-fragment: bis-o-iminosemiquinonato derivatives ( imSQ^p-N_2Ph )2Ni (1), ( imSQ^p-N_2Ph )2Cu (2), as well as mixed-ligand compound ( imSQ^p-N_2Ph )( AP^p-N_2Ph )Co (3) (where imSQ^p-N_2Ph and AP^p-N_2Ph are radical anion and dianion redox-forms of ligand APH₂^p-N_2Ph , correspondingly). The molecular structures of ligand APH₂^p-N_2Ph and complexes 1⋅С7Н8, 2⋅С7Н8 and 3⋅С7Н8 were determined using X-ray diffraction (CCDC nos. 2444549–2444553, respectively). The planar coordination environment of metal center caused the mutual planar displacement of frontier orbitals HOMO and LUMO, that is why low-energy charge transfer “ligand-to-ligand” is implemented in compounds 1–3, corresponding to the light absorption in the IR region. Obtained metal complexes are characterized by rich set of redox states, predominantly provided by redox-active nature of ligands. The compounds of nickel(II) 1 and cobalt(III) 3 are volatile and distinguished by high thermostability and complete transfer into the vapor phase, that is the favourable factor for the design of optoelectronic devices based on them using the vacuum deposition method.