Aluminum Complexes of N2O23– Formazanate Ligands Supported by Phosphine Oxide Donors

The synthesis and characterization of a new family of phosphine oxide supported aluminum formazanate complexes (7a,b, 8a, 9a) are reported. X-ray diffraction studies showed that the aluminum atoms in the complexes adopt an octahedral geometry in the solid state. The equatorial positions are occupied by an N2O23– formazanate ligand, and the axial positions are occupied by L-type phosphine oxide donors. UV–vis absorption spectroscopy revealed that the complexes were strongly absorbing (e ≈ 30000 M–1 cm–1) between 500 and 700 nm. The absorption maxima in this region were simulated using time-dependent density functional theory. With the exception of 3-cyano-substituted complex 7b, which showed maximum luminescence intensity in the presence of excess phosphine oxide, the title complexes are nonemissive in solution and the solid state. The electrochemical properties of the complexes were probed using cyclic voltammetry. Each complex underwent sequential one-electron oxidations in potential ranges of −0.12 to 0...