Synthesis and Characterization of a New Series of Binuclear Pd(II) Biscatecholato Complexes: Non-Innocent Ligand-Based Approach to a Wide Range of Variation in Near-Infrared Absorptions of Mixed-Valence Complexes

Abstract

In this study, we report synthesis of a new series of mixedvalence (MV) complexes having intervalence charge transfer (IVCT) energies variable from the first to the third telecommunication window. This wide-range modulation was achieved by variation of covalently-dimerized catecholato ligands, in combination with Pd(II) ions, which lowered the oxidation potentials and enabled access to MV states. Importantly, we found that regulation of the conjugation lengths enabled energy gap control and annulation of an additional benzene ring switched the nature of the IVCT transitions. These changes were accompanied by a cross-over from moderately delocalized Class II to delocalized Class III character according to the Robin-Day classification. Through accurate comparisons with well-known ferrocene counterparts and their heteroconjugate, our non-innocent ligand-based approach is found to be effective for controlling IVCT parameters. These findings offer a new approach to materials design for electro-optic switching.