Bis-triarylamine with a cyclometalated diosmium bridge: A multi-stage redox-active system

A tetra(pyrid-2-yl)-pyrazine-bridged cyclometalated diosmium complex 1(PF6)2 with two distal redox-active organic amine substituents has been synthesized and characterized. This complex displays four consecutive and separated anodic redox waves at +0.24, +0.38, +0.64, and +0.71 V vs. Ag/AgCl. Upon stepwise oxidation, four-step absorption spectral changes in the visible to near-infrared region have been observed. The different redox states of 1 (12+ through 16+) can be distinguished by the significantly different absorption spectra in the visible and near-infrared region. DFT calculations of 13+ show that the spin is delocalized on both osmium–amine components.

Graphical abstractThe four-center complex with the [N–Os–Os–N] array shows four consecutive redox processes at relatively low potentials. The corresponding five redox states are characterized by significantly different absorption spectra in the visible and near-infrared region.Figure optionsDownload full-size imageDownload as PowerPoint slide