Lanthanoid Semiquinonate/Tropolonate Complexes: Redox Chemistry and Luminescence

Abstract

Heteroleptic lanthanoid (Ln = Eu, Gd, Tb, Dy, Ho and Yb) complexes featuring hydro‐tris(1‐pyrazolyl)borate (Tp−) ligands combined with the bidentate O‐donor ligands tropolonate (trop−) or 3,5‐di‐tertbutylseminquinonate (dbsq●−) have been synthesized and investigated. Despite the similarity of the bidentate O‐donor trop− and dbsq●− ligands, and the lanthanoid coordination geometries, the complexes [LnTp2dbsq] (Ln‐dbsq) and [LnTp2trop] (Ln‐trop) exhibit markedly different redox and photophysical properties. The electrochemistry of Ln‐dbsq is dominated by processes associated with the readily redox‐active dbsq●− moiety. In contrast, the relative redox inactivity in Ln‐trop allows for the observation of the Eu(III) to Eu(II) reduction process. Photophysical measurements reveal no sensitized emission for the Ln‐dbsq family, while the trop− antenna ligand is able to sensitize emission in the visible range for Eu(III) and Ho(III), and in the near‐infrared for Ho(III) and Yb(III).