Electronic Structure of Ru₂⁶⁺ Complexes with Electron-Rich Anilinopyridinate Ligands

Abstract

Diruthenium paddlewheel complexes supported by electron-rich anilinopyridinate (Xap) ligands were synthesized in the course of the first in-depth structural and spectroscopic interrogation of monocationic [Ru2(Xap)4Cl]+ species in the Ru2 6+ oxidation state. Despite paramagnetism of the compounds, 1H NMR spectroscopy proved highly informative for determining the isomerism of the Ru2 5+ and Ru2 6+ compounds. While most compounds are found to have the polar (4,0) geometry, with all four Xap ligands in the same orientation, some synthetic procedures resulted in a mixture of (4,0) and (3,1) isomers, most notably in the case of the parent compound Ru2(ap)4Cl. The isomerism of this compound has been overlooked in previous reports. Electrochemical studies demonstrate that oxidation potentials can be tuned by the installation of electron donating groups to the ligands, increasing accessibility of the Ru2 6+ oxidation state. The resulting Ru2 6+ monocations were found to have the expected (π*)2 ground state, and an in-depth study of the electronic transitions by Vis/NIR absorption and MCD spectroscopies with the aid of TD-DFT allowed for the assignment of the electronic spectra. The empty δ* orbital is the major acceptor orbital for the most prominent electronic transitions. Both Ru2 5+ and Ru2 6+ compounds were studied by Ru K-edge X-ray absorption spectroscopy; however, the rising edge energy is insensitive to redox changes in the compounds due to the broad line shape observed for 4d transition metal K-edges. DFT calculations indicate the presence of ligand orbitals at the frontier level, suggesting that further oxidation beyond Ru2 6+ will be ligand-centered rather than metal-centered.

Clarifying the structures of imidines: using crystallographic characterization to identify tautomers and localized systems of π-bonding

“…Nitrogen heterocycles are of considerable interest for their ability to act as ligands in coordination chemistry, notably supporting multimetallic compounds and, in particular, compounds having metal-metal bonds (Chipman & Berry, 2020;Beach et al, 2021;Kerru et al, 2020). Examples of these types of ligands can be seen in 2-naphthyridylphenylamine (Ding et al, 2015;Liu, Wang et al, 2009;Liu, Chen et al, 2009;Tsai et al, 2013), 1,8-naphthyridin-2(1H)-one (Chang et al, 2017), 2-anilinopyridinate (Roy et al, 2022) and 2,2 0 -dipyridylamine (Hdpa) (Chipman & Berry, 2018a,b;Lescoue ¨zec et al, 2001;Berry et al, 2003;Hsiao et al, 2008).…”