Abstract
Using the RuCl(m-tppz)ClRu2+ tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine platform for bridging two o-quinone/catecholate two-step redox systems (unsubstituted, Qn, or 3,5-di-tert-butyl-substituted, DTBQn), the authors have obtained the stable complexes (Q·-)RuIICl(m-tppz)ClRuII(Q·-) (1) and the structurally characterized (DTBQ·-)RuIICl(m-tppz)ClRuII(DTBQ·-) (2). The compds. exhibit mostly quinone-ligand-based redox activity within a narrow potential range, high-intensity near-IR absorptions (lmax $\approx$ 920 nm; e \textgreater 50,000 M-1/cm-1), and variable intra- and intermol. spin-spin interactions. D. functional theory calcns., EPR, and spectroelectrochem. results (UV-visible-near-IR region) for three one-electron-redn. and two one-electron-oxidn. processes were used to probe the electronic structures of the systems in the various accessible valence states. EPR spectroscopy of the singly charged doublet species showed semiquinone-type response for 1+, 2+, and 2-, while 1 exhibits more metal based spin, a consequence of the easier redn. of Q as compared to DTBQ. Comparison with the analogous redox series involving a more basic N-phenyliminoquinone ligand reveals significant differences related to the shifted redox potentials, different space requirements, and different interactions between the metals and the quinone-type ligands. As a result, the tppz bridge is reduced here only after full redn. of the terminal quinone ligands to their catecholate states. on SciFinder(R)
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