Volume 26, Issue 43 p. 9609-9619
Full Paper

Molecular Insights into the Ligand-Based Six-Proton- and Six-Electron-Transfer Processes Between Tris-ortho-Phenylenediamines and Tris-ortho-Benzoquinodiimines

Dr. Takeshi Matsumoto

Dr. Takeshi Matsumoto

Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga Bunkyo-ku, Tokyo 112–8551, Japan

Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama, 332-0012 Japan

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Risa Yamamoto

Risa Yamamoto

Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga Bunkyo-ku, Tokyo 112–8551, Japan

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Dr. Masanori Wakizaka

Dr. Masanori Wakizaka

Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga Bunkyo-ku, Tokyo 112–8551, Japan

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Dr. Akinobu Nakada

Dr. Akinobu Nakada

Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga Bunkyo-ku, Tokyo 112–8551, Japan

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Prof. Dr. Ho-Chol Chang

Corresponding Author

Prof. Dr. Ho-Chol Chang

Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga Bunkyo-ku, Tokyo 112–8551, Japan

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First published: 01 June 2020
Citations: 5

Graphical Abstract

Proton-coupled ligand-based mixed-valent FeII complexes that exhibit considerable correlation of the spin-states, were synthesized for the first time and characterized, and their potential to serve as multi-electron and multi-proton pools was examined.

Abstract

The global demand for energy and the concerns over climate issues renders the development of alternative renewable energy sources such as hydrogen (H2) important. A high-spin (hs) FeII complex with o-phenylenediamine (opda) ligands, [FeII(opda)3]2+ (hs-[6R]2+), was reported showing photochemical H2 evolution. In addition, a low-spin (ls) [FeII(bqdi)3]2+ (bqdi: o-benzoquinodiimine) (ls-[0R]2+) formation by O2 oxidation of hs-[6R]2+, accompanied by ligand-based six-proton and six-electron transfer, revealed the potential of the complex with redox-active ligands as a novel multiple-proton and -electron storage material, albeit that the mechanism has not yet been understood. This paper reports that the oxidized ls-[0R][PF6]2 can be reduced by hydrazine giving ls-[FeII(opda)(bqdi)2][PF6]2 (ls-[2R][PF6]2) and ls-[FeII(opda)2(bqdi)][PF6]2 (ls-[4R][PF6]2) with localized ligand-based proton-coupled mixed-valence (LPMV) states. The first isolation and characterization of the key intermediates with LPMV states offer unprecedented molecular insights into the design of photoresponsive molecule-based hydrogen-storage materials.

Conflict of interest

The authors declare no conflict of interest.