Metal-metal bonded diruthenium unit axial-capped by di-tert-butylphenolate: [Ru₂(O₂CCH₃)₂(t-Busal-R′py) ₂]^- (t-Busal-R′py^2- = N-(R′-2-pyridyl)-2-oxido-3,5-di-tert-butylbenzylaminato; R′ = H, 4-Me, and 5-Me)

Three diruthenium compounds, [Na(18-crown-6)(thf)₂][Ru ₂(O₂CCH₃)₂(t-Busalpy)₂] (1), [K(18-crown-6)(thf)₂][Ru₂(O₂CCH ₃)₂(t-Busal-4-Mepy)₂] (2), and [K(18-crown-6)(thf)(H₂O)][K(18-crown-6)(thf)(MeO)][Ru ₂(O₂CCH₃)₂(t-Busal-5-Mepy) ₂] (3) (18-crown-6 = 1,4,7,10,13,16-hexaoxocyclooctadecane; 18-crown-6-ether), have been synthesized by the ligand substitution reaction of Ru₂(O₂CCH₃)₄Cl with newly prepared tridentate bridging/chelating ligands, N-(2-pyridyl)-2-oxido-3,5-di-tert- butylbenzylaminato (t-Busalpy^2-), N-(4-methyl-2-pyridyl)-2-oxido-3,5- di-tert-butylbenzylaminato (t-Busal-4-Mepy^2-), and N-(5-methyl-2-pyridyl)-2-oxido-3,5-di-tert-butylbenzylaminato (t-Busal-5-Mepy^2-), respectively, and isolated using [Na(18-crown-6)]⁺ or [K(18-crown-6)]⁺ as the counter cation. The structural features of the anionic parts are very similar to those of the previously synthesized family of [Ru₂(O₂CCH ₃)₂(5-Rsalpy)₂]^- (R = H, Me, Cl, Br, and NO₂); two acetate and two t-Busal-R′py^2- ligands are respectively located around the Ru₂ unit in a trans fashion, where the t-Busal-R′py^2- ligand acts as a tridentate ligand having both bridging and chelating characters to form the M-M bridging/axial-chelating mode. Their Ru-Ru bonded core with an electronic configuration of σ²π⁴δ²(π *δ*)³ is axial-capped by the di-t-butylphenolate groups of the t-Busal-R′py^2- ligands, and experiences multi-redox properties: a one-electron reduction to Ru₂⁴⁺ and two one-electron oxidations to Ru₂⁶⁺ followed by Ru₂⁷⁺, in addition to t-Busal-R′py^2- ligand-centered redox. The strong electron-donating ability of the t-butyl groups compared with the other R-groups leads to negative shifts of the redox potentials according to the Hammett law.