Benzoate-bridged paddlewheel diruthenium(II,II) complexes ([Ru^II,II₂(R_nArCO₂)₄(L_ax)₂] (L_ax = axial ligand); [Ru^II,II₂]) exhibit reversible redox activity involving the oxidized species [Ru^II,III₂]⁺. The redox activity can be finely tuned over a broad potential range by altering the substituent R on the benzoate-bridging ligand R_nArCO₂⁻. The electronic contributions of the substituents R depend on their type and position, as was empirically demonstrated by Hammett for substituents at the meta- and para-positions. However, the substituent effect at the ortho-position is not solely determined by the electronic contribution of R but also by steric hindrance between the o-substituents and adjacent carboxylate groups. Nevertheless, an OH group at the o-position did not provide any steric hindrance, leading to a strong electron-withdrawing effect owing to intramolecular hydrogen bonding between the o-OH group and the adjacent carboxylate group, despite the electron-donating ability of the m- and p-OH groups. The OH group at the o-position induced a significant shift in the redox potential and HOMO energy levels of the [Ru^II,II₂] complexes, thereby stabilizing the [Ru^II,II₂] state. The redox potential and HOMO can be adjusted by introducing additional substituents, such as F, Cl, Me, OMe, and CF₃ groups, to cover a wide range, in accordance with an extended Hammett law that considers the contribution of the o-position.

中文翻译：

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介绍用于调节苯甲酸盐桥式桨轮二钌 （II，II） 配合物氧化还原性能的取代基：OH 基团带来什么？


苯甲酸盐桥式桨轮二钌 （II，II） 配合物 （[Ru^II，II₂（R_nArCO₂）₄（L_ax）₂] （L_ax = 轴向配体）;[Ru^II，II₂]）表现出涉及氧化物质 [Ru^II，III₂]⁺ 的可逆氧化还原活性。通过改变苯甲酸盐桥接配体 R_nArCO₂⁻ 上的取代基 R，可以在很宽的电位范围内微调氧化还原活性。取代基 R 的电子贡献取决于它们的类型和位置，正如 Hammett 对位位和对位的取代基的经验证明的那样。然而，邻位的取代基效应不仅取决于 R 的电子贡献，还取决于 o 取代基和相邻羧酸盐基团之间的空间位阻。然而，尽管 m- 和 p-OH 基团具有电子供体能力，但 o 位的 OH 基团没有提供任何空间位阻，由于 o-OH 基团和相邻羧酸盐基团之间的分子内氢键，导致强大的吸电子效应。o 位的 OH 基团诱导 [Ru^II，II₂] 配合物的氧化还原电位和 HOMO 能级发生显着变化，从而稳定 [Ru^II，II₂] 状态。 氧化还原电位和 HOMO 可以通过引入额外的取代基（如 F、Cl、Me、OMe 和 CF₃ 基团）来调整，以覆盖较宽的范围，符合考虑 o 位置贡献的扩展哈米特定律。