Electronic Communication Across Diamagnetic Metal Bridges: A Homoleptic Gallium(III) Complex of a Redox-Active Diarylamido-Based Ligand and Its Oxidized Derivatives

Complexes with cations of the type [Ga­(L)2]n+ where L = bis­(4-methyl-2-(1H-pyrazol-1-yl)­phenyl)­amido and n = 1, 2, 3 have been prepared and structurally characterized. The electronic properties of each were probed by electrochemical and spectroscopic means and were interpreted with the aid of density functional theory (DFT) calculations. The dication, best described as [Ga­(L–)­(L0)]2+, is a Robin-Day class II mixed-valence species. As such, a broad, weak, solvent-dependent intervalence charge transfer (IVCT) band was found in the NIR spectrum in the range 6390–6925 cm–1, depending on the solvent. Band shape analyses and the use of Hush and Marcus relations revealed a modest electronic coupling, Hab of about 200 cm–1, and a large rate constant for electron transfer, ket, on the order of 1010 s–1 between redox active ligands. The dioxidized complex [Ga­(L0)2]3+ shows a half-field ΔMs = 2 transition in its solid-state X-band electron paramagnetic resonance (EPR) spectrum at 5 K, which indicates that the triplet state is thermally populated. DFT calculations (M06/Def2-SV­(P)) suggest that the singlet state is 21.7 cm–1 lower in energy than the triplet state.已合成并完成结构表征了通式为[Ga(L)₂]ⁿ⁺的阳离子配合物，其中L为双(4-甲基-2-(1H-吡唑-1-基)苯基)酰胺基，n取值为1、2、3。采用电化学与光谱学方法探究了各配合物的电子性质，并通过密度泛函理论（DFT）计算对实验结果进行了阐释。该双正电荷阳离子（最佳描述形式为[Ga(L⁻)(L⁰)]²⁺）属于罗宾-戴（Robin-Day）II类混合价物种。正因如此，在近红外（NIR）光谱的6390~6925 cm⁻¹区间内观测到了一条宽化、弱强度且溶剂依赖的价间电荷转移（IVCT）吸收带，其峰位随溶剂不同而发生变化。通过谱带形状分析并结合哈什（Hush）与马库斯（Marcus）关系式，得出该体系存在中等强度的电子耦合作用（Hab约为200 cm⁻¹），且氧化还原活性配体间的电子转移速率常数ket约为10¹⁰ s⁻¹。经两次氧化得到的配合物[Ga(L⁰)₂]³⁺在5 K下的固态X波段电子顺磁共振（EPR）光谱中，呈现出半场ΔMs=2的跃迁信号，这表明其三重态处于热占据状态。密度泛函理论（DFT，M06/Def2-SV(P)计算级别）计算结果显示，单重态的能量较三重态低21.7 cm⁻¹。