Electronic communication across diamagnetic metal bridges: a homoleptic gallium(III) complex of a redox-active diarylamido-based ligand and its oxidized derivatives

摘要

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 DFT calculations. The dication, best described as [Ga(L⁻)(L⁰)]²⁺, and 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 to 6925 cm⁻¹, depending on 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 di-oxidized complex [Ga(L⁰)2]³⁺ shows a half-field ΔMs = 2 transition in its solid-state X-Band 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.