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

Abstract

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.

Quantum-chemical insights into mixed-valence systems: within and beyond the Robin–Day scheme

“…So far it appears that mainly class II systems have been reported. 176,[179][180][181] Compounds in which thermal ET may proceed via the purely organic 2-2 0 -bipyridine part of the bridge (coordinating to different transition metals) may be a notable exception. 178 Here introduction of iridium leads to a class II/class III borderline complex, whereas Ru or Re bridges give class II behaviour.…”

“…However, the corresponding TDDFT calculations underestimated the IVCT energy significantly (3764 cm À1 compared to 6390 cm À1 ). 181 This likely reflects the fact that M06 exhibits only 27% exact-exchange admixture, i.e. less than the BLYP35-based protocol delineated above.…”

Pseudo-octahedral nickel(ii) complexes of strongly absorbing benzannulated pincer-type amido ligands: ligand-based redox and non-Aufbau electronic behaviour

“…This work is meant to contribute examples of strongly absorbing MCCs to the growing literature describing electronic communication between organic fragments mediated by metal bridges. 26,27…”

Synthesis and Characterization of Diferrocenyl Conjugates: Varying π‐Conjugated Bridging Ligands and its Consequence on Electrochemical Communication

“…The changes were also associated with appearance of one broad and very weak low‐energy absorption plateau centered at 1805 nm ( ε = 346 m –1 cm –1 ) in the NIR region. The weak band can be ascribed to IVCT (intervalence charge transfer) transition due to the formation of mixed valence species [Fc + ··· Fc 0 ] in the diferrocenyl conjugates,, and also observed in other dyads such as electroactive diarylamido ligand systems connected by Ga(III) . The IVCT transition originates from the electronic transitions from the Fe II →Fe III centers.…”