Probing the Intramolecular Metal-Selenoether Interaction in a Bis(iminosemiquinone)copper(II) Compound

Abstract: The selenoether compound [Cu(QSeMe)₂], H₂QSeMe = 4,6-Di-tert-butyl-2-(2-methylselenophenyl)aminophenol, exhibits solvate-dependent NCuO/OCuN twisting (24° and 33°) and very weak Cu-chalcogen interactions (3.30-3.55 A) in the crystal. Structural studies as well as EPR and magnetic measurements confirm a bis(iminosemiquinone)copper(II) configuration with one ligand-based spin in the S = ½ ground state. A spin up-down-up sequence is thus inferred for the (Q*-)-CuII-(Q*-) three-spin system. UV-Vis-NIR Spectroelectrochemistry in CH₂Cl₂/0.1 M Bu₄NPF₆ reveals a broad ligand-to-ligand intervalence charge transfer (Q²-  Q*-) band at 1910 nm for the monoanion whereas the stepwise two-electron oxidation leads to loss of intensity in the near infrared region. DFT calculations of structure, spin density, and electronic transitions were performed to confirm the assignments of oxidation states and absorption features.