Structural, spectroscopic and theoretical studies of diosmium(III,III) tetracarboxylates

The preparation of Os2(TiPB)4Cl2 (1; TiPB = 2,4,6-triisopropylbenzoate) and Os2(TiPB)2(OAc)2Cl2 (2) by carboxylate exchange reactions with Os2(OAc)4Cl2 is reported. The structure of 1 has been determined by single-crystal X-ray studies, and shows a paddlewheel arrangement of the ligands about the triply bonded diosmium core. Both compounds have magnetic moments at room temperature that are consistent with the presence of two unpaired electrons, and their cyclic voltammograms show a single redox process corresponding to the Os2(5+/6+) redox couple. The electronic absorption spectra of 1 and 2 display an absorption at ~395 nm, corresponding to the π(Cl) →π*(Os2) LMCT transition, as well as numerous weaker absorptions at lower energy. Density functional theory (DFT) calculations on Os2(OAc)4Cl2 at different levels of theory (B3LYP and PBE0) have been used to probe the electronic structure of diosmium tetracarboxylates. The calculations show that these compounds have a σ(2)π(4)δ(2)δ*(1)π*(1) electronic configuration, and time-dependent DFT was used to help rationalize their optical properties.