cis-Thioindigo (TI) - a new ligand with accessible radical anion and dianion states. Strong magnetic coupling in the {[TI-(μ-O),(μ-O)]Cp*Cr} dimers.

Reaction of decamethylchromocene (CpCr) with thioindigo (TI) yields a coordination complex {[TI-(μ-O), (μ-O)]CpCr}·CH (1) in which one Cp* ligand in CpCr is substituted by TI. TI adopts cis-conformation in 1 allowing the coordination of both carbonyl groups to chromium. Additionally, one oxygen atom of TI becomes a μ-bridge for two chromium atoms to form {[TI-(μ-O), (μ-O)]CpCr} dimers with a CrCr distance of 3.12 Å. According to magnetic data, diamagnetic TI dianions and two Cr atoms with a high S = 3/2 spin state are present in a dimer allowing strong antiferromagnetic coupling between two Cr spins with an exchange interaction of -35.4 K and the decrease of molar magnetic susceptibility below 140 K. Paramagnetic TI˙ radical anions with the S = 1/2 spin state have also been obtained and studied in crystalline {cryptand2,2,2}(TI˙) (2) salt showing that both radical anion and dianion states are accessible for TI.