Stable monocoordinated organobismuthinidenes were only recently isolated and analyzed toward their chemical and electronic structure. Quantum chemical calculations on Bu-MFluind-Bi(I) () predicted an unusual electronic structure dominated by a triplet ground state and a spectacular zero-field splitting (ZFS) > 4500 cm. However, experimental evidence for these predictions remained elusive due to limitations in the available magnetic characterization techniques. Herein, we determine an axial ZFS of = 5422 cm for , by direct detection of triplet electron paramagnetic resonance using magneto-optical infrared spectroscopy. To date, this represents the largest ZFS experimentally measured.
