Direct Determination of a Giant Zero-Field Splitting of 5422 cm–1 in a Triplet Organobismuthinidene by Infrared Electron Paramagnetic Resonance

Stable monocoordinated organobismuthinidenes were only recently isolated and analyzed toward their chemical and electronic structure. Quantum chemical calculations on ^tBu-M^SFluind-Bi(I) (2) predicted an unusual electronic structure dominated by a triplet ground state and a spectacular zero-field splitting (ZFS) > 4500 cm^–1. However, experimental evidence for these predictions remained elusive due to limitations in the available magnetic characterization techniques. Herein, we determine an axial ZFS of D = 5422 cm^–1 for 2, by direct detection of triplet electron paramagnetic resonance using magneto-optical infrared spectroscopy. To date, this represents the largest ZFS experimentally measured.