Crystallographic evidence for Bi(I) as the heaviest halogen bond acceptor

Complexation of a bismuthinidene (RBi) with two equivalents of a highly fluorinated aryl iodide at low temperature al-lows the crystallographic identification of an unstable species that can be regarded as an intermediate of an oxidative addition reaction. Both C-I bonds are orientated towards the filled 6p orbital of bismuth (Bi-I distances 3.44-3.52 Å), leading to an elongation of the C-I bonds by 0.05 and 0.07 Å. DFT calculations confirm that the bismuth center is indeed acting as an electron donor, establishing two strong and directional halogen bonds. As such, this study presents the first structural proof of bismuth, (and more generally of heavy organopnictogen compounds in oxidation state +1), acting as halogen bond acceptors.