PNNL

Abstract

The electronic and chemical structure of the actinide elements remains one of the final frontiers of the periodic table. Despite decades of research, many questions remain as to the role and participation of late actinide 5f electrons in bonding, aromaticity, catalysis, and reactivity. As such, we are interested in exploring the chemistry of neptunium compounds containing the linear neptunyl ion (NpO22+ or NpO2+) that can be equatorially coordinated by multidentate organic ligands. Herein, we report the synthesis, structure, and characterization of two neptunyl complexes that contain phenylene-substituted benzyl ester bis(pyrrole)phenylenediamine (named “pyrrophen”) coordination ligands. In one case, the neptunium center exists in a mixed +5 and +6 oxidation state, whereas the other is restricted a +6 oxidation state. We have identified the differences that are likely to cause this discrepancy between the two complexes by examining the ions and their coordinative environments. This is the first time pyrrophen has been utilized in Np chemistry and demonstrates a new platform to study 5f electron participation and coordination.