Unusual Structure, Bonding, and Properties in a Californium Borate

Abstract: The participation of the valence orbitals of actinides in bonding has been debated for decades. Recent experimental and computational investigations have demonstrated the involvement of 6p, 6d, and/or 5f orbitals in bonding. However, structural and spectroscopic data, as well as theory, indicate a decrease in covalency across the actinide series, and the evidence points to highly ionic, lanthanide-like bonding for late actinides. In this work, we show that chemical differentiation between californium and lanthanides can be achieved by using ligands that are both highly polarizable and that substantially rearrange upon complexation. A ligand that suits both of the above desired properties is polyborate. We demonstrate that the 5f, 6d, and 7p orbitals are all involved in bonding in a Cf(III) borate, and that large crystal field effects are present. Synthetic, structural, and spectroscopic data are complemented by quantum mechanical calculations to support these observations. i