Stable Caged Actinides Proposed

A theoretical study of actinides bound within C₂₈ cages (An@C₂₈) shows that such complexes should be stable 32-electron complexes (J. Am. Chem. Soc., DOI: 10.1021/ja806811p). Jean-Pierre Dognon of the French Atomic Energy Commission; Carine Clavaguéra of Ecole Polytechnique, in France; and Pekka Pyykkö of the University of Helsinki, in Finland, used density functional computations to study Th@C₂₈, Pa⁺@C₂₈, U²⁺@C₂₈, and Pu⁴⁺@C₂₈. They found that all of the complexes should have tetrahedral symmetry, with 16 bonds between the cage and the metal. The computations further indicated that the 7s, 7p, 6d, and 5f orbitals of the central metal should hybridize with the C₂₈ cage orbitals, and that four electrons from the metal and 28 electrons from the cage should combine to form the 32-electron system. The calculated reaction enthalpies and Gibbs free energies are exothermic, they note, indicating that the complexes should form spontaneously in the gas phase, as has been found for the related U@C₂₈ system (Science 1992, 257, 1661). The authors propose that these actinide-carbon clusters could lead to materials with novel electronic, magnetic, and optical properties.