부산대학교 도서관

The title compounds are studied with scalar relativistic, gradient-corrected (PBE) and hybrid (PBE0) density functional theory. The metal–Cp centroid distances shorten from ThCp3to NpCp3, but lengthen again from PuCp3to CmCp3. Examination of the valence molecular orbital structures reveals that the highest-lying Cp π2,3-based orbitals transform as 1e + 2e + 1a1+ 1a2. Above these levels come the predominantly metal-based 5f orbitals, which stabilise across the actinide series such that in CmCp3the 5f manifold is at more negative energy than the Cp π2,3-based levels. Mulliken population analysis shows metal d orbital participation in the e symmetry Cp π2,3-based orbitals. Metal 5f character is found in the 1a1and 1a2levels, and this contribution increases significantly from ThCp3to AmCp3. This is in agreement with the metal spin densities, which are enhanced above their formal value in NpCp3, PuCp3and especially AmCp3with both PBE and PBE0. However, atoms-in-molecules analysis of the electron densities indicates that the An–Cp bonding is very ionic, increasingly so as the actinide becomes heavier. It is concluded that the large metal orbital contributions to the Cp π2,3-based levels, and enhanced metal spin densities toward the middle of the actinide series arise from a coincidental energy match of metal and ligand orbitals, and do not reflect genuinely increased covalency (in the sense of appreciable overlap between metal and ligand levels and a build up of electron density in the region between the actinide and carbon nuclei). [ABSTRACT FROM AUTHOR]