Electronic structure of a beryllium half‐sandwich complex, Be(η 5 ‐C 5 H 5 )

Ab initio electron propagator calculations on the electron affinities of the $ {\rm Be(\eta ^5-C_5H_5)}^{+} $ complex cation and electron detachment energies of the corresponding anion have been performed at the optimized geometry of the ground state of the neutral species. These results, obtained with a basis set that includes many diffuse and polarization functions, provide the relative energies of doublet states of $ {\rm Be(\eta ^5-C_5H_5)} $ . In the former set of calculations, energy differences between the 2 A 1 ground‐state and various excited doublet states are associated with promotion of an unpaired electron from the 6a 1 molecular orbital that consists chiefly of s functions on the Be nucleus to higher Be‐centered molecular orbitals that exhibit various patterns of interference between s, p, and d functions. Differences between electron detachment energies of the anion provide the energy separation between the radical's ground state and an excited state in which an electron is promoted from ligand‐centered π orbitals to 6a 1 . Dyson orbitals and pole strengths corresponding to correlated electron binding energies calculated with various diagonal self‐energy approximations confirm these qualitative pictures of the electronic structure of the lowest states of $ {\rm Be(\eta ^5-C_5H_5)} $ . © 2012 Wiley Periodicals, Inc.