What is the structure of FeC5H6+?

Calculations performed using both density functional theory (DFT) and the modified coupled-pair functional (MCPF) approach show that FeC5H6+ is more stable than HFeC5H5+ by about 10 kcal/mol. The ground state of FeC5H6+ is a quartet state derived from the 3d7 occupation of Fe+. For HFeC5H5+, the MCPF approach yields a sextet ground state while DFT yields a quartet; however, these two states are close in energy at both levels of theory.