Structures, bonding, and stability of half-sandwich complexes with genetal formula, NgMCp(+) (Ng = He-Rn, M = Be-Ba, Cp = eta(5)-(CH5)-H-5) are analyzed through ab initio computation. MCp+ complexes possess remarkable Ng binding ability, particularly for M = Be and Mg. While for Ar- Rn bound analogues the bond dissociation energy in the former complex ranges within 17.5-28.0 kcal mol(-1), it becomes 10.4-18.7 kcal mol(-1) in the latter complex. In fact, BeCp+ is able to form a strong bond with the two most inert elements, He and Ne. Although the Ng binding ability of MCp+ gradually diminishes in moving from Be to Ba, the corresponding free energy change values show that Kr-Rn bound complexes involving the heavier congeners of Mg would remain in the bound state avoiding dissociation into Ng and MCp+. The nature of the Ng-M bond is characterized by natural bond orbital, electron density and energy decomposition analyses in conjunction with the natural orbital for chemical valence (EDA-NOCV) analysis. While the electron density analysis reveals that Ng-Be (Ng = Kr, Xe, Rn) and Ng-Mg (Ng = Xe, Rn) bonds are partly covalent in nature, the orbital interaction (Delta E-orb) is found to be the most important term in the Ng-M attractive energy as revealed by the EDA-NOCV. For all Ngs, the major contribution toward the Delta E-orb energy term originates from Ng -> MCp+ sigma-donation. Additionally, CpBeNgF (Ng = Kr-Rn) and CpNgF (Ng = Kr-Rn) are found to be viable systems with kinetic protection for the exergonic dissociation channels, CpBeNgF -> Ng + CpBeF and CpNgF -> Ng + CpF, respectively, where the activation free energy barrier in the latter systems (24.I-34.7 kcal mol(-1)) is significantly larger than that in the former ones (6:6-8.9 kcal:mol). CpNgF (Ng = Kr-Rn) complexes are predicted to be stable even above 300 K, whereas CpBeNgF (Ng = Xe, Rn) would be viable.np to similar to 100 K. While the F-Ng bonds are ionic in nature, the Ng-Be and Ng-C bonds in these complexes have significant covalent character.