Structural Characterization and Bonding Analysis of [hg{fe(co)5}2]2+ [Sbf6]- 2

The non-classical carbonyl complex [Hg{Fe(CO)(5)}(2)](2+) [SbF6](-) (2) is prepared by reaction of Hg(SbF6)(2) and excessFe(CO)(5) in anhydrous HF. The single-crystal X-ray structurereveals a linear Fe-Hg-Fe moiety as well as an eclipsedconformation of the eight basal CO ligands. Interestingly, the Hg-Febond length of 2.5745(7) & ANGS; is relatively similar to the correspondingHg-Fe bonds in literature-known [Hg{Fe(CO)(4)}(2)](2-) dianions (2.52-2.55 & ANGS;),which intrigued us to analyze the bonding situation in both the dicationsand dianions with the energy decomposition analysis with natural orbitalsfor chemical valence (EDA-NOCV) method. Both species are best describedas Hg(0) compounds, which are also confirmed by the shape of the HOMO-4and HOMO-5 of the dication and dianion, respectively, in which theelectron pair is located mainly at the Hg. Furthermore, for the dicationand the dianion, the & sigma; back-donation from Hg into the [Fe(CO)(5)](2) (2+) or the [Fe(CO)(4)](2) (2-) fragment is the most dominant orbitalinteraction and surprisingly these interaction energies are also verysimilar even in absolute values. The fact that both iron-based fragmentsare missing two electrons explains their prominent & sigma;-acceptorproperties.