A-backbonding

The pi bond between the metal and carbon atom arises as a result of a backbonding interaction between a filled metal rf-orbital of the appropriate symmetry and the empty pi star orbital of the carbonyl. Any factor that increases the electron density at the metal will increase the strength of the M C pi bond, and thus the contribution from resonance form b. The result is a... 

The principal bonding interaction occurs between metallic u and cr frontier orbitals and the a C2 orbitals. You expect this because the [Mn(CO)s]+ fragment is isolobal with [CH3]+ and the product is isolobal with 2-butyne. However, the metal fragment provides the opportunity for weaker interactions between the tt-symmetry orbitals. These are of two types. A backbonding interaction (occupied metallic 77 orbitals with unoccupied C2 tt ) transfers charge from the metal to the C2 unit, thereby reducing the C-C bond order. For this compound, the observed C-C distance is consistent with a bond order of three hence, the interac-... 

The large frequency shift (— 100 cm V ) observed for the 1200 cm band of adsorbed sulfate was attributed to a Stark effect by Kunimatsu et al. [36] and to a backbonding mechanism by Faguy et al. [141]. The potential-induced band shift in the case of sulfate ions must be analyzed in more detail. It was observed that the band center for the 1200 cm feature of adsorbed sulfate presents, additionally, a dependence on the degree of coverage [142, 165]. Since the latter is also a function of the potential, it is clear that a part of the frequency change can be due to lateral interactions, as discussed in Sec. 9.5 for sulfate ions adsorbed on Pt(lll). 

Fig. 14. A perspect view of the (O + O2) adsorption using the model slab (2X2 unit cell). The oxygen atoms are represented by black circles. One oxygen atom is inserted within a backbond and a dioxygen molecule is adsorbed on the dangling bonds and forms a triangular peroxo species.

H-terminated kink site atom on a (111) surface that reacts with water (see Figure 2.42). Models vary depending on whether a Si-H bond on the kink site atom is first attacked or whether solvolytic splitting of a backbonds initiates the dissolution reaction. Figures 2.42 and 2.43 show this situation including the initial attack for... 

When an alkene acts as a ligand, as ethylene does in Zeise s salt, it binds to the metal in a sideways manner, where the C-C T(, MO donates electron density to an empty orbital on the metal, as shown in Figure 18.15, and the m MO accepts electron density back from a filled d-orbital on the metal. As a result, the C=C bond is weakened by both the r-donation and the a -backbonding interaction. The C=C bond length in free ethylene is 133.7 pm in Zeise s salt it increases to 137.5 pm and it is as lar ge as 143 pm in [F (PPh3)2(C2H4)], where the metal is electron-rich as a result of the low oxidation number and donor ligands. 

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