Transition Blyholder model

The Blyholder model [94-96] describes the MO interaction of a CO molecule at a transition metal surface. The lone pair of electrons on the carbon atom (5cr, HOMO) donates into the metal, forming a a -bond. The d-orbitals of the metal donate electron density into the anti-bonding (2jr, LUMO) orbital of CO giving rise to a jr-bond (back donation). The energetic shift of the 5cr orbital is therefore directly related to the strength of the bond formed between CO and the surface (lower 5cr... 

The chemisorptive bond is a chemical bond. The nature of this bond can be covalent or can have a strong ionic character. The formation of the chemisorptive bond in general involves either donation of electrons from the adsorbate to the metal (donation) or donation of electrons from the metal to the adsorbate (backdonation).2 In the former case the adsorbate is termed electron donor, in the latter case it is termed electron acceptor.3 In many cases both donation and backdonation of electrons is involved in chemisorptive bond formation and the adsorbate behaves both as an electron acceptor and as an electron donor. A typical example is the chemisorption of CO on transition metals where, according to the model first described by Blyholder,4 the chemisorptive bond formation involves both donation of electrons from the 7t orbitals of CO to the metal and backdonation of electrons from the metal to the antibonding n orbitals of CO. 

The adsorption of carbon monoxide on metal surfaces can be qualitatively understood using a model originally formulated by Blyholder [45]. A simplified molecular orbital picture of the interaction of CO with a transition metal surface is given in Figure 6. The CO frontier orbitals 5a and 2n interact with the localized d metal states by splitting into bonding and antibonding hybridized metal-... 

Carbon Monoxide. Carbon monoxide is the probe molecule by far the most frequently used to probe metal nitride surfaces. As for other transition metals, the interaction of a CO molecule with metal surfaces could be understood via the Blyholder s model. Thus, CO donates electrons from the 5a orbital into metal c/-orbitals and receives back-donation from metal d-orbitals into its 27t antibonding orbitals. The 5a donation can occur without significant weakening of the CO bond. However, the backdonation to the 27t antibonding orbitals can significantly weaken the CO bond while strengthen the metal-carbon bond. 

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