Back-donation from metal

A simple description of the charge transfer process in molecular orbital terms is that electron density is back-donated from metal d-bands into the CO ir orbital, which is anti-bonding in character (14). The relatively small size of the frequency shift implies that the extent of charge transfer is small. As a result, the C-0 bond order is still close to 3.0 for linearly adsorbed molecules. 

Ti back-donation from metal to carbon increases... 

The electronic structures of the metal carbonyls have been investigated vigorously over the past few years because the interaction between CO and metals (76, 137) is essential for an understanding of both organometallic chemistry and CO chemisorption phenomena. There is continuing debate concerning the relative importance of o-donation from the carbon lone pair of carbon monoxide and back donation from metal d electrons into vacant rr ligand orbitals. The most frequently cited data in favor of n back donation are... 

Such shifts can be rationalized in terms of the model of synergic a and ir bonding of the CO ligand in metal carbonyls (29) as was proposed by Blyholder (30). The formation of a strong surface bond involves considerable back donation from metal d... 

The rhodium binding energy is 0.5 eV higher in the case of the bis-isocyanide derivative. This is in favor of the effective ji back donation from metal to ligand that is also reflected by the energy of the isocyanide stretching vibration in the IR spectrum of the complex. 

Donation from ligand Back donation from metal... 

Figure 1 Diagrammatic representation of the synergic bonding in a metal carbonyl forward a-donation from a filled CO orbital, balanced by back-donation from metal orbitals of appropriate symmetry into the CO n orbitals.

Another very interesting family of phosphorons ligands is the recently synthesized class of A-pyrrolyl phosphine componnds. The pyrrazolyl moiety is known for its n-involvement (back donation from metal to ligand) and should greatly affect the binding ability of the phosphine. 

The results shown in Table 7 indicate that the vco frequencies of the 1 2 adducts are always higher than those of 1 1 adducts. This may result from the decreased n -back donation from metal to CO which is caused by competition between two CO groups in the 1 2 adduct . For 1 2 adducts, Vco frequencies are in order of Co " " > Fe > Ru > Os " ". Thus, the degree of Jt-back donation to CO increases in the order of Co < Fe " " < Ru < Os ". ... 

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. 

The C—0 stretching vibrations in metal carbonyl complexes absorb at lower frequencies than the corresponding vibration in CO itself (2143 cm" ). 7c-Back donation from metal into the n orbitals of carbon monoxide reduces the C—0 bond order. The higher the electron density on the metal, the more the back donation and the greater reduction in C—0 bond order and frequency. In... 

The second term of Eq. (24) represents electron backdonation from adsorbate to surface, the third electron back donation from metal surface to adsorbate. 

Shows how the energy separation A between the t2g and e, molecular orbitals may be inoeased when tr- back-donation from metal to ligands occurs. 

Considering M-Ceo interaction in terms of Dewar-Chatt-Duncanson model [50, 51] one should study in a couples a-donation of 7r-electrons to the metal and a TT-bond back-donation from metal to the lowest vacant orbitals of interacting carbon (6-6 ) bond. 

The interaction between transition metal atoms (M) and fullerenes is often characterized in terms of the Dewar-Chatt-Duncanson model [67, 68], which implies electron donation from bonding orbitals at the organic ligand into unoccupied d orbitals of a symmetry at the metal as well as back donation from metal df-orbitals of 7T symmetry into vacant tt. Molecular orbitals at the interacting carbon-carbon double bond. We find that this picture describes the ) -coordinated Pd atom well at a (6-6 ) junction. The occupancy of the donating Pd -orbital remains essentially constant at 1.64 c as additional metal atoms are adsorbed. 

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