Molecular orbitals carbon monoxide

Furthermore, the binding energy difference between the 4a and 5a carbon monoxide molecular orbitals, A(4o-5o), varies by only 0.3 eV ( 7 7, 82-88). The vibrational spectra show tremendous differences, however. Both nickel (89) and palladium (68) form multiply coordinated carbonyl species at low CO exposures and the atop species are only seen at high coverage. 

A particular difference lies in the organometallic chemistry in low oxidation states. Transition metals form stable binary carbonyls—for example, Fe(CO)s and Ni(CO)4 are volatile liquids, stable at elevated temperatures, and Os3(CO)i2 decomposes at 190 °C to other carbonyls such as Os6(CO)i8. In contrast, lanthanide carbonyls, prepared by cocondensation of lanthanide atoms with Ar/CO mixtures at 4.2 K, are only stable at these very low temperatures, decomposing above 20 K. The ability of metals in the middle of the d block to form carbonyls is related to their possessing vacant d orbitals that can accept electron pairs from the o-donor CO ligand, and also some filled d orbitals that can participate in n back-donations (back-bonding). In fact, CO is not a strong enough r-donor to bind well to lanthanides, and the lanthanide 4f orbitals are not suitable to 7r-bond to carbon monoxide. Molecular orbital (MO) calculations indicate that the bonds in these compounds are very weak indeed. ... 

Fig. 29. Interaction of gas phase carbon monoxide molecular orbitals with the filled energy levels of a transition metal to form bonding orbitals for associatively adsorbed CO...

Fig. 1.16. Interaction of atomic orbitals of carbon and oxygen leading to molecular orbitals of carbon monoxide.

Fig. 1.17. Representation of the molecular orbitals of carbon monoxide. Energies are given in atomic units (1 a.u. 27.21 eV). (From W L. Jorgensen and L. Salem, 77i Organic Chemist s Book of Orbitals, Academic Press, New York, 1973. Reproduced wifli permission.)...

Figure 2.14. The molecular orbitals of gas phase carbon monoxide, (a) Energy diagram indicating how the molecular orbitals arise from the combination of atomic orbitals of carbon (C) and oxygen (O). Conventional arrows are used to indicate the spin orientations of electrons in the occupied orbitals. Asterisks denote antibonding molecular orbitals, (b) Spatial distributions of key orbitals involved in the chemisorption of carbon monoxide. Barring indicates empty orbitals.5 (c) Electronic configurations of CO and NO in vacuum as compared to the density of states of a Pt(lll) cluster.11 Reprinted from ref. 11 with permission from Elsevier Science.

G. Blyholder, Molecular Orbital View of Chemisorbed Carbon Monoxide, J. Phys. Chem. 68, 27-72 (1964). 

Figure 6-12. Schematic molecular orbital diagram for carbon monoxide.

Formally, the lone pairs on molecular nitrogen, hydrogen cyanide, and carbon monoxide are sp hybrid orbitals, whereas NLMO hybridizations calculated even lower p contributions. Hence, these lone pairs have low directionality, the electron density remains close to the coordinating atom and interaction between the lone pair and the Be2+ is comparatively weak. The Be-L bonds are easily disrupted and ligand exchange consequently can proceed with a low activation barrier. A high degree of p character, on the other hand, means that the lone pair is directed toward beryllium, with electron density close to the metal center, and thus well suited for coordination. 

The Dotz reaction mechanism has received further support from kinetic and theoretical studies. An early kinetic investigation [37] and the observation that the reaction of the metal carbene with the alkyne is supressed in the presence of external carbon monoxide [38] indicated that the rate-determining step is a reversible decarbonylation of the original carbene complex. Additional evidence for the Dotz mechanistic hyphotesis has been provided by extended Hiickel molecular orbital [23, 24] and quantum chemical calculations [25],... 

Fig. 5.19 Diagrammatic sketches of the molecular orbitals in carbon monoxide (a) one 7t bonding orbital, (b) one rr anlibonding orbital...

Fig. 520 Enragy level diagram for the molecular orbitals of carbon monoxide. Note that Upon bond Formation electrons occtjjy obitals that are more oxygen-likc than carbon-like. Note carefuBy the bond order The Icr and 3 r MOs arc essentially nonbonding. The bond order, as in the N-. molecule is three.

Considering the molecular orbital diagram of carbon monoxide (Fig. 5.201 and the discussion concerning hybridization and energy (pages 225-227). predict which end of the carbon monoxide molecule will be the more basic (i.e., will donate electrons more readily and form the stronger, direct covalent bond)... 

---