Orbital of metals

We note that the valence orbitals of metal atoms order in energy as AE>Ln>M. The d-levels of transition elements (M) range the lowest, and are therefore most sensitive for reduction, or to form a stable binary metal nitride. This may also explain the virtual absence of d-element compounds with 16 (valence) electron species, such as [N=N=N] , [N=C=N] , [N=B=N] T [C=C=CfT or [C=B=C] T at least through high-temperature syntheses. 

The redox interaction with a co-reductant permits the formation of a reversible redox cycle for one-electron reduction as shown in Scheme 2. Furthermore, the function of transition metals is potentially and sterically controlled by ligands. A more efficient interaction between the orbitals of metals and substrates leads to facile electron transfer. Another interaction with an additive as a Lewis acid towards a substrate also contributes to such electron transfer. 

Most metal oxides are ionic crystals and belong to either the class of semiconductors or insulators, in which the valence band mainly comprises the frontier orbitals of oxide ions and the conduction band contains the frontier orbitals of metal ions. In forming an ionic metal oxide ciTstal from metal ions and oxide ions, as shown in Fig. 2-21, the crystalline field shifts the frontier electron level of metal ions to higher energies to form an antibonding band (the conduction... 

Fio. 23. Diagrammatic representation of overlap between orbital of metal atom and... 

Donation of electrons from filled d orbitals of metal to empty t antibonding orbitals of ligand CO, RNC, pyridine. CN N2, NOJ, ethylene... 

An examination of Table XII shows that in all cases the M-C interaction is a dative bond, i.e., donation of electron charges from the n orbital of olefin to the vacant s orbital of metal and, simultaneously, back-donation of electron charges from the d orbitals of M to the n orbital of olefin (Fig. 12). This can be interpreted in more detail as follows. When the olefin molecule approaches M+, some electronic charge is transferred from the C=C it orbital to the valence s orbital of M+ at the same time, electrons in the filled d orbitals of metal are transferred to the symmetry-matched 7r orbital of olefin. It can be seen from Table XII that upon adsorption, the electron occupancies of the valence s orbitals of Cu and Ag always increase, whereas the total occupancy of their Ad or 5d orbitals always... 

The occupied p.bonding molecular orbital of olefin then overlaps with empty s orbital of metal while one of the filled dn orbitals of the metal interacts with the empty p -antibonding molecular orbital of olefin... 

Using sketches of the five d orbitals of metal atom M (at the origin of a cubic coordinate system, Fig. 22-22), show that tetrahedral coordination... 

Scheme 3. Interaction between the d orbitals of metal ions and cr and 7l orbitals of the cyanide bridge.

Fig. 4. Calculated energy levels for the frontier molecular orbitals of metal ineso-tetraphenyl porphyrins and for TPP (with no H atoms in the porphyrin cage). Electron occupancies are indicated for frontier molecular orbitals of the metal. Adapted from Ref (22) with neglect of various nonactive orbitals.

Donation of electrons from fliled d orbitals of metal to empty [Pg.755]

Another example of electronic interaction between the graphite and ionic solutes is the retention of metal ions on PGC supports. Such electronic interaction, either electron donation or acceptance, is presumably between the available orbitals of metal ions and the electronic cloud of the flat graphite surface. The addition of a small concentration of oxalic acid into aqueous mobile phase tends to modify the graphite surface and to increase, through complexation, the range of metal ions retained. 

Fig. 15.5 Overlap of fr and TT orbitals of bridging carbonyl ligands with the d orbitals of metal atoms. The cr orbital of CO can donate electron density to the metal orbitals and the empty tt orbital of CO can accept electron density from the d orbitals. (From Kostic. N. M. Fenske.

Main group elements like C and S have 4 valence AOs, one s and three p, and they follow the octet rule (although heavier main group elements can extend their octet). Transition metals, by contrast, have 10 valence AOs—one s, five d, and three p, in that order—and they follow the 18-electron rule. The 18-electron rule is much less rigorous for transition metals than the octet rule is for main-group elements. First, it can be difficult to surround a metal, especially an early metal, with sufficient numbers of substituents to provide 18 electrons to the metal. Second, the valence orbitals of metals are sufficiently extended from the nucleus that the nucleus doesn t care much about what s going on in its valence shell. 

The lowest I.E. band in all cases is assigned to the 2Alg ion state. This is consistent with e.s.r. evidence on [Cr(r -C6H6)2]+ 3I 33) and other bis-Jj-arene complexes34). This band is extremely sharp for an organometallic compound indicating ionization from a non-bonding orbital calculations consistently predict the alg orbital of metal sandwich compounds to be practically pure metal dz2 in character as a consequence of... 

The occupied rc bonding molecular orbital of olefin then overlaps with empty s orbital of metal while one... 

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