D-electron orbital population

Table I. d-Electron Orbital Populations in Bis(pyridine)(meso-...

Table, IV. d-Electron Orbital Population in Iron(Il) Phthalocyanine...

Hund s rule (Section 1 1) When two orbitals are of equal en ergy they are populated by electrons so that each is half filled before either one is doubly occupied Hybrid orbital (Section 2 6) An atomic orbital represented as a mixture of vanous contributions of that atom ss p d etc orbitals... 

Several characteristics of the metal beam have been studied in detail. It is well known that metal clusters and metal oxides are formed as a result of the ablation process. However, these potentially interfering species have been studied in detail130 and it has been concluded that they do not introduce any doubt as to the validity of the experimental results. Much more important than cluster or oxide formation are the atomic electronic state populations of the metal beams. For each metal reactant, these have been characterized using laser-induced fluorescence (LIF) excitation spectroscopy. For Y, only the two spin-orbit states of the ground electronic state (a Dz/2 and a D-3,/2) were observed.123... 

Metal clusters in metal oxide systems have not been well-characterized or abundantly investigated up to the present time. Only isolated examples of metal-metal bonded units in oxide lattices have appeared from time to time. It will be the thesis of this presentation to show that highly unusual structures determined by strong metal-metal bonding will be found in ternary and quaternary metal oxide systems, and that opportunities abound for creative work on the synthesis, theory and structure-property relationships of such compounds. Because of the well-known correlation of d-electron population and d-orbital radial extension with metal-metal bond formation,... 

DR. TAUBE The number of d electrons in the reducing agents does seem to be an important factor, and since above a certain number both a and n orbitals are populated, in that sense at least orbital symmetry plays a role. Perhaps the... 

These findings led to the concept of the Metal-oxo Wall or Ru-oxo Wall , namely terminal metal-oxo units are well known for nearly all early and mid-transition metal elements but simply unknown for the late transition metal elements (Fig. 1). The generic explanation for this phenomenon is that as one moves to the right in the d block, the metal center necessarily has more d electrons. This in turn requires an increasing population of orbitals that are antibonding with respect to the terminal metal-oxo unit. A simplified molecular orbital diagram for a six-coordinate C41 transition metal-oxo unit shown in Fig. 2 explains... 

Fig. 2. Significant molecular orbitals of terminal transition metal-oxo units in a six-coordinate 4 ligand environment. The d° configuration is a formal triple bond. The highest occupied molecular orbital in the d configuration is formally nonbonding (8 symmetry) so the metal-oxo bond order remains 3.0. However, d-electron counts above d populate orbitals that are antibonding between the metal and the terminal multiply bonded ligand (0x0 in this case, but alternatively, alkyl-imido, nitrido, sulfido, etc.). Note that all the equatorial ligand orbitals and the metal dx2 y2 orbital (hi in 4 symmetry) are ignored for simplicity.

If the transition metal atom has more than the six d electrons indicated on the diagram, the antibonding 2eg molecular orbitals will also be populated and the metal-ligand bonding will be weakened. An example of this quite-prevalent effect is encountered in the series FeS2, CoS2, NiS2, discussed in section 10.4.2. 

The population of the destabilized e g orbitals is larger for the Co complexes than for the Cr compounds listed, a trend with increasing number of electrons reproduced in the sulfides discussed in the following section. A population of more than two electrons of the e g orbitals implies population of the antibonding metal-ligand orbitals, a state only reached in the Co(II) complex listed in the last column. The total number of d electrons, however, seems to correlate more with the element than with the specific valence state of the element, as there is no systematic difference between the Co(II) amd Co(III) complexes. But the number of available studies is still too small to allow more general conclusions. 

Experimental orbital populations for FePc, obtained at 110 K (Coppens and Li 1984), are given in Table 10.10, together with values for the ionic configurations. The main difference between the 3EgA and 3A2g states is a shift of one electron from the dx yz orbitals to the d.2 orbital. The experimental populations are close to the almost 3 1 ratio of the dxzy,/dz2 populations predicted for 3Eg. Compared... 

TABLE 10.14 Iron d-Orbital Populations (Electrons) and Percentages of the Total Population of bis(Pyridine)(meso-tetra-phenylporphinato)iron(II) Without and With Anharmonic Treatment of the Fe Atom. Axes as Defined in Table 10.7... 

In both the Fe(II) and Fe(III) cases the spin state change involves a change in the population of the a antibonding eg orbitals of two d electrons. For the spin equilibrium of the d1 cobalt(II) complexes the population of the eg orbitals changes by only one electron. From examination of the structures of a series of [Co(terpy)2]2+ salts, a bond length difference between the two Co-N (central) distances of 21 pm was found between the spin states, with a difference of only 7 pm found between the four Co-N (distal) distances. This gives an average difference of 12 pm. 

In the planar-octahedral equilibria of nickel(II) the d orbital population changes by transfer of one electron from the d2 orbital to the dx2-y2 a antibonding orbital. This results in a substantial increase in the nickel-nitrogen distances in the plane. Accompanying this is the formation of new metal-ligand bonds in the axial positions. 

The population of the tin d orbitals may result from both (d - p)-7r and (d - d)-7t bonding. These two effects should increase over the series of substitutions of Cl - Br - I, since the more distant p and d electrons of the halogen have higher probabilities of delocalization into the tin d orbitals and are characterized by an increase in the energy of the d orbitals. 

The M-C a bond is formed by donating the lone electrons on C to the empty d,2 orbital on M (upper portion of Fig. 7.3.10). The it bond is formed by back donation of the metal d7r electrons to the it orbital (introduced in Chapter 3) of CO. Populating the it orbital of CO tends to decrease the CO bond order, thus lowering the CO stretch frequency (lower portion of Fig. 7.3.10). These two components of metal-carbonyl bonding may be expressed by the two resonance structures... 

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