D orbitals, electrons

Although this example, at face value, looks to be a case of the use of the absorption of UV/visible radiation to determine the concentration of a single ionic species (the Cu2+ ion) in solution, and, therefore, the province of the previous chapter, it is, in fact, the quantification of a molecular absorption band. In a sulfate solution, the copper ion actually exists, not as a bare ion, but as the pentaquo species, in which the central copper ion is surrounded by five water molecules and a sulfate ion in an octahedral structure (Fig. 4.1). The color of the transition metal ions arises directly from the interaction between the outer d orbital electrons of the transition metal and the electric field created by the presence of these co-ordinating molecules (called ligands). Without the aquation... 

Think back to the split d orbitals. Electrons in the lower energy d orbitals can absorb energy and move to the higher energy d orbitals. If the energy absorbed in these so-called d-d transitions is in the visible part of the electromagnetic spectrum, the colour of the transition metal compound will be the complementary colour of the absorbed colour. So the colour we see will be white light minus the colour absorbed. 

Fig. 1. Interaction of d-orbital electrons of metal ions with ligands, (a) In a hard acid-hard base combination there is no electron transfer, and the two ions bind by ionic forces, (b) In a soft acid-soft base combination there may be ir-bonding as a result of donation of electrons from the d-orbital of the metal to the ligand the transfer of electrons from metal to ligand prevents the soft metal (usually in a low oxidation state) from becoming too negative.

The Fermi Energy expressed in terms of, m, the effective electron mass, h, the Planck s constant, and n, the number of unpaired electrons residing in length, L. It is clear, the m is not easily assessed from the model, nor available from other calculations. But, for the calculation to be done here we shall assume m = 10 mo, the effective electron mass to be ten times that of electron rest mass. This assumption is not unreasonable in that while the electrons are delocalized they are still tightly bound and the effective electron mass can be this high. For example, the effective electron mass for the d-orbital electrons in transition metals is known [53] to be greater than ten times the rest- mass. ... 

The same type of data was obtained for the two isomers of the monoanion derived from pentahydroxyphosphorane (27) and (27 ) in Scheme 3. The total phosphorus electron density and the d-orbital electron density for both isomers is given in Table 12. Only the density matrices of the five d-orbitals of the phosphorus are reproduced in Table 12. It can be seen that the difference between the total phosphorus electron density in the two isomers is 0-044 units, of which 0-011 units correspond to the difference between the electron density in the d-orbitals of the two isomers. Therefore, approximately 25% of the difference in electron charge takes place via the phosphorus d-orbitals. 

Isomer with equatorial anion (0 ). Total phosphorus electron density = 4-4077. d-Orbital electron density = 1-7893... 

Table I compiles typical geometries according to the formal d-orbital electronic configuration of the central metal. Distorted-tetrahedral arrangements, only occur for all <710 systems, whereas for d4, <78, and d9 systems square-planar arrangements occur exclusively. For d5, d6, and d1 systems, square-planar arrangements are most common with some isolated distorted-tetrahedral examples. Under specific conditions, the flat square-planar units can sometimes form strongly joined dimers or trimers (Section III.A.4). In these cases, the coordination geometry about the central atom is best described as square pyramidal.

The X-ray and neutron diffraction data mentioned previously have been used in conjunction with the technique of polarized neutron diffraction (at 4.2 K) to deduce spin-density distributions in [MnPc].519,520 In further investigations514 it proved possible to determine individual 3d and 4s orbital populations on the manganese ion together with an estimate of 24% for the d-orbital electron density delocalized in the macrocyclic ring. From these studies it appears that the charge on the manganese is approximately +1 this charge appears to be achieved primarily by the loss of a 3d electron rather than a 4s electron. 

The nature of the valency forces in interstitial alloys has been variously explained. It is clear that such alloys are restricted to metals with incompletely filled d orbitals. Electrons may be donated by the interstitial atoms, leaving these as positive ions and resulting in binding of a metallic nature. 

---