Valency counting rule

On the other hand, the nonbonding orbitals (based on the octahedral geometries) dxz and dyz are unaffected by the removal of a ligand on the equatorial plane, and so these two orbitals will hold the other two pairs of nonbonding electrrMis. When we combine these with the two lone pairs on the equatorial plane, we will have four nonbonding lone pairs as predicted by the valency counting rule. 

The 8V + 6 valence electron rule has been completely substantiated by the calculated four-membered species in Table 2 [7], Boldyrev, Wang, and their collaborators presented experimental and theoretical evidence of aromaticity in the Al/ [19] Ga/" [20], In " [20] and isoelectronic heterosystems, XAl [21], The Al/" unit (14e) was found to be square planar and to possess two n electrons, thus conforming to the (An + 2)n electron counting rule for aromaticity. The n electron counting rule would be more powerful if we could predict the number of n electrons of metal atomic rings in an unequivocal manner. Our SN+6 electron rule only requires the number of valence electrons in Al/, which is easy to count. 

The location of electrons linking more than three atoms cannot be illustrated as easily. The simple, descriptive models must give way to the theoretical treatment by molecular orbital theory. With its aid, however, certain electron counting rules have been deduced for cluster compounds that set up relations between the structure and the number of valence electrons. A bridge between molecular-orbital theory and vividness is offered by the electron-localization function (cf p. 89). 

REMARKS ON THE CHEMICAL BOND FACTOR AND VALENCE-ELECTRON COUNTING RULES... 

Electron counts according to the 18-electron rule are restricted to mono- and dinuclear complexes if the latter have no /iMigands. For triple- and tetra-decker complexes the 18-electron rule has to be transformed into the 30- and 42-valence-electron rule by adding d6 + tt (or o-8) electrons once and twice. 

The complex [PbsfMofCOA I4 has been recently reported (Yong el al., 2005) and exhibits the structure shown below. Does the compound obey the electron-counting rules for clusters If not, where might one seek an explanation of its behavior Consider explicitly tripledecker complexes as well as complications caused by separating the external cluster lone pairs from cluster bonding pairs (see Chapter 2, Problem 12). For your information, the measured distance between the Mo atoms is 3.216 A, whereas twice the covalent radius of Mo is 2.90 A, the Mo-Mo distance in [Mo2(CO)h> 2 is 3.123 A and the Mo-Mo distance in the 27-valence electron tripledecker complex CpMo(r 5-As5)MoCp is 2.764 A. 

It seems to be a sort of a rule in these Zintl phases that whenever there is a trigonal prismatic cation coordination then the silicon atoms form planar fragments and vice versa. It is not yet understood why this is so. To none of the Si-Si-bonds in SrMgSi2 a i-bonding contribution can be assigned neither in terms of bond distances nor by valence electron numbers and counting rules. 

Structure and bonding in the tellurium subhalides can be well rationalized, either employing valence and electron-counting rules, in-... 

One phosphorus and three chlorine atoms supply 5 + (3 x 7) = 26 valence electrons. Since P is less electronegative than Cl, it is likely to be the central atom, so the 13 pairs of electrons are distributed as shown below. In this case, each atom obeys the octet rule, Whenever it is possible to follow the octet rule without violating other electron counting rules, you should do so. 

In many carbonyls and related compounds, the metal atoms have a total valence count of 18 electrons. This rule can break down for steric reasons with early transition metals, and is less often obeyed in later groups. 

By employing the Scalar, Vector and Tensor Harmonics, Stone derived the (7 n + 1) cluster valence MO count for deltahedral transition metal clusters and later developed the model to provide an alternative derivation of Mingos electron counting rules for condensed metal clusters1456. ... 

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