Lewis structure duodectet rule

It must be emphasized that the duodectet rule (4.6) initially has no structural connotation, but is based on composition only. Indeed, the compositional regularity expressed by (4.6) encompasses both molecular species (such as the metal alkyls) and extended lattices (such as the oxides and halides) and therefore appears to transcend important structural classifications. Nevertheless, we expect (following Lewis) that such a rule of 12 may be associated with specific electronic configurations, bond connectivities, and geometrical propensities (perhaps quite different from those of octet-rule-conforming main-group atoms) that provide a useful qualitative model of the chemical and structural properties of transition metals. 

Following the obvious parallels with p-block hybridization and bonding, the formation of a duodectet-rule-conforming Lewis-like structural formula for an idealized ML transition-metal complex5 can be pictured as occurring in several steps. 

Let us now specialize to the case of pure sd hybridization, which underlies the duodectet-rule-conforming Lewis-like structures described in Sections 4.2.2 and 4.2.3. Lor equivalent sdM hybrids, Eq. (4.27) becomes... 

Let us first consider metal-metal bonding26 in simple dinuclear hydrides H MMH . For M = Re, for example, the four possible duodectet-rule-conforming Lewis-like structures are... 

Figure 4.23 Variations of metal-metal bond length with nominal formal bond order (the number of bonds in the natural Lewis structure) in duodectet-rule-conforming dinuclear hydrides H MMH (see Table 4.15).

The remarkable Lewis-like bonding of transition metals (see V B, pp. 365-387) is based on the primacy of sd hybridization and the associated 12-electron ( duodectet rule ) modification of Lewis structure diagrams. The idealized bond angles cDy between sd hybrid h, and sd - hybrid h, are found to satisfy an equation analogous to the Coulson orthogonality theorem (4.9) for the geometric mean hybridization parameter jx = namely,... 

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