Electron counting formalism

Valence electrons of neutral atom Electron count Formal charge... 

As the C4B 4Hk series of tetracarbaboranes is classified in the electron-counting formalism as nido, these molecules are expected to have open structures even though extra hydrogens are absent. Spectroscopic studies (130) have confirmed this expectation for 2,3,4,5-C4B2H6 [28323-17-3]. One isomer of (CH3)4C4B8Hg has the open nonicosahedral structure shown in Figure 11 and another isomer, the 1,2,3,8-tetramethyl compound [54387-54-1], is apparently even more open (131). Other tetracarbaboranes include isomers of ///<5fo-C4BgH10 and ftfo-C4B H11 (132). 

Valence Electrons in Neutral Atom Electron Count Formal Charge... 

Despite the fact that the conversion of [FeIr5(CO)15]3 to [FeIr5(CO)16] leaves the relevant electron count formally unaltered, deep modifications in redox propensity are introduced. In fact, as shown in Fig. 93, [FeIr5(CO)16]- in acetonitrile solution, undergoes, an irreversible, two-electron reduction (Ep = — 1.27 V), which regenerates, as put in evidence by the reverse profiles, the parent [FeIr5(CO)15]3-, according to the overall path [162],... 

TABLE 18.1 Electron counting formalism for common ligands and types of bonding in organometallic chemistry. 

Of course, this arbitrary assignment of the valence electrons to the d-orbitals on the metal or to the li ds is simply an electron counting formalism, because there is a considerable amount of metal-ligand mbcing in all of the MOs in or ometallic compounds. The convention is not intended to predict the true oxidation state of the metal or to describe the nature of the bonding (ionic or covalent). Its only purpose is to serve as a book-keeping procedure to account for all the valence electrons. 

There are two filled molecular orbitals on the allyl ligand that act as good fT-donors. Thus, the allyl ligand is a four-electron donor in the donor pair electron counting formalism. 

FI in donor pair electron counting formalism. Both Fischer-type (low oxidation number) and Schrock-type (high oxidation number) compounds are now known to exist. 

Give the electron counts, formal oxidation states, and d configurations of the following [Pt(NH3)4p, PtCl2(NH3)2, PtQJ", (Tf -C5Hs)2Ni,... 

Table 2.1 The typical coordination geometry of NO complexes predicted by the Enemark-Feltham electron counting formalism.

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