Valence electrons count

For tetranuclear cluster complexes, three stmcture types are observed tetrahedral open tetrahedral (butterfly) or square planar, for typical total valence electron counts of 60, 62, and 64, respectively. The earliest tetracarbonyl cluster complexes known were Co4(CO)22, and the rhodium and iridium analogues. The... 

Based on its structure and valence electron count, draw a Lewis structure or series of Lewis structures for diborane Examine the bond density surface. Does it substantiate 01 refute your speculation ... 

Aluminum, in Group 13, has three valence electrons. The configurations show three electrons with a — 3, so the configuration is consistent with the valence electron count. 

The molecule has one nitrogen atom p ). Interpreting the parentheses in the formula reveals that there are four carbon atoms p ) and eleven hydrogen atoms (5 ). You should be able to verify that the valence electron count is 32 e. ... 

The crossover point for the O p jTC energy levels takes place just after N2, so the general diagram for Z < 7 in Figure 10-35 applies to all three molecules. The valence electron counts are B2 = 6 e, ... 

From Tsai s pioneering discoveries [25,27], we know that atomic size, electronegativity, and valence electron counts play substantial roles in the formation of QCs. These criteria are expressed by the Hume-Rothery rules [30,31]. However, three additional highlights are also important in the consideration of possible candidate systems, at least from the viewpoint of chemists. 

The second attribute of the catalyst concerns its electronic structure, or more simply the valence electron count. Effective catalysts must, it seems, have < 18 VE, such that coordination of a substrate or the departure of a product does not itself pose a major kinetic barrier. Furthermore, it happens that the most stable valence states of the metal will differ by two units. Thus not only will the stoichiometry of atom transfer be supported, but also the mechanism. In the case of rhenium, the oxidation states are Re(V) and Re(VII) indeed scant indication of Re(VI) has been found in this chemistry, especially in a mononuclear species. Likewise, there is no indication of the involvement of free radical chemistry. 

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

Figure 4.27. Valence electron count and vertex count in main group clusters. Notice, according to McGrady (2004), that the different classes of clusters (electron-rich, electron-precise, etc.) simply occupy different domains in a continuum defined by the two variables (electron and vertex counts).

In D3h geometry the Fe(3d) AOs transform as a, (dzi), e"(dxz, dyz), and e (dx,-y1ydxy)- Simple crystal field considerations indicate the energy sequence is a [Pg.55]

In both [Fe4X4(N0)4](X = S or Se) and [Fe4S2(NO)4(NCMe3)2] the total valence electron count is 60. This is the number characteristic of tetrahedral tetranuclear metal clusters, such as [Ir4(CO)12], in the Wade and Mingos skeletal-electron counting schemes (76, 77) and, furthermore, each iron atom in these clusters obeys the 18-electron rule, provided that it forms single Fe-Fe bonds to each of the other iron atoms in the tetrahedron. 

With regard to the valence electron count, this number determines whether the transition metal ion is using its full complement of valence shell orbitals— i.e., the five nd s, the (n + l)s, and the three (n + l)p s. If the valence electron count is eighteen, all of the orbitals are fully utilized in bond formation and electron pair storage, the effective atomic number (EAN) rule is fulfilled and the metal ion is said to be saturated. If it is seventeen, the metal ion is covalently unsaturated, and if it is sixteen or less, the metal ion possesses at least one vacant coordination site and is said to be coordinatively unsaturated. The importance of the valence electron count in homogeneously catalyzed reactions has been discussed by Tolman (7). 

Triatomic fragments involving boron and carbon, such as those found in many borocarbide structures,16 show typical valence electron counts ranging between 12 and 16 electrons. These counts are unusual for isolated triatomic molecules, which usually have 16 or more electrons, unless one of the terminal atoms is FI (12 electrons).17 Within the boron-carbon family, four of six possible arrangements for the trimeric fragments have been observed (1) C—C-C, (2) C-B-C, (3) B-B—C, and (4) B-C-B. Coincident-ally, only those with D,h point symmetry occur in metal borocarbides. They include (1) CCC units in Sc3C4 18 (2) CBC units in Si BCj 19,20... 

Figure 7.3 Differences in the calculated Miilliken populations for the terminal and central atoms in the linear triatomic groups as a function of valence electron count. Aq = qc - qt.

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