Valence electrons tetrahedral

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... 

In the families of heptanuclear clusters, two geometries are found the capped octahedron that is typical for 98-valence electrons, and the vertex-sharing open tetrahedral (butterfly) stmctures typical for 106-valence electrons. An example of the former is Osy(CO)22 (51) an example of the latter is [H2AuOsg(CO)2Q] (52). In the AuOs cluster anion, the gold atom is at the vertex-sharing position. 

Because they possess an odd number of valence electrons the elements of this group can only satisfy the 18-electron rule in their carbonyls if M-M bonds are present. In accord with this, mononuclear carbonyls are not formed. Instead [M2(CO)s], [M4(CO)i2] and [M6(CO)i6] are the principal binary carbonyls of these elements. But reduction of [Co2(CO)g] with, for instance, sodium amalgam in benzene yields the monomeric and tetrahedral, 18-electron ion, [Co(CO)4] , acidification of which gives the pale yellow hydride, [HCo(CO)4]. Reductions employing Na metal in liquid NH3 yield the super-reduced [M(CO)3] (M = Co, Rh, Ir) containing these elements in their lowest formal oxidation state. 

When we try to apply VB theory to methane we run into difficulties. A carbon atom has the configuration [HeJ2s22pvl2p l,1 with four valence electrons (34). However, two valence electrons are already paired and only the two half-filled 2/ -orbitals appear to be available for bonding. It looks as though a carbon atom should have a valence of 2 and form two perpendicular bonds, but in fact it almost always has a valence of 4 (it is commonly tetravalent ) and in CH4 has a tetrahedral arrangement of bonds. 

The Mg + dicadon [42] with AN+2 (N= 1) valence electrons has a stable structure in agreanent with the rule, but this is a local energy minimum. The linear structure is more stable because it minimizes the Coulomb repulsion. This is in contrast to the tetrahedral stmcture of the Li dication with two electrons (N= 0). The six electron systems caimot form closed-shell structures in the tetrahedron, but the two electron systems can do. 

A quantitative consideration on the origin of the EFG should be based on reliable results from molecular orbital or DPT calculations, as pointed out in detail in Chap. 5. For a qualitative discussion, however, it will suffice to use the easy-to-handle one-electron approximation of the crystal field model. In this framework, it is easy to realize that in nickel(II) complexes of Oh and symmetry and in tetragonally distorted octahedral nickel(II) complexes, no valence electron contribution to the EFG should be expected (cf. Fig. 7.7 and Table 4.2). A temperature-dependent valence electron contribution is to be expected in distorted tetrahedral nickel(n) complexes for tetragonal distortion, e.g., Fzz = (4/7)e(r )3 for com-... 

In BF4", there are a total of 1 + 3 + (4 x 7) = 32 valence electrons, or 16 electron pairs. A plausible Lewis structure has B as the central atom. This ion is of the type AX4 it has a tetrahedral electron-group geometry and a tetrahedral shape. 

According to the E.A.N. rule, all clusters of four atoms possessing the tetrahedral geometry require a total of 60 valence electrons. A tetrahedron with six two-electron/two-center bonds corresponding to the... 

In a defect tetrahedral structure not all the four vertices are occupied by an atom. A filled tetrahedral structure contains extra-atoms inserted in a normal tetrahedral structure. The bonding mechanism, however, may be different from that of the other tetrahedral structures and, generally, less simple relations are observed between the number of valence electrons and structure. 

Similar classification criteria may be made by using the total valence-electron concentration previously defined (see equation 4.27) and defining, according to Parthe (1995) the tetrahedral structure equation ... 

K4Ge4, can be described as a polyanionic compound (as a Zintl phase also) containing the ion Ge44. This tetrahedral ion can be considered a naked (that is without any ligands bounded to the vertices) tetrahedral cluster formed by a main group element (that is Ee = 5 3 = 5X4 = 20). The electron count, on the basis of the Ge valence electrons and of the ion charge results in Ee = 4 X 4 + 4 = 20. 

A simple, previously mentioned example may be represented by the tetrahedral molecule P4. In this structure there are 4 vertex atoms (n = 4) and there are no exocyclic groups. On the other hand, P has 5 valence electrons, so the number of cluster electrons is 4 X 5 = 20 electrons. This number (20) is therefore related to the number of vertices by the condition 20 = 5n. The cluster is electron-precise. 

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