Skeletal bonding orbitals

Wade s electron-counting procedures (22) start from a closed polyhedron and require that neither removing a vertex from this polyhedron nor capping a face will alter the number of skeletal bonding orbitals. This capping principle has been demonstrated to be general (31). For... 

The reason why the TSH analysis of deltahedral clusters, with n + 1 skeletal bonding orbitals, is inapplicable is that the L and L cluster orbitals are not necessarily bonding and antibonding, respectively, in three-connected clusters. This result is basically due to the low coordination number and the relatively sparse manner in which the vertices in three-connected structures cover a sphere. ... 

Molecular orbital calculations have shown that closo boranes have 2n + 1 bonding molecular orbitals, including n B—Hct bonding orbitals and n + 1 bonding orbitals in the central core (described as framework or skeletal bonding orbitals). A useful example is which has Of, symmetry. In this ion, each boron has four va-... 

The following three interactions are used to generate the skeletal bonding orbitals in nido pyramids ... 

Very similar ideas apply to Ihc structures of /c/a and amc////ocap[es. Wliereas doso species with / cage atoms require 77+ 1) skeletal pairs, nido and aradino species with u cage atoms have /7 + 2 and u + 3 skeletal bonding orbitals, respectively that is. an identical number of electrons as the parent doso species. Some examples are shown in 22.23 and 22.24 and include some rather unusual species as well as traditional molecules viewed in a rather different light. The scries in 22.23 is iso-... 

The total numbers of skeletal bonding orbitals in pyramidal nido systems generated by these three interactions are n — 1,1, and 2, respectively, leading to a total of 77 -I- 2 bonding orbitals holding 2n +4 skeletal electrons. Thus, the graph-theoretical treatment of nonpyramidal and pyramidal nido polyhedra with n vertices leads to the prediction of the same numbers of skeletal bonding orbitals, namely, n + 2, in accord with experimental observations. However,... 

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