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Clusters PSEPT

A particularly useful tool is the Polyhedral Skeletal Electron Pair Theory (PSEPT),3 originated by K. Wade, elaborated by D. M. P. Mingos and others, and known colloquially as Wade s Rules. This approach and its applications to carbocations, metal clusters, and other non-boron species, are described in numerous books and reviews. Here we simply outline the basic rules. [Pg.145]

A theory which shows greater applicability to bonding in cluster compounds is the Polyhedral Skeletal Electron Pair Theory (PSEPT) which allows the probable structure to be deduced from the total number of skeletal bond pairs (400). Molecular orbital calculations show that a closed polyhedron with n vertex atoms is held together by a total of (n + 1) skeletal bond pairs. A nido polyhedron, with one vertex vacant, is held together by (n + 2) skeletal bond pairs, and an arachno polyhedron, with two vacant vertices, by (n + 3) skeletal bond pairs. Further, more open structures are obtainable by adding additional pairs of electrons. This discussion of these polyhedral shapes is normally confined to metal atoms, but it is possible to consider an alkyne, RC=CR, either as an external ligand or as a source of two skeletal CR units. So that, for example, the cluster skeleton in the complex Co4(CO)10(RCCR), shown in Fig. 16, may be considered as a nido trigonal bipyramid (a butterfly cluster) with a coordinated alkyne or as a closo octahedron with two carbon atoms in the core. [Pg.200]

The polyhedral structures adopted by most metallacarbab-orane compounds can usually be rationalized using polyhedral skeletal electron pair theory (PSEPT) (see Electronic Structure of Clusters). This approach is summarized as follows ... [Pg.450]

Within the remit of Wade s rules (PSEPT), the addition of one or more capping units to a deltahedral cage requires no additional bonding electrons a capping unit is a cluster fragment placed over the triangular face of a central cage. [Pg.716]

Anions fig, where fi = Si, Ge, Sn, Pb, have 2n+A skeletal electrons and hence, according to PSEPT, should adopt nido stmctures, which has been confirmed experimentally, while their derivative clusters [(OC)3M(t) -E9)] (where M = Cr, Mo, W), have closo stmctures (bi-capped Archimedian antiprism) with 2 -I- 2 electrons [267]. Corbett [268] reviewed from the viewpoint of Wade s theory, the stmctures of these and many other mixed-metal clusters, a brief listing of which is given in Table 3.21 (compare with Table 3.20). [Pg.193]

It became necessary to develop new approaches for predicting electron closed-shell structures, and ideas came from Williams, Wade, Mingos, and Rudolph, which now make up the polyhedral skeletal electron pair theory (PSEPT). The bonding in clusters can sometimes be described in terms of edge-localized, two-center two-electron bonds. Thus, through the formation of element-element bonds, the atoms of a polyhedron can acquire an effective inert gas configuration (8 valence electrons for a main group element and 18 for a transition metal atom). [Pg.278]

A similar situation exists for [Ru4(jU4- 7 -CHCH)2(/i-CO)2(CO)9] and related clusters. If each alkyne ligand donates four electrons, then the molecule has a 62-electron count and again is two electrons short of the 66 c.v.e. required for the four RuRu bonds of the approximately square RU4 unit. By using the PSEPT formalism, however, the cluster has nine cluster bond pairs consistent with its f/oro-dodecahedral RU4C4 core. [Pg.875]

Yet another class of clusters where a problem exists are the [Ru4( U4-PR)2(/U-CO)(CO)io] clusters. It may appear that for highly condensed clusters the bonding is best rationalized with PSEPT. On the other hand, the [Ru4(jU4-PNR2)2(CO)i2] clusters are electron precise for the four RuRu bonds present in the molecules, but electron rich by... [Pg.875]


See other pages where Clusters PSEPT is mentioned: [Pg.167]    [Pg.22]    [Pg.32]    [Pg.54]    [Pg.146]    [Pg.159]    [Pg.160]    [Pg.162]    [Pg.167]    [Pg.200]    [Pg.201]    [Pg.450]    [Pg.451]    [Pg.1215]    [Pg.41]    [Pg.449]    [Pg.450]    [Pg.1214]    [Pg.1048]    [Pg.1090]    [Pg.1090]    [Pg.1092]    [Pg.29]    [Pg.159]    [Pg.160]    [Pg.163]    [Pg.168]    [Pg.175]    [Pg.189]    [Pg.303]    [Pg.893]    [Pg.895]    [Pg.926]    [Pg.974]    [Pg.974]   
See also in sourсe #XX -- [ Pg.189 ]




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