Mingos cluster valence electron count

The structures of many polynuclear organometallic species are not conveniently described in terms of Wade s rules, and an alternative approach is to consider the total valence electron count, also called the Mingos cluster valence electron count. 

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. 

By employing the Scalar, Vector and Tensor Harmonics, Stone derived the (7 n + 1) cluster valence MO count for deltahedral transition metal clusters and later developed the model to provide an alternative derivation of Mingos electron counting rules for condensed metal clusters1456. ... 

Examples of the application of the mentioned rules to a few naked metal clusters according to Mingos and Wales (1990) are reported in Table 4.4. For each species the valence electron (s and p) count is made both on the basis of the component valences by adding/subtracting one electron for each negative/positive charge, and on the basis of the geometry and the number of vertices. 

With a valence electron (VE) count of 46, the complexes 5 are two electrons short of the magic number required by the Wade-Mingos rules for an electronically saturated M3C cluster complex. It is therefore not surprising that these cluster complexes readily react with small inorganic and organic molecules to give elec-... 

The duster 14 contains 121 valence electrons, one electron less than predicted by the 18e rule. An electron counting rule for centered metal clusters, as proposed by Mingos, [30-33] states that the number of valence electrons in dose-packed metal clusters should be (12n, + A), where n, is the number of peripheral metal atoms and is 18 or 24 for centered cubic polyhedra. On this basis, 14 should possess either 114 or 120 valence electrons. 

---