Orbitals, for cluster bonding

What model does provide a valence electron/composition connection for [Ru6(CO)i8]2 Let s try this. Limit the metal to three orbitals for ligand binding and three orbitals for cluster bonding. Thus, we force it to act like a six rather... 

Perhaps you are thinking that the metal atoms in Fe6C(CO)i6]2 are now using more than three orbitals for cluster bonding. How else can they interact effectively with the interstitial atom But notice that the interaction described in Figure 3.8 is no different in principle than the addition of four H atoms to a square pyramidal B5H5 cluster or the addition of 4 H+ to [B5H5I4 as in the one electron MO method the electrons are added last. For the iron cluster, then, the equivalent model would be the insertion of a C4+ ion into the center of a [Fe6(CO)i6]6- cluster. No additional metal orbitals are needed. 

In addition to the close- and nido-metal-carbonyl clusters already mentioned, with structures based on the octahedron, another interesting category of structure that is found among metal-carbonyl clusters is one in which n skeletal atoms are held together formally by n skeletal bond pairs. These adopt structures based on polyhedra with ( — 1) vertices, as might be expected. The extra metal atom caps one of the triangular faces of the closo residue, where the three vacant orbitals that it can formally furnish for cluster bonding enable it to bond to the 3 metal... 

Tables II and III list the numbers of electrons provided by various potential cluster units, assuming that the skeletal atoms make available three AO s apiece for skeletal bonding, and use their remaining valence shell orbital(s) to bond ligands to the cluster. For example, a main group element E (Table II) such as boron can make three AO s available for cluster bonding if it uses its one remaining valence shell AO (an inert...

Answer. There are a total of 30 orbitals and 26 electrons to be utilized in bonding. The external B-H bonds utihze 12 orbitals and 12 electrons leaving 18 orbitals and 14 electrons for cluster bonding. Four three-center B-B-B and three two-center B-B bonds utilize 12 + 6=18 orbitals and 8 + 6 = 14 electrons. They may be placed on the framework as shown in the diagram above where the top and the bottom of the octahedron are shown separately. By counting you can find that B(l) and B(2) are associated with three three-center-two-electron bonds (and a B-H bond), B(3) and B(4) with two three-center and one two-center bonds (and a B-H), and B(5) and B(6) with one three-center and two two-center bonds (and a B-H), i.e., eight electrons around each B. Notice that one would need to draw a considerable number of resonance structures to give all the boron atoms the same electronic environment. 

Figure2.6.5 [SngCr(CO) ], the first derivative of a deltahedral Zintl anion. The Cr(CO)3 fragment caps the open pseudo-square face of the original Sn cluster and does not donate electrons for cluster bonding. The hetero-atomic cluster is a closo-species according to both shape, a bicapped square antiprism, and electron count. The three empty d orbitals, xz, andyz ofCrfCO) overlap with the filled orbitals shown in Figure 2.6.4 and, therefore, the cluster behaves as a six-electron donating ligand...

Figure 3.9. Orbitals that a CH or BH unit can use for cluster bonding and the skeletal bonding MOs they generate in 1,6-C2B4H6- (a) CH unit s AOs (b) skeleton of 1,6-C2B4H6 (c) the A,g bonding MO (d) the B> bonding MO (e) the Eg bonding MOs (f) the Aj, bonding MO (g) the Ii, bonding MOs.

Although, for bookkeeping purposes, a V-shaped (C2v) nickel bis(phosphine) complex such as Ni(PPh3)2, or its platinum analog PtfPPli Jo, can in principle act like Csv Fe(CO)3 or Co(r -C5H5) as a source of three AOs and two electrons for cluster bonding use, its makes its frontier orbitals... 

Two cluster fragments are isolobal if they possess the same frontier orbital characteristics same S5mmetry, same number of electrons available for cluster bonding, and approximately the same energy. 

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