Electron to clusters

It appears that Cluster C catalyzes the chemistry of CO oxidation and transfers electrons to Cluster B, which donates electrons to external acceptors such as ferredoxin. Since a crystal structure of this protein does not exist, the proposed structure of Cluster C is based on spectroscopic measurements. In some cases, the EPR spectrum of a metal center is diagnostic of the type of center. However, the EPR spectra of Cluster C are unusual. The paramagnetic states of Cluster C (Credi and Cred2) have g-values that are atypical of standard [4Fe-4S] clusters (Table III) and are similar to those in a variety of structurally unrelated systems including a t-oxo bridged ion dimer), a [Fe4S4] ... 

Answer. [BioHio]2- The number of valence electrons for B is three, H ligands are one-electron ligands, and the cluster charge is 2. eve =10x3 + 10x 1+2 = 42 = 4n +2. Consistent with the discussion above, the B-H external cluster bond is taken to involve one electron from H and one from B hence, the B-H fragment contributes two electrons to cluster bonding, sep = (10x2 + 2)/2 = 22/2 = ll = n + 1. 

The structure of 18 turned out to be a distorted square pyramidal cluster which retained the chemical connectivity established by the NMR observations, as well. This structure is in accordance with Wade s rules of electron counting where each RhH(DiPPE) fragment is isolobal with a B-H vertex, contributing two electrons to cluster bonding. 

The last example is of a cage containing an interstitial atom (see structure 23.12) and contributing all of its valence electrons to cluster bonding. An interstitial C atom contributes 4 electrons, a B atom, 3, an N or P atom, 5, and so on. 

Both clusters contain an interstitial N atom which contributes 5 electrons to cluster bonding. The negative charge contributes 1 electron. 

The 4t] cluster usually has 66 c.v.e. that are two more than that required for four RuRu bonds. As discussed previously however, if each CR unit donates five electrons to cluster bonding there are a total of eight cluster bonding pairs consistent with the observed capped trigonal bipyramidal RU4EC2 skeleton (Figure 6). 

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