Intramolecular Electronic Communication in Polynuclear Iron Complexes

1 Intramolecular Electronic Communication in Polynuclear Iron Complexes 

Even if the present chapter is essentially devoted to mononuclear complexes, we have already seen in Sections 3.2 and 3.3, that polynuclear complexes may hold great interest in applicative fields, in particular as far as their ability to undergo reversible multiple electron transfers such a property is typical of semiconducting materials. 

We cite here two examples of triiron complexes which can depict well the possible intramolecular electronic interactions in polymetallic complexes. First of all we take into account that, as discussed in Chapter 2, Section 1.5.1 and Chapter 4, Section 1.3, from the electrochemical viewpoint, the existence of a mutual electronic (through-space or through-bond) interaction in molecules containing two or more redox-active centres leads to the appearance of separate electron transfer processes. There are, however, two main classes of polynuclear molecules  

It is evident that the three iron centres are internally communicating. Based on the separation between the redox potential of the oxidation and that of the first reduction (AE° = 0.72 V), a Kcom of 1 X 1012 can be calculated, which allows one to classify the neutral species [FeIII2FeII0(L)3] as a fully delocalized mixed-valent species.121 

Let us now consider the linear tris(ferracarborane) [( 5 6-C6H6) Fe(Et2C2B4H3-5-)( 6-C6H6)Fe(Et2C2B4H3-5-)( 6-C6H6)Fe(Et2C2B4H4)] vaguely reminiscent of triferrocene (see Chapter 3, Section 3, and Chapter 4, Section 1.3). 

---