Organic Ion-Radicals with Several Unpaired Electrons or Charges

5 ORGANIC ION-RADICALS WITH SEVERAL UNPAIRED ELECTRONS OR CHARGES 

In principle, an organic molecule can accept as many electron pairs as it has low-lying vacant orbitals. In the same way, high-lying occupied orbitals can release not a single, but several electrons. Such multielectron processes can result in the formation of polyion-polyradicals. As will be seen from this section, the main topic of interest in poly(ion-radicals) consists of their spin multiplicity. 

Therefore, the following consideration of the corresponding negatively and positively charged species emphasizes their electronic structures. 

Anion-radicals are the first products of reductive electron transfer. Mntnal repulsion of the primary and snbseqnent excess electrons forms the basis of the impediment of polyelectron reduction at the initial step. However, an orbital, which already has one electron, can be populated by another electron if a proper redncer is chosen. This reducer must be able to overcome Coulomb repulsion. As a resnlt, more or less stable dianions are formed. Like anion-radicals, dianions can reversibly give excessive electrons back. If skeleton rearrangement is absent, the initial uncharged molecules are regenerated. 

In dianion-diradicals, two vacant orbitals are populated, that is, LUMO and the next (somewhat higher) nnoccupied one. This next orbital must, nevertheless, be situated low enough. Such an orbital can be detected in molecules of unsaturated hydrocarbons of a widespread contour. Within this expanded contour, extensible electron delocalization somewhat decreases the repulsion energy. Several electron-acceptor fragments (substituents with heteroatoms or with high conjugation ability) assist in the formation of poly(anion-radicals). 

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