Disjoint and coextensive amminium radical cations: a general problem in making amminium radical cation based high-spin polymers

A two-electron oxidation of N,N,N′,N′-tetrakis(2-methoxyphenyl)-1,3-diaminobenzene 12 gives the diradical dication 122radical dot+, which is an aza analogue of the Schlenk hydrocarbon and, like the Schlenk hydrocarbon, has a triplet ground state. However, an attempt to produce pentuplet tetraradical tetracations by extending the same ferromagnetic spin-coupling motif in a linear or a cyclic fashion was unsuccessful. Two-electron oxidations to give disjoint diradical dications (in which the charges and spins are spatially separated) are relatively easy but it proved impossible to remove the third and fourth electrons. This would require generation of coextensive radical ions in which the charges and spin distributions overlap. The results obtained with these model oligomers illustrate what is a general problem in the creation of high-spin polymers in which the spin-bearing centres are amminium radical cations. Strong ferromagnetic spin-coupling depends on the formation of coextensive rather than disjoint radical cations but the formation of coextensive radical cations with strong ferromagnetic coupling involves a large additional coulombic penalty.