Solution and solid-state studies of doubly trimethylene-bridged tetraalkyl p-phenylenediamine diradical dication...

X-ray crystallographic structures are reported for 1(Me)(2+)(SbCl(6)(-))(2) x 2 CH(3)CN, 2(Et)(2+)(SbF(6)(-))(2) x 2 CH(3)CN x 2 CH(2)Cl(2), and 1(iPr)(2+)(SbF(6)(-))(2), which also contained unresolved solvent and is in a completely different conformation than the methyl- and ethyl-substituted compounds. A quite different structure of 1(Me)(2+)(SbF(6)(-))(2) than that previously published was obtained upon crystallizing it from a mixture rich in monocation. It does not contain close intramolecular PD(+),PD(+) contacts but has close intermolecular ones. Low temperature NMR spectra of 1(Me)(2+) and 1(Et)(2+) in 2:1 CD(3)OD/CD(3)CN showed that both contain three conformations of all-gauche NCCC unit material with close intramolecular PD(+),PD(+) contacts. In addition to the both PD(+) ring syn and anti material that had been seen in the crystal structure of 1(Me)(2+)(SbF(6)(-))(2) x 2 CH(3)CN published previously, an unsymmetrical conformation having one PD(+) ring syn and the other anti (abbreviated uns) was seen, and the relative amounts of these conformations were significantly different for 1(Me)(2+) and 1(Et)(2+). Calculations that correctly obtain the relative amounts of both the methyl- and ethyl-substituted material as well as changes in the optical spectra between 1(Me)(2+) and 1(Et)(2+), which contains much less of the uns conformation, are reported.