Intramolecular Through-Space Antiferromagnetic Interactions of Cross-Conjugated Aromatic Polyaminium Radical Gels

Highly networked, cross-conjugated aromatic polyamine gels were prepared by palladium-catalyzed polycondensation. The gels were characterized by the cross-polarization magic angle spinning (CP-MAS) ¹³C NMR and IR spectroscopies, thermogravimetric analysis, and X-ray diffraction. The data confirm that the polymerization proceeded without any side reactions and that the gels possessing the significant thermal stability are composed of the mixtures of polycrystalline and amorphous moieties. Chemical oxidation of the gels with NOPF₆ solubilized with 18-crown-6 in CH₂Cl₂ gave the corresponding aminium polyradicals. Appearance of the ESR signals at g = 2.003 and the new IR peaks supported the aminium radical generation. The p-methoxy-substituted aromatic polyaminium radical, the polyradical of poly(2), realized the higher spin concentration of 65% and the enhanced chemical stability than the polyradical of poly(1) without any protecting groups. However, the magnetic measurements of the polyradical of poly(2) did not show any intramolecular ferromagnetic interactions, but indicated very strong intramolecular through-space antiferromagnetic interactions.