Influence of the Nitroxide Ring Structure, Connecting Bridge, and Solvent Nature on Intramolecular Spin Exchange

This work presents examples of the effect of the nitroxide ring structure, the bridge composition, and the solvent nature on EPR spectra of short biradicals with similar structures, on the value of the electron spin exchange integral | J |. The attenuation coefficients γ NH ≈ 4.1 and γ O ≈ 3.3 which characterize the decrease of the spin density on −NH− and −O− groups were determined for the first time. They do not depend on other groups forming the linker. The biradical O=C (NHR 6 ) 2 was found to be structurally rigid in all polar and nonpolar solvents studied, over the temperature range of 200–410 K. The suggested approach allows the prediction of the exchange integral value, | J/a | or | J |, without electronic structure computation based on the bridge composition only.