EPR studies of nitrogen-centred free radicals. Part 53. Isolation, EPR spectra and magnetic characterization of N-(arylthio)-2,4-diaryl-6-cyanophenylaminyls

Abstract

N-(Arylthio)-2,4-diaryl-6-ethoxycarbonylphenylaminyls (1), N-[(2,4-dichlorophenyl)thio]-2,4-diphenyl-6-acetylphenylaminyl (2), N-(arylthio)-2,4-diaryl-6-cyanophenylaminyls (3), N-[(2,4-dichlorophenyl)thio]-2,4-bis(4-chlorophenyl)-6-fluorophenylaminyl (4) and N-[(4-nitrophenyl)thio]-2,4-diphenylphenylaminyl (5) were generated by oxidation of the corresponding N-(arylthio)anilines. Although 4 and 5 were short-lived and decayed in 30 min, 1–3 were quite persistent and 3 could be isolated as radical crystals. EPR spectra were measured for all radicals generated and the spin density distribution was evaluated. Ab initio MO calculations (the UHF Becke 3LYP/STO 6-31G) were performed, and a quantitative discussion on the spin density distribution was made. Magnetic susceptibility measurements were performed for three isolated radicals with a SQUID magnetometer. One radical was found to couple ferromagnetically, and analysis with the one-dimensional regular Heisenberg model gave 2J/k_B = 11.2 K.