Four kinds of thioaminyls, N-(arylthio)-2-ethoxycarbonyl- (1), N-(arylthio)-2-acetyl- (2), N-(arylthio)-2-cyano- (3), and N-(arylthio)-2-fluoro-4,6-diarylphenylaminyls (4) were prepared. Thioaminyls 3 were quite persistent and could be isolated as radical crystals, For the isolated three radicals (3a, 3b and 3d) the magnetic susceptibility measurements were carried out using a SQUID magnetometer in the temperature range 1.8-300 K. The magnetic interactions of 3b and 3d were antiferromagnetic, and that of 3a was ferromagnetic. Analysis of the chi T-mol versus T plots of 3a with the one-dimensional regular Heisenberg model gave 2J/k(B) = + 11.2 K. (C) 2001 Elsevier Science Ltd, All rights reserved.