Close-packed nitronyl nitroxide radicals by Au–S self-assembly: strong ferromagnetic coupling

The study of the magnetism of tightly arranged nitronyl nitroxide (NN) radicals via Au–S self-assembly is interesting. In this study, a series of radicals (S-NN, D-NN, BS-NN, BD-NN) along with two types of nanomaterials (S-NPs, D-NPs) were synthesized. NN was chosen for the magnetic units. Their structures have been successfully synthesized and analyzed. The spin magnetic properties were characterized by electron paramagnetic resonance (EPR) and superconducting quantum interference device (SQUID) measurement. The analysis revealed that the self-assembled NN formed via Au–S bonds exhibits high packing density. Furthermore, it was gratifying to observe that the AuNPs exhibit ferromagnetism after the surface modification by NN. This results in strong ferromagnetic exchange interactions of S-NPs and D-NPs : JS-NPs = +279.715 K and JD-NPs = +254.913 K, respectively.