Novel Fe(ii) spin crossover complexes involving a chalcogen-bond and π-stacking interactions with a paramagnetic and nonmagnetic M(dmit)2 anion (M = Ni, Au; dmit = 4,5-dithiolato-1,3-dithiole-2-thione)

Abstract

To introduce both an inter-sulphur atom and π-stacking interaction between a spin crossover (SCO) cation and paramagnetic anion, we designed and synthesised two novel Fe(II) SCO compounds involving a terpyridine-type thiazole containing ligand with the paramagnetic Ni(dmit)₂ and nonmagnetic Au(dmit)₂ anion (dmit = 4,5-dithiolato-1,3-dithiole-2-thione). The temperature variations of magnetic susceptibility and Mössbauer spectroscopy revealed that both complexes exhibited an almost complete SCO conversion, and moreover, the Ni(dmit)₂ anion was in a paramagnetic state down to 2 K. The crystal structures for the Ni(dmit)₂ complex at 213 and 400 K indicated that the chalcogen-bond and π-stacking interaction would be enhanced by the electrostatic interaction between the cation and anion, preventing the π-radicals from dimerising. The light-induced excited spin state trapping effect was observed at 5 K.