Synergistic Spin Transition between Spin Crossover and Spin-Peierls-like Singlet Formation in the Halogen-Bonded Molecular Hybrid System: [Fe(Iqsal)2][Ni(dmit)2]CH3CNH2O

To introduce halogen-bond interactions between a cation and an anion, a novel FeIII complex from iodine-substituted ligands involving a paramagnetic nickel dithiolene anion was prepared and characterized. The compound exhibited the synergy between a spin-crossover transition and a spin-Peierls-like singlet formation. The halogen-bond interactions between the iodine and the sulfur atoms stabilized the paramagnetic state of π-spins and played a crucial role in the synergistic magnetic transition between d- and π-spins. In addition, the compound showed the light-induced excited spin state trapping effect.