Three novel mononuclear 4‐vinylpyridine‐based Fe(III) complexes displaying various spin‐crossover behaviour

Three novel mononuclear 4‐vinylpyridine‐based Fe(III) complexes [FeL(4‐VP)]BPh4 (4‐VP=4‐vinylpyridine; H2L=bis(salicylicdeneaminopropyl)amine, H2salten, 1; H2L=bis(salicylicdeneaminopropyl)methylamine, H2saltenMe, 2; H2L=bis(3‐methoxysalicylideneaminopropyl)methylamine, 3‐OMeH2saltenMe, 3) were synthesized and characterized. Single‐crystal X‐ray diffraction analyses revealed that 1–3 both present the mononuclear structure based on 4‐VP coordinated with bis(salicylicdeneaminopropyl)amine and its derivatives, which give 2D architectures by various interactions among cations and counter‐ions. Magnetic studies showed that both 1 and 2 exhibit one‐step complete spin‐crossover (SCO) behaviours with critical transition temperatures (T1/2) of 178 and 87 K respectively, while 3 exhibits one‐step incomplete spin crossover behaviour (T1/2,3=93 K). The introduction of methyl groups on the amine nitrogen of the Schiff base ligands in 2 and 3 give the bigger repulsive effect, further decrease the cooperation of spin centres, resulting in their spin transition occurring at lower temperatures. In addition, the presence of C−H⋯O weak interactions in 1 and 3 with synergistic effect, led to their spin transition temperatures being higher than that of 2. Three novel mononuclear Fe(III) complexes based on 4‐vinylpyridine coordinated with bis(salicylicdeneaminopropyl)amine and its derivatives exhibited different one‐step spin crossover behaviour due to the chemical modification of the pentadentate Schiff base ligands.