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-HMIDLINE HORIZONTAL ELLIPSISO 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. image