Gradual spin crossover behaviour in a linear trinuclear FeII complex

Abstract

The synthesis, structures and magnetic properties of a new trinuclear spin crossover complex, [FeII3(npt)6(EtOH)4(H2O)2](ptol)6·4EtOH (1), and of its CoII (2 and 3) and NiII (4) analogues, are reported here. The complexes were synthesized by reacting a 1,2,4-triazole-based ligand, 4-(4′-nitrophenyl)-1,2,4-triazole (npt), with the p-tolylsulfonate (ptol) metal salts in methanol or ethanol. Structural analyses revealed that all complexes are iomorphous and consist of a linear trinuclear core where metal centres are bridged by triazole groups. For 1, dc susceptibility measurements exhibit gradual spin transition with T1/2 = 148 K which corresponds to HS → LS crossover for the triazole bridged central FeII ion. This spin transition was confirmed by Single-Crystal X-Ray Diffraction data of 1 at 100 K and 181 K, where the low temperature measurement revealed a decrease in volume for the central FeII ion, which is in agreement with a HS → LS transition.