Iron(II) Complexes with 4-R-1,2,4-Triazoles (R = Ethyl, Propyl) Exhibiting 1A1 ⇄ 5T2 Spin Transition

Abstract

Iron(II) complexes with 1,2,4-triazoles of composition FeL₃A₂ · nH₂O were synthesized, where L is 4-ethyl- or 4-propyl-1,2,4-triazole (Ettrz, Prtrz, respectively) and A = NO^– ₃, ClO^– ₄, Br^–; n = 0.5, 1, 2. Magnetochemical studies showed that all these compounds exhibit ¹ A ₁ ⇄ ⁵ T ₂ spin transition (ST) which is accompanied by thermochromism (a reversible pink ⇄ white change of color). The ST pattern, i.e., the temperature of a direct (T _s↑) and reverse (T _s↓) transition, and its contrast substantially depend on the nature of both the ligand and anion and on the availability of water molecules in the complex structure. The highest ST temperatures were observed for Fe(Ettrz)₃Br₂ · 2H₂O: T _s↑ = 327 K, T _s↓ = 314 K.