Iron(II) complexes with 4-R-1,2,4-triazoles (R = ethyl, propyl) exhibiting(1)A(1)reversible arrow T-5(2) spin transition

Iron(II) complexes with 1,2,4-triazoles of composition FeL(3)A(2). nH(2)O w ere synthesized, where I, is 4-ethyl- or 4-propyl-1,2,4-triazole (Ettrz, Pr trz, respectively) and A = NO3-, ClO4-, Br-; n = 0.5, 1, 2. Magnetochemical studies showed that all these compounds exhibit (1)A(1) reversible arrow T -5(2) spin transition (ST) which is accompanied by thermochromism (a revers ible pink reversible arrow white change of color). The ST pattern, i.e., th e temperature of a direct (T(s)up arrow) and reverse (T(s)down arrow) trans ition, and its contrast substantially depend on the nature of both the liga nd and anion and on the availability of water molecules in the complex stru cture. The highest ST temperatures were observed for Fe(Ettrz)(3)Br-2. 2H(2 )O: T(s)up arrow = 327 K, T(s)down arrow = 314 K.