SPIN TRANSITION IN HETEROANION COMPLEXESIN THE Fe 2+ -4-AMINO-1,2,4-TRIAZOLE– $$\text{NO}^{-}_3$$ – $$\text{SO}^{2-}_4$$ SYSTEM

Magnetic and thermodynamic properties of heteroanion complex compounds in the Fe2+–ATrz– $$\text{NO}^{-}_3$$ – $$\text{SO}_4^{2-}$$ (ATrz = 4-amino-1,2,4-triazole) system are studied. The Fe(ATrz)3(NO3)2(1–x)(SO4)x·nH2O phases are synthesized. According to magnetochemical and calorimetry data, Fe(ATrz)3(NO3)2(1–x)(SO4)x samples demonstrate a spin transition above room temperature while the compound′s color is changed from pink in the low-spin state to white in the high-spin state. According to calorimetry data, the spin transition in Fe(ATrz)3(NO3)2(1–x)(SO4)x·nH2O phases is a first-order phase transition with hysteresis effects. It is shown that the temperature and the nature of the spin transition can be fine-tuned by synthesizing heteroanion complexes.