LAUSR

Abstract A new 1D-polymeric iron(II)-1,2,4-triazole complex, [Fe(EtTrz)3]SiF6·nH2O (EtTrz = 4-ethyl-1,2,4-triazole, n = 1, 0), demonstrates cooperative spin transition above room temperature. Under vacuum the complex loses its water molecules and shows an abrupt and reproducible spin transition with thermal hysteresis, Tc↑ ≈ 345 K, Tc↓ ≈ 328 K, ΔH ≈ 20 kJ mol−1, ΔS ≈ 57 J mol−1 K−1. In sealed ampoules the complex [Fe(EtTrz)3]SiF6·H2O shows the spin transition with a narrower hysteresis loop, Tc↑ ≈ 363 K, Tc↓ ≈ 353 K, ΔH ≈ 30 kJ mol−1, ΔS ≈ 85 J mol−1 K−1. A composite spin crossover material can be prepared by embedding the complex in the polymeric polystyrene matrix.