Thermodynamic characterization of two novel spin-crossover complexes

Two novel FeⅡspin crossover complexes [Fe(L1)3](BF4)2·5H2O (1) and [Fe(L2)3](BF4)2·2H2O (2) with 4-NHR-1,2,4-triazole (R = isopropyl, L1; cyclohexyl, L2) were synthesized. 1 and 2 remain white at room temperature, whereas they turn purple at liquid temperature. Variable temperature optical detection and magnetic susceptibilities measurement show that the spin-crossover phenomenon for 1 was observed between 120 K and 170 K. The hysteresis loop is about 10 K. The Tc temperature of 2 is 190 K, but no thermal hysteresis loop was found. The molar thermodynamic functions and the microscopic parameters were obtained from the theoretical analysis in terms of the domain model, two level Ising model and regular solution model, respectively.