Synthesis, spectroscopic, thermal and magnetic characterization of novel spin-crossover iron(II) complexes with 4-cyclopropyl-1,2,4-triazole

The new bidentate ligand 4-cyclopropyl-1,2,4-triazole (4-C3trz) has been synthesized and used for preparing 1D Fe(II) SCO compounds of the formula [Fe(4-C3trz)3](X)2·nH2O; where: X = BF4−, n = 3 for compound (1) and X = ClO4−, n = 2 for compound (2). The new complexes (1) and (2) were characterized using elemental analyses, IR-, mass spectroscopy and thermal analysis. The thermally induced spin-crossover behavior of the complexes was inspected by temperature dependent magnetic susceptibility (SQUID) and DSC measurements. The results of magnetic susceptibility (SQUID) and DSC showed abrupt and complete spin transition with a hysteresis loop T↑1/2 = 230/222, T↓1/2 = 221/208 K for complex (1) and T↑1/2 = 218/193, T↓1/2 = 202/183 K for complex (2) using SQUID/DSC, respectively. The enthalpy and entropy associated with the spin transition (ST) evaluated by DSC results were ΔtransH = +21.6 and +20.4 kJ mol−1 and ΔtransS =+ 97.5 and +105.5 J mol−1 K−1for the (1) and (2), respectively.