Synthesis, characterization, magnetic and theoretical studies on Fe(II) spin-crossover complex based on 4-cyclohexyl-1,2,4-triazole

4-cyclohexyl-1,2,4-triazole (<i>4-C₆trz</i>) was synthesized and used as a ligand to prepare Fe(II) complex of the formula [Fe^II(<i>4-C₆trz</i>)₃](BF₄)₂·4H₂O. The complex was characterized spectroscopically, magnetically, and thermally. The characterization of the complex proved the polymeric nature of the complex and the triazole ligand acted as a bridging ligand. The prepared structure has the formula confirmed to be [Fe^II(<i>4-C₆trz</i>)₃](BF₄)₂·4H₂O. The χT product of [Fe^II(<i>4-C₆trz</i>)₃](BF₄)₂·4H₂O was almost constant over 200 – 400 K, and the measured value (3.6 cm³mol⁻¹K) is expected to be the paramagnetic high-spin Fe(II) complexes (<i>S</i> = 2). Density Functional Theory (DFT) calculations were conducted on [Fe^II(<i>4-C₆trz</i>)₃](BF₄)₂·4H₂O to rationalize the experimentally observed magnetic behavior measured using the magnetometer. The results predict that the 4-cyclohexyl-1,2,4-triazole (<i>4-C₆trz</i>) ligand provides a <i>π</i>-acceptor environment in the first coordination, which helps to show spin crossover transition with a transition temperature of 215 K.