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Theoretical Study of the Spin Crossover Phenomenon for Some Molecules Using the DFT Method
Hayder Fahim Saber and Safaa M.R.H. Hussein
This study investigates the spin crossover phenomenon in three iron(II) complexes: [Fe(phen)3]2+, [FeL2][BF4]2, and Fe[phen]2[NCS]2. The geometries and electronic structures of these complexes have been examined using Density Functional Theory (DFT). Each complex exhibits distinct high-spin (HS) and low-spin (LS) characteristics, influenced by the ligand environment and geometric configurations. The structural differences between the spin states are analyzed by evaluating the Fe-N bond lengths and angles. Additionally, the vibrations of the systems are examined to establish a correlation between molecular motion and spin properties. Energy calculations provide the energy gap (Eg) for the transition and offer insights into the energetics of spin transitions, focusing on the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). Finally, thermal corrections are computed for free energy, enthalpy, and zero-point energy to predict the thermodynamic stability of the complexes.
Keywords: Spin crossover, Iron(II) complexes, DFT, high-spin, low-spin, HOMO, LUMO, zero-point energy