Geometric structure, electronic structure, and spin transition of several FeII spin-crossover molecules

We present a density functional study on the geometric structure, electronic structure, and spin transition of a series of FeII spin-crossover (SCO) molecules, i.e., [Fe(abpt)2(NCS)2] (1), [Fe(abpt)2(NCSe)2] (2), and [Fe(dpbo)(HIm)2] (3) with dpbo diethyl(E,E)-2,2'-[1,2-phenylbis(iminomethylidyne)]bis[3-oxobutanoate](2-), N',O3,O3', and abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole in order to explore more about the way to control SCO behavior of transition metal complexes. Our calculated results show that the spin transition of these FeII molecules is accompanied with charge transfer between the Fe atom and ligands. This causes change in the electrostatic energy (ΔU) as well as the total electronic energy of SCO molecules. Moreover, our calculated results demonstrate an important contribution of the interionic interactions to ΔU, and there is the relation between ΔU and the thermal hysteresis behavior of SCO molecules. These results should be helpful for developing new SCO molecules.