Chemical Bonds and Spin State Splittings in Spin Crossover Complexes. A DFT and QTAIM Analysis

TL;DR

This study uses DFT and QTAIM methods to analyze charge densities and atomic contributions in iron(II) spin crossover complexes, elucidating how ligand substituents influence spin state energy differences.

Contribution

It introduces a combined DFT and QTAIM approach to decompose and understand spin state splittings in iron(II) complexes with various ligands.

Findings

Atomic contributions explain substituent effects on spin splitting

Charge density analysis correlates with spin state stability

Decomposition aids rational design of spin crossover materials

Abstract

Density functional theory (DFT) calculations have been performed for the high-spin (HS) and low-spin (LS) isomers of a series of iron(II) spin crossover complexes with nitrogen ligands. The calculated charge densities have been analyzed in the framework of the quantum theory of atoms in molecules (QTAIM). For a number of iron(II) complexes with substituted tris(pyrazolyl) ligands the energy difference between HS and LS isomers, the spin state splitting, has been decomposed into atomic contributions in order to rationalize changes of the spin state splitting due to substituent effects.