Crossover of high and low spin states in transition metal complexes

TL;DR

This paper uses first principles calculations to analyze the crossover of high and low spin states in cobalt complexes, revealing that electron-electron interaction energy differences behave differently from total energy differences and are much larger.

Contribution

It introduces a new interpretation of spin state crossover based on chemical bonding, challenging traditional ligand field theory explanations.

Findings

Electron-electron interaction energy difference varies oppositely to total energy difference with ligand nuclear charge.

Electron-electron interaction energy difference is three to four orders of magnitude greater than total energy difference.

A new bonding-based interpretation of spin state crossover is proposed.

Abstract

The stability of high vs. low spin states of transition metal complexes has been interpreted by ligand field theory, which is a perturbation theory of the electron-electron interaction. The present first principles calculation of a series of five cobalt complexes shows that the electron-electron interaction energy difference between the two states (i) exhibits the opposite trend to the total energy difference as the ligand nuclear charge varies, and (ii) is three or four orders of magnitude greater than the total energy difference. A new interpretation of the crossover of high and low spin states is given in terms of the chemical bonding.