![Author ORCID: We display the ORCID iD icon alongside authors names on our website to acknowledge that the ORCiD has been authenticated when entered by the user. To view the users ORCiD record click the icon. [opens in a new tab]](https://chemrxiv.org/engage/assets/public/chemrxiv/images/logos/orcid.png)
Abstract
We present a simple model of molecular distortions in spin crossover complexes, based on crystal field theory and transition state theory. This allows us to model the effect of molecular distortion on T(1/2), the characteristic temperature of thermal crossover and T(LIESST), the maximum temperature at which trapped excited high spin (HS) complexes are stable. We find that T(1/2) is a purely thermodynamic quantity as the kinetics are entirely determined by the relative free energies of the HS and low spin (LS) states [G(diff)=G(HS)-G(LS)]. The average distortion across HS and LS species {Sigma(avg)=[sigma(HS)+sigma(LS)]/2} has a significant impact on G(diff) whereas the change in the metal-ligand bond length between HS and LS species [d(diff)=d(HS)-d(LS)], and the change in the molecular distortion between the HS and LS states [Sigma(diff)=Sigma(HS)-sigma(LS)] do not. Therefore, Sigma(avg) has a large effect of T(1/2), whereas d(diff) and Sigma(diff) do not. T(LIESST) is largely determined by the height of the barrier [E(barrier)] between the metastable HS state and the LS state. E(barrier) is strongly affected by d(diff), Sigma(diff), and Sigma(avg), so each of these quantities strongly impact T(LIESST). Thus, decreasing the average distortion across HS and LS species will increase T(LIESST) and decrease T(1/2), which may provide a route to high temperature spin-state switching. Increasing the change in the metal-ligand bond length between the HS and LS species or the molecular distortion between the HS and LS states will increase T(LIESST) without substantially change T(1/2).
Supplementary materials
Title
Supporting Information
Description
In this file, we provided additional data detailing the nature of the first excited state, how key structural observables vary with the model parameter delta(A), the error is evaluating the integral in equation 21, and how T(LIESST) and T(1/2) vary with key model parameters. We also provide the detailed calculations of the single electron energy terms, d^6 electron-electron interactions, and spin-orbital coupling under C(4v) symmetric ligand field based on crystal field theory, including tabulation of the relevant wavefunctions.
Actions
