Probing the Spin States of Tetra-coordinated Iron(II) Porphyrins by their Vibrational and Pre K-edge X-Ray Absorption Spectra

14 November 2022, Version 2
This content is a preprint and has not undergone peer review at the time of posting.


Tetra-coordinated iron(II) porphyrins are observed in triplet (intermediate spin, IS) ground state with low-lying quintet (high spin, HS) and singlet (low spin, LS) excited states. It is well known in the literature that the $d_{Fe-N}$ bond distances are dependent on the spin state such that the $d_{Fe-N}$ distances are larger for HS compared to the LS/IS states. This implies the existence of strong magneto-structural correlations. We address here whether it is possible to obtain the spin-state information of a molecular systems by exploiting the magneto-structural correlations i.e., probing the ground-state vibrational and structural properties, can we determine the spin state of a molecular systems? To answer this, we have studied a series of tetra-coordinated ion (II) porphyrins with various substitutions at the peripheral macrocyclic rings applying first-principles calculations. The spin-state dependent nature of the chemical bonds and spin polarization on the N-atoms plays a crucial role in the vibrational dynamics of the central Fe-atom. Theoretical nuclear resonance vibrational spectroscopy (NRVS) is adopted to investigate the vibrational dynamics and the Fe-atom associated spectral peaks and their spin-dependent features. We find that NRVS studies along with iron pre-K-edge X-ray absorption analysis convincingly provide the information on the spin state, which could be utilized to establish a new methodology to identify the spin states without adopting any magnetic probes.



Supplementary materials

Supporting Information
Spin density and population analysis, vertical spin gap from different methods, computed IR and Raman spectra, contribution of the Fe motion to a vibrational mode, and transitions in the XAS spectra.


Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.