Hirshfeld Atom Refinement for Spin State Investigations on Transition Metal Complexes

Daniel Brüx, Ben Ebel, Florian Kleemiss

Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1a, 52074 Aachen, Germany

e-mail: daniel.bruex@rwth-aachen.de

The spin states of transition metal complexes have been extensively studied using both theoretical and analytical methods. In this context, X-ray diffraction techniques are often used to study spin-crossover complexes and observe the structural changes that accompany the spin transition. Further, this technique enables the direct analysis of the valence charge density from single crystal diffraction experiments when aspherical refinement methods are employed, such as the multipole refinement [1]. While this approach has been applied to spin-crossover compounds [2], it requires high-quality diffraction data, which limits its general practicality.

Here, we demonstrate an alternative method utilising Hirshfeld Atom Refinement [3,4], which involves comparing differently refined models by calculating electron density based on different spin multiplicities. The results indicate that spin misassignment can be detected at standard resolutions using classical R-values and residual density [5]. Thus, this method provides a new, accessible way to obtain spin state information from single crystal diffraction experiments.

References:

[1] Holladay et al. Acta Crystallogr. Sect. A: Found. Crystallogr. 39, 1983

[2] V. Legrand et al. J. Am. Chem. Soc. 128,* 2006

[3] S. Capelli et al. IUCrJ 1, 2014

[4] F. Kleemiss et al. Chem. Sci 12, 2021

[5] D. Brüx et al. Chem. Eur. J. 31, 2025