Observation of the asphericity of 4f-electron density and its relation to the magnetic anisotropy axis in single-molecule magnets

Abstract

The distribution of electrons in the 4f orbitals of lanthanide ions is often assigned a crucial role in the design of single-molecule magnets, which maintain magnetization in zero external field. Optimal spatial complementarity between the 4f-electron density and the ligand field is key to maximizing magnetic anisotropy, which is an important factor in the ability of lanthanide complexes to display single-molecule magnet behaviour. Here we have experimentally determined the electron density distribution in two dysprosium molecular complexes by interpreting high-resolution synchrotron X-ray diffraction with a multipole model. The ground-state 4f-electron density is found to be an oblate ellipsoid, as is often deduced from a simplified Sievers model that assumes a pure |±15/2> ground-state doublet for the lanthanide ion. The large equatorial asymmetry—determined by a model wavefunction—was found to contain considerable MJ mixing of |±11/2> and only 81% of |±15/2>. The experimental molecular magnetic easy axes were recovered, and found to deviate by 13.1° and 8.7° from those obtained by ab initio calculations.

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Fig. 1: Structure of the complex 1A.
Fig. 2: Electron density isosurfaces and unique magnetic axes.
Fig. 3: Temperature dependence of χT for 1A.

Data availability

Crystallographic data for the structures reported in this Article have been deposited at the Cambridge Crystallographic Data Centre under deposition nos. CCDC 1900925 (1A) and 1900926 (1B). Copies of the data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures/. All other data supporting the findings of this study are available in the Article and its Supplementary Information or from the corresponding author on reasonable request.

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Acknowledgements

The authors are grateful to V. Petricek for discussions about multipole modelling of lanthanide compounds using Jana2006. M. Sist, V. Hathwar, H. Kasai and K. Sugimoto are thanked for their help during synchrotron data collection. A.S. acknowledges support from the Australian Research Council (Future Fellowship no. FT180100519). J.O. acknowledges the financial support from Independent Research Foundation Denmark, the Danish National Research Foundation (DNRF-93), VILLUM FOUNDATION and Danscatt. S.J. and S.G. appreciate the support of the National Natural Science Foundation of China (21621061, 21822301, 21601005) and the National Basic Research Program of China (2017YFA0204903, 2018YFA0306003). The synchrotron experiment was performed on beamline BL02B2 at SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute as a Partner User (proposal no. 2016B0078).

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Contributions

J.O. designed the study. C.G. analysed experimental data. A.S. performed the theoretical analysis. S.J. synthesized the crystals. A.G. calculated theoretical structure factors. J.O., A.S. and C.G. co-wrote the manuscript, with the help of the other authors.

Corresponding authors

Correspondence to Shangda Jiang or Alessandro Soncini or Jacob Overgaard.

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Supplementary information

Supplementary Information

Details about the diffraction data collection, reduction and analysis. Computational details and results of energy levels, spatial shape of the electron density and ellipsoid fitting of surfaces.

Crystallographic data

CIF for compound 1A (CCDC reference 1900925).

Crystallographic data

Structure factors for compound 1A (CCDC reference 1900925).

Crystallographic data

CIF for compound 1B (CCDC reference 1900926).

Crystallographic data

Structure factors for compound 1B (CCDC reference 1900926).

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Gao, C., Genoni, A., Gao, S. et al. Observation of the asphericity of 4f-electron density and its relation to the magnetic anisotropy axis in single-molecule magnets. Nat. Chem. 12, 213–219 (2020). https://doi.org/10.1038/s41557-019-0387-6

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