Playing with Magnetic Anisotropy in Hexacoordinated Mononuclear Ni(II) Complexes, An Interplay Between Symmetry and Geom
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Applied Magnetic Resonance
ORIGINAL PAPER
Playing with Magnetic Anisotropy in Hexacoordinated Mononuclear Ni(II) Complexes, An Interplay Between Symmetry and Geometry Nicolas Suaud1 · Guillaume Rogez2 · Jean‑Noël Rebilly3 · Mohammed‑Amine Bouammali1 · Nathalie Guihéry1 · Anne‑Laure Barra4 · Talal Mallah3 Received: 5 July 2020 / Revised: 15 July 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract The magnetic anisotropy parameters of a hexacoordinate trigonally elongated Ni(II) complex with symmetry close to D3d are measured using field-dependent magnetization and High-Field and High-Frequency EPR spectroscopy (D = + 2.95 cm−1, |E/D| = 0.08 from EPR). Wave function based theoretical calculations reproduce fairly well the EPR experimental data and allows analysing the origin of the magnetic anisotropy of the complex. Calculations on model complexes allows getting insight into the origin of the large increase in the axial magnetic anisotropy (D) when the complex is brought to a prismatic geometry with a symmetry close to D3h.
* Nathalie Guihéry [email protected]‑tlse.fr * Anne‑Laure Barra anne‑[email protected] * Talal Mallah talal.mallah@universite‑paris‑saclay.fr 1
Laboratoire de Chimie et Physique Quantiques, Université de Toulouse III, 118, route de Narbonne, 31062 Toulouse, France
2
IPCMS-GMI, UMR CNRS 7504, 23, rue du Loess, B.P. 43, 67034 Strasbourg Cedex 2, France
3
Institut de Chimie Moléculaire et des Matériaux d’Orsay, CNRS, Université Paris-Saclay, 91405 Orsay, France
4
Laboratoire National des Champs Magnétiques Intenses, UPR CNRS 3228, Univ. Grenoble Alpes, 25, avenue des Martyrs, B.P. 166, 38042 Grenoble Cedex 9, France
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1 Introduction The majority of hexacoordinate Ni(II) complexes (d8 configuration and S = 1) have an octahedral geometry that is usually distorted and present a zero-field splitting (ZFS) of the MS sub-levels (± 1 and 0) characterized by two parameters D (axial) and E (rhombic). ZFS originates from the simultaneous effects of geometrical distortions from Oh symmetry and spin–orbit coupling. In the ideal case of Oh symmetry point group, the three components ( L̂ x , L̂ y and L̂ z ) of the angular orbital momentum belong to the same irreducible representation (IRREP) T1g and the effect of the spin–orbit coupling (SOC) is the same in the three directions of space preventing the occurence of ZFS. In the presence of a weak axial distortion, a weak ZFS occurs stabilizing either the MS = ± 1 levels (negative D value corresponding to an easy axis of magnetization, see Eq. 1) or the MS = 0 (positive D value corresponding to an easy plane of magnetization). A deviation from axiality leads to a lift of degeneracy of the MS = ± 1 levels by 2E where E is the rhombic ZFS parameter based on the following spin Hamiltonian: ( ) [ ] HZFS = D Ŝ z2 − S(S + 1)∕3 + E Ŝ x2 − Ŝ y2 , (1) with Ŝ i (i = x, y, z) the components of the spin operator. For an orbitally non-degenerate ground state as for octahedral g
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