Trigonally Distorted Hexacoordinate Co(II) Single-Ion Magnets.

Ivan Nemec,Berenika Indruchová,Ondřej F Fellner,Radovan Herchel

doi:10.3390/ma15031064

Ivan Nemec, Berenika Indruchová + Show 2 more

Open Access

https://doi.org/10.3390/ma15031064

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Journal: Materials	Publication Date: Jan 29, 2022
Citations: 11	License type: CC BY 4.0

Affiliation: Palacký University, Olomouc

Abstract

By simple reactions involving various cobalt(II) carboxylates (acetate and in situ prepared pivalate and 4-hydroxybenzoate salts) and neocuproine (neo), we were able to prepare three different carboxylate complexes with the general formula [Co(neo)(RCOO)2] (R = –CH3 for 1, (CH3)3C– for 2, and 4OH-C4H6– for 3). The [Co(neo)(RCOO)2] molecules in the crystal structures of 1–3 adopt a rather distorted coordination environment, with the largest trigonal distortion observed for 1, whereas 2 and 3 are similarly distorted from ideal octahedral geometry. The combined theoretical and experimental investigations of magnetic properties revealed that the spin Hamiltonian formalism was not a valid approach and the L-S Hamiltonian had to be used to reveal very large magnetic anisotropies for 1–3. The measurements of AC susceptibility showed that all three compounds exhibited slow-relaxation of magnetization in a weak external static magnetic field, and thus can be classified as field-induced single-ion magnets. It is noteworthy that 1 also exhibits a weak AC signal in a zero-external magnetic field.

Highlights

Hexacoordinate Co(II) complexes often tend to possess very large magnetic anisotropies arising from the direct contribution of spin orbit coupling to the ground state
Angular momentum is the main contributor to the zero-field splitting (ZFS), because the spinorbit coupling operator transforms under t1g, it directly mixes with the ground state
Co(II) complexes with doubly degenerate ground states are highly interesting for synthesis of single-ion magnets (SIMs), which are a class of singe molecule magnets (SMMs) [6] containing only one paramagnetic center [7]

Summary

Introduction

Hexacoordinate Co(II) complexes often tend to possess very large magnetic anisotropies arising from the direct contribution of spin orbit coupling to the ground state. The design of highly anisotropic magnetic molecules exploits changing of the regular octahedral geometry, which can be achieved either by elongation/compression of the metal–ligand bonds or by trigonal distortion. Both types of distortion can lead to double orbitally degenerate ground states (4Eg for compressed octahedron, D4h, 4E for trigonal prism, D3h), manifesting themselves again by a large contribution of spin-orbit coupling to the ground state. We reported on two [Co(neo)(PhCOO)2] polymorphs (neo stands for neocuproine), which differed in their trigonal distortion and magnetic properties Both compounds behaved as SIMs in a weak external magnetic field (B = 0.1 T), so-called field-induced SIMs [34]. We report on the synthesis, crystal structure, and thorough experimental and theoretical investigation of static and dynamic magnetic properties of three new carboxylate complexes with the general formula [Co(neo)(RCOO)2], where RCOO– represents carboxylate ligands (acetate (1), pivalate (2), and 4-hydroxybenzoate (3))

Materials

General Methods

X-ray Crystallography

Synthesis and Crystal Structure

AC Magnetic Properties