Supramolecular Control over Molecular Magnetic Materials: γ-Cyclodextrin-Templated Grid of Cobalt(II) Single-Ion Magnets

Abstract

Single-ion magnets (SIMs) are potential building blocks of novel quantum computing devices. Unique magnetic properties of SIMs require effective separation of magnetic ions and can be tuned by even slight changes in their coordination sphere geometry. We show that an additional level of tailorability in the design of SIMs can be achieved by organizing magnetic ions into supramolecular architectures, resulting in gaining control over magnetic ion packing. Here, γ-cyclodextrin was used to template magnetic Co(II) and nonmagnetic auxiliary Li(+) ions to form a heterometallic {Co, Li, Li}4 ring. In the sandwich-type complex [(γ-CD)2Co4Li8(H2O)12] spatially separated Co(II) ions are prevented from superexchange magnetic coupling. Ac/dc magnetic and EPR studies demonstrated that individual Co(II) ions with positive zero-field splitting exhibit field-induced slow magnetic relaxation consistent with the SIMs' behavior, which is exceptional in complexes with easy-plane magnetic anisotropy.

Magnetic anisotropy in two- to eight-coordinated transition–metal complexes: Recent developments in molecular magnetism

“…Penta-coordinated complexes usually possess trigonal bipyramidal (ideal and distorted cases) [52,[82][83][84][85], tetragonal pyramidal [86,87], and distorted square-based tetragonal pyramidal [84][85][86]88] geometries (Scheme 5). The magnetic anisotropy of a metal ion was expected in this environment and it was demonstrated as early as in 1975 [89][90][91].…”

Cyclodextrin-Templated Co(II) Grids: Symmetry Control over Supramolecular Topology and Magnetic Properties

“…A new heterometallic Co/Li complex [(α-CD) 2 Co 3 Li 6 (H 2 O) 9 ] ( α-1 ) incorporating two α-CD anions was obtained by a procedure previously reported for [(γ-CD) 2 Co 4 Li 8 (H 2 O) 12 ] ( γ-1 ) 5 ( Figure 1 ) utilizing optimized amounts of reactants (see the Experimental Section ). To this aim, an aqueous solution of α-CD and CoCl 2 was slowly dropped to LiOH and α-CD suspended in water.…”

“…The complex was synthesized according to the previously reported procedure. 5 Pink-violet needle-like crystals of γ-1 were collected by filtration after crystallization by diffusion of acetone vapor into the parent solution. Results of the elemental analysis of the bulk material may vary due to difficulties with purification of the crude material from lithium salts residues.…”

New Cobalt(II) Field‐Induced Single‐Molecule Magnet and the First Example of a Cobalt(III) Complex with Tridentate Binding of a Deprotonated 4‐Amino‐3,5‐bis(pyridin‐2‐yl)‐1,2,4‐Triazole Ligand

“…The advantage of mononuclear SMMs is that the key factor – the magnetic anisotropy can be modified by the rational design of ligand field strength and the coordination geometry around central atom . The first mononuclear Co II SMM was reported in 2011, and since that time, the slow relaxation of the magnetization was reported in tetra‐, penta‐, hexa‐, hepta‐, or octacoordinate Co II coordination compounds. Recently, we have studied and described a series of mononuclear hexacoordinate Co II coordination compounds with abpt ligand and linear and non‐linear pseudohalide anions, which behave as field‐induced single ion magnets , .…”