Incorporation of Cr^III into a Keggin Polyoxometalate as a Chemical Strategy to Stabilize a Labile {Cr^IIIO₄} Tetrahedral Conformation and Promote Unattended Single-Ion Magnet Properties

Abstract

Polyoxometalates (POMs) provide rigid and highly symmetric coordination sites and can be used as a strategy for the stabilization of magnetic ions. Herein, we report a new member of the Keggin archetype, the Cr-centered Keggin anion [α-CrW12O40]5– (CrW12), with the unusual tetrahedral coordination of CrIII reported for the first time in POMs conferring unattended magnetic properties. POM chemistry has recently presented excellent examples of single-molecule and single-ion magnets (SMMs and SIMs) as well as molecular spin qubits; however, the majority of POM-based SIMs reported to date contain lanthanoid ions. CrW12, as the first example of a chromium­(III) SIM, exhibits slow relaxation of magnetization and quantum tunneling with a single-ion magnetic behavior even above 10 K with an energy barrier for the reversal of the magnetization of 3.0 K. The first 3d-metal SIM based on a nonlacunary Keggin anion is the foundation for a new research area in POM chemistry.

The rationalized pathway from field-induced slow magnetic relaxation in CoII–WIV chains to single-chain magnetism in isotopological CoII–WV analogues

“…8,10,13–17 The critical role in achieving high-performance SIMs is played by the generation of the appropriate ligand-field and coordination geometry that ensure strong single-ion anisotropy. 18–21 This can be exemplified by Co II centres for which the distinct SIM behaviour, observed without the support of external magnetic field, was induced in two-coordinated linear, 22,23 four-coordinated tetrahedral, 8,24,25 and six-coordinated trigonal prismatic complexes. 26,27 The important role is also played by the proper magnetic isolation of SIMs in the crystal lattice.…”

Nucleation mechanisms and speciation of metal oxide clusters

“…1 Although the rst-ever characterized structure was synthesized by Berzelius almost two centuries ago, 2 POMs have not ceased to attract attention. As a matter of fact, they display a broad variety of present applications in catalysis, [3][4][5][6][7][8][9][10][11] nuclear reprocessing, 12,13 electro-chemistry 14 and potential uses in information technologies, 15,16 medicine, [17][18][19] and energy. [20][21][22] The synthesis of POMs usually takes place by reacting the corresponding oxo-anion monomer, for instance [MoO 4 ] 2À , with additional acids, bases or other salts, in aqueous solution where a plethora of hydrolysis, aggregation and condensation reactions triggers the formation of discrete clusters.…”

Silver‐Templated γ‐Keggin Alkyltin‐Oxo Cluster: Electronic Structure and Optical Limiting Effect

“…And many elements in the periodic table, from initial main group atoms to the later transition metals and more recently alkali/alkaline earth metals, have been introduced as the X templates (Scheme 1). [12][13][14][15][16][17][18][19][20][21] However, despite this progress, Keggin clusters taking noble metal atoms as templates have not been reported, which may be associated with the difficult match of size, chemical stability, and coordination mode between noble metal atoms and Keggin clusters. Compared with most of the reported central heteroatoms, the heavy noble metal may introduce more sublevels into the energy hierarchy of Keggin clusters to affect their electronic structures.…”