Strong Axiality in a Dysprosium(III) Bis(borolide) Complex Leads to Magnetic Blocking at 65 K

Abstract

Substituted dysprosocenium complexes of the type [Dy(Cp R ) 2 ] + exhibit slow magnetic relaxation at cryogenic temperatures and have emerged as top-performing single-molecule magnets. The remarkable properties of these compounds derive in part from the strong axial ligand field afforded by the cyclopentadiene anions, and the design of analogous compounds with even stronger ligand fields is one promising route toward identifying new single-molecule magnets that retain a magnetic memory at even higher temperatures. Here, we report the synthesis and characterization of a dysprosium bis(borolide) compound, [K(18-crown-6)][Dy(BC 4 Ph 5 ) 2 ] (1), featuring the dysprosocenate anion [Dy(BC 4 Ph 5 ) 2 ] − with a pseudoaxial coordination environment afforded by two dianionic pentaphenyl borolide ligands. Variable-field magnetization data reveal open magnetic hysteresis up to 66 K, establishing 1 as a topperforming single-molecule magnet among its dysprosocenium analogues. Ac magnetic susceptibility data indicate that 1 relaxes via an Orbach mechanism above ∼80 K with U eff = 1500(100) cm −1 and τ 0 = 10 −12.0(9) s, whereas Raman relaxation and quantum tunneling of the magnetization dominate at lower temperatures. Compound 1 exhibits a 100 s blocking temperature of 65 K, among the highest reported for dysprosium-based single-molecule magnets. Ab initio spin dynamics calculations support the experimental U eff and τ 0 values and enable a quantitative comparison of the relaxation dynamics of 1 and two representative dysprosocenium cations, yielding additional insights into the impact of the crystal field splitting and vibronic coupling on the observed relaxation behavior. Importantly, compound 1 represents a step toward the development of alternatives to substituted dysprosocenium singlemolecule magnets with increased axiality.

AtomAccess: A predictive tool for molecular design and its application to the targeted synthesis of dysprosium single-molecule magnets

“…[4][5][6][7][8][9][10][11][12][13] Isolated dysprosocenium cations, [Dy(Cp R )2] + (Cp R = substituted cyclopentadienyl), and related derivatives, have recently provided SMMs with 100 s magnetic blocking temperatures (T100) that are tantalizingly close to what can be achieved with cheaper liquid nitrogen cooling (77 K). [14][15][16][17][18][19][20][21][22][23][24] The remarkable SMM properties of dysprosocenium cations arise from a combination of their highly axial ligand fields and molecular rigidity, which maximize magnetic anisotropy and inhibit molecular vibrations that promote magnetic relaxation. [1][2][3]5,25,26 The largest Ueff values are obtained for [Dy(Cp R )2] + cations when the Cp R ligands are close to the Dy(III) ion and the Cp R centroid ……”

Influence of pressure on a dysprosocenium single-molecule magnet

“…Single-molecule magnets (SMMs) have many potential uses as they can retain magnetic information, 1 and lanthanide (Ln) SMMs have shown the most impressive properties to date. 2 SMMs typically require liquid He cooling to show magnetic memory effects, yet highly axial Ln SMMs including dysprosocenium cations [3][4][5][6][7] and their derivatives, [8][9][10][11] a Tb 2+ metallocene, 12 and a Dy 2 complex 13 show memory effects close to the boiling point of liquid N 2 (77 K), which is a far cheaper cryogen. To increase the effective barrier to magnetic reversal (U eff ) the most magnetic m J AE15/2 ground state of Dy 3+ , which has an oblate 4f electron density, 14 is best-stabilized by an axial ligand field with no equatorially-bound ligands.…”

Circularly polarized luminescence in the one-dimensional assembly of binaphtyl-based Yb(iii) single-molecule magnets

“…Such an important role was recently reinforced by the observation of blocking temperature near the liquid nitrogen boiling temperature for a series of lanthanide organometallic complexes. [4][5][6][7] Moreover, lanthanide ions are well-known for their specific optical properties with emission line-like spectra and long emission lifetimes ranging from microseconds to milliseconds. [7][8][9][10] Such characteristics open the routes to applications in bioimaging, [11][12][13] optical telecommunication devices [14][15][16][17][18] or material science, for instance, OLED.…”

“…[4][5][6][7] Moreover, lanthanide ions are well-known for their specific optical properties with emission line-like spectra and long emission lifetimes ranging from microseconds to milliseconds. [7][8][9][10] Such characteristics open the routes to applications in bioimaging, [11][12][13] optical telecommunication devices [14][15][16][17][18] or material science, for instance, OLED. 19,20 In the context of molecular magnetism, the lanthanide luminescence could be helpful because it can be observed as a photograph of the energy diagram of the ground-state multiplet under crystal field interaction, and thus it can be correlated to the magnetic properties, [21][22][23] especially in the case of luminescent SMMs.…”