Molecular Network Approach to Anisotropic Ising Lattices: Parsing Magnetization Dynamics in Er³⁺ Systems with 0–3-Dimensional Spin Interactivity

Abstract

We present a wide-ranging interrogation of the border between single-molecule and solid-state magnetism through a study of erbium-based Ising-type magnetic compounds with a fixed magnetic unit, using three different charge-balancing cations as the means to modulate the crystal packing environment. Properties rooted in the isolated spin Hamiltonian remain fixed, yet careful observation of the dynamics reveals the breakdown of this approximation in a number of interesting ways. First, differences in crystal packing lead to a striking 3 orders of magnitude suppression in magnetic relaxation rates, indicating a rich interplay between intermolecular interactions governed by the anisotropic Ising lattice stabilization and localized slow magnetic relaxation driven by the spin-forbidden nature of quantum tunneling of the f-electron-based magnetization. By means of diverse and rigorous physical methods, including temperature-dependent X-ray crystallography, field, temperature, and time-dependent magnetometry, and the application of a new magnetization fitting technique to quantify the magnetic susceptibility peakshape, we are able to construct a more nuanced view of the role nonzero-dimensional interactions can play in what are predominantly considered zero-dimensional magnetic materials. Specifically, we use low field susceptibility and virgin-curve analysis to isolate metamagnetic spin-flip transitions in each system with a field strength corresponding to the expected strength of the internal dipole−dipole lattice. This behavior is vital to a complete interpretation of the dynamics and is likely common for systems with such high anisotropy. This collective interactivity opens a new realm of possibility for molecular magnetic materials, where their unprecedented localized anisotropy is the determining factor in building higher dimensionality.

Linear, Electron-Rich Erbium Single-Molecule Magnet with Dibenzocyclooctatetraene Ligands

“…1 is comprised of charge-separated ion pairs, owing to the presence of an encapsulated potassium cation, [K­(crypt-222)] + . Resultingly, the potassium ion remains 8.290(1) Å from the nearest Er III ion, and the Er–Er distances range from 9.621(1) to 10.854(1) Å, significantly larger than the Er–K and Er–Er distances observed for [Er­(COT) 2 ] − . ,,,, The Er–C COT distances in 1 vary between 2.577(1) and 2.647(1) Å, consistent with that of other homoleptic Er-COT complexes. − ,,,, The coordinated dbCOT ligands exhibit a remarkably linear geometry, as evidenced by a Cnt–Er–Cnt angle of 180.0°. The Er–Cnt distances of 1.837 and 1.832 Å are in agreement with those of COT-based erbocene complexes (Table S3).…”

“…A COT 2– ligand stabilizes the magnetic easy axis of the Er III ion, even in the presence of peripheral ligands . Despite the advances with [Er­(COT) 2 ] − systems, the impact of COT derivatives on crystal field (CF) splitting, and arising SMM behavior, is underexplored and prompts further elucidation. ,,,− Aside from the bare COT ligand, silylated and cycloalkylated derivatives have been employed in the design of homoleptic Er III SMMs. Complexes with ligands exhibiting fused aromatic substituents to the [8]­annulene remain elusive.…”

Dipolar Coupling as a Mechanism for Fine Control of Magnetic States in ErCOT-Alkyl Molecular Magnets

“…This is made clear by the lack of significant change in the relaxation dynamics of 2@Y , and in 3@Y , the partial removal of intramolecular coupling seems to hasten relaxation. An alternative interpretation of this result, as might be garnered from the crystal structure of 3 , is the removal of a high symmetry bulk dipolar field arising from intermolecular interactions that enhances relaxation . In the absence of further supporting data, we do not explore this beyond speculation, but the possibility invites future investigations of crystal engineering with coupled systems.…”

Modulation of the Slow Relaxation of the Magnetization Dynamics through Second Coordination Sphere in Macrocyclic Dysprosium(III) Complexes

“…In this sense, the majority of magnetic studies of SMMs are conducted in the solid state. Since the SMM property strongly depends on the coordination environment of the lanthanide site, leveraging intermolecular interactions to induce subtle structural changes through second coordination sphere interactions represents an underexplored avenue. − For instance, the effect of crystal packing and intermolecular interactions over the relaxation dynamics was recently highlighted in a series of organometallic Er-based SMMs …”

“…35−38 interactions over the relaxation dynamics was recently highlighted in a series of organometallic Er-based SMMs. 39 In this study, we propose employing intermolecular interactions in cationic complexes [DyX 2 (L)] + , involving a macrocyclic L ligand, by altering the counteranion. To investigate this concept, we selected a model macrocyclic compound [DyL N6 (OAc) 2 ][OAc] (L N6 = 2,7,13,18-Tetramethyl -3,6,14,17,23,24-hexaazatricyclo[17.3.1.1 8,12 ]tetracosa 1( 23),2,6,8,10,12 (24),13,17,19,21-decaene, OAc = acetate) (1), previously reported by Canaj et al 29 and based on a hexadentate nitrogen ligand.…”