High-Pressure Crystallographic and Magnetic Studies of Pseudo-D_5h Symmetric Dy(III) and Ho(III) Single-Molecule Magnets

Abstract

Single-ion magnets based on lanthanide ions in pseudo-D 5h symmetry have gained much attention in recent years as they are reported to possess a large blocking temperature and a large barrier for magnetization reversal. Magneto-structural correlations reveal that the axial O–Ln–O angle is an important parameter to control the barrier, and while it can be fine-tuned by chemical modification, an alternative would be to utilize hydrostatic pressure. Herein, we report the crystal structures and static magnetic properties of two air-stable isostructural lanthanide SIMs under applied pressures. The complexes exhibit pseudo-D 5h symmetry around the Ln­(III)-ion (Ln = Dy or Ho), which coordinates to five equatorial water molecules and two large neutral phosphonic diamide ligands along the axial direction. High-pressure single-crystal X-ray diffraction experiments revealed two phase-transitions and an increasing deviation from D 5h -symmetry between ambient pressure and 3.6 GPa. High-pressure direct-current magnetic measurements of the Dy­(III) compound showed large steps in the hysteresis loops near zero field, indicative of quantum tunneling of magnetization (QTM). These steps grow in size with increasing pressure, suggesting that QTM becomes progressively more active, which correlates well with the pressure-induced increased overall deviation from pseudo-D 5h symmetry and decreasing axial O–Dy–O angle. A strong temperature dependence of the step size is seen at 0.3 GPa, which shows that the SMM character persists even at this pressure. To understand the origin of significant variation in the tunneling probability upon pressure, we performed a range of ab initio calculations based on the CASSCF/RASSI-SO/SINGLE_ANISO method on both Dy and Ho complexes. From the energies and magnetic anisotropy of the m J sublevels, we find a complex variation of the energy barrier with pressure, and using a constructed geometrical parameter, R, taking into account changes in both bond angles and distances, we link the magnetic properties to the first coordination sphere of the molecules.

A study of cation-dependent inverse hydrogen bonds and magnetic exchange-couplings in lanthanacarborane complexes

“…Moreover, their physical properties are barely studied despite that dysprosiacarboranes are recently confirmed to be milestone entities for single-molecule magnets (SMMs) (Jin, et al, 2020), which may have potential applications in high-density information storage, spintronic devices, and quantum information processing, and so on (Gatteschi, et al, 2006;Mannini, et al, 2009;Leuenberger and Loss, 2001;Bogani and Wernsdorfer, 2008). In addition, the magnetic exchange coupling transferred by B d+ ÀH dÀ •••Ln 3+ IHBs is less studied although the magnetic properties affected by HBs have been discussed in some cases (Gupta et al, 2016a;2016b;Norre, et al, 2020;Canaj, et al, 2018).…”

Attaining record-high magnetic exchange, magnetic anisotropy and blocking barriers in dilanthanofullerenes

“…These U eff and T B values are generally very high for lanthanides, thanks to their strong spin-orbit coupling. [3][4][5][6][7][8][9][10] The enhancement of T B as high as 80 K in "Dysprocenium" complexes was an important breakthrough, replenishing the hope for potential applications in the information storage devices. [11][12][13][14][15] Among others, the important bottlenecks that are likely to hamper the futuristic application of these SMMs are (i) enhancing the blocking temperature beyond 80 K (ii) obtaining molecules that are stable under ambient conditions so that fabrication can be attempted (iii) retaining their intriguing magnetic properties upon fabrication -many best transition metal SMMs failed these criteria.…”

Deciphering the Role of Anions and Secondary Coordination Sphere in Tuning Anisotropy in Dy(III) Air‐Stable D5h SIMs**

“…The chosen ab initio methodology was found to provide better guidance to obtain insights and understand the single‐ion magnetism shown by lanthanide complexes [9d,16] . The magnetic anisotropy axis of 1 – 3 is found to lie along the axial O−Dy−O bond, perpendicular to the ground state beta electron density [16a,b, 17] to minimize the electrostatic repulsions (Figure 6 and S30‐32). The calculations reveal an axial set of g tensors in the ground KD ( g x = g y ∼0.0; g z =19.857 ( 1 ), 19.878 ( 2 ), 19.863 ( 3 ), Table S12–14) and first excited KD.…”