The influence of nuclear spin on the magnetic hysteresis of a single‐molecule is evidenced. Isotopically enriched DyIII complexes are synthesized and an isotopic dependence of their magnetic ...relaxation is observed. This approach is coupled with tuning of the molecular environment through dilution in an amorphous or an isomorphous diamagnetic matrix. The combination of these approaches leads to a dramatic enhancement of the magnetic memory of the molecule. This general recipe can be efficient for rational optimization of single‐molecule magnets (SMMs), and provides an important step for their integration into molecule‐based devices.
DIY magnetism: The quantum tunneling in a mononuclear Dy‐based complex, which already behaves as a single‐molecule magnet (SMM), can be drastically reduced, improving the capability of the molecule to store magnetic information. This improvement is brought about by using isotopes of DyIII without a nuclear magnetic moment, thus suppressing the hyperfine interaction, and by dilution of the SMM in a diamagnetic matrix, thus cancelling the internal field.
Elaborate chemical design is of utmost importance in order to slow down the relaxation dynamics in single‐molecule magnets (SMMs) and hence improve their potential applications. Much interest was ...devoted to the study of distinct relaxation processes related to the different crystal fields of crystallographically independent lanthanide ions. However, the assignment of the relaxation processes to specific metal sites remains a challenging task. To address this challenge, a new asymmetric Dy2 SMM displaying a well‐separated two‐step relaxation process with the anisotropic centers in fine‐tuned local environments was elaborately designed. For the first time a one‐to‐one relationship between the metal sites and the relaxation processes was evidenced. This work sheds light on complex multiple relaxation and may direct the rational design of lanthanide SMMs with enhanced magnetic properties.
One‐to‐one correspondence: Employing a new hydrazone ligand resulted in the self‐assembly of an asymmetric Dy2 single‐molecule magnet (SMM) displaying well‐separated two‐step relaxation with the anisotropic centers in fine‐tuned local environments where the correspondence between the metal sites and the relaxation processes was evidenced (QTM=quantum tunneling of magnetization).
The first dysprosium complexes with a terminal fluoride ligand are obtained as air‐stable compounds. The strong, highly electrostatic dysprosium–fluoride bond generates a large axial crystal‐field ...splitting of the J=15/2 ground state, as evidenced by high‐resolution luminescence spectroscopy and correlated with the single‐molecule magnet behavior through experimental magnetic susceptibility data and ab initio calculations.
A strong donor terminal fluoride ligand generates large crystal‐field splittings within dysprosium(III) complexes and gives rise to new air‐stable single molecule magnets with large barriers to magnetic relaxation. High‐resolution luminescence spectroscopy data are presented and correlated with the single‐molecule magnet behavior through experimental magnetic susceptibility data and ab initio calculations.
We report the study of a Dy‐based metal–organic framework (MOF) with unprecedented magnetic properties. The compound is made of nine‐coordinated DyIII magnetic building blocks (MBBs) with poor ...intrinsic single‐molecule magnet behavior. However, the MOF architecture constrains the MBBs in a one‐dimensional structure that induces a ferromagnetic coupling between them. Overall, the material shows a magnetic slow relaxation in absence of external static field and a hysteretic behavior at 0.5 K. Low‐temperature magnetic studies, diamagnetic doping, and ab initio calculations highlight the crucial role played by the Dy–Dy ferromagnetic interaction. Overall, we report an original magnetic object at the frontier between single‐chain magnets and single‐molecule magnets that host intrachain couplings that cancel quantum tunneling between the MBBs. This compound is evidence that a bottom‐up approach through MOF design can induce spontaneous organization of MBBs able to produce remarkable molecular magnetic materials.
Slow relaxation: Ferromagnetic interactions induced by a metal–organic framework (MOF) architecture turn a poor single‐molecule magnet (SMM) into a slow relaxing material. The compound is made of nine‐coordinated DyIII magnetic building blocks (MBBs) with poor intrinsic single‐molecule magnet behavior. However, the MOF architecture constrains the MBBs in a one‐dimensional structure that induces a ferromagnetic coupling between them.
A one-dimensional coordination solid 1c is synthesized by reaction of a bispyridyl dithienylethene (DTE) photochromic unit with the highly anisotropic dysprosium-based single-molecule magnet ...Dy(Tppy)F(pyridine)2PF6. Slow magnetic relaxation characteristics are retained in the chain compound 1c , and photoisomerization of the bridging DTE ligand induces a single-crystal-to-single-crystal transformation that can be monitored using photocrystallography. Notably, the resulting chain compound 1o exhibits faster low-temperature relaxation than that of 1c , which is apparent in magnetic hysteresis data collected for both compounds as high as 4 K. Ab initio calculations suggest that this photomodulation of the magnetic relaxation behavior is due to crystal packing changes rather than changes to the crystal field splitting upon ligand isomerization.
Abstract
Elaborate chemical design is of utmost importance in order to slow down the relaxation dynamics in single‐molecule magnets (SMMs) and hence improve their potential applications. Much ...interest was devoted to the study of distinct relaxation processes related to the different crystal fields of crystallographically independent lanthanide ions. However, the assignment of the relaxation processes to specific metal sites remains a challenging task. To address this challenge, a new asymmetric Dy
2
SMM displaying a well‐separated two‐step relaxation process with the anisotropic centers in fine‐tuned local environments was elaborately designed. For the first time a one‐to‐one relationship between the metal sites and the relaxation processes was evidenced. This work sheds light on complex multiple relaxation and may direct the rational design of lanthanide SMMs with enhanced magnetic properties.
A redox active dinuclear complex Yb(tta)(2)(L(1))(L(2))(2)·1.4(CH(2)Cl(2)) displays single molecule magnet behaviour with M(J) = ±7/2 ground state. The anisotropic barrier Δ is evaluated by the three ...dc data fit, ac analysis and emission spectrum demonstrating the correlation between magnetic and optical properties.
Lanthanide Single‐Molecule Magnets are fascinating objects that break magnetic performance records with observable magnetic bistability at the boiling temperature of liquid nitrogen, paving the way ...for potential applications in high‐density data storage. The switching of lanthanide SMM has been successfully achieved using several external stimuli such as redox reaction, pH titration, light irradiation or solvation/desolvation thanks to the high sensitivity of the magnetic anisotropy to any structural change in the lanthanide surrounding. Nevertheless, the use of applied high pressure as an external stimulus is largely underused, especially considering that it can be combined with high pressure X‐ray diffraction to establish a complementary structure‐property relationship. This Concept article summarizes the few relevant examples of investigations of lanthanide SMMs under applied high pressure, provides conclusions on the effect of such stimulus on molecular structures and magnetic anisotropy, and finally draws perspective on the future development of magnetic measurements under applied pressure.
Sensibility of lanthanide coordination complexes to the crystal field strength makes them ideal candidates for switching Single‐Molecule Magnet behavior and piezochromic effect under applied high pressure. A complementary structure‐property relationship is established with the combination of high pressure magnetometry and single‐crystal X‐ray diffraction allowing to explain the observed structural, optical and magnetic modifications.
Display omitted
•Mononuclear Single Molecule Magnets (SMMs) containing YbIII, CeIII, NdIII, HoIII and TmIII ions are reviewed.•Polynuclear SMMs containing YbIII, CeIII, NdIII and HoIII are ...reviewed.•Heterobimetallic ZnYbIII/CeIII and 4fYbIII SMMs are reviewed.•Dynamic parameters and mechanisms of slow magnetic relaxation are deeply analysed.•Magnetic properties and luminescence are correlated.
Since the 1990s and the discovery of the first Single Molecule Magnets (SMMs), chemists and physicists have been working in concert to elaborate such molecular systems and understand their peculiar properties. Especially the use of lanthanide ions in the design of SMMs exploded with the discovery of the first example of mononuclear TbIII-based complex which displayed a slow magnetic relaxation in 2003. This high-degree of interest comes from the diverse potential applications in quantum computing, high-density data storage devices and spintronics. Recently, the specific luminescence properties of the lanthanide ions were correlated to the magnetic ones. Even if the most common lanthanide ions used in the elaboration of SMMs are the DyIII, TbIII and ErIII ions, new SMMs involving others lanthanide ions (YbIII, CeIII, NdIII, HoIII and TmIII) started to emerge. This review presents the research endeavour in the area of these uncommon lanthanide-based SMMs and underlines the different approaches to better understand their physical properties.
The association of heptamethine cyanine cation 1 + with various counterions A (A = Br−, I−, PF6 −, SbF6 −, B(C6F5)4 −, TRISPHAT) was realized. The six different ion pairs have been characterized by ...X-ray diffraction, and their absorption properties were studied in polar (DCM) and apolar (toluene) solvents. A small, hard anion (Br−) is able to strongly polarize the polymethine chain, resulting in the stabilization of an asymmetric dipolar-like structure in the crystal and in nondissociating solvents. On the contrary, in more polar solvents or when it is associated with a bulky soft anion (TRISPHAT or B(C6F5)4 −), the same cyanine dye adopts preferentially the ideal polymethine state. The solid-state and solution absorption properties of heptamethine dyes are therefore strongly correlated to the nature of the counterion.
PDF
