Abstract:nwith Ln = Gd or Dy and n = 0, 1 or 2 are described. The gadolinium complexes with n = 0 and 2 show typically weak exchange coupling, whereas the complex bridged by the radical [ind] 3-ligand shows an unusually large coupling constant of J = -11 cm -1 (-2J formalism). The dysprosium complexes with n = 0 and 1 are single-molecule magnets in zero applied field, whereas the complex with n = 2 does not show slow magnetic relaxation. Naturally occurring indigo (H 2 ind) and many of its synthetic derivatives have… Show more
“…5, 6 and 7). This represents the second largest coupling constant yet observed for a gadolinium-containing compound, following that of a similar N 2
3− -bridged complex with J
Gd–rad = –27 cm −1
21 , and is significantly greater than the J
Gd–rad of –11 cm −1 observed for both a mononuclear gadolinium–nitronyl nitroxide radical complex 31 and an indigo radical-bridged digadolinium complex 28 . Such strong antiferromagnetic coupling reflects the diffuse character of the radical spin of the compact, highly anionic N 2
3− bridging unit, which is localized in the π * orbital perpendicular to the Ln 2 (µ−η 2 :η 2 −N 2 ) plane 32 .Fig.…”
Section: Resultsmentioning
confidence: 70%
“…In addition to creating a more classical coupled system with large total angular momentum, magnetic coupling has been postulated to generate an exchange bias field that impedes quantum tunneling of the magnetization 17–20 . In recent years, a particularly successful strategy to promote strong magnetic coupling between lanthanide centers has been the employment of paramagnetic bridging ligands 21–28 . Significantly, the diffuse spin orbitals of anionic radical ligands are better able to penetrate into the core electron density of the deeply buried 4f orbitals.…”
Increasing the operating temperatures of single-molecule magnets—molecules that can retain magnetic polarization in the absence of an applied field—has potential implications toward information storage and computing, and may also inform the development of new bulk magnets. Progress toward these goals relies upon the development of synthetic chemistry enabling enhancement of the thermal barrier to reversal of the magnetic moment, while suppressing alternative relaxation processes. Herein, we show that pairing the axial magnetic anisotropy enforced by tetramethylcyclopentadienyl (CpMe4H) capping ligands with strong magnetic exchange coupling provided by an N2
3− radical bridging ligand results in a series of dilanthanide complexes exhibiting exceptionally large magnetic hysteresis loops that persist to high temperatures. Significantly, reducing the coordination number of the metal centers appears to increase axial magnetic anisotropy, giving rise to larger magnetic relaxation barriers and 100-s magnetic blocking temperatures of up to 20 K, as observed for the complex [K(crypt-222)][(CpMe4H
2Tb)2(μ−)].
“…5, 6 and 7). This represents the second largest coupling constant yet observed for a gadolinium-containing compound, following that of a similar N 2
3− -bridged complex with J
Gd–rad = –27 cm −1
21 , and is significantly greater than the J
Gd–rad of –11 cm −1 observed for both a mononuclear gadolinium–nitronyl nitroxide radical complex 31 and an indigo radical-bridged digadolinium complex 28 . Such strong antiferromagnetic coupling reflects the diffuse character of the radical spin of the compact, highly anionic N 2
3− bridging unit, which is localized in the π * orbital perpendicular to the Ln 2 (µ−η 2 :η 2 −N 2 ) plane 32 .Fig.…”
Section: Resultsmentioning
confidence: 70%
“…In addition to creating a more classical coupled system with large total angular momentum, magnetic coupling has been postulated to generate an exchange bias field that impedes quantum tunneling of the magnetization 17–20 . In recent years, a particularly successful strategy to promote strong magnetic coupling between lanthanide centers has been the employment of paramagnetic bridging ligands 21–28 . Significantly, the diffuse spin orbitals of anionic radical ligands are better able to penetrate into the core electron density of the deeply buried 4f orbitals.…”
Increasing the operating temperatures of single-molecule magnets—molecules that can retain magnetic polarization in the absence of an applied field—has potential implications toward information storage and computing, and may also inform the development of new bulk magnets. Progress toward these goals relies upon the development of synthetic chemistry enabling enhancement of the thermal barrier to reversal of the magnetic moment, while suppressing alternative relaxation processes. Herein, we show that pairing the axial magnetic anisotropy enforced by tetramethylcyclopentadienyl (CpMe4H) capping ligands with strong magnetic exchange coupling provided by an N2
3− radical bridging ligand results in a series of dilanthanide complexes exhibiting exceptionally large magnetic hysteresis loops that persist to high temperatures. Significantly, reducing the coordination number of the metal centers appears to increase axial magnetic anisotropy, giving rise to larger magnetic relaxation barriers and 100-s magnetic blocking temperatures of up to 20 K, as observed for the complex [K(crypt-222)][(CpMe4H
2Tb)2(μ−)].
“…Here, ab-initio theoretical studies were invaluable in demonstrating that the magnetic ground state of Dy 3+ in compounds of the type [Cp2Ln(-X)]n is typically a Kramers doublet with significant MJ = ±15/2 character; the main magnetic axis in this ground doublet is oriented towards the two cyclopentadienyl ligands in every case studied. 19,[24][25][26][27][28][29][30][31][32][33] Hence, an axial direction can be defined according to Scheme 1, with the dominant crystal field being provided by the cyclopentadienyl ligands (see also Figures 1 and 2). The equatorial coordination sites comprises the ligands X, whose presence diminish the axiality, meaning that the SMM properties vary to an extent that depends on the -bridging ligand.…”
Section: Dynamic Magnetic Susceptibility Measurements and Magneto-strmentioning
The discovery of materials capable of storing magnetic information at the level of single molecules and even single atoms has fueled renewed interest in the slow magnetic relaxation properties of single-molecule magnets (SMMs). The lanthanide elements, especially dysprosium, continue to play a pivotal role in the development of potential nanoscale applications of SMMs, including, for example, in molecular spintronics and quantum computing. Aside from their fundamentally fascinating physics, the realization of functional materials based on SMMs requires significant scientific and technical challenges to be overcome. In particular, extremely low temperatures are needed to observe slow magnetic relaxation, and while many SMMs possess a measurable energy barrier to reversal of the magnetization ( U), very few such materials display the important properties of magnetic hysteresis with remanence and coercivity. Werner-type coordination chemistry has been the dominant method used in the synthesis of lanthanide SMMs, and most of our knowledge and understanding of these materials is built on the many important contributions based on this approach. In contrast, lanthanide organometallic chemistry and lanthanide magnetochemistry have effectively evolved along separate lines, hence our goal was to promote a new direction in single-molecule magnetism by uniting the nonclassical organometallic synthetic approach with the traditionally distinct field of molecular magnetism. Over the last several years, our work on SMMs has focused on obtaining a detailed understanding of why magnetic materials based on the dysprosium metallocene cation building block {CpDy} display slow magnetic relaxation. Specifically, we aspired to control the SMM properties using novel coordination chemistry in a way that hinges on key considerations, such as the strength and the symmetry of the crystal field. In establishing that the two cyclopentadienyl ligands combine to provide a strongly axial crystal field, we were able to propose a robust magneto-structural correlation for understanding the properties of dysprosium metallocene SMMs. In doing so, a blueprint was established that allows U and the magnetic blocking temperature ( T) to be improved in a well-defined way. Although experimental discoveries with SMMs occur more rapidly than quantitative theory can (currently) process and explain, a clear message emanating from the literature is that a combination of the two approaches is most effective. In this Account, we summarize the main findings from our own work on dysprosium metallocene SMMs, and consider them in the light of related experimental studies and theoretical interpretations of related materials reported by other protagonists. In doing so, we aim to contribute to the nascent and healthy debate on the nature of spin dynamics in SMMs and allied molecular nanomagnets, which will be crucial for the further advancement of this vibrant research field.
“…The interaction between Gd 3+ and the radical indigo ligand is the largest known for a lanthanide complex. The dysprosium complexes with m = 0 and 2 were shown to be single‐molecule magnets in zero applied field …”
Section: Modern Coordination Chemistry Of Indigo and Its Substitutementioning
While the first coordination compounds of indigo were reported over 100 years ago, a systematic study of the coordination chemistry of this important dye and also its structural “relatives” remained silent for over half a century. Only in the last two decades of the 20th century research on this topic started again keeps on growing ever since. It could be established, mainly by X‐ray crystallography, but also by many other modern spectroscopic techniques, that deprotonated indigo, and its deprotonated oxidized and reduced forms act as mono‐ and bidentate chelate ligands in metal complexes
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