Breakthrough in Radical‐bridged Single‐molecule Magnets

Efthymiou, Constantinos G.; Winterlich, Meghan; Papatriantafyllopoulou, Constantina

doi:10.1002/9783527809929.ch7

Cited by 4 publications

(7 citation statements)

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“…Recently, metal–radical complexes have been extensively pursued as a viable route for improved magnetically coupled systems with SMM behavior. , In 1 , the strong exchange coupling between the α-diiminato radical and the high-spin iron(II) leads to an effective S = 3/2 magnetic center in an axially distorted tetrahedral coordination environment, which is typically expected to give rise to SMM behavior. , The large magnitude of the exchange coupling constant, | J| > 250 cm –1 , ensures a large separation between the low-lying spin excited states and the ground state. Such a large separation of the excited states is expected to eliminate a possible fast relaxation pathway that could otherwise be detrimental to the thermal energy barrier.…”

Section: Resultsmentioning

confidence: 99%

“…In the pursuit of radical-ligand-containing SMMs, an emerging trend is to use strongly exchange-coupled redox-active bridging radicals to generate multinuclear transition metal-based SMMs. , This strategy has proven to be very effective and productive, generating diiron, − dicobalt, − and dinickel SMMs with strong exchange couplings (in one example, | J| > 900 cm –1 ) and U eff values up to 267(3) K 26 ( U eff is the effective spin-reversal barrier). A wide range of bridging radicals have been employed to construct these dinuclear transition metal-radical SMMs, including semiquinone radical, tetraoxolene radical, tetraazalene radical, , nindigo radical, 2,2′-bipyrimidine radical, tetrazine radical, tetrapyridophenazine radical, and 1,2,4,5-tetrakis(methanesulfonamido)benzene) radical ligands .…”

Section: Introductionmentioning

confidence: 99%

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Molecular and Electronic Structures and Single-Molecule Magnet Behavior of Tris(thioether)–Iron Complexes Containing Redox-Active α-Diimine Ligands

et al. 2021

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Incorporating radical ligands into metal complexes is one of the emerging trends in the design of single-molecule magnets (SMMs). While significant effort has been expended to generate multinuclear transition metal-based SMMs with bridging radical ligands, less attention has been paid to mononuclear transition metal−radical SMMs. Herein, we describe the first α-diiminato radicalcontaining mononuclear transition metal SMM, namely, [κ 2 -PhTt tBu ] -Fe(AdNCHCHNAd) (1), and its analogue [κ 2 -PhTt tBu ]Fe-(CyNCHCHNCy) (2) (PhTt tBu = phenyltris(tert-butylthiomethyl)borate, Ad = adamantyl, and Cy = cyclohexyl). 1 and 2 feature nearly identical geometric and electronic structures, as shown by X-ray crystallography and electronic absorption spectroscopy. A more detailed description of the electronic structure of 1 was obtained through EPR and Mossbauer spectroscopies, SQUID magnetometry, and DFT, TD-DFT, and CAS calculations. 1 and 2 are best described as high-spin iron(II) complexes with antiferromagnetically coupled α-diiminato radical ligands. A strong magnetic exchange coupling between the iron(II) ion and the ligand radical was confirmed in 1, with an estimated coupling constant J < −250 cm −1 (J = −657 cm −1 , DFT). Calibrated CAS calculations revealed that the ground-state Fe(II)−α-diiminato radical configuration has significant ionic contributions, which are weighted specifically toward the Fe(I)-neutral α-diimine species. Experimental data and theoretical calculations also suggest that 1 possesses an easy-axis anisotropy, with an axial zero-field splitting parameter D in the range from −4 to−1 cm −1 . Finally, dynamic magnetic studies show that 1 exhibits slow magnetic relaxation behavior with an energy barrier close to the theoretical maximum, 2|D|. These results demonstrate that incorporating strongly coupled α-diiminato radicals into mononuclear transition metal complexes can be an effective strategy to prepare SMMs.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Molecular and Electronic Structures and Single-Molecule Magnet Behavior of Tris(thioether)–Iron Complexes Containing Redox-Active α-Diimine Ligands

et al. 2021

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“…34−38 Strong exchange coupling between a given metal and ligand radical has been shown to facilitate slow magnetic relaxation by discouraging quantum tunneling and increasing the energy gap between the ground and excited states. 27,39 In addition to these benefits, redox-noninnocent ligands capable of undergoing reversible redox events could serve as "on−off" switches for SMM behavior. 40,41 The present work examines the magnetic anisotropy of a series of five-coordinate Co(II) complexes that feature redoxactive ligands in varying oxidation and spin states.…”

Section: Introductionmentioning

confidence: 99%

Probing the Magnetic Anisotropy of Co(II) Complexes Featuring Redox-Active Ligands

et al. 2020

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Coordination complexes that possess large magnetic anisotropy (otherwise known as zero-field splitting, ZFS) have possible applications in the field of magnetic materials, including single molecule magnets (SMMs). Previous studies have explored the role of coordination number and geometry in controlling the magnetic anisotropy and SMM behavior of high-spin (S = 3/2) Co(II) complexes. Building upon these efforts, the present work examines the impact of ligand oxidation state and structural distortions on the spin states and ZFS parameters of pentacoordinate Co(II) complexes. The five complexes included in this study (1−5) have the general formula, [Co(Tp Ph2 )(L X,Y )] n+ (X = O, S; Y = N, O; n = 0 or 1), where Tp Ph2 is the scorpionate ligand hydrotris(3,5-diphenyl-pyrazolyl)borate(1−) and L X,Y are bidentate dioxolenetype ligands that can access multiple oxidation states. The specific L X,Y ligands used herein are 4,6-di-tert-butyl substituted oaminophenolate and o-aminothiophenolate (1 and 2, respectively), o-iminosemiquinonate and o-semiquinonate radicals (3 and 4, respectively), and o-iminobenzoquinone (5). Each complex exhibits a distorted trigonal bipyramidal geometry, as revealed by singlecrystal X-ray diffraction. Direct current (dc) magnetic susceptibility experiments confirmed that the complexes with closed-shell ligands (1, 2, and 5) possess S = 3/2 ground states with negative D-values (easy-axis anisotropy) of −41, −78, and −30 cm −1 , respectively. For 3 and 4, antiferromagnetic coupling between the Co(II) center and o-(imino)semiquinonate radical ligand results in S = 1 ground states that likewise exhibit very large and negative anisotropy (−100 > D > −140 cm −1 ). Notably, ZFS was measured directly for each complex using far-infrared magnetic spectroscopy (FIRMS). In combination with high-frequency and -field electron paramagnetic resonance (HFEPR) studies, these techniques provided precise spin-Hamiltonian parameters for complexes 1, 2, and 5. Multireference ab initio calculations, using the CASSCF/NEVPT2 approach, indicate that the strongly negative anisotropies of these Co(II) complexes arise primarily from distortions in the equatorial plane due to constrictions imposed by the Tp Ph2 ligand. This effect is further amplified by cobalt(II)-radical exchange interactions in 3 and 4.

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“…Ghirri end co-authors [176], reported the direct magnetic measurements for monolayers of molecular nanomagnets investigated by SHPM. In the paper, the magnetic response of Cs 0.7 Ni[Cr(CN) 6 ] 0.9 (Prussian blue analogue) molecular structure is illustrated by studying the dependency of the magnetic images on the temperature and the applied fields.…”

Section: Scanning Hall Probe Microscopy (Shpm)mentioning

confidence: 99%

“…Although the current interest in this field is shifted to f-elements, it is our opinion that the chemistry of transition-metal SMMs and SIMs has brilliant perspectives. In the SMM area, the major advantage of using d-block metal ions is their ability to create strongly coupled systems; this is in contrast to the situation with the lanthanoid ions (with the exception of radical-bridged 4f-metal SMMs [176]) where the core-like character of the 4f orbitals prohibits this. The d-block SIM chemistry appears to grow exponentially and it is striking that few of the compounds reported to date are SIMs in zero field.…”

Section: Concluding Comments and Brief Prognosis For The Futurementioning

confidence: 99%

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2021

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She is currently working in the group of Professor E. Terreno at the molecular and preclinical imaging center in Turin as a member of the research team in the development and testing of innovative molecular imaging probes. Her interest is mainly focused on the visualization and monitoring of inflammatory processes using 1H and 19F magnetic resonance and optical and photoacoustic Imaging. Most of her research activities deal with the active targeting and tracking of the immune system cells in vivo, the visualization of the inflamed endothelium, and cell surveillance after transplantation using newly synthesized nano-and microsystems.Roberto Nisticò obtained his Ph.D. in Chemical and Materials Sciences at the University of Torino (Department of Chemistry, Italy). His research is focused on several aspects at the interface between nanotechnology and materials science, always looking for novel and appealing solutions for a sustainable future. His principal fields of interest are magnetic and/or metallic nanomaterials, functional/porous coatings, plasma treatments, biomaterials (for biomedical applications), valorization of natural resources, (bio)polymers and carbons, nanomaterials for photocatalysis, and AOPs. Federico Cesano received his Degree in Chemistry in 1999 at the University of Torino. After spending two years at the Italian National Research Council (2000-2002), he completed his Ph.D. in Material Science and Technology in 2005. Since 2006, he has been working at the Chemistry Dept. of the University of Turin. He is co-author of more than 70 papers and several book chapters published in the main journals of chemistry and materials science. His main research interests are 1D, 2D, and 3D nanostructured materials (including oxides, carbon nanomaterials, transition metal dichalcogenides, polymers), either alone or combined to form hybrid structures and composites. vii inorganics

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Breakthrough in Radical‐bridged Single‐molecule Magnets

Cited by 4 publications

References 91 publications

Molecular and Electronic Structures and Single-Molecule Magnet Behavior of Tris(thioether)–Iron Complexes Containing Redox-Active α-Diimine Ligands

Molecular and Electronic Structures and Single-Molecule Magnet Behavior of Tris(thioether)–Iron Complexes Containing Redox-Active α-Diimine Ligands

Probing the Magnetic Anisotropy of Co(II) Complexes Featuring Redox-Active Ligands

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