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Magnetochemistry, Volume 5, Issue 1 (March 2019)

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Cover Story (view full-size image) A heterodinuclear cobalt(III)–manganese(II) complex, [MnII{CoIII(µ-Himn)3}Cl2(CH3OH)], was prepared [...] Read more.
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Open AccessArticle
rDEER: A Modified DEER Sequence for Distance Measurements Using Shaped Pulses
Magnetochemistry 2019, 5(1), 20; https://doi.org/10.3390/magnetochemistry5010020 - 08 Mar 2019
Cited by 3 | Viewed by 882
Abstract
The DEER (double electron-electron resonance, also called PELDOR) experiment, which probes the dipolar interaction between two spins and thus reveals distance information, is an important tool for structural studies. In recent years, shaped pump pulses have become a valuable addition to the DEER [...] Read more.
The DEER (double electron-electron resonance, also called PELDOR) experiment, which probes the dipolar interaction between two spins and thus reveals distance information, is an important tool for structural studies. In recent years, shaped pump pulses have become a valuable addition to the DEER experiment. Shaped pulses offer an increased excitation bandwidth and the possibility to precisely adjust pulse parameters, which is beneficial especially for demanding biological samples. We have noticed that on our home built W-band spectrometer, the dead-time free 4-pulse DEER sequence with chirped pump pulses suffers from distortions at the end of the DEER trace. Although minor, these are crucial for Gd(III)-Gd(III) DEER where the modulation depth is on the order of a few percent. Here we present a modified DEER sequence—referred to as reversed DEER (rDEER)—that circumvents the coherence pathway which gives rise to the distortion. We compare the rDEER (with two chirped pump pulses) performance values to regular 4-pulse DEER with one monochromatic as well as two chirped pulses and investigate the source of the distortion. We demonstrate the applicability and effectivity of rDEER on three systems, ubiquitin labeled with Gd(III)-DOTA-maleimide (DOTA, 1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraacetic acid) or with Gd(III)-DO3A (DO3A, 1,4,7,10-Tetraazacyclododecane-1,4,7-triyl) triacetic acid) and the multidrug transporter MdfA, labeled with a Gd(III)-C2 tag, and report an increase in the signal-to-noise ratio in the range of 3 to 7 when comparing the rDEER with two chirped pump pulses to standard 4-pulse DEER. Full article
(This article belongs to the Special Issue Electron Paramagnetic Resonance)
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Open AccessArticle
Spin Cross-Over (SCO) Complex Based on Unsymmetrical Functionalized Triazacyclononane Ligand: Structural Characterization and Magnetic Properties
Magnetochemistry 2019, 5(1), 19; https://doi.org/10.3390/magnetochemistry5010019 - 07 Mar 2019
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Abstract
The unsymmetrical ligand 1-(2-aminophenyl)-4,7-bis(pyridin-2-ylmethyl)-1,4,7-triazacyclononane (L6) has been prepared and characterized by NMR spectroscopy. The L6 ligand is based on the triazamacrocycle (tacn) ring that is functionalized by two flexible 2-pyridylmethyl and one rigid 2-aminophenyl groups. Reaction of this ligand with Fe(ClO4) [...] Read more.
The unsymmetrical ligand 1-(2-aminophenyl)-4,7-bis(pyridin-2-ylmethyl)-1,4,7-triazacyclononane (L6) has been prepared and characterized by NMR spectroscopy. The L6 ligand is based on the triazamacrocycle (tacn) ring that is functionalized by two flexible 2-pyridylmethyl and one rigid 2-aminophenyl groups. Reaction of this ligand with Fe(ClO4)2·xH2O led to the complex [Fe(L6)](ClO4)2 (1), which was characterized as the first Fe(II) complex based on the unsymmetrical N-functionalized tacn ligand. The crystal structure revealed a discrete monomeric [FeL6]2+ entity in which the unsymmetrical N-functionalized triazacyclononane molecule (L6) acts as hexadentate ligand. As observed in the few parent examples that are based on the symmetrical N-functionalized tacn ligands, the triazacyclononane ring is facially coordinated and the N-donor atoms of the three functional groups (two pyridine and one aniline groups) are disposed in the same side of the tacn ring, leading to a distorted FeN6 environment. The magnetic studies of 1 revealed the presence of an incomplete spin crossover (SCO) transition above 425 K, whose progress would be prevented by a very exothermic thermal decomposition at ca. 472 K, as shown by thermogravimetric and DSC measurements. Full article
(This article belongs to the Special Issue Spin-Crossover Beyond the Immediate Tribute)
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Open AccessArticle
Magnetic and Electrochemical Properties of Lantern-Type Dinuclear Ru(II,III) Complexes with Axial Chloride Ions or Water Molecules
Magnetochemistry 2019, 5(1), 18; https://doi.org/10.3390/magnetochemistry5010018 - 06 Mar 2019
Viewed by 576
Abstract
By using [Ru2(O2CC3H7)4Cl]n (1) as a starting material, nBu4N[Ru2(O2CC3H7)4Cl2] (nBu4N+ [...] Read more.
By using [Ru2(O2CC3H7)4Cl]n (1) as a starting material, nBu4N[Ru2(O2CC3H7)4Cl2] (nBu4N+ = tetra(n-butyl)ammonium cation) (2) and [Ru2(O2CC3H7)4(H2O)2]BF4 (3) were prepared. The lantern-type dinuclear structures with axial chloride ions or water molecules were confirmed for 2 and 3 by X-ray crystal structure analyses. The crystal structures of 2 and 3 were compared with that of 1. In the crystal of 2, there were three crystallographically different dinuclear units; the Ru–Ru distances of each unit were 2.3094(3), 2.3046(4), and 2.3034(4) Å, respectively, which were longer than those of 1 (2.281(4) Å) and 3 (2.2584 (7) Å). Temperature dependent magnetic susceptibility measurements were performed for 1 and 2 as well as 3. The effective magnetic moments (µeff) at 300 K were 3.97 (for 1), 4.00 (for 2), and 3.97 µB (for 3), respectively. The decreases in the µeff value were confirmed for all of the complexes due to the large zero-field splitting (D): D = 68 cm−1 for 1, 78 cm−1 for 2, and 60 cm−1 for 3. Cyclic voltammograms measured in CH2Cl2 with a electrolyte of nBu4N(BF4) showed the Ru25+/Ru24+ process at −0.2–−0.4 V (vs. SCE) and the Ru26+/Ru25+ one at 1.3–1.4 V (vs. SCE), of which potentials were confirmed by the DFT calculation for nBu4N[Ru2(O2CC3H7)4Cl2]. Full article
(This article belongs to the Special Issue Coordination Compounds for Coordination Molecule-Based Devices)
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Open AccessArticle
Theoretical Equations of Zeeman Energy Levels for Distorted Metal Complexes with 3T1 Ground Terms
Magnetochemistry 2019, 5(1), 17; https://doi.org/10.3390/magnetochemistry5010017 - 03 Mar 2019
Viewed by 617
Abstract
The theoretical equations of Zeeman energy levels, including the zero-field energies and the first- and second-order Zeeman coefficients, have been obtained in closed form for nine states of the 3 T 1 ( g ) ground term, considering the axial ligand-field splitting and [...] Read more.
The theoretical equations of Zeeman energy levels, including the zero-field energies and the first- and second-order Zeeman coefficients, have been obtained in closed form for nine states of the 3 T 1 ( g ) ground term, considering the axial ligand-field splitting and the spin-orbit coupling. The equations are expressed as the functions of three independent parameters, Δ , λ , and κ , where Δ is the axial ligand-field splitting parameter, λ is the spin-orbit coupling parameter, and κ is the effective orbital reduction factor, including the admixing. The equations are useful in simulating magnetic properties (magnetic susceptibility and magnetization) of the complexes with 3 T 1 ( g ) ground terms, e.g., octahedral vanadium(III), octahedral low-spin manganese(III), octahedral low-spin chromium(II), and tetrahedral nickel(II) complexes. Full article
(This article belongs to the Special Issue Coordination Compounds for Coordination Molecule-Based Devices)
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Open AccessArticle
Effects of High Magnetic Fields on Phase Transformations in Amorphous Nd2Fe14B
Magnetochemistry 2019, 5(1), 16; https://doi.org/10.3390/magnetochemistry5010016 - 02 Mar 2019
Cited by 2 | Viewed by 675
Abstract
We briefly summarize the results from a set of experiments designed to demonstrate the effects of high magnetic fields applied during thermal annealing of amorphous Nd2Fe14B produced through melt-spinning. A custom-built differential scanning calorimeter was used to determine the [...] Read more.
We briefly summarize the results from a set of experiments designed to demonstrate the effects of high magnetic fields applied during thermal annealing of amorphous Nd2Fe14B produced through melt-spinning. A custom-built differential scanning calorimeter was used to determine the crystallization temperatures in zero-field and in applied fields of 20 kOe and 90 kOe, which guided subsequent heat treatments to evaluate phase evolution. X-ray diffraction was used for phase identification and transmission electron microscopy was employed for observation of the crystallite size and morphology. Magnetization measurements were also used to evaluate the resulting magnetic phases after thermomagnetic processing. While the applied magnetic fields do not appear to affect the crystallization temperature, significant effects on the kinetics of phase evolution are observed and correlated strongly to the magnetic behavior. Full article
(This article belongs to the Special Issue Permanent Magnets)
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Open AccessReview
DFT Investigations of the Magnetic Properties of Actinide Complexes
Magnetochemistry 2019, 5(1), 15; https://doi.org/10.3390/magnetochemistry5010015 - 17 Feb 2019
Cited by 1 | Viewed by 857
Abstract
Over the past 25 years, magnetic actinide complexes have been the object of considerable attention, not only at the experimental level, but also at the theoretical one. Such systems are of great interest, owing to the well-known larger spin–orbit coupling for actinide ions, [...] Read more.
Over the past 25 years, magnetic actinide complexes have been the object of considerable attention, not only at the experimental level, but also at the theoretical one. Such systems are of great interest, owing to the well-known larger spin–orbit coupling for actinide ions, and could exhibit slow relaxation of the magnetization, arising from a large anisotropy barrier, and magnetic hysteresis of purely molecular origin below a given blocking temperature. Furthermore, more diffuse 5f orbitals than lanthanide 4f ones (more covalency) could lead to stronger magnetic super-exchange. On the other hand, the extraordinary experimental challenges of actinide complexes chemistry, because of their rarity and toxicity, afford computational chemistry a particularly valuable role. However, for such a purpose, the use of a multiconfigurational post-Hartree-Fock approach is required, but such an approach is computationally demanding for polymetallic systems—notably for actinide ones—and usually simplified models are considered instead of the actual systems. Thus, Density Functional Theory (DFT) appears as an alternative tool to compute magnetic exchange coupling and to explore the electronic structure and magnetic properties of actinide-containing molecules, especially when the considered systems are very large. In this paper, relevant achievements regarding DFT investigations of the magnetic properties of actinide complexes are surveyed, with particular emphasis on some representative examples that illustrate the subject, including actinides in Single Molecular Magnets (SMMs) and systems featuring metal-metal super-exchange coupling interactions. Examples are drawn from studies that are either entirely computational or are combined experimental/computational investigations in which the latter play a significant role. Full article
(This article belongs to the Special Issue Magnetic Properties of Complexes of Actinide Elements)
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Open AccessArticle
Tetranuclear Hetro-Metal [MnIII2NiII2] Complexes Involving Defective Double-Cubane Structure: Synthesis, Crystal Structures, and Magnetic Properties
Magnetochemistry 2019, 5(1), 14; https://doi.org/10.3390/magnetochemistry5010014 - 14 Feb 2019
Viewed by 572
Abstract
Tetranuclear hetero-metal MnIII2NiII2 complexes, [Mn2Ni2(L)4(OAc)2] (1) and [Mn2Ni2(L)4(NO3)2] (2) [H2L = N-(2-hydroxymethylphenyl)-5,6-benzosalicylideneimine], have [...] Read more.
Tetranuclear hetero-metal MnIII2NiII2 complexes, [Mn2Ni2(L)4(OAc)2] (1) and [Mn2Ni2(L)4(NO3)2] (2) [H2L = N-(2-hydroxymethylphenyl)-5,6-benzosalicylideneimine], have been synthesized and characterized by X-ray crystal structure analyses, infrared spectra, and elemental analyses. The structure analyses revealed that the complexes have a defective double-cubane metal core connected by μ3-alkoxo bridges. Complexes consist of two bis-μ-alkoxo bridged MnIIINiII heteronuclear units making a dimer-of-dimers structure. The double-cubane cores are significantly distorted due to an effect of syn–syn mode acetato or nitrato bridges. Magnetic measurements indicate that weak antiferromagnetic interactions (Mn-Ni = −0.66 ~ −4.19 cm–1) are dominant in the hetero-metal core. Full article
(This article belongs to the Special Issue Coordination Compounds for Coordination Molecule-Based Devices)
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Open AccessReview
Molecular Probes for Evaluation of Oxidative Stress by In Vivo EPR Spectroscopy and Imaging: State-of-the-Art and Limitations
Magnetochemistry 2019, 5(1), 13; https://doi.org/10.3390/magnetochemistry5010013 - 05 Feb 2019
Cited by 1 | Viewed by 781
Abstract
Oxidative stress, defined as a misbalance between the production of reactive oxygen species and the antioxidant defenses of the cell, appears as a critical factor either in the onset or in the etiology of many pathological conditions. Several methods of detection exist. However, [...] Read more.
Oxidative stress, defined as a misbalance between the production of reactive oxygen species and the antioxidant defenses of the cell, appears as a critical factor either in the onset or in the etiology of many pathological conditions. Several methods of detection exist. However, they usually rely on ex vivo evaluation or reports on the status of living tissues only up to a few millimeters in depth, while a whole-body, real-time, non-invasive monitoring technique is required for early diagnosis or as an aid to therapy (to monitor the action of a drug). Methods based on electron paramagnetic resonance (EPR), in association with molecular probes based on aminoxyl radicals (nitroxides) or hydroxylamines especially, have emerged as very promising to meet these standards. The principles involve monitoring the rate of decrease or increase of the EPR signal in vivo after injection of the nitroxide or the hydroxylamine probe, respectively, in a pathological versus a control situation. There have been many successful applications in various rodent models. However, current limitations lie in both the field of the technical development of the spectrometers and the molecular probes. The scope of this review will mainly focus on the latter. Full article
(This article belongs to the Special Issue Electron Paramagnetic Resonance)
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Open AccessArticle
Field Induced Single Ion Magnetic Behaviour in Square-Pyramidal Cobalt(II) Complexes with Easy-Plane Magnetic Anisotropy
Magnetochemistry 2019, 5(1), 12; https://doi.org/10.3390/magnetochemistry5010012 - 02 Feb 2019
Viewed by 723
Abstract
Two penta-coordinate CoII complexes with formulae [Co(14-TMC)Cl](BF4) (1, 14-TMC = 1,4,8,11-Tetramethyl-1,4,8,11-tetraazacyclotetradecane) and [Co(12-TBC)Cl](ClO4)·(MeCN) (2, 12-TBC = 1,4,7,10-Tetrabenzyl-1,4,7,10-tetraazacyclododecane) were synthesized and characterized. Structural analysis revealed that ligand coordinates to the CoII centre in a [...] Read more.
Two penta-coordinate CoII complexes with formulae [Co(14-TMC)Cl](BF4) (1, 14-TMC = 1,4,8,11-Tetramethyl-1,4,8,11-tetraazacyclotetradecane) and [Co(12-TBC)Cl](ClO4)·(MeCN) (2, 12-TBC = 1,4,7,10-Tetrabenzyl-1,4,7,10-tetraazacyclododecane) were synthesized and characterized. Structural analysis revealed that ligand coordinates to the CoII centre in a tetradentate fashion and the fifth position is occupied by chloride ion and the geometries around CoII centres are best described as distorted square pyramidal. Detailed magnetic measurements disclose the presence of significant easy-plane magnetic anisotropy and field induced slow magnetic relaxation behaviours of the studied complexes. More insight into the magnetic anisotropy has been given using ab initio theory calculations, which agree well with the experimental values and further confirmed the easy-plane magnetic anisotropy. Full article
(This article belongs to the Special Issue A Themed Issue in Honor of Late Professor Samiran Mitra)
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Open AccessReview
Brain Redox Imaging Using In Vivo Electron Paramagnetic Resonance Imaging and Nitroxide Imaging Probes
Magnetochemistry 2019, 5(1), 11; https://doi.org/10.3390/magnetochemistry5010011 - 02 Feb 2019
Cited by 2 | Viewed by 656
Abstract
Reactive oxygen species (ROS) are produced by living organisms as a result of normal cellular metabolism. Under normal physiological conditions, oxidative damage is prevented by the regulation of ROS by the antioxidant network. However, increased ROS and decreased antioxidant defense may contribute to [...] Read more.
Reactive oxygen species (ROS) are produced by living organisms as a result of normal cellular metabolism. Under normal physiological conditions, oxidative damage is prevented by the regulation of ROS by the antioxidant network. However, increased ROS and decreased antioxidant defense may contribute to many brain disorders, such as stroke, Parkinson’s disease, and Alzheimer’s disease. Noninvasive assessment of brain redox status is necessary for monitoring the disease state and the oxidative damage. Continuous-wave electron paramagnetic resonance (CW-EPR) imaging using redox-sensitive imaging probes, such as nitroxides, is a powerful method for visualizing the redox status modulated by oxidative stress in vivo. For conventional CW-EPR imaging, however, poor signal-to-noise ratio, low acquisition efficiency, and lack of anatomic visualization limit its ability to achieve three-dimensional redox mapping of small rodent brains. In this review, we discuss the instrumentation and coregistration of EPR images to anatomical images and appropriate nitroxide imaging probes, all of which are needed for a sophisticated in vivo EPR imager for all rodents. Using new EPR imaging systems, site-specific distribution and kinetics of nitroxide imaging probes in rodent brains can be obtained more accurately, compared to previous EPR imaging systems. We also describe the redox imaging studies of animal models of brain disease using newly developed EPR imaging. Full article
(This article belongs to the Special Issue Electron Paramagnetic Resonance)
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Open AccessArticle
Five 2,6-Di(pyrazol-1-yl)pyridine-4-carboxylate Esters, and the Spin States of their Iron(II) Complexes
Magnetochemistry 2019, 5(1), 9; https://doi.org/10.3390/magnetochemistry5010009 - 01 Feb 2019
Cited by 1 | Viewed by 620
Abstract
Two phenyl ester and three benzyl ester derivatives have been synthesized from 2,6-di(pyrazol-1-yl)pyridine-4-carboxylic acid and the appropriate phenyl or benzyl alcohol using N,N′-dicyclohexylcarbodiimide as the coupling reagent. Complexation of the ligands with Fe[BF4]2·6H2O in [...] Read more.
Two phenyl ester and three benzyl ester derivatives have been synthesized from 2,6-di(pyrazol-1-yl)pyridine-4-carboxylic acid and the appropriate phenyl or benzyl alcohol using N,N′-dicyclohexylcarbodiimide as the coupling reagent. Complexation of the ligands with Fe[BF4]2·6H2O in acetone yielded the corresponding [FeL2][BF4]2 complex salts. Four of the new ligands and four of the complexes have been crystallographically characterised. Particularly noteworthy are two polymorphs of [Fe(L3)2][BF4]2·2MeNO2 (L3 = 3,4-dimethoxyphenyl 2,6-di{pyrazol-1-yl}pyridine-4-carboxylate), one of which is crystallographically characterised as high-spin while the other exhibits the onset of spin-crossover above room temperature. The other complexes are similarly low-spin at low temperature but exhibit gradual spin-crossover on heating, except for an acetone solvate of [Fe(L5)2][BF4]2 (L5 = benzyl 2,6-di{pyrazol-1-yl}pyridine-4-carboxylate), which exhibits a more abrupt spin-transition at T½ = 273 K with 9 K thermal hysteresis. Full article
(This article belongs to the Special Issue Spin-Crossover Beyond the Immediate Tribute)
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Open AccessArticle
High-temperature Spin Crossover of a Solvent-Free Iron(II) Complex with the Linear Hexadentate Ligand [Fe(L2-3-2Ph)](AsF6)2 (L2-3-2Ph = bis[N-(1-Phenyl-1H-1,2,3-triazol-4-yl)methylidene-2-aminoethyl]-1,3-propanediamine)
Magnetochemistry 2019, 5(1), 10; https://doi.org/10.3390/magnetochemistry5010010 - 01 Feb 2019
Cited by 1 | Viewed by 677
Abstract
A novel mononuclear iron(II) complex with a linear hexadentate N6 ligand, containing two 1,2,3-triazole moieties, [Fe(L2-3-2Ph)](AsF6)2 (1), was synthesized (L2-3-2Ph = bis[N-(1-Phenyl-1H-1,2,3-triazol-4-yl)methylidene-2-aminoethyl]-1,3-propanediamine). Variable-temperature magnetic susceptibility measurements revealed a [...] Read more.
A novel mononuclear iron(II) complex with a linear hexadentate N6 ligand, containing two 1,2,3-triazole moieties, [Fe(L2-3-2Ph)](AsF6)2 (1), was synthesized (L2-3-2Ph = bis[N-(1-Phenyl-1H-1,2,3-triazol-4-yl)methylidene-2-aminoethyl]-1,3-propanediamine). Variable-temperature magnetic susceptibility measurements revealed a gradual one-step spin crossover (SCO) between the high-spin (HS, S = 2) and low-spin (LS, S = 0) states above room temperature (T1/2 = 468 K). The spin transition was further confirmed by differential scanning calorimetry (DSC). A single-crystal X-ray diffraction study showed that the complex was in the LS state (S = 0) at room temperature (296 K). In the crystal lattice, a three-dimensional (3D) supramolecular network was formed by intermolecular CH⋯π and π–π interactions of neighboring complex cations [Fe(L2-3-2Ph)]2+. AsF6 ions were located interstitially in the 3D network of complex cations, with no solvent-accessible voids. The crystal structure at 448 K (mixture of HS and LS species) was also successfully determined thanks to the thermal stability of the solvent-free crystal. Full article
(This article belongs to the Special Issue Coordination Compounds for Coordination Molecule-Based Devices)
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Open AccessFeature PaperArticle
Synthesis, Crystal Structures, and Magnetic Properties of Mixed-Valent Tetranuclear Complexes with Y-Shaped MnII2MnIII2 Core
Magnetochemistry 2019, 5(1), 8; https://doi.org/10.3390/magnetochemistry5010008 - 28 Jan 2019
Viewed by 584
Abstract
Tetranuclear MnII2MnIII2 complexes with 1,3-bis(5-bromo-3-metoxysalicylidenaminomethyl)-2-propanol (H3bmsap) and 1,3-bis(5-chloro-3-methoxysalicylidenaminomethyl)-2-propanol (H3cmsap), [Mn4(bmsap)2(CH3CO2)3(CH3O)] (3) and [Mn4(cmsap)2(CH3CO2 [...] Read more.
Tetranuclear MnII2MnIII2 complexes with 1,3-bis(5-bromo-3-metoxysalicylidenaminomethyl)-2-propanol (H3bmsap) and 1,3-bis(5-chloro-3-methoxysalicylidenaminomethyl)-2-propanol (H3cmsap), [Mn4(bmsap)2(CH3CO2)3(CH3O)] (3) and [Mn4(cmsap)2(CH3CO2)3(CH3O)] (4), were synthesized and characterized by elemental analysis, infrared and diffused reflectance spectra and variable-temperature magnetic susceptibility measurements in the 2–300 K range. The crystal structures of 3 and 4 revealed a Y-shaped tetranuclear manganese cluster formed by the two Schiff-base ligands, three kinds of acetato ligands (bidentate, syn–anti-bridging, and syn–syn-bridging), and µ-methoxido ligand. The magnetic data showed the magnetic interactions among the four manganese atoms are antiferromagnetic as a whole within the tetranuclear cluster. Full article
(This article belongs to the Special Issue Coordination Compounds for Coordination Molecule-Based Devices)
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Open AccessEditorial
Acknowledgement to Reviewers of Magnetochemistry in 2018
Magnetochemistry 2019, 5(1), 7; https://doi.org/10.3390/magnetochemistry5010007 - 24 Jan 2019
Viewed by 478
Abstract
Rigorous peer-review is the corner-stone of high-quality academic publishing [...] Full article
Open AccessArticle
Microstructure and Magnetic Properties of Grain Refined Pr2Co14B Melt-Spun Ribbons
Magnetochemistry 2019, 5(1), 6; https://doi.org/10.3390/magnetochemistry5010006 - 22 Jan 2019
Viewed by 601
Abstract
The correlation between the grain refining effect of TiC on the microstructure of Pr2Co14B melt-spun ribbons and the magnetic properties is presented in this study. TiC enabled greater control of microstructure both in the as-spun and heat treated Pr [...] Read more.
The correlation between the grain refining effect of TiC on the microstructure of Pr2Co14B melt-spun ribbons and the magnetic properties is presented in this study. TiC enabled greater control of microstructure both in the as-spun and heat treated Pr2Co14B, compared with the material without TiC. As a result, coercivity of the sample with TiC was nearly twice that of the sample without TiC. In addition to Pr2Co14B, two other phases were found in the sample with TiC: one rich in Co and the other having a composition near PrCo2. TiC was found near the grain boundaries and at triple junctions. Also no Ti or C was found in the matrix phase indicating extreme low solubility of the elements when both are present with Pr2Co14B. As expected, both the samples with and without TiC have similar anisotropy field but the presence of room temperature non-ferromagnetic phases (TiC and PrCo2), caused a small decrease in magnetization of the sample with TiC although the romance of the isotropic materials were comparable. Full article
(This article belongs to the Special Issue Permanent Magnets)
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Open AccessArticle
Stepwise Synthesis, Hydrogen-Bonded Supramolecular Structure, and Magnetic Property of a Co–Mn Heterodinuclear Complex
Magnetochemistry 2019, 5(1), 5; https://doi.org/10.3390/magnetochemistry5010005 - 20 Jan 2019
Viewed by 794
Abstract
A cobalt(III)–manganese(II) heterometallic dinuclear complex, [MnII{CoIII(µ-Himn)3}Cl2(CH3OH)], was prepared by a metalloligand approach. X-ray crystallographic analysis indicated that the metalloligand [CoIII(Himn)3] underwent mer/fac geometrical isomerization upon coordination to a Mn [...] Read more.
A cobalt(III)–manganese(II) heterometallic dinuclear complex, [MnII{CoIII(µ-Himn)3}Cl2(CH3OH)], was prepared by a metalloligand approach. X-ray crystallographic analysis indicated that the metalloligand [CoIII(Himn)3] underwent mer/fac geometrical isomerization upon coordination to a Mn ion. Owing to the non-coordinating N–H bonds in the [CoIII(Himn)3] moiety, the heterodinuclear complex exhibited hydrogen bond interactions with the Cl ligand of the neighboring complex to construct two-dimensional hydrogen-bond networks. The bond distances around the Mn center and the χMT value at 300 K indicate that the Mn center is in a divalent state. The temperature dependence of the χMT product and field dependence of the magnetization showed the isotropic nature of the MnII center. Full article
(This article belongs to the Special Issue Coordination Compounds for Coordination Molecule-Based Devices)
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Open AccessArticle
A Clock Transition in the Cr7Mn Molecular Nanomagnet
Magnetochemistry 2019, 5(1), 4; https://doi.org/10.3390/magnetochemistry5010004 - 14 Jan 2019
Cited by 1 | Viewed by 876
Abstract
A viable qubit must have a long coherence time T 2 . In molecular nanomagnets, T 2 is often limited at low temperatures by the presence of dipole and hyperfine interactions, which are often mitigated through sample dilution, chemical engineering and isotope substitution [...] Read more.
A viable qubit must have a long coherence time T 2 . In molecular nanomagnets, T 2 is often limited at low temperatures by the presence of dipole and hyperfine interactions, which are often mitigated through sample dilution, chemical engineering and isotope substitution in synthesis. Atomic-clock transitions offer another route to reducing decoherence from environmental fields by reducing the effective susceptibility of the working transition to field fluctuations. The Cr7Mn molecular nanomagnet, a heterometallic ring, features a clock transition at zero field. Both continuous-wave and spin-echo electron-spin resonance experiments on Cr7Mn samples, diluted via co-crystallization, show evidence of the effects of the clock transition with a maximum T 2 390 ns at 1.8 K. We discuss improvements to the experiment that may increase T 2 further. Full article
(This article belongs to the Special Issue Controlling Molecular Nanomagnets)
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Open AccessArticle
Modelling the Effect of Zero-Field Splitting on the 1H, 13C and 29Si Chemical Shifts of Lanthanide and Actinide Compounds
Magnetochemistry 2019, 5(1), 3; https://doi.org/10.3390/magnetochemistry5010003 - 11 Jan 2019
Viewed by 777
Abstract
The prediction of paramagnetic NMR (pNMR) chemical shifts in molecules containing heavy atoms presents a significant challenge to computational quantum chemistry. The importance of meeting this challenge lies in the central role that NMR plays in the structural characterisation of chemical systems. Hence [...] Read more.
The prediction of paramagnetic NMR (pNMR) chemical shifts in molecules containing heavy atoms presents a significant challenge to computational quantum chemistry. The importance of meeting this challenge lies in the central role that NMR plays in the structural characterisation of chemical systems. Hence there is a need for reliable assignment and prediction of chemical shifts. In a previous study [Trends in Physical Chemistry, 17, 25–57, (2017)] we looked at the computation of pNMR chemical shifts in lanthanide and actinide complexes using a spin Hamiltonian approach. In that study we were principally concerned with molecules with S = 1/2 ground states. In the present work we extend that study by looking at the effect of zero field splitting (ZFS) for six complexes with S = 3/2 ground states. It is shown that the inclusion of ZFS can produce substantial shifts in the predicted chemical shifts. The computations presented are typically sufficient to enable assignment of experimental spectra. However for one case, in which the peaks are closely clustered, the inclusion of ZFS re-orders the chemical shifts making assignment quite difficult. We also observe, and echo, the previously reported importance of including the paramagnetic spin-orbit hyperfine interaction for 13 C and 29 Si atoms, when these are directly bound to a heavy element and thus subject to heavy-atom-light-atom effects. The necessary computations are very demanding, and more work is needed to find theoretical and computational approaches that simplify the evaluation of this term. We discuss the computation of each term required in the spin Hamiltonian. The systems we study in this work are restricted to a single heavy atom ion (one Nd(III) and five U(III) complexes), but typify some of the computational complexity encountered in lanthanide and actinide containing molecules. Full article
(This article belongs to the Special Issue Magnetic Properties of Complexes of Actinide Elements)
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Open AccessArticle
Interfacial Spin Manipulation of Nickel-Quinonoid Complex Adsorbed on Co(001) Substrate
Magnetochemistry 2019, 5(1), 2; https://doi.org/10.3390/magnetochemistry5010002 - 24 Dec 2018
Cited by 1 | Viewed by 2646
Abstract
We studied the structural, electronic, and magnetic properties of a recently synthesized Ni(II)-quinonoid complex upon adsorption on a magnetic Co(001) substrate. Our density functional theory + U (DFT+U) calculations predict that the molecule undergoes a spin-state switching from low-spin S = [...] Read more.
We studied the structural, electronic, and magnetic properties of a recently synthesized Ni(II)-quinonoid complex upon adsorption on a magnetic Co(001) substrate. Our density functional theory + U (DFT+U) calculations predict that the molecule undergoes a spin-state switching from low-spin S = 0 in the gas phase to high-spin S 1 when adsorbed on the Co(001) surface. A strong covalent interaction of the quinonoid rings and surface atoms leads to an increase of the Ni–O(N) bond lengths in the chemisorbed molecule that support the spin-state switching. Our DFT+U calculations show that the molecule is ferromagnetically coupled to the substrate. The Co surface–Ni center exchange mechanism was carefully investigated. We identified an indirect exchange interaction via the quinonoid ligands that stabilizes the molecule’s spin moment in ferromagnetic alignment with the Co surface magnetization. Full article
(This article belongs to the Special Issue Spin-Crossover Beyond the Immediate Tribute)
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Open AccessCommunication
Improved 19F{1H} Saturation Transfer Difference Experiments for Sensitive Detection to Fluorinated Compound Bound to Proteins
Magnetochemistry 2019, 5(1), 1; https://doi.org/10.3390/magnetochemistry5010001 - 21 Dec 2018
Viewed by 612
Abstract
The 19F{1H} saturation transfer difference (STD) method was improved for sensitive 19F detection using a human serum albumin-diflunisal complex. Because NMR (nuclear magnetic resonance) experiments with 19F detection are feasible for the selective detection of fluorinated compounds, more [...] Read more.
The 19F{1H} saturation transfer difference (STD) method was improved for sensitive 19F detection using a human serum albumin-diflunisal complex. Because NMR (nuclear magnetic resonance) experiments with 19F detection are feasible for the selective detection of fluorinated compounds, more sensitive NMR methods are required to be developed for purposes of practicality. The present research focused on the investigations of 19F{1H} STD pulse techniques and experimental parameters, leading to the development of detection methods with higher sensitivity. Full article
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