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Magnetochemistry
Volume 7
Issue 6
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Magnetochemistry, Volume 7, Issue 6 (June 2021) – 16 articles

Cover Story (view full-size image): Crystal-to-crystal transformation is a path to obtain crystals with different crystal structures and physical properties. Orange crystal K2[Co(C2O4)2(H2O)2]·4H2O (1) is obtained from K2C2O4·2H2O and CoCl2·6H2O in H2O with a yield of 60%. It quantitatively transfers to pink crystal K2[Co(μ-C2O4)(C2O4)] (2) by dehydration. Co2+ is coordinated by two bisbendentate oxalate anions and one bidentated oxalate anion in a trigonal prism. View this paper
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2 pages, 156 KiB  
Editorial
Special Issue: Advances in Computational Electromagnetics
by Valerio De Santis
Magnetochemistry 2021, 7(6), 89; https://doi.org/10.3390/magnetochemistry7060089 - 21 Jun 2021
Viewed by 1684
Abstract
Recent advances in computational electromagnetics (CEMs) have made the full characterization of complex magnetic materials possible, such as superconducting materials, composite or nanomaterials, rare-earth free permanent magnets, etc [...] Full article
(This article belongs to the Special Issue Advances in Computational Electromagnetics)
15 pages, 2127 KiB  
Article
Simulation and Theory of Classical Spin Hopping on a Lattice
by Richard Gerst, Rodrigo Becerra Silva and Nicholas J. Harmon
Magnetochemistry 2021, 7(6), 88; https://doi.org/10.3390/magnetochemistry7060088 - 20 Jun 2021
Viewed by 2335
Abstract
The behavior of spin for incoherently hopping carriers is critical to understand in a variety of systems such as organic semiconductors, amorphous semiconductors, and muon-implanted materials. This work specifically examined the spin relaxation of hopping spin/charge carriers through a cubic lattice in the [...] Read more.
The behavior of spin for incoherently hopping carriers is critical to understand in a variety of systems such as organic semiconductors, amorphous semiconductors, and muon-implanted materials. This work specifically examined the spin relaxation of hopping spin/charge carriers through a cubic lattice in the presence of varying degrees of energy disorder when the carrier spin is treated classically and random spin rotations are suffered during the hopping process (to mimic spin–orbit coupling effects) instead of during the wait time period (which would be more appropriate for hyperfine coupling). The problem was studied under a variety of different assumptions regarding the hopping rates and the random local fields. In some cases, analytic solutions for the spin relaxation rate were obtained. In all the models, we found that exponentially distributed energy disorder led to a drastic reduction in spin polarization losses that fell nonexponentially. Full article
(This article belongs to the Special Issue Functional Magnetic Materials)
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16 pages, 5911 KiB  
Article
Chiral Radical Cation Salts of Me-EDT-TTF and DM-EDT-TTF with Octahedral, Linear and Tetrahedral Monoanions
by Nabil Mroweh, Alexandra Bogdan, Flavia Pop, Pascale Auban-Senzier, Nicolas Vanthuyne, Elsa B. Lopes, Manuel Almeida and Narcis Avarvari
Magnetochemistry 2021, 7(6), 87; https://doi.org/10.3390/magnetochemistry7060087 - 20 Jun 2021
Cited by 5 | Viewed by 2677
Abstract
Methyl-ethylenedithio-tetrathiafulvalene (Me-EDT-TTF (1) and dimethyl-ethylenedithio-tetrathiafulvalene (DM-EDT-TTF (2) are valuable precursors for chiral molecular conductors, which are generally obtained by electrocrystallization in the presence of various counter-ions. The number of the stereogenic centers, their relative location on the molecule, the [...] Read more.
Methyl-ethylenedithio-tetrathiafulvalene (Me-EDT-TTF (1) and dimethyl-ethylenedithio-tetrathiafulvalene (DM-EDT-TTF (2) are valuable precursors for chiral molecular conductors, which are generally obtained by electrocrystallization in the presence of various counter-ions. The number of the stereogenic centers, their relative location on the molecule, the nature of the counter-ion and the electrocrystallization conditions play a paramount role in the crystal structures and conducting properties of the resulting materials. Here, we report the preparation and detailed structural characterization of the following series of radical cation salts: (i) mixed valence (1)2AsF6 as racemic, and (S) and (R) enantiomers; (ii) [(S)-1]AsF6·C4H8O and [(R)-1]AsF6·C4H8O where a strong dimerization of the donors is observed; (iii) (1)I3 and (2)I3 as racemic and enantiopure forms and (iv) [(meso)-2]PF6 and [(meso)-2]XO4 (X = Cl, Re), based on the new donor (meso)-2. In the latter, the two methyl substituents necessarily adopt axial and equatorial conformations, thus leading to a completely different packing of the donors when compared to the chiral form (S,S)/(R,R) of 2 in its radical cation salts. Single crystal resistivity measurements, complemented by thermoelectric power measurements in the case of (1)2AsF6, suggest quasi-metallic conductivity for the latter in the high temperature regime, with σRT ≈ 1–10 S cm–1, while semiconducting behavior is observed for the (meso)-2 based salts. Full article
(This article belongs to the Special Issue Perspectives on Molecular Materials—A Tribute to Professor Peter Day)
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22 pages, 3493 KiB  
Review
Magnetotactic Bacteria and Magnetosomes: Basic Properties and Applications
by Kamil G. Gareev, Denis S. Grouzdev, Petr V. Kharitonskii, Andrei Kosterov, Veronika V. Koziaeva, Elena S. Sergienko and Maxim A. Shevtsov
Magnetochemistry 2021, 7(6), 86; https://doi.org/10.3390/magnetochemistry7060086 - 18 Jun 2021
Cited by 29 | Viewed by 12736
Abstract
Magnetotactic bacteria (MTB) belong to several phyla. This class of microorganisms exhibits the ability of magneto-aerotaxis. MTB synthesize biominerals in organelle-like structures called magnetosomes, which contain single-domain crystals of magnetite (Fe3O4) or greigite (Fe3S4) characterized [...] Read more.
Magnetotactic bacteria (MTB) belong to several phyla. This class of microorganisms exhibits the ability of magneto-aerotaxis. MTB synthesize biominerals in organelle-like structures called magnetosomes, which contain single-domain crystals of magnetite (Fe3O4) or greigite (Fe3S4) characterized by a high degree of structural and compositional perfection. Magnetosomes from dead MTB could be preserved in sediments (called fossil magnetosomes or magnetofossils). Under certain conditions, magnetofossils are capable of retaining their remanence for millions of years. This accounts for the growing interest in MTB and magnetofossils in paleo- and rock magnetism and in a wider field of biogeoscience. At the same time, high biocompatibility of magnetosomes makes possible their potential use in biomedical applications, including magnetic resonance imaging, hyperthermia, magnetically guided drug delivery, and immunomagnetic analysis. In this review, we attempt to summarize the current state of the art in the field of MTB research and applications. Full article
(This article belongs to the Special Issue Synthetic, Natural and Natural-Synthetic Hybrid Magnetic Structures: Technology and Application)
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8 pages, 4648 KiB  
Article
Development of Magnetic Particle Distribution Imaging Using Magnetic Field Reconstruction for Biopsy of the Sentinel Lymph Node
by Akari Inagaki, Tomoko Suzuki, Yuki Mima and Kenjiro Kimura
Magnetochemistry 2021, 7(6), 85; https://doi.org/10.3390/magnetochemistry7060085 - 15 Jun 2021
Cited by 1 | Viewed by 2587
Abstract
The sentinel lymph node is the first lymph-node-draining cancer metastasis. The identification of the sentinel lymph node using magnetic particles and a magnetic sensor has attracted attention in recent years, as this method is less invasive than the conventional method of radiotracer injection. [...] Read more.
The sentinel lymph node is the first lymph-node-draining cancer metastasis. The identification of the sentinel lymph node using magnetic particles and a magnetic sensor has attracted attention in recent years, as this method is less invasive than the conventional method of radiotracer injection. However, the development of a two-dimensional measurement method for sentinel lymph nodes using magnetic nanoparticles remains an issue. In the present study, a method and apparatus for the two-dimensional imaging of magnetic particle distribution were developed to detect a lymph node with magnetic particles concentrated within lymphoid tissues. The method comprises the reconstruction of the magnetic field measured with a high-sensitivity magnetic sensor and with a magnetic detection ability of 2 nT/√Hz at 100 Hz (5 nT/√Hz at 1 Hz). The proposed system measures the two-dimensional magnetic field distribution in an area of up to 25 × 25 mm2 using a coil generating a 0.77 mT external magnetic field applied to the measurement target. The improved spatial resolution of the images makes it possible to use two-dimensional imaging for diagnostics of breast cancer metastases. Full article
(This article belongs to the Special Issue Quantum Magnetic Sensors and Magnetochemistry)
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11 pages, 5075 KiB  
Review
Artificial Intelligence—Engineering Magnetic Materials: Current Status and a Brief Perspective
by Elio A. Périgo and Rubens N. de Faria
Magnetochemistry 2021, 7(6), 84; https://doi.org/10.3390/magnetochemistry7060084 - 7 Jun 2021
Cited by 3 | Viewed by 4217
Abstract
The implementation of artificial intelligence into the research and development of (currently) the most economically relevant classes of engineering hard and soft magnetic materials is addressed. Machine learning is nowadays the key approach utilized in the discovery of new compounds, physical–chemical properties prediction, [...] Read more.
The implementation of artificial intelligence into the research and development of (currently) the most economically relevant classes of engineering hard and soft magnetic materials is addressed. Machine learning is nowadays the key approach utilized in the discovery of new compounds, physical–chemical properties prediction, microstructural/magnetic characterization, and applicability of permanent magnets and crystalline/amorphous soft magnetic alloys. Future opportunities are envisioned on at least two fronts: (a) ultra-low losses materials, as well as processes that enable their manufacturing, unlocking the next step for higher efficiency electrification, power conversion, and distribution; (b) additively manufactured magnetic materials by predicting and developing novel powdered materials properties, generative design concepts, and optimal processing conditions. Full article
(This article belongs to the Special Issue Advances in Amorphous and Nanocrystalline Magnetic Materials)
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15 pages, 2268 KiB  
Article
Influence of the Size and Shape of Halopyridines Guest Molecules G on the Crystal Structure and Conducting Properties of Molecular (Super)Conductors of (BEDT-TTF)4A+[M3+(C2O4)3]·G Family
by Tatiana G. Prokhorova, Eduard B. Yagubskii, Andrey A. Bardin, Vladimir N. Zverev, Gennadiy V. Shilov and Lev I. Buravov
Magnetochemistry 2021, 7(6), 83; https://doi.org/10.3390/magnetochemistry7060083 - 4 Jun 2021
Cited by 4 | Viewed by 2421
Abstract
New organic (super)conductors of the β″-(BEDT-TTF)4A+[M3+(C2O4)3]G family, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene; M is Fe; A is the monovalent cation NH4+; G is 2-fluoropyridine (2-FPy) (1); 2,3-difluoropyridine (2,3-DFPy) (2); [...] Read more.
New organic (super)conductors of the β″-(BEDT-TTF)4A+[M3+(C2O4)3]G family, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene; M is Fe; A is the monovalent cation NH4+; G is 2-fluoropyridine (2-FPy) (1); 2,3-difluoropyridine (2,3-DFPy) (2); 2-chloro-3-fluoropyridine (2-Cl-3-FPy) (3); 2,6-dichloropyridine (2,6-DClPy) (4); 2,6-difluoropyridine (2,6-DFPy) (5), have been prepared and their crystal structure and transport properties were studied. All crystals have a layered structure in which the conducting layers of BEDT-TTF radical cations alternate with paramagnetic supramolecular anionic layers {A+[Fe3+(C2O4)3]3−G0}2−. Crystals 1 undergo a structural phase transition from the monoclinic (C2/c) to the triclinic (P1¯) symmetry in the range 100–150 K, whereas crystals 2–5 have a monoclinic symmetry in the entire range of the X-ray experiment (100–300 K). The alternating current (ac) conductivity of salts 1–4 exhibits metallic behavior down to 1.4 K, whereas the salt 5 demonstrates the onset of a superconducting transition at 3.1 K. The structures and conducting properties of 1–5 are compared with those of the known monoclinic phases of the family containing different monohalopyridines as “guest” solvent molecules G. Full article
(This article belongs to the Special Issue Perspectives on Molecular Materials—A Tribute to Professor Peter Day)
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17 pages, 4984 KiB  
Article
Effect of the Alkaline Metal Ion on the Crystal Structure and Magnetic Properties of Heterometallic GdIII-VIV Complexes Based on Cyclobutane-1,1-Dicarboxylate Anions
by Evgeniya S. Bazhina, Alexander A. Korlyukov, Julia K. Voronina, Konstantin A. Babeshkin, Elena A. Ugolkova, Nikolay N. Efimov, Matvey V. Fedin, Mikhail A. Kiskin and Igor L. Eremenko
Magnetochemistry 2021, 7(6), 82; https://doi.org/10.3390/magnetochemistry7060082 - 3 Jun 2021
Cited by 4 | Viewed by 2557
Abstract
A series of heterometallic GdIII-VIV compounds were synthesized by the reaction of VOSO4·3H2O with cyclobutane-1,1-dicarboxylic acid salts M2(cbdc) (M = Na, Rb, Cs). The new compounds were formed by [Gd(VO)2(cbdc)4(H [...] Read more.
A series of heterometallic GdIII-VIV compounds were synthesized by the reaction of VOSO4·3H2O with cyclobutane-1,1-dicarboxylic acid salts M2(cbdc) (M = Na, Rb, Cs). The new compounds were formed by [Gd(VO)2(cbdc)4(H2O)8]− trinuclear anionic units that were similar in composition but differed in structure, depending on the nature of the alkali metal cation incorporated in the crystal structure of the compound. In the case of Na+, the {GdV2}− units were characterized by identical V···Gd distances and were linked into the 1D-polymeric chain [NaGd(VO)2(cbdc)4(H2O)10]n (1). In the systems with Rb+ and Cs+, the V···Gd distances were different, and the {GdV2}− units were linked into the 3D-framework {[RbGd(VO)2(cbdc)4(H2O)10]·2.5H2O}n (2) and the octanuclear molecule {[CsGd(VO)2(cbdc)4(H2O)11]·5H2O}2 (3), respectively. According to dc-magnetic measurements, the VIV and GdIII ions were ferromagnetically coupled in compound 1 (JVGd = 0.163 ± 0.008 cm−1), while in compounds 2 and 3, ferro- and weak antiferromagnetic exchange interactions were observed (JVGd = 0.989 ± 0.028 and −0.089 ± 0.008 cm−1 for 2, 0.656 ± 0.009 and −0.050 ± 0.004 cm−1 for 3). Analysis of the EPR spectra of 1 revealed the presence of weak magnetic anisotropy of GdIII ions (D ~ 0.08 cm−1 and E/D ~ 0.1–0.15). Ac-susceptibility measurements showed an occurrence the field-induced slow relaxation of magnetization in 1–3. Full article
(This article belongs to the Special Issue Magnetic Coordination Polymers)
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8 pages, 1970 KiB  
Article
Engineered Magnetization Dynamics of Magnonic Nanograting Filters
by Rawana Yagan, Ferhat Katmis and Mehmet C. Onbaşlı
Magnetochemistry 2021, 7(6), 81; https://doi.org/10.3390/magnetochemistry7060081 - 3 Jun 2021
Viewed by 2340
Abstract
Magnonic crystals and gratings could enable tunable spin-wave filters, logic, and frequency multiplier devices. Using micromagnetic models, we investigate the effect of nanowire damping, excitation frequency and geometry on the spin wave modes, spatial and temporal transmission profiles for a finite patterned nanograting [...] Read more.
Magnonic crystals and gratings could enable tunable spin-wave filters, logic, and frequency multiplier devices. Using micromagnetic models, we investigate the effect of nanowire damping, excitation frequency and geometry on the spin wave modes, spatial and temporal transmission profiles for a finite patterned nanograting under external direct current (DC) and radio frequency (RF) magnetic fields. Studying the effect of Gilbert damping constant on the temporal and spectral responses shows that low-damping leads to longer mode propagation lengths due to low-loss and high-frequency excitations are also transmitted with high intensity. When the nanowire is excited with stronger external RF fields, higher frequency spin wave modes are transmitted with higher intensities. Changing the nanowire grating width, pitch and its number of periods helps shift the transmitted frequencies over super high-frequency (SHF) range, spans S, C, X, Ku, and K bands (3–30 GHz). Our design could enable spin-wave frequency multipliers, selective filtering, excitation, and suppression in magnetic nanowires. Full article
(This article belongs to the Special Issue Micromagnetics and Magnetization Processes in Nanomagnetism)
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13 pages, 2507 KiB  
Article
The Effect of pH and Viscosity on Magnetophoretic Separation of Iron Oxide Nanoparticles
by Leonie Wittmann, Chiara Turrina and Sebastian P. Schwaminger
Magnetochemistry 2021, 7(6), 80; https://doi.org/10.3390/magnetochemistry7060080 - 3 Jun 2021
Cited by 22 | Viewed by 4195
Abstract
Magnetic nanoparticles (MNPs) are used for magnetophoresis-based separation processes in various biomedical and engineering applications. Essential requirements are the colloidal stability of the MNPs and the ability to be separated even in low magnetic field gradients. Bare iron oxide nanoparticles (BIONs) with a [...] Read more.
Magnetic nanoparticles (MNPs) are used for magnetophoresis-based separation processes in various biomedical and engineering applications. Essential requirements are the colloidal stability of the MNPs and the ability to be separated even in low magnetic field gradients. Bare iron oxide nanoparticles (BIONs) with a diameter of 9.2 nm are synthesized via coprecipitation, exhibiting a high saturation magnetization of 70.84 Am2 kg−1 and no remanence. In our study, zeta potential, dynamic light scattering (DLS), and sedimentation analysis show that the aggregation behavior of BIONs is influenced by pH and viscosity. Small aggregate clusters are formed with either low or high pH values or increased viscosity. Regarding magnetophoresis-based separation, a higher viscosity leads to lower magnetophoretic velocities, similar to how small aggregates do. Additionally, cooperative magnetophoresis, the joint motion of strongly interacting particles, affects the separation of the BIONs, too. Our study emphasizes the effect of pH and viscosity on the physicochemical characteristics of MNPs, resulting in different aggregation behavior. Particularly, for high viscous working media in downstream processing and medicine, respectively, the viscosity should be taken into account, as it will affect particle migration. Full article
(This article belongs to the Special Issue Magnetic Cell Separation)
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20 pages, 3744 KiB  
Article
Near-Infrared Emissive Cyanido-Bridged {YbFe2} Molecular Nanomagnets Sensitive to the Nitrile Solvents of Crystallization
by Michal Liberka, Kseniia Boidachenko, Jakub J. Zakrzewski, Mikolaj Zychowicz, Junhao Wang, Shin-ichi Ohkoshi and Szymon Chorazy
Magnetochemistry 2021, 7(6), 79; https://doi.org/10.3390/magnetochemistry7060079 - 2 Jun 2021
Cited by 10 | Viewed by 3361
Abstract
One of the pathways toward luminescent single-molecule magnets (SMMs) is realized by the self-assembly of lanthanide(3+) ions with cyanido transition metal complexes. We report a novel family of emissive SMMs, {YbIII(4-pyridone)4[FeII(phen)2(CN)2]2}(CF [...] Read more.
One of the pathways toward luminescent single-molecule magnets (SMMs) is realized by the self-assembly of lanthanide(3+) ions with cyanido transition metal complexes. We report a novel family of emissive SMMs, {YbIII(4-pyridone)4[FeII(phen)2(CN)2]2}(CF3SO3)3·solv (solv = 2MeCN, 1·MeCN; 2AcrCN, 1·AcrCN; 2PrCN, 1·PrCN; 2MalCN·1MeOH; 1·MalCN; MeCN = acetonitrile, AcrCN = acrylonitrile, PrCN = propionitrile, MalCN = malononitrile). They are based on paramagnetic YbIII centers coordinating diamagnetic [FeII(phen)2(CN)2] metalloligands but differ in the nitrile solvents of crystallization. They exhibit a field-induced slow magnetic relaxation dominated by a Raman process, without an Orbach relaxation as indicated by AC magnetic data and the ab initio calculations. The Raman relaxation is solvent-dependent as represented by the power “n” of the BRamanTn contribution varying from 3.07(1), to 2.61(1), 2.37(1), and 1.68(4) for 1·MeCN, 1·PrCN, 1·AcrCN, and 1·MalCN, respectively, while the BRaman parameter adopts the opposite trend. This was correlated with the variation of phonon modes schemes, including the number of available vibrational modes and their energies, dependent on the increasing complexity of the applied nitrile. 1·MeCN and 1·MalCN show the additional T-independent relaxation assignable to dipole-dipole interactions as confirmed by its suppression in 1·AcrCN and 1·PrCN revealing longer Yb–Yb distances and the disappearance in the LuIII-diluted 1·MeCN@Lu. All compounds exhibit YbIII–centered near-infrared photoluminescence sensitized by organic ligands. Full article
(This article belongs to the Special Issue Advances in Lanthanide Coordination Chemistry)
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20 pages, 7413 KiB  
Article
A Ti/Pt/Co Multilayer Stack for Transfer Function Based Magnetic Force Microscopy Calibrations
by Baha Sakar, Sibylle Sievers, Alexander Fernández Scarioni, Felipe Garcia-Sanchez, İlker Öztoprak, Hans Werner Schumacher and Osman Öztürk
Magnetochemistry 2021, 7(6), 78; https://doi.org/10.3390/magnetochemistry7060078 - 1 Jun 2021
Cited by 4 | Viewed by 3536
Abstract
Magnetic force microscopy (MFM) is a widespread technique for imaging magnetic structures with a resolution of some 10 nanometers. MFM can be calibrated to obtain quantitative (qMFM) spatially resolved magnetization data in units of A/m by determining the calibrated point spread function of [...] Read more.
Magnetic force microscopy (MFM) is a widespread technique for imaging magnetic structures with a resolution of some 10 nanometers. MFM can be calibrated to obtain quantitative (qMFM) spatially resolved magnetization data in units of A/m by determining the calibrated point spread function of the instrument, its instrument calibration function (ICF), from a measurement of a well-known reference sample. Beyond quantifying the MFM data, a deconvolution of the MFM image data with the ICF also corrects the smearing caused by the finite width of the MFM tip stray field distribution. However, the quality of the calibration depends critically on the calculability of the magnetization distribution of the reference sample. Here, we discuss a Ti/Pt/Co multilayer stack that shows a stripe domain pattern as a suitable reference material. A precise control of the fabrication process, combined with a characterization of the sample micromagnetic parameters, allows reliable calculation of the sample’s magnetic stray field, proven by a very good agreement between micromagnetic simulations and qMFM measurements. A calibrated qMFM measurement using the Ti/Pt/Co stack as a reference sample is shown and validated, and the application area for quantitative MFM measurements calibrated with the Ti/Pt/Co stack is discussed. Full article
(This article belongs to the Special Issue Soft and Hard Magnetic Materials: Latest Advances and Prospects)
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6 pages, 1869 KiB  
Article
Crystal-to-Crystal Transformation from K2[Co(C2O4)2(H2O)2]·4H2O to K2[Co(μ-C2O4)(C2O4)]
by Bin Zhang, Yan Zhang, Guangcai Chang, Zheming Wang and Daoben Zhu
Magnetochemistry 2021, 7(6), 77; https://doi.org/10.3390/magnetochemistry7060077 - 28 May 2021
Cited by 2 | Viewed by 3351
Abstract
Crystal-to-crystal transformation is a path to obtain crystals with different crystal structures and physical properties. K2[Co(C2O4)2(H2O)2]·4H2O (1) is obtained from K2C2O4·2H [...] Read more.
Crystal-to-crystal transformation is a path to obtain crystals with different crystal structures and physical properties. K2[Co(C2O4)2(H2O)2]·4H2O (1) is obtained from K2C2O4·2H2O, CoCl2·6H2O in H2O with a yield of 60%. It is crystallized in the triclinic with space group P1 and cell parameters: a = 7.684(1) Å, b = 9.011(1) Å, c = 10.874(1) Å, α = 72.151(2)°, β = 70.278(2)°, γ = 80.430(2)°, V = 670.0(1) Å3, Z = 2 at 100 K. 1 is composed of K+, mononuclear anion [Co(C2O4)2(H2O)22−] and H2O. Co2+ is coordinated by two bidentated oxalate anion and two H2O in an octahedron environment. There is a hydrogen bond between mononuclear anion [Co(C2O4)2(H2O)22−] and H2O. K2[Co(μ-C2O4)(C2O4)] (2) is obtained from 1 by dehydration. The cell parameters of 2 are a = 8.460(5) Å, b = 6.906 (4) Å, c = 14.657(8) Å, β = 93.11(1)°, V = 855.0(8) Å3 at 100 K, with space group in P2/c. It is composed of K+ and zigzag [Co(μ-C2O4)(C2O42−]n chain. Co2+ is coordinated by two bisbendentate oxalate and one bidentated oxalate anion in trigonal-prism. 1 is an antiferromagnetic molecular crystal. The antiferromagnetic ordering at 8.2 K is observed in 2. Full article
(This article belongs to the Special Issue Perspectives on Molecular Materials—A Tribute to Professor Peter Day)
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31 pages, 10509 KiB  
Article
Reciprocating Thermal Behavior in Multichannel Relaxation of Cobalt(II) Based Single Ion Magnets
by Cyril Rajnák, Ján Titiš and Roman Boča
Magnetochemistry 2021, 7(6), 76; https://doi.org/10.3390/magnetochemistry7060076 - 25 May 2021
Cited by 14 | Viewed by 2770
Abstract
A series of mononuclear Co(II) complexes showing slow magnetic relaxation is assessed from the point of view of relaxation mechanisms. In certain cases, the reciprocating thermal behavior is detected: On cooling, the slow relaxation time is prolonged until a certain limit and then, [...] Read more.
A series of mononuclear Co(II) complexes showing slow magnetic relaxation is assessed from the point of view of relaxation mechanisms. In certain cases, the reciprocating thermal behavior is detected: On cooling, the slow relaxation time is prolonged until a certain limit and then, unexpectedly, is accelerated. The low-temperature magnetic data can be successfully fitted by assuming Raman and/or phonon bottleneck mechanisms of the slow magnetic relaxation for the high-frequency relaxation channel. An additional term with the negative temperature exponent is capable of reproducing the whole experimental dataset. Full article
(This article belongs to the Special Issue Stimuli-Responsive Magnetic Molecular Materials)
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14 pages, 5286 KiB  
Article
Solvent-Induced Hysteresis Loop in Anionic Spin Crossover (SCO) Isomorph Complexes
by Emmelyne Cuza, Samia Benmansour, Nathalie Cosquer, Françoise Conan, Carlos J. Gómez-García and Smail Triki
Magnetochemistry 2021, 7(6), 75; https://doi.org/10.3390/magnetochemistry7060075 - 23 May 2021
Cited by 3 | Viewed by 2533
Abstract
Reaction of Fe(II) with the tris-(pyridin-2-yl)ethoxymethane (py3C-OEt) tripodal ligand in the presence of the pseudohalide ancillary NCSe− (E = S, Se, BH3) ligand leads to the mononuclear complex [Fe(py3C-OEt)2][Fe(py3C-OEt)(NCSe)3]2 [...] Read more.
Reaction of Fe(II) with the tris-(pyridin-2-yl)ethoxymethane (py3C-OEt) tripodal ligand in the presence of the pseudohalide ancillary NCSe− (E = S, Se, BH3) ligand leads to the mononuclear complex [Fe(py3C-OEt)2][Fe(py3C-OEt)(NCSe)3]2·2CH3CN (3), which has been characterised as an isomorph of the two previously reported complexes, Fe(py3C-OEt)2][Fe(py3C-OEt)(NCE)3]2·2CH3CN, with E = S (1), BH3 (2). X-ray powder diffraction of the three complexes (1–3), associated with the previously reported single crystal structures of 1–2, revealed a monomeric isomorph structure for 3, formed by the spin crossover (SCO) anionic [Fe(py3C-OEt)(NCSe)3]− complex, associated with the low spin (LS) [Fe(py3C-OEt)2]2+ cationic complex and two solvent acetonitrile molecules. In the [Fe(py3C-OEt)2]2+ complex, the metal ion environment involves two py3C-OEt tridentate ligands, while the [Fe(py3C-OEt)(NCSe)3]− anion displays a hexacoordinated environment involving three N-donor atoms of one py3C-OEt ligand and three nitrogen atoms arising from the three (NCSe)− coligands. The magnetic studies for 3 performed in the temperature range 300-5-400 K, indicated the presence of a two-step SCO transition centred around 170 and 298 K, while when the sample was heated at 400 K until its complete desolvation, the magnetic behaviour of the high temperature transition (T1/2 = 298 K) shifted to a lower temperature until the two-step behaviour merged with a gradual one-step transition at ca. 216 K. Full article
(This article belongs to the Special Issue Perspectives on Molecular Materials—A Tribute to Professor Peter Day)
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18 pages, 4534 KiB  
Article
Neutron Studies of a High Spin Fe19 Molecular Nanodisc
by Francis L. Pratt, Tatiana Guidi, Pascal Manuel, Christopher E. Anson, Jinkui Tang, Stephen J. Blundell and Annie K. Powell
Magnetochemistry 2021, 7(6), 74; https://doi.org/10.3390/magnetochemistry7060074 - 21 May 2021
Cited by 2 | Viewed by 2558
Abstract
The molecular cluster system [Fe19(metheidi)10(OH)14O6(H2O)12]NO3·24H2O, abbreviated as Fe19, contains nineteen Fe(III) ions arranged in a disc-like structure with the total spin S = 35/2. For [...] Read more.
The molecular cluster system [Fe19(metheidi)10(OH)14O6(H2O)12]NO3·24H2O, abbreviated as Fe19, contains nineteen Fe(III) ions arranged in a disc-like structure with the total spin S = 35/2. For the first order, it behaves magnetically as a single molecule magnet with a 16 K anisotropy barrier. The high spin value enhances weak intermolecular interactions for both dipolar and superexchange mechanisms and an eventual transition to antiferromagnetic order occurs at 1.2 K. We used neutron diffraction to determine both the mode of ordering and the easy spin axis. The observed ordering was not consistent with a purely dipolar driven order, indicating a significant contribution from intermolecular superexchange. The easy axis is close to the molecular Fe1–Fe10 axis. Inelastic neutron scattering was used to follow the magnetic order parameter and to measure the magnetic excitations. Direct transitions to at least three excited states were found in the 2 to 3 meV region. Measurements below 0.2 meV revealed two low energy excited states, which were assigned to S = 39/2 and S = 31/2 spin states with respective excitation gaps of 1.5 and 3 K. Exchange interactions operating over distances of order 10 Å were determined to be on the order of 5 mK and were eight-times stronger than the dipolar coupling. Full article
(This article belongs to the Special Issue Perspectives on Molecular Materials—A Tribute to Professor Peter Day)
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