Magnetic Susceptibility Measurements Research Articles

Regulating Fe-spin state by doping P heteroatom in Fe-N-C catalyst derived from colloidal nanoparticles encapsulated ZIF-8 to boost oxygen reduction activity

Over the past decades, Fe-N-C carbon materials have been considered as one of the most ideal alternatives to the noble metal catalysts (e.g. Pt/C) for the sluggish oxygen reduction reaction (ORR) in zinc-air batteries and fuel cells. In this research, ZIF-8 cage encapsulation confinement strategy coupled with post P-doping has been employed to design porous P, N and Fe co-doped carbon (FeNC-P) for efficient oxygen reduction reaction (ORR). The zero-field cooling (ZFC) temperature-dependent magnetic susceptibility measurement revealed that incorporation of P in the Fe-N-C catalysts can induce the transition of spin polarization configuration, which promotes the desorption of *OH in the crucial step of the ORR reaction process. The best-performing FeNC-P catalyst displays a 1.00 V (vs RHE) of Eonset (onset potential) and a 0.90 V (vs RHE) of E1/2 (half-wave potential) in an alkaline solution, which exceeds the benchmark Pt/C catalyst. Moreover, it also delivers a high power density of 130 mW·cm−2 in the self-made zinc-air battery, surpassing the benchmark Pt/C catalyst (90 mW·cm−2).

Preparation of high-purity magnetite from iron ore concentrate

In pursuit of environmental protection and green, low-carbon economic development, China has proposed the dual-carbon strategies of carbon peak and carbon neutrality. To achieve the dual-carbon goals, traditional steel metallurgical production processes are gradually shifting towards green and low-carbon hydrogen metallurgical processes. However, hydrogen metallurgical processes have strict requirements for raw materials and typically require the utilization of high-grade iron concentrates. The scarcity of high-grade iron ore in China severely constrains the development of hydrogen metallurgical processes. Therefore, this study proposes the utilization of ordinary magnetite concentrate to produce high-grade magnetite. Comprehensive analytical methods, including chemical analysis, X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD) analysis, laser particle size testing, optical microscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), and mineral liberation analysis, were employed to elucidate the mineralogical characteristics of the iron concentrate. The analysis revealed that the iron concentrate had a total iron (TFe) grade of 65.56 %, with SiO2 and Al2O3 contents of 8.28 % and 0.38 %, respectively. Subsequently, a combined beneficiation process involving magnetic separation, flotation, and chemical leaching was conducted. Experimental results showed that a single magnetic separation obtained an iron concentrate grade of 67.52 % with an overall recovery of 86.18 %. Following magnetic separation, flotation was conducted to increase the concentrate grade. With one roughing and four cleaning flotation stages, a concentrate grade of 72.19 % and a 36.36 % overall recovery were achieved. A subsequent leaching operation after flotation yielded high-purity magnetite with a Fe grade of 72.30 % and an overall recovery of 35.68 %. The high-purity magnetite was confirmed to have a purity of up to 99.9 % based on chemical titration, XRD analysis, magnetic susceptibility measurement, and SEM analysis. Furthermore, detailed kinetics studies on leaching were conducted to elucidate the reaction mechanism, revealing an apparent activation energy of 25.70 kJ/mol. The successful implementation of this process will provide a benchmark for producing similar high-purity magnetite concentrates and contribute to China’s dual-carbon goals.

Facile synthesis of imidazolidinyl phenolate supported Dicopper(II/II) Complexes: Activation and fixation of atmospheric CO2 as MeOCO2− showing exogenous bridge modulating magnetic exchange coupling

Two imidazolidine grafted Schiff bases H3L2 and H3L3 have been utilized to fasten the Cu2 core in four new complexes [Cu2(μ-L2)(μ-O2CMe)]·H2O (1·H2O), [Cu2(μ-L2)(μ-O2COMe)]·H2O (2·H2O), [Cu2(μ-L2)(μ-NO3)]·H2O (3·H2O) and [Cu2L3(μ-OAc)]·5H2O (4·5H2O). Room temperature solution reaction of H3L2 with Cu2(OAc)4·2H2O provided 1·H2O in good yield. Follow-up reaction of 1·H2O with Et4NOH in air replaces μ-O2CMe (acetato) bridge by MeOCO2− (monomethyl carbonato) linker in 2·H2O. Single crystal X-ray structure established the individual complexes and confirmed the fixation of atmospheric CO2. Variable temperature (2 to 300 K) magnetic susceptibility measurements recognized the antiferromagnetic exchange interactions between the adjacent copper(II) centers in complexes 2 and 3. The amount of spin–spin interactions are found to be higher for ancillary NO3− bridge (−284 cm−1) compared to the in situ transformed MeOCO2− bridged (−1.64 cm−1).

Superconductivity in TiZrNb and TiZrNbHf bulk equimolar alloys

We have prepared and investigated superconducting equimolar medium-entropy alloys of TiZrNb and TiZrNbHf. Their basic superconducting parameters, as the values of the critical temperature Tc, upper critical magnetic field Bc2 and the superconducting energy gap Δ have been studied with the use of magnetic susceptibility and point-contact Andreev reflection (PCAR) spectroscopy measurements. Although our samples have different critical temperatures, namely Tc ∼ 8.2 K for TiZrNb and Tc ∼ 6.3 K for TiZrNbHf, their zero-temperature critical magnetic field has the same value Bc2(0) = 12 T, from the vicinity of the Clogston limit. We have observed the presence of degraded phases on the surfaces of all the investigated samples using PCAR measurements. Still, we were able to show that the bulk phase in both systems exhibits BCS weakly coupled superconductivity with 2Δ(0)/kBTc ∼ 3.5.

Ferrimagnetic structures with rare-earth induced spin-reorientation in the Mn self-doped perovskite (Er0.7Mn0.3)MnO3

The search for spin-reorientation (SR) phase transitions, a spontaneous rotation of ordered magnetic moments, in ferrimagnetic (FiM) materials, which carry a net magnetization, is of fundamental and practical interest for applications in the field of spintronics. In this work, we have investigated Mn self-doped (Er0.7Mn0.3)MnO3 solid solution with GdFeO3-type Pnma perovskite structure by combining specific heat, magnetic susceptibility and neutron powder diffraction measurements. We provide experimental evidence for FiM order below TC = 104 K, and a spontaneous SR transition at TSR = 11 K. A FiM structure appears in all (R1-xMnx)MnO3 compounds with R = Dy–Lu for x ≥ 0.2. But in this structural family, R = Er is the only material with a SR transition. FiM order in (Er0.7Mn0.3)MnO3 appears with ferromagnetic (FM) ordering of Mn3+ and Mn4+ cations at the B site along the a-direction, which are antiferromagnetically (AFM) coupled with Er3+ and Mn2+ cations at the A site. At TSR, ordered Er3+ change direction from the magnetically harder a-axis to the magnetically easy b-axis and induce a change of the whole FiM structure, including the direction of all Mn spins from the irreducible representation mGM3+ to mGM4+. We calculated the crystal-field (CF) anisotropy for Ho3+ in (Ho0.8Mn0.2)MnO3 and Er3+ in (Er0.7Mn0.3)MnO3, based on the point charge model; the results revealed large magnetic anisotropies. For the FiM structure of (Ho0.8Mn0.2)MnO3, the magnetically easy a-axis of Ho3+ keeps the high-temperature magnetic directions along the a-axis and gives rise to a pronounced magnetization reversal effect at low temperature because of a significant rise of Ho3+ ordered moments. On the other hand, for the FiM structure of (Er0.7Mn0.3)MnO3, the magnetically easy b-axis of Er3+ gives rise to a SR phase transition at TSR, which does not lead to magnetization reversal even though Er3+ ordered moments rise significantly at low temperatures.

Exploration of iron(III) complexes with bidentate N, O-donor Schiff base ligands through synthesis, characterization, DFT, and antibacterial studies

Iron(III) complexes [Fe(SBn)2(H2O)2]NO3 (1, 2) (n=1 or 2) were synthesized via a reaction of Fe(NO3)3.9H2O with N, O-donor Schiff-base ligands (HSBn) in a ratio of 1:2 in terms of moles. Schiff-base ligands (HSBn) were synthesized when a solution of salicylaldehyde in methanol underwent reflux with aniline (HSB1) or 4-chloroaniline (HSB2) in methanol respectively. These aquated iron(III) complexes, 1 & 2 were further reacted with nitrogen-containing molecules as neutral donors (L) (such as pyridine, imidazole, and benzimidazole) in a ratio of 1 part to 2 parts by moles, yielding mixed-ligand complexes [Fe(SBn)2(L)2]NO3(3-8). The synthesized complexes were characterized by elemental analyses, mass spectrometry, and spectroscopic studies (electronic, infrared & NMR spectra), as well as measurements of magnetic susceptibility and conductance. Infrared spectra revealed that Schiff bases coordinated with iron(III) centers in bidentate and chelating mode, primarily through phenolic –O and azomethine–N groups. Electronic spectra confirmed the existence of octahedral iron(III) in a high-spin state within these complexes, consistent with assessments of magnetic susceptibility. DFT-based parameters were determined for ligands HSB1, & HSB2, and complexes 1, 2, & 8 using Gaussian 09 at the B3LYP level. Structural analysis showed slightly distorted octahedral geometry with high spin (d5) and sextet multiplicity in all complexes. The global hardness exhibited an increasing trend: HSB2 < 8 < 2 < 1 < HSB1, while chemical reactivity showed the opposite trend: HSB2 > 8 > 2 > 1 > HSB1. The antibacterial activity of ligands, HSB1 and HSB2, along with complexes 1 and 2, was evaluated against various bacterial strains. Schiff bases, HSB1 and HSB2 inhibited several strains, with complexes 1 and 2 demonstrating improved efficacy, possibly due to altered chemical properties from the complex formation. Despite lower potency than Ciprofloxacin, they offer therapeutic alternatives.

A Redox‐Active Phenothiazine‐based Pd2L4‐Type Coordination Cage and Its Isolable Crystalline Polyradical Cations

AbstractPolyradical cages are of great interest because they show very fascinating physical and chemical properties, but many challenges remain, especially for their synthesis and characterization. Herein, we present the synthesis of a polyradical cation cage 14⋅+ through post‐synthetic oxidation of a redox‐active phenothiazine‐based Pd2L4‐type coordination cage 1. It′s worth noting that 1 exhibits excellent reversible electrochemical and chemical redox activity due to the introduction of a bulky 3,5‐di‐tert‐butyl‐4‐methoxyphenyl substituent. The generation of 14⋅+ through reversible electrochemical oxidation is investigated by in situ UV/Vis‐NIR and EPR spectroelectrochemistry. Meanwhile, chemical oxidation of 1 can also produce 14⋅+ which can be reversibly reduced back to the original cage 1, and the process is monitored by EPR and NMR spectroscopies. Eventually, we succeed in the isolation and single crystal X‐ray diffraction analysis of 14⋅+, whose electronic structure and conformation are distinct to original 1. The magnetic susceptibility measurements indicate the predominantly antiferromagnetic interactions between the four phenothiazine radical cations in 14⋅+. We believe that our study including the facile synthesis methodology and in situ spectroelectrochemistry will shed some light on the synthesis and characterization of novel polyradical systems, opening more perspectives for developing functional supramolecular cages.

A Redox-Active Phenothiazine-based Pd2L4-Type Coordination Cage and Its Isolable Crystalline Polyradical Cations.

Polyradical cages are of great interest because they show very fascinating physical and chemical properties, but many challenges remain, especially for their synthesis and characterization. Herein, we present the synthesis of a polyradical cation cage 14⋅+ through post-synthetic oxidation of a redox-active phenothiazine-based Pd2L4-type coordination cage 1. It's worth noting that 1 exhibits excellent reversible electrochemical and chemical redox activity due to the introduction of a bulky 3,5-di-tert-butyl-4-methoxyphenyl substituent. The generation of 14⋅+ through reversible electrochemical oxidation is investigated by in situ UV/Vis-NIR and EPR spectroelectrochemistry. Meanwhile, chemical oxidation of 1 can also produce 14⋅+ which can be reversibly reduced back to the original cage 1, and the process is monitored by EPR and NMR spectroscopies. Eventually, we succeed in the isolation and single crystal X-ray diffraction analysis of 14⋅+, whose electronic structure and conformation are distinct to original 1. The magnetic susceptibility measurements indicate the predominantly antiferromagnetic interactions between the four phenothiazine radical cations in 14⋅+. We believe that our study including the facile synthesis methodology and in situ spectroelectrochemistry will shed some light on the synthesis and characterization of novel polyradical systems, opening more perspectives for developing functional supramolecular cages.

Synthesis and in vitro Biological Assessments of Novel Thiazole-Based Thiosemicarbazone Complexes

In the present work, novel heterocyclic thiazole-based thiosemicarbazone Ag(I) complexes (Hc1, Hc2, Hc3) were obtained using the template method. The structures of synthesized thiosemicarbazone compounds were determined by some spectroscopic techniques (element analysis, infrared spectra (IR), thermogravimetric analysis (TGA), organic elemental analysis, and magnetic susceptibility measurements). The biological activities of novel heterocyclic thiazole-based thiosemicarbazone Ag(I) complexes werev screenedv in vitro against selected disease-causing pathogens (Micrococcus luteus ATCC9341, Staphylococcus epidermidis ATCC12228, Bacillus cereus RSKK863, Pseudomonas aeroginosa ATCC27853, Klebsiella pneumonia ATCC27853, Enterobacter aerogenes ATCC51342, Salmonellav typhi H NCTC9018394, Shigella dysenteria NCTC2966, Proteus vulgaris RSKK96026, Candidav albicans Y-1200-NIH) were as potential antimicrobial agents. It was determined that the thiazole-based thiosemicarbazone Ag(I) complexes exhibited high or moderate antibacterial and antifungal activity.

Highly Fluorescent π-Conjugated Azomethines and Divalent Metal Complexes as Antibacterial and Antibiofilm Nominees.

π-Conjugated azomethine ligands differing in the naphthalene or phenylmethane-centered core structure and their divalent cobalt, nickel, copper, and zinc metal complexes were prepared and well-characterized by spectral analyses in solid state. Magnetic natures of the complexes were determined by magnetic susceptibility measurements in solid-state. Their remarkable photophysical characteristics were recorded by Uv-vis and Fluorescence spectroscopic techniques. At their excitation wavelenght of 265 nm, all molecules exhibited triple fluorescence emission bands with promising intensities above 673 nm in near infra-red region. Antibacterial and antibiofilm activities of the π-conjugated azomethines are promising for potential applications in medical and healthcare settings. Hence, the antibacterial/antibiofilm activity of the π-conjugated azomethine ligands and their metal complexes against some clinically important bacteria namely Staphylococcus aureus (MSSA), Methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis, Escherichia coli, Pseudomonas aeruginosa and Proteus mirabilis was investigated, and the obtained results have shown that the ligands and complexes had a remarkable antibacterial effect, especially on Proteus mirabilis. Metal complexes have been found to have a significant inhibitory effect on biofilm formation by MRSA, MSSA, and P. mirabilis compared to ligands. The copper (II) complex of ligand-2 showed the highest inhibition percentage, significantly reducing biofilm formation for MRSA and MSSA. Furthermore, cobalt (II) complexes of the ligands selectively inhibited the growth of the opportunistic pathogen P. mirabilis biofilms, indicating that metal complexes might be a good choice for future antibiofilm studies.

Disordered magnetic ground state in a quasi-1-D d4columnar iridate Sr3LiIrO6.

Spin-orbit coupling (SOC) offers a large variety of novel and extraordinary magnetic and electronic properties in otherwise 'ordinary pool' of heavy ion oxides. Here we present a detailed study on an apparently isolated hexagonal 2Hspin-chain d4iridate Sr3LiIrO6(SLIO) with geometric frustration. Our structural studies reveal Li-Ir chemical order with desired stoichiometry in this compound, while x-ray absorption together with x-ray photoemission spectroscopic characterizations establish pure 5+ valence of Ir. We have established a magnetic ground state with finite Ir5+magnetic moments in this compound, contrary to the anticipated nonmagnetic Jeff= 0 state, through combined dc susceptibility,7Li nuclear magnetic resonance (NMR), muon spin relaxation (μSR) and ab-initio electronic structure studies. These investigations together with ac magnetic susceptibility and specific heat measurements reveal that despite having noticeable antiferromagnetic correlation among the Ir5+local moments, this system does not magnetically order down to at least 0.05 K, possibly due to geometrical exchange frustration, arising from the comparable nearest- and next-nearest-neighbor interchain Ir-O-O-Ir superexchange interaction strengths with opposite signs. However, the zero-field (ZF) μSR analysis shows emergence of a considerable proportion of spin-freezing on top of a spin-fluctuating dynamic magnetic background down to the lowest measured&#xD;temperature of 1.7 K, possibly due to some inhomogeneity and/or the much stronger intra-column Ir-Ir magnetic exchange interaction&#xD;strength relative to the inter-column Ir-Ir ones. The linear temperature dependence of the magnetic specific heat (Cm) in both zero and applied magnetic fields, plus the power-law behavior of the NMR spin-lattice relaxation rate suggest a gapless spinon density of states in this charge gapped disordered magnetic ground state of Sr3LiIrO6.

Valence-state mixing and reduced magnetic moment in Fe3−δGeTe2 single crystals with varying Fe content probed by x-ray spectroscopy

We present a spectroscopic study of the magnetic properties of Fe3−δGeTe2 single crystals with varying Fe content, achieved by tuning the stoichiometry of the crystals. We carried out x-ray absorption spectroscopy and analyzed the x-ray circular magnetic dichroism spectra using the sum rules, to determine the orbital and spin magnetic moments of the materials. We find a clear reduction of the spin and orbital magnetic moment with increasing Fe deficiency. Magnetic susceptibility measurements show that the reduction in magnetization is accompanied by a reduced Curie temperature. Multiplet calculations reveal that the Fe2+ state increasingly mixes with a higher valence state when the Fe deficiency is increased. This effect is correlated with the weakening of the magnetic moment. As single crystals are the base material for exfoliation processes, our results are relevant for the assembly of 2D magnetic heterostructures.

High-temperature magnetic anomaly via suppression of antisite disorder through synthesis route modification in a Kitaev candidate Cu2IrO3

By incorporating inert KCl into the Na2IrO3 + 2CuCl → Cu2IrO3 + 2NaCl topochemical reaction, we significantly reduced the synthesis temperature of Cu2IrO3 from the 350 °C reported in previous studies to 170 °C. This adjustment decreased the Cu/Ir antisite disorder concentration in Cu2IrO3 from ∼19% to ∼5%. Furthermore, magnetic susceptibility measurements of the present Cu2IrO3 sample revealed a weak ferromagnetic-like anomaly with hysteresis at a magnetic transition temperature of ∼70 K. Our research indicates that the spin-disordered ground state reported in chemically disordered Cu2IrO3 is an extrinsic phenomenon, rather than an intrinsic one, underscoring the pivotal role of synthetic chemistry in understanding the application of Kitaev model to realistic materials.

Synthesis, characterization, in vitro and in silico assessment of novel diclofenac derivative metal complexes

A novel hydrazone ligand was synthesized by condensing diclofenac hydrazide with salicylaldehyde. This ligand was then used to create complexes with cobalt(II), nickel(II), copper(II), gadolinium(III), lanthanum(III), and silver(I). Structural characterization of these compounds was achieved through various techniques, including nuclear magnetic resonance spectroscopy, infrared spectroscopy, ultraviolet-visible spectroscopy, mass spectrometry, elemental analysis, thermal analysis, magnetic susceptibility measurements, electron spin resonance spectroscopy, X-ray diffraction, and conductivity measurements. The inhibitory effects of the synthesized compounds on cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) enzymes, critical targets for anti-inflammatory drugs, were assessed. Notably, the cobalt(II) and silver(I) complexes exhibited high selectivity for inhibiting COX-2, with selectivity indices of 118.75 and 105.00, respectively. The antitumor potential of the compounds was evaluated against MCF-7 (breast cancer) and HepG-2 (liver cancer) cell lines. The copper(II) and gadolinium(III) complexes demonstrated the highest efficacy, significantly inhibiting the growth of both cancer cell lines with half-maximal inhibitory concentration (IC50) values as low as 0.37 µM and 0.58 µM (MCF-7) and 0.35 µM and 0.67 µM (HepG-2), respectively. These complexes outperformed the original ligand in inhibiting cancer cell growth. In silico studies, using the SwissADME web tool and AutoDocke Vina, corroborated the experimental findings and provided insights into the compounds' physicochemical properties, pharmacokinetics, drug-likeness, and potential binding interactions with COX-1, COX-2, and the target proteins in the cancer cell lines.

Optical Probe of Magnetic Ordering Structure and Spin‐Entangled Excitons in Mn‐Substituted NiPS3

AbstractIn van der Waals magnets, the interplay between magneto‐excitonic coupling and optical phenomena opens avenues for directly probing magnetic ordering structures, manipulating excitonic properties through magnetic fields, and exploring quantum entanglement between electronic and magnetic states. Notably, NiPS3 stands out for its capacity to host spin‐entangled excitons, where the excitonic states are intricately tied with the material's spin configuration. Herein, it is experimentally showcased that the spin‐entangled excitons can be utilized for detecting the magnetic easy axis in Ni1‐xMnxPS3 (x = 0–0.1). The end members of this series exhibit distinct magnetic ordering patterns and easy axes: zigzag ordering with magnetic moments aligned along the a‐axis for NiPS3 versus Néel ordering with the out‐of‐plane easy axis for MnPS3. By combining angle‐resolved exciton photoluminescence with magnetic susceptibility measurements, it is observed that the magnetic easy axis rotates away from the local spin chain direction with increasing Mn content. Moreover, through a comprehensive thermal and substitution study, it is demonstrated that the energy and lifetime of spin‐entangled excitons are governed by two spin‐flip processes and are drastically influenced by disparate electronic states. These findings not only provide optical means to map out magnetic ordering structures but also offer insights into decoherence processes in spin‐exciton entangled states.

Using Soil Magnetic Susceptibility Proxies to Estimate Overburden Thickness Overlying Ore of Lateritic Soils in Sulawesi Island Indonesia

Sulawesi Island is one of the largest Ni ore producers in Indonesia. It is also expected to be a significant potential source of some critical metals (e.g., Co, Sc, rare-earth elements, and platinum-group elements). However, few studies show the post-mining impact on some heavy metal elements concentrated in this area. Therefore, improving the efficiency and effectiveness of soil organization and its effect on soil reclamation after mining is helpful. This study aimed to determine the accuracy in estimating the thickness of the overburden covering the nickel ore body profile from lateritic nickel post-mining areas by magnetic susceptibility measurements to discrepancy the overall laterite horizon, whereas χLF and χFD are used to distinguish the overburden zona and limonite and saprolite zone. The lateritic profile studied consists of soil formation of Fe-rich material in the Morowali, and Pomalaa block. We also evaluated the chemical element content of the soil and understood the relationship between the magnetic and geochemical properties of the soil. This study reveals the superparamagnetic (SP)-enriched soils indicated with the increase of the FD% values into the upward horizon, where the maximum values of FD are generally found at ranges 1 to 4m, indicating the overburden layers. Meanwhile, in the depth of 4m to 6m, the values of FD vary only slightly in the lower part initiated by the limonite layers, and then &gt; 6m decreases sharply to the bottom, indicating the saprolite layers. The chemical element mobility trends indicate that Fe, Co, Cr, Mn, and Ti increase toward the layers, which is the same pattern as in FD. Due to this, parameters magnetics may also be a new geophysical approach for estimating the distribution of economically valued minerals on lateritic soils. The strong correlation of Co with Fe, Mn, and Cr in all layers indicates the influence of weathering o n these ultramafic rocks. This suggests an increasing trend toward prolonged pedogenesis.

Expected and unexpected structural phase transitions in K2ReBr6 and K2ReI6

The structure and magnetic properties of the two vacancy ordered double perovskites, K2ReBr6 and K2ReI6, are described. At room temperature, K2ReBr6 has a cubic structure in space group Fm3‾m that transforms to a tetragonal structure described in P4/mnc just below 290 K. Further cooling results in a second phase transition to a monoclinic structure in P21/n. The larger size of the iodide anion, compared to bromide, reduces the Goldschmidt tolerance factor and results in the monoclinic structure appearing at room temperature. The sequence of structures observed for K2ReBr6, Fm3‾m→P4/mnc→P21/n, mirrors that of other 5d potassium hexabromides including K2OsBr6 and K2PtBr6 but is different than that seen for K2ReCl6. Unexpectedly, K2ReI6 undergoes a first-order transition from P21/n→Fm3‾m upon heating with both phases co-existing over a limited temperature range. K2ReI6 decomposes upon standing or heating, while K2ReBr6 remains stable in the laboratory for several months. Magnetic susceptibility measurements show both compounds undergo antiferromagnetic ordering at low temperatures and the Néel temperature, estimated from the magnetic susceptibility measurements, increases as the size of the halide increases; 8.2 K for K2ReCl6, 16.1 K for K2ReBr6, 26.9 K for K2ReI6.

Thermal Jahn-Teller Distortion Changes and Slow Relaxation of Magnetization in Mn(III) Schiff Base Complexes.

The impact that the anion and alkyl group has on the electronic structures and magnetic properties of four mononuclear Mn(III) complexes is explored in [Mn(salEen-Br)2]Y (salEen-Br = 2-{[2-(ethylamino)ethylimino]methyl}-4-Br-phenol; Y = ClO4- 1 and BF4-·1/3CH2Cl2 2) and [Mn(salBzen-Br)2]Y (salBzen-Br = 2-{[2-(benzylamino)ethylimino]methyl}-4-Br-phenol; Y = ClO4- 3 and BF4- 4). X-ray structures of [Mn(salEen-Br)2]ClO4·0.45C6H14 1-hexane, [Mn(salEen-Br)2]BF4·0.33CH2Cl2·0.15C6H14 2-dcm-hexane, and 3-4 reveal that they crystallize in ambient conditions in the monoclinic P21/c space group. Lowering the temperature, 2-dcm-hexane uniquely exhibits a structural phase transition toward a monoclinic P21/n crystal structure determined at 100 K with the unit cell trebling in size. Remarkably, at room temperature, the axially elongated Jahn-Teller axis in 2-dcm-hexane is poorly defined but becomes clearer at low temperature after the phase transition. Magnetic susceptibility measurements of 1-4 reveal that only 3 and 4 show slow relaxation of magnetization with Δeff/kB = 27.9 and 20.7 K, implying that the benzyl group is important for observing single-molecule magnet (SMM) properties. Theoretical calculations demonstrate that the alkyl group subtly influences the orbital levels and therefore very likely the observed SMM properties.

A new S = 2 kagomé lattice compound with ferromagnetic behaviors

A new compound NaMn3(SeO3)2(HSeO3)6 was obtained by a conventional hydrothermal method. This compound crystallizes in a trigonal system with space group R-3, exhibiting a typical kagomé structure, where the kagomé layers are composed of [MnO6] octahedra linked by [SeO3] groups. Magnetic susceptibility measurements confirm that this compound exhibits a ferromagnetic transition at ∼13 K, as further confirmed by the heat capacity data. The magnetic entropy was estimated, indicating that the system may release almost the entire entropy at low temperature.

Structure and magnetism of DyIII2 based triple-stranded helicates derived from dinucleating Schiff base ligands

We report herein the synthesis of three dinuclear DyIII helicates, [DyIII2(H2LR)3](NO3)3·xH2O (1–3, R = Me, Cl, Br), by reacting Dy(NO3)3·5H2O and three closely related Schiff bases derived from 3-Hydroxy-2-naphthohydrazide and three different 2,6-diformylphenols. Single crystal X-ray structural characterization revealed that all these complexes are isostructural and composed of complex cations of general formula [DyIII2(H2LR)3]3+, in which three monoanionic Schiff base ligands are wrapped around two DyIII centers, leading to triple-stranded helical structures. Notably, the configuration of monoanionic H2LR ligands imparts a coordination-induced chirality on individual complex cation, and the presence of equivalent amounts of enantiopure Λ and Δ complex cations made the solid products as racemic mixtures, crystalizing in the centrosymmetrical space groups. Variable-temperature magnetic susceptibility measurements have been performed in the temperature range 2 − 300 K for a representative complex 2, and AC susceptibility studies further disclose the slow relaxation of magnetization in 2, characteristics for single-molecule magnets.