Neighboring Mn Ions Research Articles

Two Cd(Ⅱ)/Mn(Ⅱ) complexes based on multinuclear metal clusters for Fe(Ⅲ) and Cr(Ⅵ) fluorescence detection and magnetic properties

Two novel complexes, {[Cd3(L)2(H2O)2]·(H2O)4}n (1) and {[Mn(HL)(H2O)2]·(H2O)}n (2), which are synthesized by the reaction of 3-(2, 4-dicarboxyphenyl)-4-carboxypyridine ligand with cadmium and manganese metal ions under the solvothermal method. The complex 1 is a 3D framework based upon trinuclear [Cd3(μ2-COO)4(μ1-COO)4(N)2] SBUs, and the complex 2 is a one-dimensional metal oxygen chain based upon binuclear [Mn2(μ2-COO)2(μ1-COO)2(N)2] SBUs. The solid fluorescence analysis of complex 1 reveals that the emission peak of 451 nm when its excitation peak is 336 nm. The fluorescence detection experiments of complex 1 showed that Fe3+, Cr2O72− and CrO42− can effectively to be detected. Furthermore, their limits of detection are 1.47 × 10−3 M, 1.31 × 10−3 M and 1.25 × 10−3 M, respectively. It has good recovery properties as a potential multifunctional fluorescence sensor. Besides, the quenching mechanism of fluorescence sensing is also discussed. In addition, the magnetic studies of complex 2 show strong antiferromagnetic interactions between its neighboring Mn(II) ions.

Tuning Discharge Behavior of Hollandite α-MnO2 in Hydrated Zinc Ion Battery by Transition Metal Substitution

The tunnel-type hollandite α-MnO2 is a promising cathode material for rechargeable aqueous zinc-ion batteries (ZIBs) due to its low cost in synthesis and high energy density. However, irreversible structural degradation upon continuous cycling prevents the cathode from being utilized commercially. Herein, density functional theory (DFT) was utilized to conduct a systematic study on tuning the behavior of α-MnO2 by substituting the Mn ions on the tunnel wall with a transition metal (V or Cr) during the H+-/Zn2+-intercalation in hydrated ZIB. Our study revealed that both substituents aid cyclability and capacity retention with Cr outperforming V. In term of discharge voltage, only the Cr-substitution displays clear promotion at the early stage of discharge. The superior performance of substituted Cr4+ comes from its unique atomic and electronic structures. Upon discharge, it can be reduced to Cr3+ more readily than Mn4+ and thereby limits the formation of unstable Mn3+ or Mn2+ centers; the formed Cr3+ is more stable than Mn3+ and Mn2+ from the reduction of Mn4+; and Cr3+ can also greatly stabilize the neighboring Mn ions. This study highlights the significant tuning effect of transition metal substitution on the electrochemical and physical performance of α-MnO2 as a cathode in hydrated ZIBs.

Formation of oxygen vacancies in Li-rich Mn-based cathode material Li<sub>1.167</sub>Ni<sub>0.167</sub>Co<sub>0.167</sub>Mn<sub>0.5</sub>O<sub>2</sub>

Using the first-principles method based on the density functional theory, the oxygen vacancy formations in the lithium-rich manganese-based ternary cathode material Li<sub>1.167</sub>Ni<sub>0.167</sub>Co<sub>0.167</sub>Mn<sub>0.5</sub>O<sub>2</sub> are calculated. The changes of oxygen vacancy formation energy with temperature, oxygen partial pressure and point defects in the material are discussed, meanwhile, the effect of oxygen vacancies on the capacity is also discussed. The calculation results show that the increase of temperature and the decrease of oxygen partial pressure can lead the formation energy of an oxygen vacancy to decline. For the charged oxygen vacancies (<inline-formula><tex-math id="M4">\begin{document}$ {\mathrm{V}}_{\mathrm{O}}^{+1} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220274_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220274_M4.png"/></alternatives></inline-formula>, <inline-formula><tex-math id="M5">\begin{document}$ {\mathrm{V}}_{\mathrm{O}}^{+2} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220274_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220274_M5.png"/></alternatives></inline-formula>), the formation energy of an O-vacancy increases with Fermi level increasing. It is also found that the presence of an oxygen vacancy will trigger off a very local charge density redistributions, mainly around the neighboring Mn ions next to the O-vacancy. Furthermore, the effects of point defects, including cation vacancies and substitutional defects in the vicinity of the O-vacancy, on the formation energy of O-vacancy are also calculated. The results show that the presence of Mn vacancy near the O-vacancy is beneficial to the formation of the O-vacancy. In addition, the formation of oxygen vacancy is suppressed when the Mn atoms near the O-vacancy are substituted by the Mo or Fe atoms.

S3 State Models of Nature's Water Oxidizing Complex: Analysis of Bonding and Magnetic Exchange Pathways, Assessment of Experimental Electron Paramagnetic Resonance Data, and Implications for the Water Oxidation Mechanism.

Broken symmetry density functional theory (BS-DFT) calculations on large models of Nature's water oxidizing complex (WOC) are used to investigate the electronic structure and associated magnetic interactions of this key intermediate state. The electronic origins of the ferromagnetic and antiferromagnetic couplings between neighboring Mn ions are investigated and illustrated by using corresponding orbital transformations. Protonation of the O4 and/or O6 atoms leads to large variation in the distribution of spin around the complex with associated changes in its magnetic resonance properties. Models for Sr2+ exchange and methanol addition indicate minor perturbations reflected in slightly altered spin projection coefficients for the Mn1 and Mn2 ions. These are shown to account for the observed changes observed experimentally via electron paramagnetic resonance methods and suggest a reinterpretation of the experimental findings. By comparison with experimental determinations, we show that the spin projections and resulting calculated 55Mn hyperfine couplings support the open cubane form of an oxo (O5)-hydroxo (O6) cluster in all cases with no need to invoke a closed cubane intermediate. The implications of these findings for the water oxidation mechanism are discussed.

A new approach to prepare the Mn(II)-based magnetic refrigerant through incorporating diamagnetic Cd(II) ion

One one-dimensional Cd(II)-Mn(II) heterometallic coordination polymer with 2-methylenesuccinate (MSA2−), [CdMn(MSA)2(H2O)5]·3H2O (1), has been successfully prepared and characterized. Single crystal X-ray diffraction analysis reveals that 1 crystallizes in monoclinic P21/c space group and has a 1D chain structure. The introduction of diamagnetic Cd(II) ion helps separate the neighboring Mn(II) ions well to prevent the strong Mn(II)-Mn(II) antiferromagnetic interaction. Magnetic studies show that 1 has a great cryogenic magnetocaloric effect with the maximum − ΔSm value of 21.93 J K−1 kg−1 at 2 K and ΔH = 7 T. This is the first example for Cd(II)-Mn(II) based molecule magnetic refrigerant.

Investigation of non-local screening in K-edge XANES for Pr0.67Sr0.33MnO3 under high pressure

The electronic excitation of 3d transition metal oxide depends on the hybridization between orbitals of different ions, and is related to the materials properties. In this work, we systematically study the effect of hydrostatic pressure up to ∼20 GPa on the crystal structure and electronic structure of Pr0.67Sr0.33MnO3 powder, using Mn K-edge X-ray absorption near edge structure and X-ray diffraction at room temperature. With the increase of pressure, the energy position of non-local screened feature moves towards feature without screening due to the enhanced transition energy; however, the intensity (probability) of non-local screened feature increases with the pressure. Further study suggests that the pressure-induced antiferromagnetic phase, affecting hybridization between neighboring Mn ions with spin sensitivity, increase the probability of non-local charge transfer and corresponding intensity of non-local screened feature. The spin-sensitivity of non-local screening may be a useful parameter for characterization of material properties.

Orbital- and spin-order sensitive nonlocal screening in Mn 2p X-ray photoemission of La1−xSrxMnO3

The Mn 2p X-ray photoemission spectra (XPS) of LaMnO3 (LMO) and hole-doped La0.7Sr0.3MnO3 (LSMO) are investigated using a dp model simulating Mn 3d and O 2p electrons under the perovskite-type crystal structure. The observed 2p XPS features, especially the low-binding-energy structure (LBES) of the main line, are reproduced well using an impurity Anderson model optimized from the dp model within the dynamical mean-field approximation. The LBES in both compounds is due to the nonlocal screening (NLS) between the neighboring Mn ions in the final state, but the screening character is quite different: The NLS in LSMO directly reflects the character of the ferromagnetic metal, while that in undoped LMO the C-type orbital order between and orbitals in the ab-plane. We emphasize the directive nature of the NLS in the orbital order system, which can be a sensitive probe to the order pattern.

Anomalous magnetic behavior for Mn-site doped La0.7Ca0.3MnO3: internal magnetic interactions and extrinsic inhomogeneity

Magnetic properties of Mn-site doped La0.7Ca0.3Mn0.94TM0.06O3+Δ (TM=Cu, Zn) were experimentally and theoretically studied. The low-temperature magnetization and magnetic phase transition temperature TC of the samples combining with simulations of 2D doped Ising model suggest that Cu2+ ions have an antiferromagnetic interaction with their nearest neighboring Mn ions. Interestingly, an anomalous magnetic behavior, a “step-like” magnetic phase transition, is observed. The existence and magnitude of this step vary with different doping ions and oxygen ratio, which is experimentally suggested to be relevant to the interaction between magnetic ions and oxygen content. A superposition between two independent magnetic systems with different values of an exchange integral J well explains the anomalous magnetic phase transition, which suggests that this step-like behavior results from extrinsic inhomogeneity and negligible coupling between grains in polycrystalline.

Correlation between Mn and Ru valence states and magnetic phases inSrMn1−xRuxO3

The electronic structures of ${\mathrm{SrMn}}_{1\ensuremath{-}x}{\mathrm{Ru}}_{x}{\mathrm{O}}_{3}$ $(0\ensuremath{\le}x\ensuremath{\le}1)$ have been investigated by employing soft x-ray absorption spectroscopy (XAS) and soft x-ray magnetic circular dichroism (XMCD). Both Mn and Ru ions are nearly tetravalent $({\mathrm{Mn}}^{4+},\phantom{\rule{0.28em}{0ex}}{\mathrm{Ru}}^{4+})$ for the end members of $x=0$ $({\mathrm{SrMnO}}_{3})$ and $x=1$ $({\mathrm{SrRuO}}_{3})$. In the Ru-dilute concentration $(x\ensuremath{\le}\ensuremath{\sim}0.2)$, Ru ions are pentavalent $({\mathrm{Ru}}^{5+})$, which transform neighboring Mn ions into the trivalent ${\mathrm{Mn}}^{3+}$ states via electron charge transfer. In the intermediate substitution regime, Mn and Ru ions are in the inhomogeneously mixed-valent states $({\mathrm{Mn}}^{3}\ensuremath{-}{\mathrm{Mn}}^{4+}$ and ${\mathrm{Ru}}^{4}\ensuremath{-}{\mathrm{Ru}}^{5+})$. Finite Mn $2p$ XMCD signals are observed for $x>0$, in agreement with the ferromagnetic, spin-glass, cluster-glass ground states depending on $x$. The unoccupied Mn $3d$ and Ru $4d$ states, determined from the measured O $1s$ XAS spectra and the calculated density of states, support these findings.

Electronic structure and magnetic properties of (Mn, N)-codoped ZnO

The electronic structures and magnetic properties of (Mn, N)-codoped ZnO are investigated by using the first-principles calculations. In the ferromagnetic state, as N substitutes for the intermediate O atom of the nearest neighboring Mn ions, about 0.5 electron per Mn2+ ion transfers to the N2− ion, which leads to the high-state Mn ions (close to +2.5) and trivalent N3− ions. In an antiferromagnetic state, one electron transfers to the N2− ion from the downspin Mn2+ ion, while no electron transfer occurs for the upspin Mn2+ ion. The (Mn, N)-codoped ZnO system shows ferromagnetism, which is attributed to the hybridization between Mn 3d and N 2p orbitals.

Orbital structure and magnetic ordering in stoichiometric and doped crednerite CuMnO2

The exchange interactions and magnetic structure in layered system CuMnO${}_{2}$ (mineral crednerite) and in nonstoichiometric system Cu${}_{1.04}$Mn${}_{0.96}$O${}_{2}$, with triangular layers distorted due to orbital ordering of the Mn${}^{3+}$ ions, are studied by ab initio band-structure calculations, which were performed within the GGA + $U$ approximation. The exchange interaction parameters for the Heisenberg model within the Mn planes and between the Mn planes are estimated. We explain the observed in-plane magnetic structure by the dominant mechanism of the direct $d\text{\ensuremath{-}}d$ exchange between neighboring Mn ions. The superexchange via O ions, with 90${}^{\ensuremath{\circ}}$ Mn--O--Mn bonds, plays a less important role for the in-plane exchange. The interlayer coupling is largely dominated by one exchange path between the half-filled $3{z}^{2}\ensuremath{-}{r}^{2}$ orbitals of Mn${}^{3+}$. The change of interlayer coupling from antiferromagnetic in pure CuMnO${}_{2}$ to ferromagnetic in doped material is also explained by our calculations.

Materials synthesis and annealing-induced changes of microstructure and physical properties of one-dimensional perovskite–wurtzite oxide heterostructures

RF sputtering at 750°C was conducted to synthesize (La,Sr)MnO3 (LSMO)-ZnO one-dimensional (1D) heterostructures on cross-linked ZnO nanostructures. The prepared LSMO-ZnO 1D heterostructures were subsequently annealed at a range of thermal annealing temperatures (800–950°C) to investigate the structural and physical properties of the 1D heterostructures. X-ray diffraction patterns show how well crystalline LSMO nanolayers formed on the ZnO nanostructures. Auger electron spectroscopy analysis shows that the constituent elements of LSMO were homogeneously distributed on the ZnO surfaces of interest. Scanning electron microscopy and transmittance electron microscopy images show that the morphology of the as-deposited 1D heterostructures consists of round LSMO tiny grains covering the ZnO nanostructures; however, the high-temperature annealed samples are transformed to feature relatively large and oval grains. The high-temperature annealing procedure in oxygen-rich ambient conditions enhanced the saturation magnetization and Curie temperature of the LSMO-ZnO 1D heterostructures. This is associated with an enhancement of the exchange interaction between two neighboring Mn ions through the 2p oxygen orbital in the LSMO nanolayers with reduced crystal defects after high-temperature annealing.

A simple mathematical model for manganese oxide-coated montmorillonite as a catalyst for water oxidation: from nano to macro sized manganese oxide

Here, we propose a mathematical model that gives a good fit to the experimental data for water oxidation by Mn oxide-coated montmorillonite with different Mn content. Our data show that the water oxidation may progress by cooperation among only neighbor Mn ions on montmorillonite. It is a promising model for finding more about the mechanism of multi-electron reactions.

Origin of the Giant Negative Thermal Expansion inMn3(Cu0.5Ge0.5)N

The giant negative thermal expansion in the Ge-doped antiperovskite Mn3CuN compound is theoretically studied by using the first principles calculations. We propose that such a negative thermal expansion property is essentially attributed to the magnetic phase transition, rather than to the lattice vibration of the Ge-doped compound. Furthermore, we found that the doped Ge atoms in the compound significantly enhance the antiferromagnetic couplings between the nearest neighboring Mn ions, which effectively stabilizes the magnetic ground states. In addition, the nature of the temperature-dependent changes in the volume of the Ge-doped compound was revealed.

Electronic States of Metal Ions Incorporated in Mn-DNA

It is known that DNA forms compounds with a variety of divalent metal ions, which are located between the bases of a base pair, and that the net charge transfer from the metal ions to DNA occurs only in the Fe-DNA case. However, the electronic states of the metal ions have not been well established, so far. The findings of this study suggest that the water molecules within the DNA double helix play an important role for the exchange coupling between the neighboring Mn ions and that the electronic states of the Mn ions in Mn-DNA are highly ionic on the basis of the Mn hyperfine splitting parameters in solution ESR spectra. The present result should be highly helpful in further investigation of engineering DNA so that it can be used for nanowires.

Synthetic manganese–calcium oxides mimic the water-oxidizing complex of photosynthesis functionally and structurally

In the worldwide search for sustainable energy technologies, water oxidation by abundant low-cost materials is of key importance. In nature, this process is efficiently catalyzed by an intricate manganese–calcium (Mn4Ca) complex bound to the proteins of photosystem II (PSII). Recently synthetic manganese–calcium oxides were found to be active catalysts of water oxidation but at the atomic level their structure has remained elusive. To investigate these amorphous catalysts, extended-range X-ray absorption spectroscopy (XAS) at the K-edges of both manganese and calcium was performed. The XAS results reveal striking similarities between the synthetic material and the natural Mn4Ca complex. The oxidation state of manganese in the active oxides was found to be close to +4, but MnIII ions are present as well at a level of about 20%. Neighboring Mn ions are extensively interconnected by two bridging oxygens, a characteristic feature of layered manganese oxides. However, the oxides do not exhibit long-range order, as opposed to canonical, but catalytically inactive MnIII- or MnIV-oxides. Two different Ca-containing motifs were identified. One of them results in the formation of Mn3CaO4 cubes, as also proposed for the natural paragon in PSII. Other calcium ions likely interconnect oxide-layer fragments. We conclude that these readily synthesized manganese–calcium oxides are the closest structural and functional analogs to the native PSII catalyst found so far. Evolutionary implications are considered. From the differences to inactive manganese oxides, we infer structural features facilitating the catalysis of water oxidation in both the protein-bound Mn4Ca complex of PSII and in the synthetic oxides.

Glycine-Templated Manganese Sulfate with New Topology and Canted Antiferromagnetism

A new glycine-templated manganese(II) sulfate, (C(2)NO(2)H(5))MnSO(4) (1), has been solvothermally synthesized and characterized crystallographically and magnetically. Crystal data for 1: monoclinic, space group P2(1)/m, a = 4.8884(10) A, b = 7.8676(14) A, c = 8.0252(15) A, beta = 106.524(2) degrees , V = 295.90(10) A(3), Z = 2. The glycine bridges Mn(II) ions in mu(2) mode and sulfate in eta(3),mu(4) mode. Along the b direction, the neighboring Mn(II) ions were bridged to each other by two sulfate ions and one glycine ligand to form a triple-stranded braid. The adjacent braids were connected via the sulfate ions to give a two-dimensional framework with a novel binodal 4,6-connected (3(2);4(2);5(2))(3(4);4(4);5(4);6(3)) topology. The compound exhibits a spin-canted antiferromagnetic behavior with a weak ferromagnetic transition below 9 K, and the estimated canting angle is 0.13 degrees.

Synthesis and crystal structure of potassium and manganese complexes of 1,2,3-triazole-4,5-dicarboxylic acid

Three coordination compounds [K(H2TDA)H2O] n (1), [K(H2TDA)(H3TDA)2H2O] n (2), and Mn2(phen)2(HTDA)2(H2O)4 (3) have been synthesized and characterized structurally by X-ray diffraction, where H3TDA = 1,2,3-triazole-4,5-dicarboxylic acid and phen = 1,10-phenanthroline. Their solid-state structures have been characterized by elemental analysis and IR spectroscopy. In 1, a 3-D (4, 8)-connected metal-organic framework has been constructed using dinuclear potassium clusters as eight-connected nodes and the ligands as four-connected nodes; it represents the fluorite topology network. Compound 2 exhibits 1-D chains along c-axis, which are connected by strong hydrogen-bond interactions in 2-D layers; the layers are further stacked via hydrogen bonds in the b-direction. In 3, two neighboring Mn(II) ions are bridged by two 1,2,3-triazole-4,5-dicarboxylic groups, forming a binuclear structure, with Mn(II) ··· Mn(II) distance of 4.356 Å, which is further linked to generate a 2-D layer structure via interdimer hydrogen bonds. The fluorescence for these compounds was investigated.

Slow Relaxation of Resistance in Manganite Perovskite Nanoconstrictions

The time decay of the surface resistance RS(t) was measured for the La0.7Sr0.3MnO3 perovskite nanocontacts obtained by break technique at liquid nitrogen. The corresponding time relaxation can be described by two-term formula: stretched exponential function and logarithmic dependence. The characteristic times τ1 and τ2 of the relaxation processes are of order of seconds and few tens of seconds, respectively. The appearance of both contributions evidences the existence of two sources of relaxation, which can be assigned to inhomogeneous changes of the angle between the magnetic moments of the neighboring Mn ions inside spin blocks (τ1) and between the spin blocks (τ2) occurring near surface of the nano-electrodes. Similar to magnetic viscosity, the dependence of resistance viscosity SR on basis current is characterized by bell-shaped curve. These results point out the important role of the structural arrangements of the Mn-ions into spin blocks on the surfaces electrodes of the nanocontact.

Crystal and magnetic structure of Cr- and Ni-substituted(La0.50Ca0.50)MnO3

The crystal and magnetic structure of(La0.50Ca0.50)(Mn1−xBx)O3 (x = 0.00, 0.03,0.08; B = Cr, Ni) has been investigated between 5 and 300 K by means of dc magnetic measurementsand neutron powder diffraction followed by Rietveld refinement. In the pristinecompound an orthorhombic to monoclinic phase transition is detected oncooling, accompanied by a CE-type antiferromagnetic (AFM) ordering arising.Ni2+ and Cr3+ substitutions have similar effects on the structural and magnetic properties of(La0.50Ca0.50)MnO3, despite the fact that these ions are characterized by different external electronicconfigurations. After substitution, the orthorhombic to monoclinic phase transitionis hindered. As a consequence, charge and orbital orderings are suppressed, asis the superexchange; double exchange takes place inducing ferromagnetic(FM) interactions. No evidence for stable magnetic interaction betweenCr3+ orNi2+ and the neighbouring Mn ions was detected. Nevertheless, in the Ni-substituted samples adetectable quantity of monoclinic phase forms during cooling, inside which AFMinteractions take place. The amount of this secondary monoclinic phase decreases onincreasing Ni substitution; the global FM magnetic moment decreases as well, due to aspin-cluster glass-type state arising. As a result a FM state is found to coexist with aspin-cluster glass-type state.