Interaction Of Mn Research Articles

First-principles study of antisite defects effect on electronic and magnetic properties of Mn2+xCo1−xGa

The electronic structures and magnetic properties are reported for Mn2+xCo1−xGa (x=0.0, 0.25, 0.5) and Mn2.25Co0.75Ga with antisite defects (AS) using first-principles density functional theory within the generalized gradient approximation (GGA) schemes. Electronic band structure calculations indicate that the perfect Mn2CoGa is half-metallic and the half-metallic character is preserved for x=0.25 and x=0.5. AS defects of type(i) can maintain the half-metallic while AS defects of type(ii) are found to destroy the half-metallic and show metallic behavior. Based on the magnetic property calculations, the experimentally observed reduction of the magnetic moment mainly arises from weaker magnetic interactions of Mn and Co for higher Mn concentrations and the magnetic interactions are further weakening in the AS defect models.

Ferrimagnetism up to 200 K in Ti-rich double perovskites ACu3Ti4−xMnxO12: Role of double exchange mechanism

We report the striking switching of the antiferromagnetic ground state of copper-based double perovskites (Ca/La2/3)Cu3Ti4O12 to the ferrimagnetic state by introduction of small amounts of Mn on Ti-sites. CaCu3Ti3MnO12, La2/3Cu3Ti3.5Mn0.5O12, LaCu3Ti3MnO12, and LaCu3Ti2Mn2O12 were synthesized at normal pressure. These Ti-rich oxides are ferrimagnetic despite their strong magnetic dilution. The 200 K ferrimagnet LaCu3Ti2Mn2O12 exhibits intrinsic magnetoresistance, maximum at TC, which is unique in all the series of double distorted perovskites actually known. These properties are discussed in terms of strong antiferromagnetic superexchange Cu–O–Mn interactions. The role of double exchange in the properties of the mixed valent oxide LaCu3Ti2Mn2O12 is discussed.

Interaction of Mn with reducible CeO2(1 1 1) thin films

The structure and interaction of Mn/ceria interfaces were investigated under ultrahigh vacuum conditions with X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) techniques. Mn was deposited on well-ordered reducible CeO2(111) thin films by thermal evaporation at room temperature. Deposition of Mn on both oxidized and reduced ceria surfaces can form the mixed Mn–Ce oxide at the interface. XPS data indicate that Ce4+ is partially reduced to Ce3+, while Mn is formally in the +2 oxidation state. STM results show the formation of two-dimensional manganese oxide features on ceria, which is consistent with the thermodynamics data. Our study demonstrates that Mn can modify both electronic and structural properties of ceria.

Addition of Mn to Ge quantum dot surfaces—interaction with the Ge QD {105} facet and the Ge(001) wetting layer

The interaction of Mn with Ge quantum dots (QD), which are bounded by {105} facets, and the strained Ge wetting layer (WL), terminated by a (001) surface, is investigated with scanning tunneling microscopy (STM). These surfaces constitute the growth surfaces in the growth of Mn-doped QDs. Mn is deposited on the Ge QD and WL surface in sub-monolayer concentrations, and subsequently annealed up to a temperature of 400 ° C. The changes in bonding and surface topography are measured with STM during the annealing process. Mn forms flat islands on the Ge{105} facet, whose shape and position are guided by the rebonded step reconstruction of the facet. Voltage-dependent STM images reflect the Mn-island interaction with the empty and filled states of the Ge{105} reconstruction. Scanning tunneling spectra (STS) of the Ge{105} facet and as-deposited Mn-islands show a bandgap of 0.8 eV, and the Mn-island spectra are characterized by an additional empty state at about 1.4 eV. A statistical analysis of Mn-island shape and position on the QD yields a slight preference for edge positions, whereas the QD strain field does not impact Mn-island position. However, the formation of ultra-small Mn-clusters dominates on the Ge(001) WL, which is in contrast to Mn interaction with unstrained Ge(001) surfaces. Annealing to T < 160 °C leaves the Mn-clusters on the WL unchanged, while the Mn-islands on the Ge{105} facet undergo first a ripening process, followed by a volume gain which can be attributed to the onset of intermixing with Ge. This development is supported by the statistical analysis of island volume, size and size distribution. Increasing the annealing temperature to 220° and finally 375 ° C leads to a rapid increase in the Mn-surface diffusion, as evidenced by the formation of larger, nanometer size clusters, which are identified as germanide Mn5Ge3 from a mass balance analysis. This reaction is accompanied by the disappearance of the original Mn-surface structures and de-wetting of Mn is complete. This study unravels the details of Mn–Ge interactions, and demonstrates the role of surface diffusion as a determinant in the growth of Mn-doped Ge materials. Surface doping of Ge-nanostructures at lower temperatures could provide a pathway to control magnetism in the Mn–Ge system.

Two polyoxometalate-based coordination polymers constructed from Mn(II)-4,4′-bipyridine-N,N′-dioxide building blocks and Keggin-type clusters: Syntheses, crystal structures and spectral properties

Two polyoxometalate-based coordination polymers {[Mn2(dpdo)4(H2O)6](GeMo12O40)(H2O)4}n (1) and {[Mn2(dpdo)4(H2O)6](GeW12O40)(H2O)3}n (2) (dpdo=4,4′-bipyridine-N,N′-dioxide) have been synthesized and characterized by IR, elemental analysis, XRPD, TG technique and X-ray crystallography. The polymers 1 and 2 are basically isostructural and feature a 3D supramolecular framework decorated with Keggin-type polyanion clusters based on one-dimension polymeric chains, which formed through the coordination interaction of Mn(II) and dpdo. The luminescent properties of the polymers were investigated in the solid state at room temperature.

ChemInform Abstract: Ni—Mn—X Heusler Materials

AbstractReview: X: Al, Ga, In; 45 refs.

Interaction Modes and Absolute Affinities of α‐Amino Acids for Mn2+: A Comprehensive Picture

Manganese is involved as a cofactor in the activation of numerous enzymes as well as the oxygen-evolving complex of photosystem II. Full understanding of the role played by the Mn(2+) ion requires detailed knowledge of the interaction modes and energies of manganese with its various environments, a knowledge that is far from complete. To bring detailed insight into the local interactions of Mn in metallopeptides and proteins, theoretical studies employing first-principles quantum mechanical calculations are carried out on [Mn-amino acid](2+) complexes involving all 20 natural α-amino acids (AAs). Detailed investigation of [Mn-serine](2+), [Mn-cysteine](2+), [Mn-phenylalanine](2+), [Mn-tyrosine](2+), and [Mn-tryptophan](2+) indicates that with an electron-rich side chain, the most stable species involves interaction of Mn(2+) with carbonyl oxygen, amino nitrogen, and an electron-rich section of the side chain of the AA in its canonical form. This is in sharp contrast with aliphatic side chains for which a salt bridge is formed. For aromatic AAs, complexation to manganese leads to partial oxidation as well as aromaticity reduction. Despite multisite binding, AAs do not generate strong enough ligand fields to switch the metal to a low- or even intermediate-spin ground state. The affinities of Mn(2+) for all AAs are reported at the B3LYP and CCSD(T) levels of theory, thereby providing the first complete series of affinities for a divalent metal ion. The trends are compared with those of other cations for which affinities of all AAs have been previously obtained.

Electrical detection of spin reorientation transition in ferromagnetic La0.4Sm0.3Sr0.3MnO3

Field-cooled magnetization of La0.4Sm0.3Sr0.3MnO3 samples shows an anomalous maximum at a temperature T* = 45 K within the ferromagnetic state, which is suggested to spin reorientation transition of the Mn sublattice aided by antiferromagnetic Sm(4f)-Mn(3d) interaction. While dc resistivity does not show any specific feature at T*, ac electrical impedance shows anomalous features at both T* and at the ferromagnetic transition temperature even in the absence of an external magnetic field. Our results indicate that ac electrical transport can be used to detect multiple magnetic phase transitions whose impact on the dc electrical transport is either weak or masked completely.

Structural Acid–Base Chemistry in the Metallic State: How μ3-Neutralization Drives Interfaces and Helices in Ti21Mn25

Intermetallic phases remain a large class of compounds whose vast structural diversity is unaccounted for by chemical theory. A recent resurgence of interest in intermetallics, due to their potential in such applications as catalysis and thermoelectricity, has intensified the need for models connecting their compositions to their structures and stability. In this Article, we illustrate how the μ3-acidity model, an extension of the acid/base concept based on the Method of Moments, offers intuitive explanations for puzzling structural progressions occurring in intermetallics formed between transition metals. Simple CsCl-type structures are frequently observed for phases with near 1:1 ratios of transition metals. However, in two compounds, TiCu and Ti21Mn25, structures are adopted which deviate from this norm. μ3-Acidity analysis shows that the formation of CsCl-type phases in these exceptional systems would yield an imbalance in the acid/base strength pairing, resulting in overneutralization of the weaker partner and thus instability. Intriguing geometrical features emerge in response, which serve to improve the neutralization of the constituent elements. In both TiCu and Ti21Mn25, part of the structure shields weaker acids or bases from their stronger partners by enhancing homoatomic bonding in the sublattice of the weaker acid or base. In TiCu, this protection is accomplished by developing doubled layers of Ti atoms to reduce their heteroatomic contacts. In Ti21Mn25 the structural response is more extreme: Ti-poor TiMn2 domains are formed to guard Mn from the Ti atoms, while the remaining Ti segregates to regions between the TiMn2 domains. The geometrical details of this arrangement fine-tune the acid/base interactions for an even greater level of stability. The most striking of these occurs in the Ti-rich region, where a paucity of Mn neighbors leads to difficulty in achieving strong neutralization. The Ti atoms arrange themselves in helical tubes, maximizing the surface area for Ti-Mn interactions. Through these examples, we show how the μ3-acidity model provides simple explanations for some of the beautiful structural motifs observed in intermetallic crystals. The foundation of the model in the Method of Moments makes it applicable to a variety of other contexts, including glasses, defects, and nanostructured surfaces.

DNA binding and nuclease activity of a water-soluble sulfonated manganese(III) corrole

The interaction of a water-soluble sulfonated Mn(III) corrole Mn(tpfc)(SO3Na)2 [tpfc = 5,10,15-tris(pentafluorophenyl)corrole] with calf thymus DNA (ct-DNA) has been studied by spectroscopic methods, and the nuclease activity of this complex has also been examined by agarose gel electrophoresis. Mn(tpfc)(SO3Na)2 exhibits weak aggregation tendency in buffer solution and can bind to ct-DNA via an outside binding mode with a binding constant of 1.25 × 104 M−1. The observed increase in Stern–Volmer quenching constant with increasing temperature indicates that the competition of the manganese corrole and ethidium bromide with ct-DNA is a dynamic process. Moreover, the manganese corrole displays good chemical nuclease activity in the presence of hydrogen peroxide via oxidative cleavage of DNA.

First-principles study of the crystal structures and electronic properties of LaNi4.5M0.5 (M = Al, Mn, Fe, Co)

The structure, stability and electronic properties of the different B-site partial substituted derivatives LaNi4.5M0.5 (M=Al, Mn, Fe, Co) have been investigated by means of the density functional theory using the full-potential linearized augmented plane wave (FLAPW) method with the generalized gradient approximation (GGA). The optimized results indicate that all of Al, Mn, Fe, Co atoms prefer to substitute Ni atoms in the 3g sites. Due to the different radius of elements, the cell volume would increase with the doping Ni (3g) atoms. And the sequence of volume is LaNi4.5Al0.5>LaNi4.5Mn0.5>LaNi4.5Fe0.5>LaNi4.5Co0.5>LaNi5, which is in agreement with the experimental result. The calculated data of formation and cohesive energies indicate that LaNi4.5Mn0.5 has the stablest structure among five alloys. Based on the analysis of the density of states and charge density, the interactions of Mn–Ni, Fe–Ni, Co–Ni atoms are greatly stronger compared to the Ni–Ni interaction, while the interaction of Al–Ni atoms is weakened. Based on the formation energy of hydrogen atom in LaNi4.5M0.5H0.5, the sequence of bounding hydrogen atoms is LaNi4.5Mn0.5>LaNi4.5Fe0.5>LaNi4.5Co0.5>LaNi4.5Al0.5>LaNi5.

Mesostructured Co–Ce–Zr–Mn–O composite as a potential catalyst for efficient removal of carbon monoxide from hydrogen-rich stream

Mesostructured CoxCe0.85Zr0.15MnyOe composites were firstly prepared by a simple one-pot surfactant-assisted co-precipitation (SACP) method and then employed to catalyze the CO preferential oxidation (CO PROX) reaction in an H2-rich stream. Effects of the Co and Mn contents (x and y, respectively) in the formula, as well as the presence of H2O and CO2 in feed were investigated. The as-synthesized Co0.4Ce0.85Zr0.15Mn0.10Oe catalyst showed excellent catalytic performance in the CO PROX reaction: 100% CO conversion could be observed in a wide temperature range of 140–200 °C; even in the simulated syngas, the almost complete CO removal could still be achieved at 175–225 °C; no obvious change in both CO conversion and CO2 selectivity over the catalyst took place during the CO PROX process with simulated syngas as feed. N2 physisorption (BET), temperature-programmed reduction (TPR), X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopic (XPS) characterization techniques were employed to reveal the relationship between the catalyst nature and catalytic performance. The outstanding catalytic performance in CO PROX reaction was remarkably dependent on a larger specific surface area, more reducible Co3+ and the high dispersity of the Co3O4, affected by the Co and Mn contents through strong Co–Ce–Zr–Mn interactions. The mesostructured Co0.4Ce0.85Zr0.15Mn0.10Oe catalyst prepared by the simple one-pot SACP protocol can be a promising candidate for CO PROX reaction in excess H2.

Perovskite‐like Mn2O3: A Path to New Manganites

Among complex oxides, perovskite-based manganites play a special role in science and technology. They demonstrate colossal magnetoresistance, and can be employed as memory and resistive switching elements or multiferroics. The perovskite structure ABO3 has two different cation sites: B-sites that are octahedrally coordinated by oxygen, and cuboctahedrally-coordinated (often heavily distorted) Asites. The magnetic and transport properties of perovskite manganites are largely determined by the Mn O Mn interactions in the perovskite framework of corner-sharing MnO6 octahedra. Although the A cations do not directly participate in these interactions, they control the Mn valence and the geometry of the Mn O Mn bonds. Complex phenomena, such as charge and orbital ordering, often accompany chemical substitutions on the A-site. Requirements on formal charge and ionic radius are usually different for cations adopting theA or B positions and prevent A/B mixing. Small and often highly charged transition-metal B-cations are unfavorable for the large 12coordinated A-site. Partial filling of the A-position with transition metals is, nevertheless, possible in a unique class of A-site ordered perovskites AA’3B4O12 (where A= alkali, alkali-earth, rare-earth, Pb, or Bi cations, A’=Cu or Mn, and B= transition metals, Ga, Ge, Sb, or Sn). A key ingredient of such compounds is the A’ cation that should be prone to a first-order Jahn–Teller effect (Cu or Mn). An oxygen environment suitable for such transition-metal cations at the A’ position is created by the aaa octahedral tilt system (in Glazer s notation) with a notably large magnitude of the tilt (for example, in CaCu3Ti4O12 the Ti O Ti bond angle is only 140.78). The tilt creates a square-planar anion coordination, favorable for Jahn–Teller-active A’ cations. The ap= ffiffiffi

Efficient cobalt–manganese oxide catalyst deposited on modified AC with unprecedented catalytic performance in CO preferential oxidation

In comparison to the supported cobalt–cerium oxide catalyst on AC, we first fabricated a novel and highly-efficient cobalt–manganese non-precious metal catalyst deposited on modified AC with unprecedented catalytic activity and extremely wide temperature-operation window for CO complete removal from an H 2 -rich stream, which resulted from the strong interaction of finely dispersed cobalt–manganese primarily confirmed by various characterization results. The high catalytic activity and extremely broad temperature-operation window allow the developed catalyst to possess a fascinating perspective for large-scale application in industry. ► A novel and highly-efficient Co Mn/AC–DP CO PROX catalyst was first fabricated. ► It shows much high activity and extremely wide temp-window for 100% CO removal. ► High activity is ascribed to dispersity, crystallinity and interaction of Co Mn. ► The physiochemical properties are strongly affected by diverse supporting methods. ► Unprecedented properties allow it to possess fascinating perspective in industry.

Chemical and structural investigations of the incorporation of metal manganese into ruthenium thin films for use as copper diffusion barrier layers

The incorporation of manganese into a 3 nm ruthenium thin-film is presented as a potential mechanism to improve its performance as a copper diffusion barrier. Manganese (∼1 nm) was deposited on an atomic layer deposited Ru film, and the Mn/Ru/SiO2 structure was subsequently thermally annealed. X-ray photoelectron spectroscopy studies reveal the chemical interaction of Mn with the SiO2 substrate to form manganese-silicate (MnSiO3), implying the migration of the metal through the Ru film. Electron energy loss spectroscopy line profile measurements of the intensity of the Mn signal across the Ru film confirm the presence of Mn at the Ru/SiO2 interface.

Interactions of Mn2+ with a non-self-complementary Z-type DNA duplex.

Crystal structures of the hexanucleotide d(CACGCG)·d(CGCGTG) were determined in two crystal lattices when different concentrations of the counterion Mn2+ were used in crystallization. The availability of Mn2+ during the crystallization process appears to play an important role in inducing different crystal packings that lead to crystals belonging to the two space groups P2(1) and P6(5). Analysis of the molecular interactions of Mn2+ with the Z-form duplexes shows direct coordination to the purine residues G and A.

Competing interactions at the interface between ferromagnetic oxides revealed by spin-polarized neutron reflectometry

We have investigated the magnetization profiles in superlattices composed of the two ferromagnets La${}_{0.7}$Sr${}_{0.3}$MnO${}_{3}$ and SrRuO${}_{3}$ using spin-polarized neutron reflectometry. In combination with magnetometry, the neutron data indicate a noncollinear spin configuration where orientation of the Ru moments changes from in plane at the interface to out of plane deep inside the SrRuO${}_{3}$ layers. The spin structure originates in a competition between antiferromagnetic exchange interactions of Mn and Ru moments across the interface, and the magnetocrystalline anisotropy of the Ru moments, and it is closely related to the ``exchange spring'' structures previously observed in multilayers composed of ferromagnetic elements and alloys.

Conversion of syngas to C2+ oxygenates over Rh-based/SiO2 catalyst: The promoting effect of Fe

The effect of Fe promoter on the catalytic properties of Rh–Mn–Li/SiO2 catalyst for CO hydrogenation was investigated. The catalysts were comprehensively characterized by means of X-ray diffraction (XRD), N2 adsorption–desorption, temperature programmed reduction (TPR), temperature programmed desorption (TPD), temperature programmed surface reaction (TPSR), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Activity testing results showed that low loading of Fe (≤0.1wt%) improved the reactivity and yield of C2+ oxygenates; however, the opposite effect appeared at the high values of Fe (>0.1wt%). Characterization results suggested that the addition of Fe strengthened the Rh–Mn interaction and increased the desorption/transformation rate of adsorbed CO, which could be responsible for the increase of CO conversion. But on the other hand, the existence of Fe might deposit over the Rh surface, and decreased the number of active sites, resulting in the decrease of CO conversion when the Fe amount was excessive. The selectivity to C2+ oxygenates varied inversely with the reducibility of Rh oxide species. Moreover, it is proposed that the transformation of dicarbonyl Rh+(CO)2 into H–Rh–CO is favorable for the formation of C2+ oxygenates, and the hydrogenation ability of Fe can increase the hydrogenation of acetaldehyde to ethanol.

Utilization of Phosphinoamide Ligands in Homobimetallic Fe and Mn Complexes: The Effect of Disparate Coordination Environments on Metal–Metal Interactions and Magnetic and Redox Properties

A series of homobimetallic phosphinoamide-bridged diiron and dimanganese complexes in which the two metals maintain different coordination environments have been synthesized. Systematic variation of the steric and electronic properties of the phosphinoamide phosphorus and nitrogen substituents leads to structurally different complexes. Reaction of [(i)PrNKPPh(2)] (1) with MCl(2) (M = Mn, Fe) affords the phosphinoamide-bridged bimetallic complexes [Mn((i)PrNPPh(2))(3)Mn((i)PrNPPh(2))] (3) and [Fe((i)PrNPPh(2))(3)Fe((i)PrNPPh(2))] (4). Complexes 3 and 4 are iso-structural, with one metal center preferentially binding to the three amide ligands in a trigonal planar arrangement while the second metal center is ligated by three phosphine donors. A fourth phosphinoamide ligand caps the tetrahedral coordination sphere of the phosphine-ligated metal center. Mössbauer spectroscopy of complex 4 suggests that the metals in these complexes are best described as Fe(II) centers. In contrast, treatment of MnCl(2) or FeI(2) with [MesNKP(i)Pr(2)] (2) leads to the formation of the halide-bridged species [(THF)Mn(μ-Cl)(MesNP(i)Pr(2))(2)Mn(MesNP(i)Pr(2))] (5) and [(THF)Fe(μ-I)(MesNP(i)Pr(2))(2)FeI (7), respectively. Utilization of FeCl(2) in place of FeI(2), however, leads exclusively to the C(3)-symmetric complex [Fe(MesNP(i)Pr(2))(3)FeCl] (6), structurally similar to 4 but with a halide bound to the phosphine-ligated Fe center. The Mössbauer spectrum of 6 is also consistent with high spin Fe(II) centers. Thus, in the case of the [(i)PrNPPh(2)](-) and [MesNP(i)Pr(2)](-) ligands, zwitterionic complexes with the two metals in disparate coordination environments are preferentially formed. In the case of the more electron-rich ligand [(i)PrNP(i)Pr(2)](-), complexes with a 2:1 mixed donor ligand arrangement, in which one of the ligand arms has reversed orientation relative to the previous examples, are formed exclusively when [(i)PrNLiP(i)Pr(2)] (generated in situ) is treated with MCl(2) (M = Mn, Fe): (THF)(3)LiCl[Mn(N(i)PrP(i)Pr(2))(2)(P(i)Pr(2)N(i)Pr)MnCl] (8) and [Fe(N(i)PrP(i)Pr(2))(2)(P(i)Pr(2)N(i)Pr)FeCl] (9). Bimetallic complexes 3-9 have been structurally characterized using X-ray crystallography, revealing Fe-Fe interatomic distances indicative of metal-metal bonding in complexes 6 and 9 (and perhaps 4, to a lesser extent). All of the complexes appear to adopt high spin electron configurations, and magnetic measurements indicate significant antiferromagnetic interactions in Mn(2) complexes 5 and 8 and no discernible magnetic superexchange in Fe(2) complex 4. The redox behavior of complexes 3-9 has also been investigated using cyclic voltammetry, and theoretical investigations (DFT) were performed to gain insight into the metal-metal interactions in these unique asymmetric complexes.

First-principles DFT + U studies of the atomic, electronic, and magnetic structure of α-MnO2 (cryptomelane)

Density functional theory DFT+U calculations are used to investigate α-MnO2, a structure containing a framework of corner and edge sharing MnO6 octahedra with tunnels in between. Placing K+ ions into the tunnels stabilizes α-MnO2 with respect to the rutile-structure β-MnO2 phase, in agreement with experiment. The computed magnetic structure has antiferromagnetic (ferromagnetic) Mn–Mn interactions between corner-sharing (edge-sharing) octahedra. Pure α-MnO2 is found to be a semiconductor with an indirect band gap of 1.3eV. Water and related hydrides (OH−; H3O+) can also be accommodated in the tunnels; the equilibrium K–O distance increases with increasing oxygen hydride charge.