High Magnetic Moments in Manganese‐Doped Silicon Clusters

We report on the structural, electronic, and magnetic properties of manganese‐doped silicon clusters cations, Si_nMn⁺ with n=6–10, 12–14, and 16, using mass spectrometry and infrared spectroscopy in combination with density functional theory computations. This combined experimental and theoretical study allows several structures to be identified. All the exohedral Si_nMn⁺ (n=6–10) clusters are found to be substitutive derivatives of the bare Si_n+1⁺ cations, while the endohedral Si_nMn⁺ (n=12–14 and 16) clusters adopt fullerene‐like structures. The hybrid B3P86 functional is shown to be appropriate in predicting the ground electronic states of the clusters and in reproducing their infrared spectra. The clusters turn out to have high magnetic moments localized on Mn. In particular the Mn atoms in the exohedral Si_nMn⁺ (n=6–10) clusters have local magnetic moments of 4 μ_B or 6 μ_B and can be considered as magnetic copies of the silicon atoms. Opposed to other 3d transition‐metal dopants, the local magnetic moment of the Mn atom is not completely quenched when encapsulated in a silicon cage.     

Structure,magnetic, and electrical properties of bismuth niobates doped with <Emphasis Type="Italic">d</Emphasis>-elements: XVI. Magnetic properties of manganese-containing solid solutions of bismuth orthoniobate BiNiO<Subscript>4</Subscript>

Magnetic susceptibility and ESR properties of manganese-containing solid solutions of bismuth orthoniobate BiNb_1–x Mn_xO_4–δ have been studied. Mn(II), Mn(III), and Mn(IV) atoms as well as their dimers exhibiting antiferro- and ferromagnetic types of exchange have been found in the solid solutions. Parameters of the exchange interactions in the clusters and the distribution of monomers and dimers of manganese atoms in the solid solutions have been calculated as functions of the paramagnetic atom fraction.     

X射线吸收谱研究碳纳米管内Rh-Mn纳米粒子结构的变化

利用X射线吸收谱技术研究了负载于多壁碳纳米管内的Rh-Mn纳米粒子在不同气氛和温度下的结构. 结果表明,Rh-Mn粒子在空气中是由氧化铑团簇和混合锰氧化物组成. 经过氢气在300 ℃下还原后,混合锰氧化物种转化成MnO. 而氧化铑团簇在He气氛下当温度达到250 ℃时就会发生分解而形成金属铑团簇. 对形成的铑团簇用H₂或CO进行热处理,发现其分散性随温度升高而提高; 同时,X射线吸收谱实验没有观察到Mn和Rh之间存在显著的相互作用,助剂Mn的主要作用是提高了Rh的分散性.     

Structure and dynamics of Lennard-Jones clusters with impurities

Molecular dynamics simulations and Lennard-Jones potentials have been used to study binary mixed clusters. The low temperature structures, impurity solvation and the melting and freezing transitions for different values of the relative atomic size and interaction energy have been studied forA ₁₃ B,A ₁₂ B,A ₅₅ B andA ₁₃ B ₁₃ clusters. ForA ₁₃ B large impurities do not solvate even for high interaction energy. ForA ₅₅ B larger impurities remain on the surface for low interaction energies but solvate as the energy of interaction increases. The presence of the impurity very strongly affects the solid-liquid transition. Icosahedral structures remain as the minimum energy configurations forA ₁₃ B ₁₃ clusters with atoms of the same size and different interaction energies. ForA ₁₃ B ₁₃ clusters with atoms of the same interaction energy and different size, smaller atoms go inside surrounded by the bigger surface atoms.     

SYNTHESIS AND STRUCTURE OF A POLYMERIC 1,3-BENZENEDICARBOXYLATO COMPLEX OF Mn(II) WITH PHENANTHROLINE

Abstract

A novel Mn(II) complex bridged by 1,3-benzenedicarboxylate (BDC) has been synthesized by the diffusion method. The complex crystallizes in space group P2₁/c with a = 8.345(2), b = 10.427(1), c = 18.756(2) Å, β = 100.19(1)°. Each BDC bridges three Mn(II) atoms through two carboxyl groups with different coordination modes to form a complex polymeric chain. The coordination geometry around the Mn(II) atom is seriously distorted from the normal octahedron. Large deviations of the donor atoms out of the coordination planes and unexpected bond angles around Mn(II) and donor O atoms suggest the existence of an electrostatic interaction between Mn(II) and donor atoms in the complex. Close stacking of aromatic rings is observed in the complex, the distance between the neighboring phen planes being 3.2085 Å.     

A one-dimensional Mn(II)-based metal organic oxide: structure and properties

A one-dimensional metal organic oxide of Mn(II), with formula [Mn₃(OH)₂(Hpdc)₂]_n (H₃pdc = 3,5-pyrazoledicarboxylic acid), was prepared via the hydrothermal method and its structure solved by single-crystal X-ray diffraction. The compound exhibits a three-dimensional framework structure, comprising three crystallographically unique Mn atoms bridged by OH ligands (O9 and O10) and O atoms from the Hpdc ligands, forming one-dimensional metal–organic oxide chains. Two kinds of magnetic exchange are observed: a strong antiferromagnetic intra-chain interaction, arising from the short distance between Mn(II) centers, and a ferromagnetic inter-chain interaction, due to the larger distances between the chains. The compound shows good photocatalytic activity for the decomposition of methylene blue in aqueous medium under simulated sunlight.     

Using the Interaction between Copper and Manganese to Stabilize Copper Single-atom for CO Oxidation.

The interaction between Cu and Mn has been used to immobilize the Cu single-atom on MnO₂ surface by redox-driven hydrolysis. Comprehensive structure and property characterizations demonstrate that the existence of an Cu−Mn interaction on the catalyst surface can effectively restrain the aggregation of Cu single atoms and improve carbon monoxide (CO) oxidation activity. The interaction of forming the Cu−O−Mn entity is beneficial for CO catalytic activity as the migration of reactive oxygen species and the coordination effect of active centers accelerate the reaction. In particular, 3%-Cu₁/MnO₂ shows an oxygen storage capacity (OSC) value (342.75 μmol/g) more than ten times that of pure MnO₂ (27.79 μmol/g) and has high CO catalytic activity (T_90%=80 °C), it can maintain CO conversion of 95 % after 15 cycles. This work offers a reliable method for synthesizing Cu single-atom catalysts and deepens understanding of the interaction effect between single transition metal atoms and supports that can improve the catalytic activity of CO oxidation.     

Synthesis,crystal structure and magnetic properties of [Mn(LH)2(H2O)2] n with a two-dimensional layered structure and three-dimensional hydrogen bonding network

A new manganese polymer [Mn(LH)₂(H₂O)₂] _n (LH₂ = iminodiacetic acid) (1) has been prepared and structurally and magnetically characterized. The polymer has a two-dimensional (2D) layered structure with the unique Mn atom on an inversion center, surrounded by six oxygen atoms. In each layer, all iminodiacetic acid entities are coordinated to Mn atoms in a bridging/bidentate mode, thus linking the [Mn(LH)₂(H₂O)₂] monomeric units together to form a 2D layered polymer. Hydrogen bonding is responsible for an extended three-dimensional network. Analysis of variable-temperature magnetic susceptibility data (2–300) K shows that the polymer displays weak antiferromagnetic exchange interaction with a coupling constant, J = –0.28 cm^–1.     

Fragmentation of large ionized clusters of rare gas atoms

Molecular dynamics is used to examine the fragmentation of clusters of rare gas atoms after ionization. The cohesive energy is given by a quantum mechanical model with a delocalized hole. Very small clusters dissociate entirely into single atoms and a positively charged dimer. Larger clusters (e.g. Ne₁₃, Xe₁₃ and Ne₅₅) first eject rapid atoms, then thermalize and evaporate further atoms, which strongly decreases their size. Very large clusters (e.g. Xe₅₅) are only heated up after ionization and do not loose atoms. Thus the peaks in mass spectra do not show the atomic shell structure of neutral clusters up to rather large cluster sizes. Instead the stability of ionized clusters is reflected.     

A 1,2,4‐Triazole‐based Polynuclear Mixed‐valence MnIIMnIII Complex: Synthesis,Characterization, and Magnetic Property

A mixed‐valence Mn complex {[Mn^IIMn^III(HL)₂(4,4′‐bpy)(H₂O)₂] · (ClO₄)(DMF)₃(4,4′‐bpy)_0.5}_n ( 1 ) [H₂L = 3‐(2‐phenol)‐5‐(pyridin‐2‐yl)‐1,2,4‐triazole] was synthesized and characterized by X‐ray single‐crystal structure analysis and magnetic susceptibility. Single‐crystal X‐ray analysis revealed that complex 1 has a dinuclear core, in which adjacent central Mn^III atoms are linked by 4,4′‐bipyridine to form an infinite one‐dimensional (1D) molecular configuration. According to the Mn surrounding bond lengths and bond valence sum (BVS) calculations, we demonstrated that the Mn atom coordinated to the pyridine N atoms is in the +2 oxidation state, while another Mn atom coordinated to the phenolic oxygen atoms is in the +3 oxidation state. Magnetic susceptibility data of the complex 1 indicate that the ferromagnetic interaction dominates in this complex.     

Structure and Magnetic Properties of Mn(II) Complexes with Enaminoketone Derivatives of 3-Imidazoline Nitroxide

The crystal structures of two manganese complexes with the enaminoketone derivatives of 3-imidazoline nitroxide: MnL ₂ ^COOMe (layered polymeric) and MnL ₂ ^CF3 (DMF)₂ (molecular) have been determined. The polymer structure of MnL ₂ ^COOMe is the result of direct coordination of the nitroxyl O atoms of the neighboring bischelate fragments by the Mn atoms. This forms heterospin exchange clusters >N-O–Mn(II)–O-N< with strong antiferromagnetic interactions between the odd electrons of the paramagnetic centers. The structure of MnL ₂ ^CF3 (DMF)₂ is characterized by ligand cis-coordination in the octahedral coordination polyhedron. Due to the molecular nature of the complex, the solid compound has only weak ferromagnetic intramolecular indirect exchange interactions. The charge states of atoms in coordination units was confirmed by X-ray photoelectron data.     

Noble gas clusters in model zeolite cavities

Noble gas atoms trapped in the intracrystalline cavities of zeolites may form clusters. A classical-mechanical isoenergetic molecular dynamics simulation is performed to simulate the dynamical behavior of noble gas clusters in zeolite cavities. To implement the simulation, a model is adopted of a homogeneous spherical cavity with Morse interaction between the noble gas atoms and cavity walls. The results for Ar₆ clusters indicate that the noble gas clusters in the cavity undergo the same solid/liquid phase changes as in free space, and, at high enough energies, a rapid exchange between atoms adsorbed on the inner surface and thosein the interior of the cavity. Mathematical quenching is used to investigated the multidimensional potential surface of Ar clusters in the cavity.     

Synthesis and structure of linear hexanuclear manganese (II) benzoate cluster

From a reaction system including benzoic acid and Mn(NO₃)₂ in alkali medium, two hexanuclear manganese benzoate cluster compounds have been synthesized. A compound [Et₄N]₂[Mn₆(PhCOO)₁₄] has been structurally characterized, which contains hexanuclear Mn^II moieties extending unlimitedly to form one-dimensional linear structure. Carboxyl oxygen atoms are bridged in variety of modes to the Mn atoms, forming an arrangement like a sinusoid for the Mn atoms. The structural parameters of these compounds were compared with the data obtained from EXAFS determination for the Mn cluster in the OEC of PSII, supporting that the coordination sphere of the Mn site in the OEC may contain carboxyl bridges. The possible combination modes between the carboxyl group and the Mn atoms have been suggested. The NMR signals exhibit widening and shift produced by the influence of the paramagnetic Mn^II sites. The red-shift of the absorption in IR spectrum was observed to be attributed to the coordination of the carboxyl group to the Mn atom, supporting the result of the study on crystal structure.     

Trigonal‐Bipyramidal and Square‐Pyramidal Chromium?Manganese Chalcogenide Clusters, [E2CrMn2(CO)n]2− (E=S,Se, Te; n=9, 10): Synthesis,Electrochemistry, UV/Vis Absorption,and Computational Studies

The reactions of E powder (E=S, Se) with a mixture of Cr(CO)₆ and Mn₂(CO)₁₀ in concentrated solutions of KOH/MeOH produced two new mixed Cr? Mn? carbonyl clusters, [E₂CrMn₂(CO)₉]^2? (E=S, 1 ; Se, 2 ). Clusters 1 and 2 were isostructural with one another and each displayed a trigonal‐bipyramidal structure, with the CrMn₂ triangle axially capped by two μ₃‐E atoms. The analogous telluride cluster, [Te₂CrMn₂(CO)₉]^2? ( 3 ), was obtained from the ring‐closure of Te₂Mn₂ ring complex [Te₂Mn₂Cr₂(CO)₁₈]^2? ( 4 ). Upon bubbling with CO, clusters 2 and 3 were readily converted into square‐pyramidal clusters, [E₂CrMn₂(CO)₁₀]^2? (E=Se, 5 ; Te, 6 ), accompanied with the cleavage of one Cr? Mn bond. According to SQUID analysis, cluster 6 was paramagnetic, with S=1 at room temperature; however, the Se analogue ( 5 ) was spectroscopically proposed to be diamagnetic, as verified by TD‐DFT calculations. Cluster 6 could be further carbonylated, with cleavage of the Mn? Mn bond to produce a new arachno‐cluster, [Te₂CrMn₂(CO)₁₁]^2? ( 7 ). The formation and structural isomers, as well as electrochemistry and UV/Vis absorption, of these clusters were also elucidated by DFT calculations.     

Geometry and electronic properties of alkali metal (rubidium) doped boron clusters

Alkali metal-doped boron clusters have captured much attention because of their novel electronic properties and structural evolution. In the study of RbB_n^0/− (n = 2–12) clusters, the minimum global search of the potential energy surface and structure optimization at the level of PBE1PBE by using the CALYPSO method and Gaussian package coupled with DFT calculation; the geometrical structures and electronic properties are systematically investigated. At n = 8, the ground-state structures are composed of an Rb atom above B atoms, forming a structurally stable pagoda cone. By stability analysis and charge transfer calculation, the RbB₈⁻ cluster shows more stability. It found that s-p hybridization between Rb atom and B atoms as well as s-p hybridization between B atoms is one of the reasons for the outstanding stability exhibited in the RbB₈^0/− clusters by using DOS and HOMO–LUMO orbital contour maps. The chemical bonding of the RbB₈^0/− groups was analyzed by using the AdNDP method, and B atoms with larger numbers readily form multi-center chemical bonds with the Rb atom. From the results of the bonding analysis, the interaction between the Rb atom and B atoms strengthens the stability of the RbB₈^0/− clusters. It is hoped that this work provides a direction for experimental manipulation.     

Hydration preferences for Mn4Ca cluster models of photosystem II: location of potential substrate-water binding sites

Density functional theory calculations are reported on a set of three model structures of the Mn₄Ca cluster in the water‐oxidizing complex of Photosystem II (PSII), which share the structural formula [CaMn₄C₉H₁₀N₂O₁₆]^q+ ? (H₂O)_n (q=?1, 0, 1, 2, 3; n=0–7). In these calculations we have explored the preferred hydration sites of the Mn₄Ca cluster across five overall oxidation states (S₀ to S₄) and all feasible magnetic‐coupling arrangements to identify the most likely substrate–water binding sites. We have also explored charge‐compensated structures in which the overall charge on the cluster is maintained at q=0 or +1, which is consistent with the experimental data on sequential proton loss in the real system. The three model structures have skeletal arrangements that are strongly reminiscent, in their relative metal‐atom positions, of the 2.9‐, 3.7‐, and 3.5 Å‐resolution crystal structures, respectively, whereas the charge states encompassed in our study correspond to an assignment of (Mn^III)₃Mn^II for S₀ and up to (Mn^IV)₃Mn^III for S₄. The three models differ principally in terms of the spatial relationship between one Mn (Mn(4)) and a generally robust Mn₃Ca tetrahedron that contains Mn(1), Mn(2), and Mn(3). Oxidation‐state distributions across the four manganese atoms, in most of the explored charge states, are dependent on details of the cluster geometry, on the extent of assumed hydration of the clusters, and in some instances on the imposed magnetic‐coupling between adjacent Mn atoms. The strongest water‐binding sites are generally those on Mn(4) and Ca. However, one structure type displays a high‐affinity binding site between Ca and Mn(3), the S‐state‐dependent binding‐energy pattern of which is most consistent with the substrate water‐exchange kinetics observed in functional PSII. This structure type also permits another water molecule to access the cluster in a manner consistent with the substrate–water interaction with the Mn cluster, seen in electron spin‐echo envelope modulation (ESEEM) studies of the functional enzyme in the S₀ and S₂ states. It also rationalizes the significant differences in hydrogen‐bonding interactions of the substrate water observed in the FTIR measurements of the S₁ and S₂ states. We suggest that these two water‐binding sites, which are molecularly close, model the actual substrate‐binding sites in the enzyme.     

Tetra­aqua­bis(5‐carb­oxy‐2‐nitro­benzo­ato‐κO)manganese(II) dihydrate: a metal–water chain complex containing cyclic water tetra­mers

In the title complex, [Mn(C₈H₄NO₆)₂(H₂O)₄]·2H₂O, cyclic water tetra­mers forming one‐dimensional metal–water chains have been observed. The water clusters are trapped by the co‐­operative association of coordination inter­actions and hydrogen bonds. The Mn^II ion resides on a center of symmetry and is in an octa­hedral coordination environment comprising two O atoms from two 5‐carboxy‐2‐nitrobenzoate ligands and four O atoms from water mol­ecules.     

Structural,Relative Stable,and Electronic Properties of Pb<Subscript>n</Subscript>Sn<Subscript>n</Subscript> (n = 2–12) Clusters were Investigated Using Density Functional Theory

The structural, relative stable and electronic properties of Pb_nSn_n (n = 2–12) alloy clusters were systematically studied using density functional theory. The isomers of Pb_nSn_n alloy clusters were generated and determined by ab initio molecular dynamics. By comparing the calculated parameters of Pb₂ dimer and Sn₂ dimers with the parameters from experiments, our calculations are reasonable. With the lowest-energy structures for Pb_nSn_n clusters, the average binding energies, fragmentation energies, second- order energy differences, vertical ionization potentials, vertical electron affinities, HOMO–LUMO gaps, and density of states were calculated and analyzed. The results indicate that the Sn atoms have a tendency to bond together, the average binding energies tend to be stable up to n = 8, Pb₈Sn₈ cluster is a good candidate to calculate the molecular interaction energy parameter in Wilson equation, the clusters become less chemical stable and show an insulator-to-metallic transition, 3, 6, 8 and 11 are magic numbers of Pb_nSn_n (n = 2–12) clusters, the charges always transfer from Sn atoms to Pb atoms in Pb_nSn_n clusters except for Pb₁₀Sn₁₀ cluster, and density of states of Pb_nSn_n clusters becoming continuous and shifting toward negative with the increasing size n.     

Radiative neutralization of small clusters impinging on solid surfaces

Light emission during the interaction of slow singly-charged clusters with solid surfaces is studied theoretically. More precisely, we consider positive ions of Ag _n clusters (n = 1...5) impinging on silver surfaces. In such systems, the charge transfer process involved during the cluster-surface interaction is mainly resonant capture. However, photon emission due to radiative capture is also a possible charge transfer channel. Our simple theoretical model including both processes allows us to calculate the light spectra and the total photon yield for the different cluster sizes, n. Our results show that light emission strongly depends on the electronic level dynamics of the clusters in front of the surface, providing a tool for electronic structure analysis of atoms, clusters and solid surfaces.     

Atomic Velocity Distributions and Diffusing Behaviors in a Nano-Alloy Cluster

This paper studies the velocity distributions and diffusing behaviors of the atoms in a nano-alloy cluster. A series of ternary alloy clusters, Au₅₀Cu₂₅Ni₂₅, and binary alloy clusters, Cu_100−aNi_a are introduced in the molecular dynamics simulations. The velocity distributions of different types of atoms in both static and moving clusters are found to obey the Maxwell’s velocity distribution with the individual mass of atoms and the inner temperature of clusters. Furthermore, the velocity distribution of whole atoms of the cluster is obtained by synthesizing the velocity distributions of compositions in the cluster according to the proportions. The consistency of the atomic motions in a moving cluster is discussed by inspecting the backward velocities of atoms, which are correlated to the translational velocity and the inner temperature of the cluster. The diffusing behaviors of the atoms in a cluster are also investigated from a viewpoint of the interatomic interactions, i.e. Cu atoms enhance the activities of Ni atoms, or Ni atoms reduce that of Cu atoms in the alloy clusters.