Mn Chains Research Articles

Alternating chains with the new J1J2J3J1⋯ sequence in a three-dimensional MnII complex

A three-dimensional carboxylate-bridged MnII compound [Mn6(tci)4(H2O)3]·7H2O}n (1) (tci=tris(2-carboxyethyl) isocyanurate) have been synthesized. The structure contains unique manganese chains in which the MnII ions are alternatively bridged by carboxylate groups in different coordination modes. The first example of such alternating Mn chain shows Mn1–(COO)3–Mn2–(COO)2–Mn3–(COO)3–Mn1–(COO)3–Mn2-sequence arranged as J1J2J3J1S⋯ mode. Magnetic susceptibility measurement reveals an antiferromagnetism behavior derived from the topology of the chain. There is no suitable analytical expression for determining the exchange parameters in a 1-D Heisenberg ferrimagnet consisting of alternating interactions J1J2J3J1⋯. The best way to fit the magnetic behavior of these complexes is to proceed by using a Hamiltonian that corresponds to a 12-membered of S=5/2 with 4 fragments repeating the sequence J1J2J3. The fit was performed by means of the computer program MAGPACK. The fitting for the observed magnetic data gives J1=−2.31cm−1, J2=−1.60cm−1, J3=−3.10cm−1, zJ′=−0.03cm−1 and g=1.98, with R=7.2×10−3.

High proton mobility, solvent induced single crystal to single crystal structural transformation, and related studies on a family of compounds formed from Mn3 oxo-clusters.

The reaction between 4,4'-sulfonyldibenzoic acid (H2SDBA) and manganese under mild conditions resulted in the isolation of two new three-dimensional compounds, [Mn4(C14H8O6S)4(DMA)2]·3DMA, I, and [Mn3(C14H8O6S)3(DMA)2(MeOH)]·DMA, IIa. Both structures have Mn3 trimer oxo cluster units. While the Mn3 oxoclusters are connected through octahedral manganese forming one-dimensional Mn-O-Mn chains in I, the Mn3 units are isolated in IIa. The SDBA units connect the Mn-O-Mn chains and the Mn3 clusters giving rise to the three-dimensional structure. Both compounds have coordinated and free solvent molecules. In IIa, two different solvent molecules are coordinated, of which one solvent can be reversibly exchanged by a variety of other similar solvents via a solvent-mediated single crystal to single crystal (SCSC) transformation. The free lattice DMA solvent molecules in I can be exchanged by water molecules resulting in hydrophilic channels. Proton conductivity studies on I reveals a high proton mobility with conductivity values of ∼0.87 × 10(-3) Ω(-1) cm(-1) at 34 °C and 98% RH, which is comparable to some of the good proton conductivity values observed in inorganic coordination polymers. We have also shown structural transformation of I to IIa through a possible dissolution and recrystallization pathway. In addition, both I and IIa appear to transform to two other manganese compounds [H3O][Mn3(μ3-OH)(C14H8O6S)3(H2O)](DMF)5 and [H3O]2[Mn7(μ3-OH)4(C14H8O6S)6(H2O)4](H2O)2(DMF)8 under suitable reaction conditions. We have partially substituted Co in place of Mn in the Mn3 trimer clusters forming [CoMn2(C14H8O6S)3(DMA)2(EtOH)]·DMA, III, a structure that is closely related to IIa. All the compounds reveal antiferromagnetic behavior. On heating, the cobalt substituted phase (compound III) forms a CoMn2O4 spinel phase with particle sizes in the nanometer range.

Enzymatic ring-opening (co)polymerization of lactide stereoisomers catalyzed by lipases. Toward the in situ synthesis of organic/inorganic nanohybrids

Lipase-based catalysts were tested for the ring-opening polymerization of d-, l- and d,l-lactide isomers, highlighting the different specificity of the enzyme toward these isomers. Free form of Candida antarctica lipase B (CALB) and its clay- and acrylic resin- immobilized forms were compared. For l- and d,l-lactide monomers only short oligomers were obtained. The acrylic resin immobilized form of CALB (NOVO-435) led to a complete conversion of d-lactide to PDLA with a Mn of 2600g/mol, whereas the clay-immobilized and free forms of CALB exhibited slower kinetics and produced chains of lower Mn. Copolymerization reactions between ɛ-caprolactone and lactide isomers were performed using NOVO-435 as bio-catalyst. Random copolyesters were successfully synthesized by copolymerizing d-lactide with ɛ-caprolactone. Better results were obtained with a two-step reaction, starting from presynthesized polycaprolactone chains, compared with the one-pot copolymerization. Conducting this two-step copolymerization in the presence of organo-modified montmorillonite allowed the successful synthesis of copolymer/clay nanohybrids.

Electronic and transport properties of noncollinear magnetic monatomic Mn chains: Fano resonances in the superlattice of noncollinear magnetic barriers and magnetic anisotropic bands

Abstract By means of the density functional theory combined with non-equilibrium Green's function method, ballistic transport properties of one-dimensional noncollinear magnetic monatomic chains were investigated using the single-atomic Mn chains as a model system. Fano resonances are found to exist in the monatomic Mn chains with spin-spiral structure. Furthermore, in the monatomic Mn chains with magnetic soliton lattice, Fano resonances are enhanced and cause the conductance splitting in the transmission spectra. The Fano resonances in the noncollinear magnetic single-atomic Mn chains are arising from the coupling of the localized d -states and the extended states of the quantum channels. By constructing a theoretical model and calculating its conductance, it is found that the phenomena of Fano resonances and the accompanying conductance splitting exist universally in the superlattice of one-dimensional noncollinear magnetic barriers, due to the interference of the incident waves and reflected waves by the interfaces between the neighboring barriers. Moreover, the band structures of the ferromagnetic and spin-spiral monatomic Mn chains exhibit a strong dependence on the spatial arrangement of the magnetic moments of Mn atoms when spin–orbit coupling is considered.

Enantiopure and racemic alanine as bridging ligands in Ca and Mn chain polymers.

Under accelerated and controlled evaporation, chain polymers crystallize from aqueous solutions of Ca(II) and Mn(II) halides with enantiopure L-alanine or racemic DL-alanine. In all ten solids thus obtained zwitterionic amino acid ligands bridge neighbouring cations. The exclusively O-donor-based coordination sphere around the metal cations is completed by aqua ligands; the halides remain uncoordinated and act as counter-anions for the cationic strands. Despite the differences in ionic radii and electronic structure between the main group and the transition metal cation, their derivatives with L-alanine share a common structure type. In contrast, the solids derived from DL-alanine differ and adopt structures depending on the metal cation and the halide. Homochiral chains of either chirality or heterochiral chains with different arrangements of crystallographic inversion centres along the polymer strands are encountered. On average, the six-coordinated Ca(II) cations, devoid of any ligand field effect, show more pronounced deviation from idealized octahedral geometry than the d-block cation Mn(II).

The performance of La0.6Sr1.4MnO4 layered perovskite electrode material for intermediate temperature symmetrical solid oxide fuel cells

A layered perovskite electrode material, La0.6Sr1.4MnO4+δ (LSMO4), has been studied for intermediate temperature symmetrical solid oxide fuel cells (IT-SSOFCs) on La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) electrolyte. The chemical compatibility tests indicate that no reaction occurred between LSMO4 oxide and LSGM electrolyte at temperature up to 1000 °C both in air and 5% H2. The lower conductivity in 5% H2 and higher conduction activation energy than those in air would be caused by poorer overlap of both σ and π bonds. DFT + U calculations also show that oxygen vacancies which formed in reducing atmosphere may block the 3D hopping path for electrons or holes through Mn–O–Mn chains. For LSMO4 electrode, SEM results indicate that the electrode formed good contact with the electrolyte after being sintered at 900 °C for 2 h. At 800 °C, the polarization resistance of the LSMO4 cathode is about 0.87 Ω cm2 in air, while the polarization resistance of the LSMO4 anode is about 2.07 Ω cm2 in 5% H2. LSMO4 exhibits better electrochemical activity for oxygen reduction than that for hydrogen oxidation. A cell with LSGM electrolyte, LSMO4–LSGM mixture as anode and cathode simultaneously displays a maximum power density of 59 mW cm−2 at 800 °C.

Synthesis, structure and magnetic properties of manganese(II) coordination polymer with azido and zwitterionic dicarboxylate ligand

Abstract A coordination polymer formulated as {[Mn2L(N3)4]·2H2O}n(1) [L = 1,4-bis(pyridinil-3-carboxylato)-l,4-dimethylbenzene] was synthesized and structurally and magnetically characterized. The uniform Mn(II) chains with mixed (μ-EO-N3)2(μ-COO) triple bridges (EO = end-on) are linked by L ligands to generate a 2-fold interpenetrating 3D framework. Meanwhile, magnetism analysis reveals antiferromagnetic coupling for 1.

Peierls distortion, magnetism, and high hardness of manganese tetraboride

We report crystal structure, electronic structure, and magnetism of manganese tetraboride, ${\text{MnB}}_{4}$, synthesized under high-pressure, high-temperature conditions. In contrast to superconducting ${\text{FeB}}_{4}$ and metallic ${\text{CrB}}_{4}$, which are both orthorhombic, ${\text{MnB}}_{4}$ features a monoclinic crystal structure. Its lower symmetry originates from a Peierls distortion of the Mn chains. This distortion nearly opens the gap at the Fermi level, but despite the strong dimerization and the proximity of ${\text{MnB}}_{4}$ to the insulating state, we find indications for a sizable paramagnetic effective moment of about 1.7 \ensuremath{\mu}${}_{B}$/f.u., ferromagnetic spin correlations, and, even more surprisingly, a prominent electronic contribution to the specific heat. However, no magnetic order has been observed in standard thermodynamic measurements down to 2 K. Altogether, this renders ${\text{MnB}}_{4}$ a structurally simple but microscopically enigmatic material; we argue that its properties may be influenced by electronic correlations.

Structural distortion and band gap opening of hard MnB4 in comparison with CrB4 and FeB4

MnB4 was newly synthesized to crystallize in a monoclinic P21/c structure, different from previous experimental and theoretical reports. Here, based on first-principles calculations, we perform a comparative study of geometric and energetic features, mechanical behaviors, electronic property and chemical bonding of the experimentally identified monoclinic MnB4, as well as orthorhombic CrB4 and FeB4. The results demonstrate that the presence of distorted rhomboidal-B4 units and one-dimensional Mn chains in the monoclinic MnB4 breaks the structural symmetry and lowers the total energy in comparison to the orthorhombic phase. The opening of band gap in MnB4 is induced by Peierls-paired Mn atoms, differing from the metallic behaviors of recently studied tetraborides. Specifically, the preservations of covalent bonding in distorted boron-rhomboids in MnB4 explain the relatively higher incompressibility and hardness.

Nuclearity control of manganese polymers dependent on structural differences in the coligands and magnetic properties studies

A series of polymers containing MnII clusters varying from dinuclear, tetranuclear, hexanuclear, to rod-shaped uniform chains has been synthesized. The polymer [Mn4(Htci)2(ptptp)2(H2O)6]·8H2O (1) (H3tci = tris(2-carboxyethyl)isocyanurate, H2ptptp = 2-(5-{6-[5-(pyrazin-2-yl)-1H-1,2,4-triazol-3-yl]pyridin-2-y-1H-1,2,4-triazol-3-yl}pyrazine) shows an interesting ladder based on dinuclear Mn clusters. The polymer {[Mn3(tci)2(pbbm)(H2O)3]·H2O}n (2) (pbbm = 1,1′-(1,5-pentanediyl)bis-1H-benzimidazole) has a 2D 3,6-connected framework with tetranuclear and dinuclear Mn clusters. The polymer {[Mn3(tci)2(bbbm)(H2O)3](H2O)}n (3) (bbbm = 1,1′-(1,4-butanediyl)bis-1H-benzimidazole) belongs an uncommon 3D 3,12-connected framework assembled by hexanuclear clusters. And the polymer {Mn(Htci)(dpp)}n (4) (dpp = 1,3-di(4-pyridyl)propane) based upon rod-shaped uniform Mn chains exhibits a 2D framework. Magnetic susceptibility measurements indicate that all of the polymers show weak antiferromagnetic interactions.

Supramolecular Assembly of Bis(benzimidazole)pyridine: An Extended Anisotropic Ligand For Highly Birefringent Materials

Four new bis(benzimidazole)pyridine (BBP)-containing compounds Zn(BBP)Cl[Au(CN)2], Mn(BBP)[Au(CN)2]2·H2O, Mn(BBP)Br2(MeOH) and Mn(BBP)Cl2(MeOH)·MeOH have been synthesized and structurally characterized and their birefringence values (Δn) determined. The structure of Zn(BBP)Cl[Au(CN)2] contains a hydrogen-bonded dimer of Zn(BBP)Cl[Au(CN)2] units which propagate into a 1D chain through Au-Au interactions, although the crystals are of poor optical quality. The supramolecular structure of Mn(BBP)[Au(CN)2]2·H2 O forms a 1D coordination polymer through chains of Mn(BBP)[Au(CN)2]2 units, each containing one bridging Au(CN)2 and one forming a 2D sheet through Au-Au interactions. The supramolecular structures of Mn(BBP)Br2(MeOH) and Mn(BBP)Cl2(MeOH)·MeOH are very similar, consisting of a complex hydrogen-bonded network between NH imidazole, methanol and halide groups to align BBP building blocks. In the plane of the primary crystal growth direction, the birefringence values of the three Mn-containing materials were Δn=0.08(1), 0.538(3) and 0.69(3), respectively. The latter two birefringence values are larger than in the related 2,2';6'2''-terpyridine systems, placing them among the most birefringent solids reported. These compounds illustrate the utility of extending the π-system of the building block and incorporating hydrogen-bonding sites as design elements for highly birefringent materials and also illustrates the effect on the measurable birefringence of the crystal quality, growth direction and structural alignment of the anisotropic BBP building blocks.

Principles and Applications of Anion Order in Solid Oxynitrides

Metal oxynitrides are emerging materials that may combine the advantages of oxides and nitrides. Anion order is important for controlling and tuning properties, and neutron diffraction provides good O/N contrast for experimental determinations of local or long-range O/N order in solids. Differences between oxide and nitride in charge, size, and covalent bonding are the important factors that drive anion order. An important example is the robust partial anion order in SrMO2N (M = Nb, Ta) and related oxynitride perovskites driven by covalency that results in disordered zigzag MN chains which segregate into planes within the perovskite lattice. This leads to unusual subextensive scaling of entropy, described as “open order”. Local anion order is important to optical materials. Size mismatch between host and dopant cations leads to local O/N clustering that tunes photoluminescence shifts systematically in M1.95Eu0.05Si5–xAlxN8–xOx phosphors, leading to a red shift when the M = Ba and Sr host cations are larger than the Eu2+ dopant but a blue shift when the M = Ca host is smaller.

Influence of lone pair doping on the multiferroic property of orthorhombic HoMnO3: ab initio prediction

Using first principles density functional theory, we predict new multiferroic compounds Ho1/2A1/2MnO3 (A = As, Sb, Bi) with enhanced polarization. We find that doping of lone pair cations with different ionic radii, at the A-site of orthorhombic HoMnO3, results in a marked increase of the electronic polarization and its development along the b-axis. This development of electronic polarization along the b-axis is attributed to the breaking of the two-fold rotational symmetry which leads to the emergence of a polar b-axis. Furthermore, this symmetry breaking leads to the emergence of two inequivalent Mn ions (Mn(0) and Mn(1)) and the variance in their octahedral (Mn(0)O6 and Mn(1)O6) distortions. We rationalize the observed trends in the total polarization in terms of disparate eg electron hopping along the two different Mn(0) and Mn(1) chains. We expect large ionic polarization in the doped compounds due to the presence of 4s2 As, 5s2 Sb and 6s2 Bi lone pairs, but surprisingly the effect of the lone pairs seems to be inactive. This is attributed to the strong GdFeO3 distortions exhibited by the MnO6 octahedron which hinders polar displacement of the lone pair cations.

Local unitary transformation method toward practical electron correlation calculations with scalar relativistic effect in large-scale molecules

In order to perform practical electron correlation calculations, the local unitary transformation (LUT) scheme at the spin-free infinite-order Douglas-Kroll-Hess (IODKH) level [J. Seino and H. Nakai, J. Chem. Phys. 136, 244102 (2012); and ibid. 137, 144101 (2012)], which is based on the locality of relativistic effects, has been combined with the linear-scaling divide-and-conquer (DC)-based Hartree-Fock (HF) and electron correlation methods, such as the second-order Mo̸ller-Plesset (MP2) and the coupled cluster theories with single and double excitations (CCSD). Numerical applications in hydrogen halide molecules, (HX)n (X = F, Cl, Br, and I), coinage metal chain systems, Mn (M = Cu and Ag), and platinum-terminated polyynediyl chain, trans,trans-{(p-CH3C6H4)3P}2(C6H5)Pt(C≡C)4Pt(C6H5){(p-CH3C6H4)3P}2, clarified that the present methods, namely DC-HF, MP2, and CCSD with the LUT-IODKH Hamiltonian, reproduce the results obtained using conventional methods with small computational costs. The combination of both LUT and DC techniques could be the first approach that achieves overall quasi-linear-scaling with a small prefactor for relativistic electron correlation calculations.

Identification of complex anions in La1 − x A x MnO3 manganites (A = Ca, Sr) from neutron diffraction data and refinement of their structures on the basis of raman spectroscopy data

The consideration of the Mn(-O…Mn)6 structure unit of the LaMnO3 orthorhombic phase constructed on the basis of neutron diffraction data revealed the presence of atomic groups in the form of (MnO2)− complex anions and separate O2− ions. The Raman spectra have demonstrated that complex anions have a nearly linear O=Mn-O− structure. Comparison of the Raman spectra of the rhombohedral CaMnO3 and BaTiO3 phases and pyramidal molecules of the ZXY2 type has shown that the CaMnO3 phase is composed of pyramidal MnO32− molecules with one Mn=O double bond and two Mn-O− ordinary bonds. The complex anions are linked by O=Mn-O− intermolecular bonds to form planar zigzag Mn=O…Mn chains similar to C=C-C planar chains in some organic compounds exhibiting high electrical conductivity. With decreasing temperature, the Mn…O intermolecular distances decrease, and the Mn=O…Mn chains become even more similar to the C=C-C chains and exhibit high electrical conductivity.

A Co16 cluster and a 1-D Mn chain complex supported by benzohydroxamic acid

The syntheses, crystal structures and magnetic properties are described for a {Co16} cluster [Co(II)16O(OH)2(bha)12(PhCO2)4(Phen)2(MeOH)4]·2MeOH (1) and a 1-D Mn(II) chain complex [Mn(Hbha)2]n·(2MeOH)n (2) (H2bha = benzohydroxamic acid; Phen = 1,10-phenanthroline). The 1 : 1 : 0.5 reaction of Co(O2CMe)2·4H2O, H2bha and 1,10-phenanthroline in MeOH at 100 °C under autogenous pressure gave cluster 1. Complex 2 was obtained from the 1 : 1 reaction mixture of Mn(O2CMe)2·2H2O and H2bha in MeOH under solvothermal conditions. The {Co16} cluster can be thought as a face-centered cube with two wings. The H2bha ligands show hydroximic form in 1 and exhibit hydroxamic mode in 2. The hydroximate ligands in 1 display three distinct binding modes, one of which is novel. Variable-temperature solid-state dc magnetic susceptibility studies have been performed in the 2.0-300 K range for complexes 1 and 2. Antiferromagnetic M(II)···M(II) exchange interactions were found for both 1 and 2. This work also demonstrates that solvothermal method is a potential synthetic approach for the design and growth of high nuclearity clusters or chain complexes of the H2bha ligand.

Structure and magnetism of a Mn(iii)–Mn(ii)–Mn(ii)–Mn(iii) chain complex

A novel tetranuclear manganese(II/III) complex with anions of pyridine-2,6-dicarboxylic acid (dipicolinic acid) has been synthesised and magneto-structurally characterised. The crystal structure of [Mn(II)2Mn(III)2(dipic)6(H2O)4]·2CH3OH·4H2O has been determined by single-crystal X-ray diffraction. The tetranuclear complex molecule [Mn(II)2Mn(III)2(dipic)6(H2O)4] is centrosymmetric and two manganese(II) and two manganese(III) atoms are bridged by four dipicolinate ligands. The complex molecules and uncoordinated water and methanol molecules are connected through hydrogen bonds and they form a 3D supramolecular hydrogen-bonding network.

Synthesis, crystal structure and magnetic characterization of two Mn(III) chains with Schiff-base ligands

Two new one-dimensional manganese(III) complexes [Mn2III(L1)4(piv)2] (1) and [MnIII(L2)(bix)]·2H2O⋅ClO4 (2) (H2L1=N-(2-hydroxyethyl)-3-methoxysalicylaldimine, H2L2=N,N′-bis(salicylidene)phenylenediamine, bix=1,4-bis-(imidazol-1-ylmethyl)benzene, piv=pivalate) have been synthesized and characterized by X-ray crystallography and magnetic measurements. Crystal structure studies reveal that complex 1 consists one-dimensional manganese(III) chains linked by L12- ligand in η1:η1:η1:μ2 mode. In complex 2, the Mn(III) ion is coordinated by the tetradentate L22- ligand in the equatorial plane, whereas bix ligand acts as bridge in the axial direction. Magnetic studies show that both complexes exhibit weak antiferromagnetic exchange coupling between Mn(III) ions.

Growth of self-assembled Mn, Sb and MnSb nanostructures on highly oriented pyrolytic graphite

The surface morphology of Mn, Sb and MnSb nanostructures grown on highly-oriented pyrolytic graphite (HOPG) has been studied in detail with scanning tunneling microscopy in ultrahigh vacuum. At the initial stage of growth, three dimensional (3D) clusters and islands of Mn, Sb and MnSb are formed at step edges and other defect sites. In middle stage, crystalline 2D islands and 1D nanorods of Sb can be observed together with crystalline 3D islands, whereas single- and double-layer cluster chains of Mn are obtained at room temperature (RT). MnSb crystallites form after deposition of both Mn and Sb on HOPG surface and annealing at T~375K. The ex-situ X-ray photoemission spectroscopy measurement revealed the formation of MnSb compound on graphite. Ferromagnetism was observed at RT for the 50-nm MnSb thin film using vibrating sample magnetometer.

A Mn(III) chain derived from Mn12–acetate that exhibits both glauber dynamics and antiferromangetic ordering regimes

In this work, we present a detailed AC magnetic susceptibility investigation of the metamagnet {[Mn(OH)(CH3CO2)2]·CH3CO2H·H2O}∞ (1). Compound 1 was previously reported and the magnetic properties were investigated. The data revealed that the compound is a linear-chain antiferromagnet with a phase transition at TN=6.1K to an ordered antiferromagnetic state and a metamagnetic transition at approximately 1000Oe from the antiferromagnetic phase to a paramagnetic phase. In this new study we report detailed AC susceptibility measurements which reveal frequency dependent data indicative of a slow relaxation process which was not previously described. These additional magnetic data support the conclusion that this compound is a rare example of an antiferromagnetic ordered system that displays magnetic relaxation properties induced by the intrinsic single chain magnet (SCM) properties of the canted homospin chains composing the material.