Octahedral Mn Research Articles

Challenges in assignment of orbital populations in a high spin manganese(III) complex.

Magnetic, structural and computational data of four complex salts with the same mononuclear high spin octahedral Mn(iii) complex cation are reported. The manifestation of Jahn-Teller-like distortions in the Mn(iii) cation is dependent on the nature of the charge-balancing anion, with small anions yielding a planar elongation and large anions freezing out a preferential axial elongation along one of the amine-Mn-imine directions within that same plane. Modulation of the lattice by changing the charge balancing anion results in mixing of the orbital symmetry due to vibrational perturbation.

Synthesis and characterization of dopamine substitue tripodal trinuclear [(salen/salophen/salpropen)M] (M[dbnd]Cr(III), Mn(III), Fe(III) ions) capped s-triazine complexes: Investigation of their thermal and magnetic properties

In this work, we aimed to synthesize and characterize a novel tridirectional ligand including three catechol groups and its novel tridirectional-trinuclear triazine core complexes. For this purpose, we used melamine (2,4,6-triamino-1,3,5-triazine) (MA) as starting material. 2,4,6-tris(4-carboxybenzimino)-1,3,5-triazine (II) was synthesized by the reaction of an equivalent melamine (I) and three equivalent 4-carboxybenzaldehyde. 4,4′,4″-((1E,1′E,1″E)-((1,3,5-triazine-2,4,6-triyl)tris(azanylylidene))tris(methanylylidene))tris(N-(3,4-dihydroxyphenethyl)benzamide) L (IV) was synthesized by the reaction of one equivalent (II) and three equivalent dopamine (3,4-dihydroxyphenethylamine) (DA) by using two different methods. (II, III, IV) and nine novel trinuclear Cr(III), Mn(III) and Fe(III) complexes of (IV) were characterized by means of elemental analyses, 1H NMR, FT-IR spectrometry, LC-MS (ESI+) and thermal analyses. The metal ratios of the prepared complexes were performed using Atomic Absorption Spectrophotometry (AAS). We also synthesized novel tridirectional-trinuclear systems and investigated their effects on magnetic behaviors of [salen, salophen, salpropen Cr(III)/Mn(III)/Fe(III)] capped complexes. The complexes were determined to be low-spin distorted octahedral Mn(III) and Fe(III), and distorted octahedral Cr(III) all bridged by catechol group.

Syntheses and X-ray structures of heteroleptic octahedral Mn(II)-xanthato complexes involving N-donor ligands

A series of octahedral manganese(II) complexes involving xanthates and N-donor ligands, [Mn(S2COiBu)2(phen)] (1), [Mn(S2COiBu)2(2,2′-bpy)] (2), [Mn(S2COnPr)2(phen)] (3), [Mn(S2COnPr)2(2,2′-bpy)] (4), [Mn(S2COMe)2(2,2′-bpy)] (5), [Mn(S2COnPr)2(4,4′-bpy)]n, and [Mn2(S2COnPr)4(4,4′-bpy)3] (6) (phen = 1,10-phenanthroline, bpy = bipyridine) was prepared. Complexes were characterized by elemental analysis, FTIR spectroscopy, TG/DSC analysis, and single-crystal X-ray diffraction. The structures are built of monomeric molecules of the complexes, except for 6 with the 4,4′-bipyridine ligand, which contains a binuclear complex and 1D polymeric zigzag chain in one crystal.

Two 3-Amino-1,2,4-triazole-based Manganese(II) Complexes Incorporated With Different Dicarboxylate Coligands: Synthesis, Structure, and Magnetism

Two 3-amino-1,2,4-triazole (Hatz)-based magnetic complexes, {[Mn3(H2O)2(Hatz)2(sip)2]·2H2O}n (1) and {[Mn(H2O)3(Hatz)(bda)]·H2O}n (2) (sip3− = 5-sulfoisophthalate and bda2− = trans-butenedioate), were respectively prepared by varying dicarboxylate-containing coligands, and were structurally and magnetically characterized. Structural determinations reveal that 1 exhibits a two-dimensional layered structure with linear {Mn3(μ-N1,N2-Hatz)2}6+ subunits extended by tritopic sip3− connectors. By contrast, 2 is an infinite zigzag chain constructed from octahedral Mn(II) ions and μ-N1,N4-Hatz linkers. Magnetically, typically antiferromagnetic interaction observed in the local MnII3 subunit of 1 mediated by mixed μ-syn, syn-COO− and μ-N1,N2-Hatz heterobridges is slightly stronger than that of 2 transmitted by single μ-N1,N4-Hatz mediator.

EPR investigation of local structure for the [Mn(H2O)6]2+cluster in M(ClO4)2· 6H2O:Mn2+(M = Cd, Hg) systems at different temperatures

Local lattice structure distortion studies of the octahedral Mn 2+ center in M(ClO 4 ) 2 · 6H 2 O:Mn 2+ (M = Cd, Hg) systems have been performed systematically based on the diagonalization of the complete energy matrices of electron-electron repulsion, spin-orbit coupling and trigonal ligand-field interaction for a d 5 configuration ion in a trigonal ligand field. From the EPR calculation, the local structure distortion parameters R and θ are determined, respectively. Results show that the local lattice structure around a trigonal Mn 2+ center has a compressed distortion along the crystalline C 3 axis. The compression distortion may be ascribed to the fact that the radius of the Mn 2+ ion is smaller than that of the Hg 2+ ion and the Cd 2+ ion. The local lattice structure parameters for Mn 2+ in M(ClO 4 ) 2 · 6H 2 O:Mn 2+ (M = Cd, Hg) systems are determined at liquid-nitrogen temperature and room temperature.

High field electron paramagnetic resonance characterization of electronic and structural environments for paramagnetic metal ions and organic free radicals in Deepwater Horizon oil spill tar balls.

In the first use of high-field electron paramagnetic resonance (EPR) spectroscopy to characterize paramagnetic metal-organic and free radical species from tar balls and weathered crude oil samples from the Gulf of Mexico (collected after the Deepwater Horizon oil spill) and an asphalt volcano sample collected off the coast of Santa Barbara, CA, we are able to identify for the first time the various paramagnetic species present in the native state of these samples and understand their molecular structures and bonding. The two tar ball and one asphalt volcano samples contain three distinct paramagnetic species: (i) an organic free radical, (ii) a [VO](2+) containing porphyrin, and (iii) a Mn(2+) containing complex. The organic free radical was found to have a disc-shaped or flat structure, based on its axially symmetric spectrum. The characteristic spectral features of the vanadyl species closely resemble those of pure vanadyl porphyrin; hence, its nuclear framework around the vanadyl ion must be similar to that of vanadyl octaethyl porphyrin (VOOEP). The Mn(2+) ion, essentially undetected by low-field EPR, yields a high-field EPR spectrum with well-resolved hyperfine features devoid of zero-field splitting, characteristic of tetrahedral or octahedral Mn-O bonding. Although the lower-field EPR signals from the organic free radicals in fossil fuel samples have been investigated over the last 5 decades, the observed signal was featureless. In contrast, high-field EPR (up to 240 GHz) reveals that the species is a disc-shaped hydrocarbon molecule in which the unpaired electron is extensively delocalized. We envisage that the measured g-value components will serve as a sensitive basis for electronic structure calculations. High-field electron nuclear double resonance experiments should provide an accurate picture of the spin density distribution for both the vanadyl-porphyrin and Mn(2+) complexes, as well as the organic free radical, and will be the focus of follow-up studies.

Syntheses, crystal structures, and magnetic properties of Mn–Nb and Co–Nb cyanido-bridged bimetallic assemblies

We report three-dimensional (3D) cyanido-bridged Mn–Nb and Co–Nb bimetal assemblies, MnII2[NbIV(CN)8]·(L)2·nH2O (1: L=5-aminopyrimidine, n=5; 2: L=5-methylpyrimidine, n=4), and CoII2[NbIV(CN)8] (4-pyridinealdoxime)8·2H2O (3). The single-crystal X-ray structural analyses show that 1 and 2 consist of isomorphic 3D cyanido-bridged network (monoclinic, P21/n) composed of square antiprism Nb sites and distorted octahedral Mn sites. Both 1 and 2 show ferrimagnetism with Curie temperatures (TC) of 32 and 34K, respectively, which is caused by the antiferromagnetic superexchange interaction between MnII (S=5/2) and NbIV (S=1/2) through the CN groups. 3 has a 3D cyanido-bridged network (tetragonal, I41/a) composed of a dodecahedral Nb site and axially distorted pseudo-octahedral Co site. This compound shows ferromagnetic ordering with a TC of 18K. Magnetization versus rotation angle of single crystal reveals that 3 has a large coercive field of 15000Oe as crystal is oriented to a-axis, which is due to the strong magnetic anisotropy on distorted CoII.

Hybrid Density Functionals for Clusters of Late Transition Metals: Assessing Energetic and Structural Properties.

We present the first application of hybrid density functional theory (DFT) methods to larger transition-metal clusters. To assess such functionals for this class of systems, we compare the performance of three modern hybrid DFT methods (PBE0, TPSSh, M06) and their semilocal counterparts (PBE, TPSS, M06L) regarding average bond distances and binding energies per atom for a series of octahedral model clusters Mn (M = Ni, Pd, Pt; n = 13, 38, 55, 79, 116). With application to large particles in mind, we extrapolated the results to their respective bulk limits and compared them to experimental values. In some cases, average nearest-neighbor distances are notably overestimated by the PBE0 and M06 hybrid functionals. Results on energies allow a grouping of the tested functionals into sets of similar behavior for the three metals studied. Among the methods examined, the TPSSh hybrid density functional shows the best overall performance.

Experimental Characterization of a Theoretically Designed Candidate p-Type Transparent Conducting Oxide: Li-Doped Cr2MnO4

The development of a p-type transparent conducting oxide (p-TCO) requires the deliberate design of a wide band gap and high hole conductivity. Using high-throughput theoretical screening, Cr2MnO4 was earlier predicted to be a p-TCO when doped with lithium. This constitutes a new class of p-TCO, one based on a tetrahedrally coordinated d5 cation. In this study, we examine and experimentally validate a few central properties of this system. Combined neutron diffraction and anomalous X-ray diffraction experiments give site occupancy that supports the theoretical prediction that lithium occupies the tetrahedral (Mn) site. The lattice parameter of the spinel decreases with lithium content to a solubility limit of [Li]/([Li] + [Mn]) ∼ 9.5%. Diffuse reflectance spectroscopy measurements show that at higher doping levels the transparency is diminished, which is attributed to both the presence of octahedral Mn and the increased hole content. Room-temperature electrical measurements of doped samples reveal an increase in conductivity of several orders of magnitude as compared to that of undoped samples, and high-temperature measurements show that Cr2MnO4 is a band conductor, as predicted by theory. The overall agreement between theory and experiment illustrates the advantages of a theory-driven approach to materials design.

Octahedral Mn(II) complex with new NNO donor Schiff base ligand: Synthesis, structure, photoluminescent behavior and computational studies

Octahedral Mn(II) complex with NNO donor Schiff base ligand (HL) containing 8-aminoquinoline moiety with general formula, [Mn(L)2] (1) has been synthesized and characterized. The structural, electronic and photoluminescent properties have been studied. The X-ray structure of complex (1) shows distorted octahedral geometry around manganese(II). Cyclic voltammetry study of the complex shows quasi-reversible Mn(II)/Mn(III) oxidation and ligand reduction. The π(L)→π∗(L) (ILCT) based emission properties of the ligand HL and Mn(II) complex, 1 have been studied. The electronic structure and spectral properties are interpreted by DFT and TDDFT computations.

A microporous manganese-based metal–organic framework for gas sorption and separation

A metal–organic framework [Mn3(HCOO)6]·DMF (1) with in situ generated formate ligand from the decomposition of N,N-dimethylformamide (DMF) solvent has been solvothermally synthesized and structurally characterized by single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), Infrared Spectroscopy (IR) and Elemental analysis (EA). Each formate ligand acts as μ3-bridge to link three octahedral Mn(II) centers to form a neutral three-dimensional (3D) framework with interesting 1D zigzag channel along the b axis, in which the DMF fill the free spaces. The desolvated samples exhibit interesting adsorption properties and show high selectivity for the adsorption of CO2 over N2 under ambient conditions.

Uranyl sorption onto birnessite: A surface complexation modeling and EXAFS study

This work investigates the mechanism of the uranyl interaction with birnessite, one of the most common layer-type MnO2 mineral at the Earth's surface, by coupling macroscopic (surface complexation experiments) and microscopic (EXAFS measurements) approaches. The sorption of uranyl on synthetic hexagonal birnessite, the low-pH birnessite form, was studied under various conditions of pH (3–6), electrolyte backgrounds (0.1M NaClO4, NaNO3 and Na2CO3), and solid/liquid ratios (from 0.27 to 4.5g/L). Sorption isotherms exhibit a complex form indicative of at least two types of sorption sites. EXAFS data reveal the presence of two equatorial O shells at ca. 2.32Å and 2.46Å for all the samples, and a Mn shell at ca. 3.38Å in the low-pH (≤5) samples only. No U–U pair was detected, despite the presence of polynuclear dissolved species in some of the samples.From the combination of the sorption isotherms and EXAFS results, a structural model for the sorption of uranyl onto hexagonal birnessite is proposed, in which two energetically different sites are involved. At low pH (≤5) a bidentate edge-sharing complex with Mn octahedra of the mineral edges can be inferred, whereas bidentate corner-sharing and/or monodentate complexation to layer vacancies would most likely describe EXAFS features of higher pH samples. A diffuse double layer model of surface complexation was developed for describing within the same framework the uranyl sorption against pH, involving both high-affinity (Mn octahedra edge) and low-affinity (above layer vacancies) sites.The comparison of the uranyl sorption onto hexagonal birnessite and various related environmental minerals shows that the affinity of uranyl for birnessite largely exceeds the sorption observed on montmorillonite and zeolite and turns out to be comparable to iron oxides, confirming the potential role of phyllomanganates to the control of uranyl mobility in post-oxic acidic environments.

Isomeric chain structures of {[Mn(H₂O)₄]₂Ru₂(CO₃)₄Br₂}n(n-): syntheses, structural diversity and magnetic properties.

The self-assembly of Ru2(CO3)4(3-) paddle-wheel precursors and Mn(2+) ions in aqueous solution yields various carbonate complexes. With appropriate selection of the synthetic conditions, we are able to intentionally tune the composition and structure of Mn-Ru2-carbonate assemblies to form infinite chain structural complexes, e.g., K[{Mn(H2O)4}2Ru2(CO3)4Br2]·H2O (1) and H[{Mn(H2O)4}2Ru2(CO3)4Br2]·6H2O (2). Complexes 1 and 2 are obtained at different temperatures (25 °C for 1 and 5 °C for 2, respectively), and their crystal structures consist of brick-wall stacked chains, in which neighboring Ru2(CO3)4Br2(5-) units are linked by two disubstituted octahedral Mn(H2O)4(2+) in a cis manner, resulting in two isomeric (twisted and zigzag) negative double-chain α- and β-{[Mn(H2O)4]2Ru2(CO3)4Br2}n(n-). The magnetic properties of complexes 1 and 2 were highly characterized. The alternating current (AC) susceptibility analysis of complex 1 reveals a two-step magnetism transition at T1 = 5.0 K and T2 = 2.6 K, respectively. Complex 2 exhibits metamagnetism behavior, with a transition field H(C) = ~1.2 kOe at 2.0 K.

Analyses of supramolecular interactions present in a coordination polymer of Mn(II) with 2-picolinate and 4,4′-Azobis(pyridine)

A new 2D coordination polymer [MnII(pic)(4,4′ -azpy)(H2O)]ClO4·EtOH (pic=2-picolinate) has been synthesized where each of the octahedral Mn(II) center is connected by trans coordinating 4,4′-azpy and syn-anti bridging picolinate, resulting in a sheet like structure. Density functional theory (DFT) calculations, at the BLYP-D3/def2-TZVPD level of theory, are performed to explore the interplay of various supramolecular interactions present within the coordination polymer.

Visible light induced oxidation of water by rare earth manganites, cobaltites and related oxides

A study of the visible light induced oxidation of water by perovskite oxides of the formula LaMO3 (M=transition metal) has revealed the best activity with LaCoO3 which contains Co3+ in the intermediate-spin (IS) with one eg electron. Among the rare earth manganites, only orthorhombic manganites with octahedral Mn3+ ions exhibit good catalytic activity, but hexagonal manganites are poor catalysts. Interestingly, not only the perovskite rare earth cobaltites but also solid solutions of Co3+ in cubic rare earth sesquioxides exhibit catalytic activity comparable to LaCoO3, the Co3+ ion in all these oxides also being in the IS t2g5eg1 state.

Gas and vapor adsorption in octacyanometallate-based frameworks Mn2[M(CN)8] (M = W, Mo) with exposed Mn2+ sites

Dehydration of the isostructural three-dimensional (3D) octacyanometallate-based materials Mn2M(CN)8·7H2O (M = Mo, 1·7H2O; W, 2·7H2O) generates robust porous frameworks (1 and 2). In the structure, the [M(CN)8]4− units are linked via octahedral Mn2+ centers to form an open 3D framework with 1D channels, in which the non-coordinated and coordinated water molecules are involved. The permanent porosities have been confirmed by thermogravimetric analysis, variable-temperature X-ray diffraction and Raman spectra, and adsorption (H2O, N2 and H2) measurements. H2 adsorption at 1.1 bar and 77 K was 0.60 wt% for 1 and 0.49 wt% for 2. At initial loading ΔHads has the value of ca. 10.0 kJ mol−1 for both materials, which represents the highest value reported for any cyanide-based assemblies. The high enthalpy can be attributed to the presence of coordinatively-unsaturated Mn2+ sites left exposed by the removal of coordinated water molecules in the structure.

3,3′-dihydroxy-4,4′-[1,2-cyclohexanediyl-bis(nitrilomethylidyne)]-bis-phenol schiff-base and its Mn(II) complex: Synthesis, experimental, and theoretical characterization

In this work, a 3,3′-dihydroxy-4,4′-[1,2-cyclohexanediyl-bis(nitrilomethylidyne)]-bis-phenol [=H2L] Schiff-base ligand and its Mn(II) complex [Mn(L)(H2O)2] are newly synthesized and characterized by elemental analysis, IR and NMR spectroscopies. Also the geometry optimizations, assignment of the IR bands and NMR chemical shifts are computed using the density functional theory (DFT) method. The DFT optimized geometry of the ligand is not planar; each of the cyclohexane and two benzene rings are located in separate planes. The phenolic protons are engaged in the intramolecular-hydrogen-bonding interactions with azomethine nitrogen atoms. In the optimized geometry of the octahedral Mn2+ complex, the dianionic L2− acts as a tetradentate ligand in the N, N, O−, O− manner, where the coordinating atoms occupy the four equatorial positions. The two axial positions are occupied by two H2O ligands. The theoretical and experimental results are in good agreement, confirming the validity of the optimized geometries for the H2L ligand and its Mn complex.

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.

Temperature dependent red luminescence from a distorted Mn^4+ site in CaAl_4O_7:Mn^4+

Thermal luminescence quenching behavior of a phosphor is essential for application in phosphor converted white light emitting diodes (pc-WLEDs) because the phosphor layer can be heated up to 473K in a working high power WLEDs. Here, we have confirmed indeed a red luminescence of Mn(4+) substituting for calcium sites rather than tetrahedral aluminum sites in CaAl(4)O(7):Mn which can be synthesized in pure phase even with boron acid as flux, and examined the low and high temperature luminescent properties in the range of 10 to 500K. We have revealed as well as thermal quenching mechanism that distorted octahedral Mn(4+) sites suffer severe thermal quenching. This work, thus, hints a strategy to find a new Mn(4+) phosphor with better resistance to thermal impact in the future.

Scalable properties of metal clusters: A comparative DFT study of ionic-core treatments

To assess various ionic-core approximations we carried out density functional calculations on a series of octahedral palladium and gold model clusters Mn with n=13–147. We compared results for average bond lengths, cohesive energies, vertical ionization potentials, and electron affinities to the corresponding all-electron scalar relativistic results. We used extrapolated bulk values to compare with experiments. The results of the projector-augmented wave method agree best with the all-electron results. When modeling palladium–gold nanoalloy particles, one should keep in mind that current ECP or PAW modeling of palladium moieties appears to be more accurate than modeling of gold species.