MnII Ions Research Articles

Three-Dimensional Supramolecular Architectures with MnII Ions Assembled from Hydrogen Bonding Interactions: Crystal Structures and Antiferromagnetic Properties.

Two novel cocrystal MnII compounds were successfully synthesized. The composition of two kinds crystals correspond to [Mn(hfac)2La2·Mn(hfac)2La(H2O)·Mn(hfac)2(H2O)2] (1) and [Mn(hfac)2Lb2·Mn(hfac)2(H2O)2·0.5(C6H14)] (2) [La = 1,3-bis(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-dihydro-1H-imidazol-2-y1)benzene; Lb = 1-(1′-oxyl-4′,4′,5′,5′-tetramethylimidazolin-2-yl)-3-(1′-oxyl-3′-oxo-4′,4′,5′,5′-tetramethylimidazolin-2-yl)benzene; hfac = hexafluoroacetylacetonato). Surprisingly, the compounds were not polymeric or clusters but, more interestingly, different ratio biradical–metal coordination compound cocrystals. The extensive intramolecular H-bonds are the cause of formation of the cocrystal structures by assembly in the two manganese(II) derivatives; and another factor is the halogen bonds between CF3 of hfac groups. Furthermore, three-dimensional supramolecular architectures were formed. The magnetic susceptibility of both compounds showed strong antiferromagnetic interactions involving the coordinated radical unit and the metal and lesser contribution from ferromagnetic interactions between the radical units. For compound 1, a good fit was obtained for gMn = 2.08, grad = 2.00 (fixed), J1 = −294.3 cm–1, J2 = 6.2 cm–1 and J3 = 10.8 cm–1. A reasonable fit for compound 2 was obtained for gMn = 2.04, grad = 2.00 (fixed), J1′ = −273.4 cm–1 and J2′ = 8.6 cm–1.

MnII/III and CeIII/IV Units Supported on an Octahedral Molecular Nanoparticle of CeO2.

The preparation of three new heterometallic clusters [Ce6Mn12O17(O2CPh)26] (1), [Ce10Mn14O24(O2CPh)32] (2), and [Ce23Mn20O48(OH)2(tbb)46(H2O)4](NO3)2 (3; tbb- = 4-tBu-benzoate) is reported. They all possess unprecedented structures with a common feature being the presence of an octahedral CeIV-oxo core: a Ce6 in 1, two edge-fused Ce6 giving a Ce10 bioctahedron in 2, or a larger Ce19 octahedron in 3. Complex 1 is the first Ce6 cluster with a central μ6-O2-. 2 and the cation of 3 are molecular nanoparticles of CeO2 (ceria) because they possess the fluorite structure of bulk ceria and are thus ultrasmall ceria nanoparticles in molecular form. The {Ce19O32} octahedral subunit of the cation of 3 had been predicted from density functional theory studies to be one of the stable fragments of the CeO2 lattice, but has never been previously synthesized in molecular chemistry. Around the Ce/O core of 1-3 is an incomplete monolayer of Mnn ions disposed as four Mn3, two Mn7, and four Mn5 units, respectively. This represents a clear structural similarity with composite (phase-separated) CeO2/MnOx mixtures where at high Ce:Mn ratios the Mn atoms segregate on the surface of CeO2 phases. Variable-temperature dc and ac magnetic susceptibility studies have revealed S = 2, S = 1/2, and S = 3/2 ground states for 1-3, respectively. Fitting of the 5.0-300 K dc data for 1 to a two-J model for an asymmetrical V-shaped Mn3 unit with no interaction between the end MnIII ions gave an excellent fit with the following values: J1 = 5.2(3) cm-1, J2 = -7.4(3) cm-1, and g = 1.96(2).

Synthesizing Mechanism of the Mn4 Ca Cluster Mimicking the Oxygen-Evolving Center in Photosynthesis.

The photosynthetic oxygen-evolving center (OEC) is a unique Mn4 CaO5 cluster that serves as a blueprint to develop superior water-splitting catalysts for the generation of solar fuels in artificial photosynthesis. It is a great challenge and long-standing issue to reveal the synthesizing mechanism of this Mn4 CaO5 cluster in both natural and artificial photosynthesis. Herein, efforts were made to reveal the synthesizing mechanism of an artificial Mn4 CaO4 cluster, a close mimic of the OEC. Four key intermediates were successfully isolated and structurally characterized for the first time. It was demonstrated that the Mn4 CaO4 cluster could be formed through a reaction between a thermodynamically stable Mn3 CaO4 cluster and an unusual four-coordinated MnIII ion, followed by stabilization process through binding an organic base (e.g., pyridine) on the "dangling" Mn ion. These findings shed new light on the synthesizing mechanism of the OEC and rational design of new artificial water-splitting catalysts.

Synthesis and characterization of a new monometallic layered double hydroxide using manganese.

This article reports for the first time the synthesis of an LDH using only manganese as the divalent and trivalent metallic ion. Analysis of the pH, redox potential, and chemical composition during the oxidation of a manganese basic salt using persulfate indicates the oxidation of 1/3 of the initial MnII ions, in agreement with the paramagnetic structure and XPS analysis. Infrared, Raman spectra and thermogravimetric analysis results were similar to the ones obtained with Fe-LDH also known as green rust. X-Ray diffractograms and Rietveld refinement were used to determine the structure of this solid. Thermodynamic considerations predict that this solid could reduce nitrate into gaseous nitrogen without further reduction to ammonium or ammonia unlike what is observed for Fe-LDH.

Spodium bonds and metal–halogen···halogen–metal interactions in propagation of monomeric units to dimeric or polymeric architectures

In this work we report on crystal structures of a heteroleptic coordination polymer [Hg2(HL)Cl4]n (1) where the nitrogen atom of the peripheral pyridine fragment is linked to another HgCl2 molecule and two discrete mononuclear heteroleptic complexes [Hg(HL)I2] (2) and [Mn(HL)Cl2]·MeOH (3·MeOH), which were obtained through self-assembling of N'-(1-(pyridin-2-yl)ethylidene)isonicotinohydrazide (HL) with HgCl2, HgI2 or MnCl2, respectively. HL coordinates the HgII salts in its keto-form, while MnCl2 is chelated by a zwitterionic form of HL confirmed by the solid state IR spectroscopy. The studied here ligand molecule has a tendency to involve the 4-pyridyl nitrogen atom in coordination bonding which is correlated with the ability to transfer the electric charge and production of a zwitterionic form. The crystal structure and Hirshfeld surface data analysis show a great importance of spodium bonds and metal–halogen⋯halogen–metal interactions. A prominent consequence of lack of σ- or π-hole interactions in case of MnII ion is the isolation of metal center from the external contacts. Apart form this in 3·MeOH the halogen⋯halogen interactions are absent. It seems that the σ- or π-hole regions formed at the HgII cation in 1 and 2 favor the participation of coordinated Cl or I atoms in the M–Hal⋯Hal'–M' halogen⋯halogen interactions, whereas in complex 3·MeOH there are no metal or halogen centered σ-hole interactions. Thus, the 1D coordination polymer in 1 is stabilized by the Hg⋯Cl spodium bonding. Additionally, the observed intermolecular halogen⋯halogen interactions in 1 provide cross-linking of the 1D coordination polymers, yielding a 2D supramolecular double-layered sheet. In 2 an additional contact between halogen and mercury atoms results in a dimeric unit. These dimers are linked into a 1D polymer by halogen⋯halogen interactions between metal bounded iodine atoms. The DFT theoretical studies were applied to analyze the Hg⋯X non-covalent spodium interactions that govern the formation of the 1D polymeric structure in 1 and self-assembled dimers in 2.

Structural diversity of Mn(II) and Cu(II) complexes based on 2-carboxyphenoxyacetate linker: Syntheses, conformation comparison and magnetic properties

Four new binary complexes with 2-carboxyphenoxyacetic acid ligand (2-H2cpa), namely [Mn(2-cpa)(H2O)3] (0D-Mn), [Cu(2-cpa)(H2O)3] (0D-Cu), [Mn(2-cpa)(H2O)]n (1D-Mn) and [Cu(2-cpa)(H2O)]n (2D-Cu), have been successfully prepared and systematically characterized. Structure analyses indicated that 0D-Mn and 0D-Cu are isomorphous mononuclear species in which the 2-carboxyphenoxyacetate (2-cpa) is a tridentate chelate anionic ligand. 1D-Mn is a 1D zigzag chain structure formed by the tetradentate bridging chelate-μ2 coordination pattern of 2-cpa connecting adjacent MnII ions. While 2D-Cu is a 2D corrugated (4,4)-connected layer and 2-cpa adopts pentadentate double bridging chelate-μ3 coordination mode in it. The different synthetic conditions, crystal structures and conformation of 2-cpa in the above compounds have been carefully analyzed and the results revealed that the synthetic conditions and flexible conformation of 2-cpa may be responsible for the structural diversity of binary 2-cpa metal complex system. In addition, the magnetic measurements showed that between the neighbouring metal ions there are weak ferromagnetic exchange in 0D-Mn and 0D-Cu, but antiferromagnetic coupling in 1D-Mn and 2D-Cu, respectively.

Synthesis, Crystal Structures, Magnetic Properties and Hirshfeld Surface Analysis of Cu/Mn Coordination Polymers

AbstractTwo new coordination polymers [Cu(L)(phen)]n (1) and {[Mn2(L)2(phen)2]⋅H2O}n (2, H2L is 4,4′‐(azanediylbis(methylene))dibenzoic acid, phen is o‐phenanthroline) were synthesized using hydrothermally method. Complexes 1 and 2 were characterized by powder XRD, FT‐IR, elemental analysis, thermogravimetry, and X‐ray single‐crystal diffraction. Complex 1 belongs to monoclinic system with space group P21/n while complex 2 belongs to triclinic system with space group Pī. Complex 1 is 1D coordination polymers while complex 2 is 2D coordination polymers. Hirshfeld surface analysis of 1 and 2 were investigated and discussed in detail. Moreover, Magnetic studies reveal that complex 2 displays dominant antiferromagnetic interactions between MnII ions through syn‐syn‐carboxyl bridges.

Synthesis, Crystal Structure and Magnetic Properties of 1D Chain Complexes Based on Azo Carboxylate Oxime Ligand

Two carboxylate-bridged one-dimensional chain complexes, {[MnII(MeOH)2][FeIII(L)2]2}n (1) and {[MnII(DMF)2][MnIII(L)2]2·DMF}n (2) [H2L = ((2-carboxyphenyl)azo)-benzaldoxime], containing a low-spin [FeIII(L)2]− or [MnIII(L)2]− unit were synthesized. Magnetic measurements show that the adjacent high-spin MnII and low-spin MIII ions display weak antiferromagnetic coupling via the syn–anti carboxyl bridges, with J = −0.066(2) cm−1 for complex 1 and J = −0.274(2) cm−1 for complex 2.

A single-chain magnet based on bis(end-on azido/alkoxo)-bridged linear [MnIII2MnII] repeating units

The synthesis, structural characterization and magnetic studies of the 1D coordination polymer [MnIII2MnII(L)2(N3)2(MeOH)2]n (1) is presented. Compound 1 consists of MnIII-MnII-MnIII strictly linear trinuclear repeating units with bis(end-on azido/alkoxo) bridges between the central MnII ion and each one of the terminal MnIII ions, defining two rhombic units [MnIIIMnII(μ1,1-N3)(μ-OR)]. Each repeating unit is further linked to its neighboring ones through two μ-OR groups, defining rhombic units [MnIII2(μ-OR)2], thus promoting the chain structure of 1. The magnetic studies revealed that 1 displays single-chain magnet behavior (SCM) with energy barrier Δ = 53 ± 1 K. Compound 1 is the first example of SCM based on a mixed-valence linear trinuclear unit [MnIII2MnII(μ1,1-N3)2(μ-OR)2].

Effects of MnII and EuIII Cation Exchange in Sepiolite‐Titanium Dioxide Nanocomposites in the Photocatalytic Degradation of Orange G

AbstractTwo primary mechanisms of titanium dioxide (TiO2) efficiency inhibition in ultraviolet (UV)‐driven photocatalytic reactions are the high recombination rate and sintering. To address these challenges, TiO2 nanocrystals were grown in‐situ onto sepiolite modified with MnII and EuIII ions. The resulting nanocomposites were characterized and evaluated for photocatalytic activity for Orange G (OG) degradation under UV irradiation. Resultant reduction in activity over Mn‐sepiolite‐TiO2 is attributed to charge‐carrier scavenging by unstable Mn and adsorption‐mediated chromophore protection by Mn‐oxyhydroxide. Dye removal over Eu‐sepiolite‐TiO2 was only slightly more efficient than over the control despite relevant Eu concentrations; potentially related to inhibited TiO2‐Eu interfacial synergy and superoxide radical scavenging. The results of this investigation corroborate prior observations that substrate cation‐exchange results in unpredictable behavior of the cations introduced during subsequent fabrication steps which may be of benefit or detriment to the final material.

Orientational Jahn–Teller Isomerism in the Dark‐Stable State of Nature's Water Oxidase

AbstractThe tetramanganese–calcium cluster of the oxygen‐evolving complex of photosystem II adopts electronically and magnetically distinct but interconvertible valence isomeric forms in its first light‐driven oxidized catalytic state, S2. This bistability is implicated in gating the final catalytic states preceding O−O bond formation, but it is unknown how the biological system enables its emergence and controls its effect. Here we show that the Mn4CaO5 cluster in the resting (dark‐stable) S1 state adopts orientational Jahn–Teller isomeric forms arising from a directional change in electronic configuration of the “dangler” MnIII ion. The isomers are consistent with available structural data and explain previously unresolved electron paramagnetic resonance spectroscopic observations on the S1 state. This unique isomerism in the resting state is shown to be the electronic origin of valence isomerism in the S2 state, establishing a functional role of orientational Jahn–Teller isomerism unprecedented in biological or artificial catalysis.

Orientational Jahn-Teller Isomerism in the Dark-Stable State of Nature's Water Oxidase.

The tetramanganese–calcium cluster of the oxygen‐evolving complex of photosystem II adopts electronically and magnetically distinct but interconvertible valence isomeric forms in its first light‐driven oxidized catalytic state, S2. This bistability is implicated in gating the final catalytic states preceding O−O bond formation, but it is unknown how the biological system enables its emergence and controls its effect. Here we show that the Mn4CaO5 cluster in the resting (dark‐stable) S1 state adopts orientational Jahn–Teller isomeric forms arising from a directional change in electronic configuration of the “dangler” MnIII ion. The isomers are consistent with available structural data and explain previously unresolved electron paramagnetic resonance spectroscopic observations on the S1 state. This unique isomerism in the resting state is shown to be the electronic origin of valence isomerism in the S2 state, establishing a functional role of orientational Jahn–Teller isomerism unprecedented in biological or artificial catalysis.

A Force Field for a Manganese-Vanadium Water Oxidation Catalyst: Redox Potentials in Solution as Showcase

We present a molecular mechanics force field in AMBER format for the mixed-valence manganese vanadium oxide cluster [Mn4V4O17(OAc)3]3−—a synthetic analogue of the oxygen-evolving complex that catalyzes the water oxidation reaction in photosystem II—with parameter sets for two different oxidation states. Most force field parameters involving metal atoms have been newly parametrized and the harmonic terms refined using hybrid quantum mechanics/molecular mechanics reference simulations, although some parameters were adapted from pre-existing force fields of vanadate cages and manganese oxo dimers. The characteristic Jahn–Teller distortions of d4 MnIII ions in octahedral environments are recovered by the force field. As an application, the developed parameters have been used to calculate the redox potential of the [MnIIIMn3IV] ⇌ [Mn4IV]+e− half-reaction in acetonitrile by means of Marcus theory.

A supertetrahedral T2 [Mn4Ce6] cluster showing second-harmonic generation response

The self-assembly reaction of MnCl2·4H2O, Ce(acac)3·xH2O (acac = deprotonated acetylacetone), and acenaphthenequinone dioxime (acndH2) in a mixture of methanol and dimethyl formamide (DMF) has led to a [MnIII4CeIV6] cluster MnIII4CeIV6(μ-O)8(acnd)4(OAc)4(acac)4(CH3O)4(DMF)4 (1) with a supertehedral T2 metal topology. Owing to the helical alignment of the supertetrahedral clusters, compound 1 shows a weak second-harmonic generation (SHG) response. Magnetic studies reveal very weak antiferromagnetic couplings between the paramagnetic MnIII ions.

Unusual Mn5 cluster with a ‘twisted bow-tie’ topology and MnIIMnIII2MnIV2 oxidation states: Synthesis, structure, and magnetic properties

The ‘reductive aggregation’ procedure involving the reaction of MnO4- in MeOH in the presence of a carboxylic acid has been extended for the first time to the use of a dicarboxylic acid and the additional presence of a chelate, namely phthalic acid (phthH2) and 2,2′-bipyridine (bpy), respectively. The MnO4-:phthH2:bpy = 1:2:1 reaction in MeOH has led to isolation of [Mn5O4(phth)3(phthH)(bpy)4](phthH2)(phthH) (1), whose Mn5 cation possesses a ‘twisted bow-tie’ topology comprising two near-perpendicular MnII,III,IV3 scalene triangles fused at the MnII ion. Each triangle is bridged by a central μ3-O2- and a μ2-O2- on the MnIIIMnIV edge. Peripheral ligation is provided by the phthalate groups bridging in various modes, and a chelating bpy on each MnIII and MnIV ion. The cation is a rare example of a cluster with three Mn oxidation states, and it is also the first MnIV-containing phthalate complex. Fitting of variable-temperature, solid-state dc magnetic susceptibility data collected in a 0.1 T field in the 5.0–300 K range gave J1 = J(MnIIIMnIV) = − 116(3) cm−1, J2 = J(MnIIMnIV) = − 6.0(4) cm−1, J3 = J(MnIIMnIII) = +3.8(8) cm−1, and g = 1.95, with TIP = 500 × 10-6 cm3 mol−1. These indicate an S = 7/2 spin ground state, which was confirmed by a fit of magnetization data collected in the 0.1–7.0 T and 1.8–10.0 K ranges, and by ac in-phase susceptibility data in zero dc field and a 3.5 G ac field at a 1000 Hz frequency.

Versatile Reactivity of MnII Complexes in Reactions with N-Donor Heterocycles: Metamorphosis of Labile Homometallic Pivalates vs. Assembling of Endurable Heterometallic Acetates.

Reaction of 2,2′-bipyridine (2,2′-bipy) or 1,10-phenantroline (phen) with [Mn(Piv)2(EtOH)]n led to the formation of binuclear complexes [Mn2(Piv)4L2] (L = 2,2′-bipy (1), phen (2); Piv− is the anion of pivalic acid). Oxidation of 1 or 2 by air oxygen resulted in the formation of tetranuclear MnII/III complexes [Mn4O2(Piv)6L2] (L = 2,2′-bipy (3), phen (4)). The hexanuclear complex [Mn6(OH)2(Piv)10(pym)4] (5) was formed in the reaction of [Mn(Piv)2(EtOH)]n with pyrimidine (pym), while oxidation of 5 produced the coordination polymer [Mn6O2(Piv)10(pym)2]n (6). Use of pyrazine (pz) instead of pyrimidine led to the 2D-coordination polymer [Mn4(OH)(Piv)7(µ2-pz)2]n (7). Interaction of [Mn(Piv)2(EtOH)]n with FeCl3 resulted in the formation of the hexanuclear complex [MnII4FeIII2O2(Piv)10(MeCN)2(HPiv)2] (8). The reactions of [MnFe2O(OAc)6(H2O)3] with 4,4′-bipyridine (4,4′-bipy) or trans-1,2-(4-pyridyl)ethylene (bpe) led to the formation of 1D-polymers [MnFe2O(OAc)6L2]n·2nDMF, where L = 4,4′-bipy (9·2DMF), bpe (10·2DMF) and [MnFe2O(OAc)6(bpe)(DMF)]n·3.5nDMF (11·3.5DMF). All complexes were characterized by single-crystal X-ray diffraction. Desolvation of 11·3.5DMF led to a collapse of the porous crystal lattice that was confirmed by PXRD and N2 sorption measurements, while alcohol adsorption led to porous structure restoration. Weak antiferromagnetic exchange was found in the case of binuclear MnII complexes (JMn-Mn = −1.03 cm−1 for 1 and 2). According to magnetic data analysis (JMn-Mn = −(2.69 ÷ 0.42) cm−1) and DFT calculations (JMn-Mn = −(6.9 ÷ 0.9) cm−1) weak antiferromagnetic coupling between MnII ions also occurred in the tetranuclear {Mn4(OH)(Piv)7} unit of the 2D polymer 7. In contrast, strong antiferromagnetic coupling was found in oxo-bridged trinuclear fragment {MnFe2O(OAc)6} in 11·3.5DMF (JFe-Fe = −57.8 cm−1, JFe-Mn = −20.12 cm−1).

Syntheses and Crystal Structures of a Series of Dysprosium–Manganese–Sodium 12-Metallacrown-4 Compounds with Halogenated Benzoate Bridging Anions

A series of heterotrimetallic dysprosium–manganese–sodium 12-metallacrown-4 compounds has been synthesized and characterized by single-crystal X-ray analysis: DyNaX4[12-MCMn(III)N(shi)-4], where X− = 2-fluorobenzoate (1), 3-fluorobenzoate (2), 4-fluorobenzoate (3), 2-chlorobenzoate (4), 4-chlorobenzoate (5), 3-bromobenzoate (6), and 2-iodobenzoate (7); MC is metallacrown; and shi3− is salicylhydroximate. Each 12-MC-4 framework is comprised of four ring MnIII ions and four shi3− ligands. The oxime oxygen atoms of the shi3− ligands produce a central cavity which then binds one DyIII ion and one Na+ ion on opposite sides. In each molecule four halogenated benzoate anions bridge between the central DyIII ion and the ring MnIII ions via the carboxylate groups. The identity of the halogenated benzoate anion has little effect on the structure of the [12-MCMn(III)N(shi)-4] framework as determined by several metrical parameters: the MC cavity radius, the average cross cavity MnIII–MnIII distance, the average cross cavity oxime oxygen-oxime oxygen distance, and the distance of the DyIII from the oxime oxygen mean plane. For 1–7 these metrical parameters are strikingly similar; thus, providing further reinforcement of one hallmark of metallacrown chemistry—the ability to substitute various components of the molecule without affecting the overall structure which can be used for the fine-tuning of molecular properties. Four 4-fluorobenzoate (4-Fben) anions bridge between the central DyIII ion and the ring MnIII ions in the metallacrown compound DyNa(4-Fben)4[12-MCMn(III)N(shi)-4](H2O)4·4DMF.

Catena-Poly[[(2,2'-bi-pyridine-κ2 N,N')manganese(II)]-di-μ-bromido

In the polymeric title complex, [MnBr2(C10H8N2)] n , the MnII ion, situated on a twofold axis of symmetry, is six-coordinated in a distorted octa-hedral coordination geometry defined by two N atoms from the chelating 2,2'-bi-pyridine ligand and four bridging Br- anions. The crystal reveals a one-dimensional Br-bridged chain along the c-axis direction with a zigzag topology. In the crystals, contacts between chains include π-π inter-actions between pyridyl rings [inter-centroid separation = 4.082 (1) Å].

Assembly of CeO2–MoO3–SiO2(CH2)3-(Alginate)2 As A novel nanocomposite for removal of MnII/CrVI and 56Mn/51Cr radionuclides from water

A new nanocomposite, CeO2–MoO3–SiO2(CH2)3-(Alg)2, has been synthesized via a simple synthesis method using a microwave irradiation technique. The morphological characterization indicated that the average particle size of the nanocomposite is 94.26–141.54 nm.The adsorptive remediation was established for MnII and CrVI ions by the nanocomposite under the influence of the microwave sorption process. Additionally, remediation of 51Cr and 56Mn radioactive nuclides was established using column technique. In this study, all the adsorption controlling parameters were explored like, solutions pH, contact time, amount of nanocomposite, and ionic concentration of the target metals. The maximum metal up-take capacities were estimated as 122.06 mg/g for MnII and 151.96 mg/g for CrVI by utilizing 5.0 mg of the nanocomposite at pH values 7.0 for MnII, and 2.0 for CrVI, while the equilibrium time at 25, and 20 s for MnII, and CrVI ions, respectively. The adsorption kinetics of MnII, and CrVI ions onto the CeO2–MoO3–SiO2(CH2)3-(Alg)2 nanocomposite proved to fit with the pseudo-second-order kinetics model and the adsorption mechanism fitted to the Langmuir and Freundlich isotherm models compared to the other models.

Simultaneous quantitative recognition of all purines including N6-methyladenine via the host-guest interactions on a Mn-MOF

Simultaneous quantitative recognition of all purines including N6-methyladenine via the host-guest interactions on a Mn-MOF