Mn-N Bond Research Articles

Interfacial structuring of Mn[sbnd]N and Mn[sbnd]C bonds by defect engineering for high-performance Zn-Mn battery

Zinc‑manganese batteries (ZMBs), with their non-flammable aqueous electrolyte and lower electrode material costs, offer a safer and more economical solution to the problem of energy intermittency. However, current ZMBs still face significant challenges, such as the presence of low electrical conductivity and poor structural stability of the manganese-based cathode, as well as unclear mechanisms of structural changes during charge storage. Here, we present a strategy to construct MnO2 containing MnC and MnN bonds (PAMO) by defect engineering and interface bonding design. This strategy benefits from the fact that MnN and MnC bonds can stabilize the structure and promote the interfacial dynamics of MnO2, thus effectively mitigating manganese dissolution. Meanwhile, the oxygen defects generated by interfacial bonding increase the electrical conductivity of MnO2. In addition, in terms of morphology and structure, the leafy vein-like secondary compartmentalized structure formed by PAMO provides more reactive sites for the redox reaction of MnO2, accelerating charge transfer and ion diffusion. The experimental results show that compared with pure MnO2 (326.8 mAh g−1), the capacity of PAMO material is enhanced by 30.1% (426.6 mAh g−1), and the battery still has 85.4% residual capacity (144.2–123.1 mAh g−1) after 6000 cycles, and coulombic efficiency is always maintained above 99.5%. This heterostructure design strategy of C- and N-doped MnO2 provides high electronic conductivity while playing an important role in improving structural stability.

A Simple Manganese(I) Catalyst for the Efficient and Selective Hydrophosphination of Olefins with PH3, Primary, and Secondary Phosphanes.

A tridentate ligand L with a P,NH,N donor motif was synthesized in few steps from commercially available precursors. Upon reaction with [MnBr(CO)5], an octahedral 18-electron complex [Mn(CO)3(L)]Br (1) is obtained in which L adopts a facial arrangement. After deprotonation of the NH group in the cationic complex unit, a neutral Mn(I) amido complex [Mn(CO)2(L-H)] (2) is formed under loss of CO. Rearrangement of L-H leads to a trigonal bipyramidal structure in which the P and N donor centers are in trans position. Further deprotonation of 2 results in a dep-blue anionic complex fragment [Mn(CO)2(L-2H)]- (3). DFT calculations and a QTAIM analysis show that the amido complex 2 contains a Mn-N bond with partial double bond character and 3 an aromatic MnN2C2 ring. The anion [Mn(CO)2(L-2H)]- reacts with Ph2PH to give a phosphido complex, which serves as phosphide transfer reagent to activated olefins. But the catalytic activity is low. However, the neutral amido complex 2 is an excellent catalyst and with loadings as low as 0.04 mol %, turn over frequencies of >40'000 h-1 can be achieved. Furthermore, secondary and primary alkyl phosphines as well as PH3 can be added in a catalytic hydrophosphination reaction to a wide range of activated olefins such as α,β-unsaturated aldehydes, ketones, esters, and nitriles. But also, vinyl pyridine and some styrene derivatives are converted into the corresponding phosphanes.

Effect of density functional approximations on the calculated Jahn–Teller distortion in bis(terpyridine)manganese(III) and related compounds

ContextBis(terpyridine)manganese(III) exhibits Jahn–Teller distortion due to the inequivalent occupation of the degenerate eg orbitals of this high-spin d4 pseudo octahedral complex. Due to the spatially constrained nature of the terpyridine ligand, the central Mn-N bonds will always be shorter than the Mn-N terminal bonds, making it more difficult to distinguish between compression and elongation Jahn–Teller structures for bis(terpyridine)manganese(III). Density functional theory (DFT) calculations were utilized as a tool to evaluate the type of Jahn–Teller distortion in the high-spin d4 bis(terpyridine)manganese(III). The nature of the Jahn–Teller distortion calculated does depend upon the choice of density functional approximation (DFA) with the B3LYP, M06, and OLYP-D3 DFAs giving compression and the PW6B95D3, MN15, and MN15-D3 DFAs giving elongation in gas-phase calculations. All solvent-phase calculations yield an elongated structure for the bis(terpyridine)manganese(III) compound, which is yet to be structurally characterized experimentally. However, both gas and solvent OLYP-D3 calculations result in a compressed structure for the only experimentally isolated and characterized bis(terpyridine)manganese(III) complex, specifically the complex with terpyridine = 4′-(4-methylphenyl)-2,2′:6′,2′′-terpyridine. This alignment with the experimentally observed compression Jahn–Teller structure enhances the credibility of OLYP-D3 calculations in reproducing the observed geometries. The compressed Jahn–Teller geometries were near D2d symmetry with the z-axis for compression defined along the Mn-N central bonds. Elongation Jahn–Teller distortion is not possible along the Mn-N central bonds, due to their spatially constrained nature. Thus, elongation occur along one pair of opposite Mn-N terminal bonds that are longer than the other pair of opposite terminal bonds, with shorter central bonds. The highest symmetry of the elongation Jahn–Teller distortion geometry of bis(terpyridine)manganese(III) is C2v. Criteria to distinguish between a compression and elongation Jahn–Teller geometry for bis(terpyridine)manganese(III) are identified. The nature of the singly occupied eg molecular orbital, exhibiting anti-bonding interaction with the nitrogen-p MOs involved, dictates the type of Jahn–Teller distortion that occurs. The low-energy occupied bonding t2g molecular orbitals establish bonds with and undergo mixing with the ligand molecular orbitals. The OLYP-D3 functional is recommended for calculating bis(terpyridine)manganese(III) and related compounds due to its consistent generation of metal–ligand bonds slightly longer than observed in experiments, in line with the required behavior. Additionally, OLYP-D3 offers a realistic electronic structure for Jahn–Teller distorted bis(terpyridine)manganese(III), correctly identifying alpha eg molecular orbitals as the highest occupied molecular orbital and lowest unoccupied molecular orbital in agreement with experimental electrochemical studies. Furthermore, OLYP-D3 accurately reproduces the experimental compression geometry for the only structurally known bis(terpyridine)manganese(III) compound, instilling confidence in its reliability for such calculations.MethodsDFT geometry optimization and frequency calculations were done on the two different modes of Jahn–Teller distortion of bis(terpyridine)manganese(III), using the OLYP, B3LYP, M06, PW6B95D3, and MN15 functionals, with and without the Grimme’s D3 dispersion correction, and the 6-311G(d,p) or def2TZVPP basis set, as implemented in Gaussian 16. All optimizations were in the gas phase and also in the solvent phase with CH3CN as implicit solvent using IEFPCM.Graphical DFT calculations were utilized to determine the Jahn–Teller effect on the geometry of high-spin d4 bis(terpyridine)manganese(III) complex containing two structurally constrained tridentate ligands.

Morphological and microstructural engineering of Mn-N-C with strengthened Mn-N bond for efficient electrochemical oxygen reduction reaction

Revealing the correlation between the micro–macro structures and active sites of transition metal-nitrogen-carbon (M−N−C) for electrochemical oxygen reduction reaction (ORR) is essential to develop non-precious metal catalyzed fuel cells and metal-air batteries. Herein, Mn-N-C catalysts with various morphologies and microstructures were prepared using Mn2+ coordinated bis(imino)-pyridine-based polymer with N-rich content as a new platform of precursor, which was synthesized via a condensation reaction of 1H-1, 2, 4-Triazole-3, 5-Diamine and 2, 6-Diacetylpyridine. Results demonstrate that morphologies and fine structures (pore structure, N dopants, surface area, and atomic Mn-N bond length, etc.) of Mn-N-C catalysts are strongly dependent on the growth of the specific precursor with and without NaCl as a template and the secondary calcination temperature can further optimize the bond length of Mn-Nx moieties, resulting in significant activity differences between correspondingly derived Mn-N-C catalysts for ORR. Compared to Mn-N-C derived from the synthesized precursor without NaCl, Mn-N-C obtained by the precursor grown directly on NaCl features an ultra-thin nanosheet-like structure with a hierarchical pore distribution and a shorter Mn-N bond, presenting high ORR performance with a half-wave potential of 0.88 V in 0.1 M KOH and a tiny potential loss of 11 mV after 30 K cycles, which is also proved by high-performance practical single Zn-Air battery (139 mW·cm−2) and proton exchange membrane fuel cell (400 mW·cm−2). This work provides a new understanding of the critical role of morphology and Mn-N bonding length of M−N−C for enhancing ORR and a new route of developing non-Fe/Co-based M−N−C catalysts for electrocatalysis.

Improving stability and reversibility of manganese dioxide cathode materials via nitrogen and sulfur doping for aqueous zinc ion batteries

Manganese based oxides are one of the most promising cathode materials for secondary aqueous zinc ion batteries. However, its structural instability and slow reaction kinetics have hampered its large-scale application. Here, a rational nitrogen and sulfur diatomic doping strategy is suggested to enhance the electrochemical activity and reversibility of manganese dioxide. The nitrogen and sulfur-doped manganese dioxide (N-MnxOy-S) electrode material is synthesized by a simple hydrothermal approach combined with a low temperature vulcanization treatment. The electrode exhibits an excellent initial discharge capacity of 178 mA h g−1 at 1 A g−1. Even at a high rate of 2 A g−1, the capacity retention rate exceeds 90% for 3000 cycles. The large number of oxygen defects increases the storage sites for zinc ions, resulting in the excellent electrochemical properties of N-MnxOy-S. Additionally, the Mn-S and Mn-N bonds in N-MnxOy-S boost the interfacial dynamics of manganese dioxide, which can effectively reduce the dissolution of manganese and efficiently improve the electronic conductivity. The current study demonstrates that nitrogen and sulfur co-doping is a successful method for enhancing the electrochemical performance of manganese-based oxide cathodes, which serves as an important benchmark for the development of cathode materials appropriate for aqueous zinc ion batteries.

Pressure-induced first-order antiferromagnetic to ferromagnetic transition in MnN

MnN systems have been widely used to investigate Mn incorporated into Ш–V compounds, which combines the spin and electron charge as promising diluted magnetic semiconductors (DMS). However, few experiments have demonstrated the magnetic transformation of MnN with lattice constant changes, although it has been mentioned many times in previous theoretical calculations. In this study, we synthesize MnN single crystal under high pressure and temperature. Furthermore, we perform high-pressure resistance, magnetic resistance and synchrotron radiation on MnN single crystal/polycrystalline and observe the first-order phase transition accompanied with antiferromagnetic (AFM) to ferromagnetic (FM) magnetic structure transition under 34 GPa. The experimental result and first-principles calculations reveal the same magnetic and structural transition of MnN in the compression process from equilibrium volume 18.2 to16 Å3. An analysis of electronic structure and magnetic interactions in terms of the Heisenberg Hamiltonian indicates a strong FM coupling in the [001] plane due to the double exchange mechanism of Mn eg orbitals. With the reduced Mn-N bond length under high pressure, the enhanced FM double exchange interactions could induce the magnetic transition from AFM to FM and subsequently lead to a structural transition from a face-centered tetragonal structure to a cubic structure. These findings provide the foundations for GaMnN or MnN layer DMS.

Interfacial Designing of MnO2 Half-Wrapped by Aromatic Polymers for High-Performance Aqueous Zinc-Ion Batteries.

Due to the excellent specific capacity and high working voltage, manganese oxide (MnO2 ) has attracted considerable attention for aqueous zinc-ion batteries (AZIBs). However, the irreversible structural collapse and sluggish ionic diffusion lead to poor rate capability and inferior lifespan. Herein, we proposed a novel organic/inorganic hybrid cathode of carbon-based poly(4,4'-oxybisbenzenamine)/MnO2 (denoted as C@PODA/MnO2 ) for AZIBs. Various in/ex situ analyses and theoretical calculations prove that PODA chains with C=N groups can provide a more active surface/interface for ion/electron mobility and zinc ion storage in the hybrid cathode. More importantly, newly formed Mn-N interfacial bonds can effectively promote ion diffusion and prevent Mn atoms dissolution, enhancing redox kinetics and structural integrity of MnO2 . Accordingly, C@PODA/MnO2 cathode exhibits high capacity (321 mAh g-1 or 1.7 mAh cm-2 at 0.1 A g-1 ), superior rate performance (88 mAh g-1 at 10 A g-1 ) and excellent cycling stability over 2000 cycles. Hence, rational interfacial designs shed light on the development of organic/inorganic cathodes for advanced AZIBs.

Simultaneous Improvement of Oxygen Reduction and Catalyst Anchoring via Multiple Dopants on Mesoporous Carbon Frameworks for Flexible Al-Air Batteries.

Mesoporous carbon supported non-noble metals, as promising catalysts for boosting the oxygen reduction reaction (ORR) in metal-air batteries, usually face challenges of low activity and performance degradation caused by the catalyst detachment from carbon substrates. Herein, a one-stone-two-birds strategy is reported to simultaneously improve the ORR activity and anchor nanosized MnS catalysts on a mesoporous carbon framework via nitrogen (N) and sulfur (S) dopants (MnS/NS-C). Synchrotron-based X-ray absorption spectroscopy (XAS) confirms the existence of Mn-N and Mn-S bonds, which firmly anchor active MnS nanoparticles. Density functional theory (DFT) calculations reveal that the N, S codoping lowers the d-band center of Mn and optimizes ORR intermediate adsorption. An excellent ORR performance (the onset and half-wave potential of 1.07 and 0.91 V) and long-term durability are achieved for MnS/NS-C in alkaline media. The flexible Al-air battery, using MnS/NS-C as the cathode catalyst, shows a power density of 134.6 mW cm-2 in comparison to the Pt/C-based counterpart of 106.2 mW cm-2. This study constructs a stable interaction with non-noble catalysts and carbon substrates for enhancing catalytic activity and durability in metal-air batteries.

Tracking the pyrolysis process from 2D Mn2n polymer to high-rate anode materials for lithium ion batteries

By manipulating the pyrolysis of multidimensional precursors, excellent energy storage materials can be obtained. On the molecular level, however, the pyrolysis tracking and evolution of two-dimensional (2D) precursors require additional study. Here, we designed a 2D layered Mn-based polymer (Mn2n, [Mn2L2(CH3OH)2]n, L = 3-ethoxylsalicylate iso-nicotinyl hydrazone) bridged with L as a precursor, and obtained a 2D porous nanosheet N-doped carbon skeleton embedded with Mn2+O (Mn2+O/NC) through controlled pyrolysis under an inert atmosphere. The pyridine nitrogen coordination of isoniazid is astonishingly essential for the formation of 2D layered Mn2n polymers. The formation of Mn-N(pyridine) bonds serves as a bridge between the basic units of Mn2. Thermogravimetric mass spectrometry (TG-MS) could track the pyrolysis process and provide a potential evolutionary from a 2D Mn2n precursor to a 2D porous nanosheet Mn2+O/NC structure. The specific capacity of Mn2+O/NC-800 electrode reaches up to 614.1 mAh g−1 after 600 cycles at 200 mA g−1 current density when the pyrolysis product is used as the anode material of lithium ion battery. Dynamic analysis indicates that the 2D porous nanosheet structure of Mn2+O/NC has a high pseudocapacitance contribution and charge transfer efficiency, which effectively improves the performance of lithium ion batteries. This work will provide a useful guidance for the design of new electrode materials.

The Full d3-d5 Redox Series of Mononuclear Manganese Complexes: Geometries and Electronic Structures of [Mn(dgpy)2]n.

Although manganese ions exhibit a rich redox chemistry, redox processes are often accompanied by structural reorganization and a high propensity for ligand substitution, so that no complete structurally characterized manganese(II,III,IV) complex series without significant ligand sphere reorganization akin to the manganese(II,III,IV) oxides exists. We present here the series of pseudo-octahedral homoleptic manganese complexes [Mn(dgpy)2]n+ (n = 2-4) with the adaptable tridentate push-pull ligand 2,6-diguanidylpyridine (dgpy). Mn-N bond lengths and N-Mn-N bond angles change characteristically from n = 2 to n = 4, while the overall [MnN6] coordination sphere is preserved. The manganese(III) complex [Mn(dgpy)2]3+ exhibits a Jahn-Teller elongated octahedron and a negative D = -3.84 cm-1. Concomitantly with the consecutive oxidation of [Mn(dgpy)2]2+ to [Mn(dgpy)2]4+, the optical properties evolve with increasing ligand-to-metal charge transfer character of the absorption bands culminating in the panchromatic absorption of the purple-black manganese(IV) complex [Mn(dgpy)2]4+.

Nitrene Photochemistry of Manganese N-Haloamides*.

Manganese complexes supported by macrocyclic tetrapyrrole ligands represent an important platform for nitrene transfer catalysis and have been applied to both C-H amination and olefin aziridination catalysis. The reactivity of the transient high-valent Mn nitrenoids that mediate these processes renders characterization of these species challenging. Here we report the synthesis and nitrene transfer photochemistry of a family of MnIII N-haloamide complexes. The S=2 N-haloamide complexes are characterized by 1 H NMR, UV-vis, IR, high-frequency and -field EPR (HFEPR) spectroscopies, and single-crystal X-ray diffraction. Photolysis of these complexes results in the formal transfer of a nitrene equivalent to both C-H bonds, such as the α-C-H bonds of tetrahydrofuran, and olefinic substrates, such as styrene, to afford aminated and aziridinated products, respectively. Low-temperature spectroscopy and analysis of kinetic isotope effects for C-H amination indicate halogen-dependent photoreactivity: Photolysis of N-chloroamides proceeds via initial cleavage of the Mn-N bond to generate MnII and amidyl radical intermediates; in contrast, photolysis of N-iodoamides proceeds via N-I cleavage to generate a MnIV nitrenoid (i.e., {MnNR}7 species). These results establish N-haloamide ligands as viable precursors in the photosynthesis of metal nitrenes and highlight the power of ligand design to provide access to reactive intermediates in group-transfer catalysis.

Catalytic oxidation of NO over LaMnO3(001) surface: A DFT-based study

NO oxidation over LaMnO3(001) surface was studied using first-principle calculations based on density functional theory (DFT). The calculated results indicate that the surface energies of (001) are lower than that of the (011) and (111) surfaces. Three adsorbates (O2 NO and NO2) after adsorption are activated due to remarkable elongation of bond length, notable change in DOS and large electron transfer. The analysis of the electron localization function (ELF) reveal the typical feature of a ionic bond in the Mn-N and Mn-O bond intersecting planes. Difference charge density (DCD) analysis show that electron accumulation occurs at the Mn-O and Mn-N bonds as charge is transferred from adsorbate (NO, O2 or NO2) to the substrate, so that the ability bonding of the adsorbate and substrate is enhanced. The reaction of NO adsorbed at Mn2 with Oc is faster and more feasible due to the low energy barrier and short Oc-N bond distance. Dissociation of O2 is an exothermic process (−1.290 eV) with a small activation energy (0.345 eV). The NO activation and desorption of NO2 are energetically the most demanding steps.

Rational design of Prussian blue analogues as conversion anodes for lithium-ion batteries with high capacity and long cycle life

Prussian blue analogues (PBAs) have garnered much attentions in energy fields due to their three-dimensional open framework and electrochemical tunability. Noticeably, PBAs are also deemed extremely attractive as anode materials for batteries by virtue of their abundant internal active sites. However, their unclear redox mechanisms at lower potential severely restricts PBAs anodes to realize stable cycling performances. In this work, low-cost KxMn[Fe(CN)6]y□1−y·nH2O with diverse H2O content and structure are harvested via controlling the crystallization rate. It is firstly discovered that the KxMn[Fe(CN)6]y anodes undergoes multi-electron conversion reactions involving the fracture and recombination of MnN bonds, while the stronger FeC bond is preserved. Then, it is confirmed that weaker MnN bond which need to be prepared at a faster crystallization rate is more conducive to the fast electrochemical kinetics of the reversible conversion paths. Accordingly, the K0.09Mn[Fe(CN)6]0.66□0.34·3.40 H2O with higher H2O content and weaker MnN bond achieve the best Li-storage performances, exhibiting a reversible capacity of 480 mAh g−1 at a high current density of 1 A g−1 and considerable cycling stability exceeding 1000 cycles. The results also suggest that interstitial H2O could be beneficial for the better cycling stability of the KxMn[Fe(CN)6]y anodes. This work can provide new insights for the rational design of novel conversion anodes with high reversible capacity and superior cycling stability.

Adsorption of NO and O2 on MnO2 and (MnO2)3/Al2O3

Based on first-principles density functional theory (DFT), the adsorption performance of MnO2(110) surface for NO and O2 was calculated, and the deposition of (MnO2)3cluster on the γ-Al2O3(110) surface was studied. In addition, the adsorption and co-adsorption of NO and O2 on the surface of (MnO2)3/Al2O3 were further calculated. The results showed that NO was more inclined to adsorb on the four-coordinated Mn(Ⅳ) sites on the MnO2(110) surface (the maximum Eads was −75.35KJ·mol−1). There were very few O2 adsorption sites on the MnO2(110) surface, and only the vacancies between adjacent Mn(IV) could adsorb O2 stably. PDOS analysis showed that the hybridization between Mn 3d orbital and N 2p (or O 2p) orbital was the main reason for Mn-N bonds (or Mn-O bonds). The (MnO2)3 cluster tended to load on Al2O3(110) surface in a flat six-membered ring structure. There are abundant active oxygen sites on the (MnO2)3/Al2O3 surface, which had an excellent ability to adsorb NO (the maximum Eads was −278.24 KJ·mol−1). NO molecules interacted with surface-active oxygen to generate nitroso, and NO2 was easily desorbed from the (MnO2)3/Al2O3 surface. The co-adsorption of NO and O2 on the (MnO2)3/Al2O3 surface formed an ONOO* structure, which could decompose to form adsorbed NO2* and O*. Compared with single-phase manganese oxide crystals, manganese oxide clustered on γ-Al2O3 had superior NO adsorption performance and may have excellent catalytic oxidation properties.

MnO2 cathode materials with the improved stability via nitrogen doping for aqueous zinc-ion batteries

The research and exploration of manganese-based aqueous zinc-ion batteries have been controversial of cycle stability and mechanism investigation, thus improving the stability and exploring storage mechanism are still the most main issue. Defect engineering has become an effective method to improve cycle stability. Herein, a nitrogen-doped ε-MnO2 (MnO2@N) has been prepared using electrochemical deposition and heat treatment under nitrogen atmosphere. As the cathode for zinc-ion batteries, the capacity retention rate of MnO2@N cathode is close to 100% after 500 cycles at 0.5 A g−1, while the capacity retention rate for the initial MnO2 cathode is 62%. At 5 A g−1, the capacity retention rate of MnO2@N cathode is 83% after 1000 cycles, which is much higher than the 27% capacity retention rate for the original MnO2 cathode. And it can be found that the oxygen vacancies increase after nitrogen doping, which can improve the conductivity of the MnO2@N cathode. Also, there is Mn-N bond in MnO2@N, which can enhance the electrochemical stability of MnO2@N cathode. In addition, the electrochemical mechanism of MnO2@N cathode has been explored by the CV, GCD and GITT tests. It is found that nitrogen doping promotes the intercalation of H+ and the corresponding capacity contribution. Compared with the original MnO2 cathode, the diffusion coefficient of H+ and Zn2+in MnO2@N cathode increases. Also, the reactions during the charging and discharging process are explored through the ex-situ XRD test. And this work may provide some new ideas for improving the stability of manganese-based zinc-ion batteries.

THz, Raman, IR and DFT studies of noncentrosymmetric metal dicyanamide frameworks comprising benzyltrimethylammonium cations

We report density functional theory (DFT) studies of vibrational modes for benzyltrimethylammonium cations (BeTriMe+) as well as THz, IR and Raman studies of [BeTriMe][M(dca)3(H2O)] (dca = N(CN)2−, dicyanamide; M = Mn2+, Co2+, Ni2+) and their anhydrous analogues. These studies show that the anhydrous BeTriMeMn and BeTriMeNi have the same or very similar structures and loss of water molecules leads to significant changes in the metal-dicyanamide frameworks. In particular, the number of dca modes decreases, suggesting increase of crystal symmetry, probablly related with decrease in the number of non-equivalent dca bridges from two to one. Although it is possible that dehydration leads to a replacement of the coordinate Mn-O (Ni-O) bonds by Mn-N (Ni-N) bonds, wherein N atoms come from the C≡N groups of previously non-bridged dca units, reversibility of the dehydration process indicates that such new bonds are either not formed or are very weak. The anhydrous Mn and Ni compounds undergo similar reversible phase transitions to lower symmetry phases. The driving force for these transitions is most likely ordering of dca linkers but this process is accompanied by weak distortion of the metal-dicyanamide frameworks. In the case of BeTriMeCo, the loss of water molecules also leads to significant changes in the cobalt-dicyanamide framework. However, the structure of this analogue is different from the structures of the Mn and Ni counterparts, the number of unique dca linkers is preserved and the dehydration process is irreversible, suggesting more drastic rearrangement of the metal-dicynamide framework.

Solvation and coordination chemistry of manganese(II) in some solvents. A transfer thermodynamic, complex formation, EXAFS spectroscopic and crystallographic study

The solvation and coordination chemistry of the manganese(II) ion in water, methanol, dimethylsulfoxide (dmso), N,N’-dimethylpropylene urea (dmpu), acetonitrile and N,N-dimethylthioformamide (dmtf) have been studied from solvation thermodynamic, structural and complex formation ability point of view by calorimetry and EXAFS spectroscopy. The heats of transfer from water to methanol, dmso, acetonitrile and dmtf have been determined to −37.7, −71.6, –23.1 and −36.3 kJ mol−1, respectively, from the heats dissolution of anhydrous manganese(II) trifluoromethanesulfonate by ampoule calorimetry in the neat solvents. Refinement of the EXAFS data of the hydrated and methanol and dmso solvated manganese(II) ions in solution show octahedral configuration and mean Mn-O bond distances of 2.165(3), 2.161(2) and 2.157(3) Å, respectively. The Mn-O bond distance is significantly shorter in dmpu solution, 2.087(3) Å. As dmpu is a space-demanding solvent upon coordination, the manganese(II) ion is only allowed to bind five dmpu molecules in the solvate complex. The acetonitrile solvated manganese(II) ion is six-coordinate in octahedral fashion in solution with a mean Mn-N bond distance of 2.193(3) Å. The relative permittivity of pyridine is too low to allow dissociation of salts of divalent metal ions and neutral pyridine solvated complexes are formed in pyridine solution. In concentrated manganese(II) trifluoromethanesulfonate dmtf solution a contact ion-pair is formed with one trifluoromethanesulfonate ion. In this complex manganese(II) binds five dmtf molecules and a trifluoromethanesulfonate oxygen with Mn-S and Mn-O bond distances of 2.598(6) and 2.16(1) Å, respectively, in an octahedral complex. Complex formation studies performed by titration calorimetry of the manganese(II)-bromide system show significantly more stable complexes in dmpu than in solvents where the solvated manganese(II) ion has regular octahedral symmetry. The dmpu solvated MnBr2 complex in dmpu solution is five coordinate with mean Mn-Br and Mn-O bond distances of 2.494(3) and 2.076(3) Å, respectively. The structure of the [MnBr2(dmpu)2] complex in solid state has distorted tetrahedral geometry with mean Mn-Br and Mn-O bond distances of 2.473(3) and 2.014(3) Å, respectively, and a Br-Mn-Br bond angle of 116.3(1) degrees.

Insights into the interactions of g-C3N4/LaMnO3 hetero-junction to their structures and electronic properties by DFT calculations

The hetero-junctions of LaMnO3 and g-C3N4 nano-materials are expected to have suitable band structure for the Z-scheme mechanism, but the electronic structures and interfaces have been scarcely studied. In this work, g-C3N4/LaMnO3 hetero-junction composed of g-C3N4 and LaMnO3 layers is studied using the DFT calculations with plane-wave ultrasoft pseudopotential basis sets. The calculated g-C3N4/LaMnO3 heterostructure has a small lattice-mismatch compared with LaMnO3 and g-C3N4. There are reformed Mn-N bonds across the interface, which indicates the strong interaction existing in two layers between LaMnO3 and g-C3N4. When g-C3N4 and LaMnO3 are in contact, the electrons will transfer from LaMnO3 layer to g-C3N4 layer. On the basis of the band structure analysis, the photo-generated electrons in LaMnO3 can combine with the photo-induced holes in g-C3N4, which leads the higher reduction ability of photo-generated electrons in g-C3N4, and the stronger oxidation of photo-induced holes in LaMnO3. As a result, the Z-scheme heterojunction could be generated between the g-C3N4 layer and LaMnO3 layer, which not only has the better visible light adsorption capability, but also the more efficient charge carrier separation.

Effect of Lewis Acids on the Structure and Reactivity of a Mononuclear Hydroxomanganese(III) Complex.

The addition of Sc(OTf)3 and Al(OTf)3 to the mononuclear MnIII-hydroxo complex [MnIII(OH)(dpaq)]+ (1) gives rise to new intermediates with spectroscopic properties and chemical reactivity distinct from those of [MnIII(OH)(dpaq)]+. The electronic absorption spectra of [MnIII(OH)(dpaq)]+ in the presence of Sc(OTf)3 (1-ScIII) and Al(OTf)3 (1-AlIII) show modest perturbations in electronic transition energies, consistent with moderate changes in the MnIII geometry. A comparison of 1H NMR data for 1 and 1-ScIII confirm this conclusion, as the 1H NMR spectrum of 1-ScIII shows the same number of hyperfine-shifted peaks as the 1H NMR spectrum of 1. These 1H NMR spectra, and that of 1-AlIII, share a similar chemical-shift pattern, providing firm evidence that these Lewis acids do not cause gross distortions to the structure of 1. Mn K-edge X-ray absorption data for 1-ScIII provide evidence of elongation of the axial Mn-OH and Mn-N(amide) bonds relative to those of 1. In contrast to these modest spectroscopic perturbations, 1-ScIII and 1-AlIII show greatly enhanced reactivity toward hydrocarbons. While 1 is unreactive toward 9,10-dihydroanthracene (DHA), 1-ScIII and 1-AlIII react rapidly with DHA (k2 = 0.16(1) and 0.25(2) M-1 s-1 at 50 °C, respectively). The 1-ScIII species is capable of attacking the much stronger C-H bond of ethylbenzene. The basis for these perturbations to the spectroscopic properties and reactivity of 1 in the presence of these Lewis acids was elucidated by comparing properties of 1-ScIII and 1-AlIII with the recently reported MnIII-aqua complex [MnIII(OH2)(dpaq)]2+ ( J. Am. Chem. Soc. 2018, 140, 12695-12699). Because 1-ScIII and 1-AlIII show 1H NMR spectra essentially identical to that of [MnIII(OH2)(dpaq)]2+, the primary effect of these Lewis acids on 1 is protonation of the hydroxo ligand caused by an increase in the Brønsted acidity of the solution.

Effect of Water and Alkali-Ion Content on the Structure of Manganese(II) Hexacyanoferrate(II) by a Joint Operando X-ray Absorption Spectroscopy and Chemometric Approach.

Manganese hexacyanoferrate (MnHCF) is made of earth‐abundant elements by a safe and easy synthesis. The material features a higher specific capacity at a higher potential than other Prussian blue analogs. However, the effect of hydration is critical to determine the electrochemical performance as both the electrochemical behavior and the reaction dynamics are affected by interstitial/structural water and adsorbed water. In this study, the electrochemical activity of MnHCF is investigated by varying the interstitial ion content through a joint operando X‐ray absorption spectroscopy and chemometric approach, with the intent to assess the structural and electronic modifications that occur during Na release and Li insertion, as well as the overall dynamic evolution of the system. In MnHCF, both the Fe and Mn centers are electrochemically active and undergo reversible oxidation during the interstitial ion extraction (Fe2+/Fe3+ and Mn2+/Mn3+). The adsorption of water results in irreversible capacity during charge but only on the Fe site, which is suggested by our chemometric analysis. The local environment of Mn experiences a substantial yet reversible Jahn–Teller effect upon interstitial ion removal because of the formation of trivalent Mn, which is associated with a decrease of the equatorial Mn−N bond lengths by 10 %.