Synthesis and Characterization of Nanostructured Manganese Dioxide Used as Positive Electrode Material for Electrochemical Capacitor with Lithium Hydroxide Electrolyte

A nanostructured manganese dioxide electrode material was prepared using a solid‐reaction route starting with MnCl₂·4H₂O and NH₄HCO₃, and its electrochemical performance as a positive electrode for MnO₂/activated carbon hybrid supercapacitor with 1 mol·L^?1 LiOH electrolyte was reported. The material was proved to be a mixture of nanostructured γ‐MnO₂ and α‐MnO₂ containing some bound water in the structure, which was characterized by X‐ray diffraction analysis, infrared spectrum analysis, and transmission electron microscope observation. Electrochemical properties of the MnO₂ electrode and the MnO₂/AC capacitor were investigated by cyclic voltammetry, ac impedance and galvanostatic charge/discharge methods. Experimental results showed that the MnO₂ electrode exhibited faradaic pseudocapacitance behavior and higher specific capacitance in 1 mol·L^?1 LiOH electrolyte. The MnO₂/AC hybrid capacitor with 1 mol·L^?1 LiOH electrolyte presented excellent rate charge/discharge ability and cyclic stability.     

How different is pyrimidine as a core component of DNA base from its diazine isomers: A DFT study?

Recent photoemission spectroscopic (X‐ray photoemission spectra) study revealed less dramatic chemical changes for pyrimidine (PyM, 1, 3‐diazine) with in its ionization potential. Present systematic study using density functional theory calculations shows that PyM is indeed quite different from its diazine isomers (PyD, 1, 2‐diazine and PyA, 1, 4‐diazine). It is discovered that the most stable isomer PyM is relaxed from C_2V to C₁ point symmetry with a total electronic energy deduction of ?15.86 kcal.mol^?1. Although not substantial, PyM has the smallest molecule shape (electronic spatial extent) and the largest HOMO‐LUMO energy gap of 5.65 eV; only one absorption band in the region of 200–300 nm of the UV‐Vis spectrum but three clusters of chemical shift in the carbon and hydrogen NMR spectra. The energy decomposition analyses revealed that the interaction energy (ΔE_Int) of PyM is preferred over PyA by 4.08 kcal.mol^?1 and over PyD by 22.32 kcal.mol^?1, with the preferred N? C? N bond revealed by graph theory.     

Solvent Migration in Microhydrated Aromatic Aggregates: Ionization‐Induced Site Switching in the 4‐Aminobenzonitrile–Water Cluster

The dependence of the preferred microhydration sites of 4‐aminobenzonitrile (4ABN) on electronic excitation and ionization is determined through IR spectroscopy of its clusters with water (W) in a supersonic expansion and through quantum chemical calculations. IR spectra of neutral 4ABN and two isomers of its hydrogen‐bonded (H‐bonded) 4ABN–W complexes are obtained in the ground and first excited singlet states (S₀, S₁) through IR depletion spectroscopy associated with resonance‐enhanced multiphoton ionization. Spectral analysis reveals that electronic excitation does not change the H‐bonding motif of each isomer, that is, H₂O binding either to the CN or the NH site of 4ABN, denoted as 4ABN–W(CN) and 4ABN–W(NH), respectively. The IR spectra of 4ABN⁺–W in the doublet cation ground electronic state (D₀) are measured by generating them either in an electron ionization source (EI‐IR) or through resonant multiphoton ionization (REMPI‐IR). The EI‐IR spectrum shows only transitions of the most stable isomer of the cation, which is assigned to 4ABN⁺–W(NH). The REMPI‐IR spectrum obtained through isomer‐selective resonant photoionization of 4ABN–W(NH) is essentially the same as the EI‐IR spectrum. The REMPI‐IR spectrum obtained by ionizing 4ABN–W(CN) is also similar to that of the 4ABN⁺–W(NH) isomer, but differs from that calculated for 4ABN⁺–W(CN), indicating that the H₂O ligand migrates from the CN to the NH site upon ionization with a yield of 100 %. The mechanism of this CN→NH site‐switching reaction is discussed in the light of the calculated potential energy surface and the role of intracluster vibrational energy redistribution.     

Correlation between the O 2p Orbital and Redox Reaction in LiMn0.6Fe0.4PO4 Nanowires Studied by Soft X‐ray Absorption

The changes in the electronic structure of LiMn_0.6Fe_0.4PO₄ nanowires during discharge processes were investigated by using ex situ soft X‐ray absorption spectroscopy. The Fe L ‐edge X‐ray absorption spectrum attributes the potential plateau at 3.45 V versus Li/Li⁺ of the discharge curve to a reduction of Fe³⁺ to Fe²⁺. The Mn L ‐edge X‐ray absorption spectra exhibit the Mn²⁺ multiplet structure throughout the discharge process, and the crystal‐field splitting was slightly enhanced upon full discharge. The configuration‐interaction full‐multiplet calculation for the X‐ray absorption spectra reveals that the charge‐transfer effect from O 2p to Mn 3d orbitals should be considerably small, unlike that from the O 2p to Fe 3d orbitals. Instead, the O K‐edge X‐ray absorption spectrum shows a clear spectral change during the discharge process, suggesting that the hybridization of O 2p orbitals with Fe 3d orbitals contributes essentially to the reduction.     

Aqueous Manganese Dioxide Ink for Paper‐Based Capacitive Energy Storage Devices

We report a simple approach based on a chemical reduction method to synthesize aqueous inorganic ink comprised of hexagonal MnO₂ nanosheets. The MnO₂ ink exhibits long‐term stability and continuous thin films can be formed on various substrates without using any binder. To obtain a flexible electrode for capacitive energy storage, the MnO₂ ink was printed onto commercially available A4 paper pretreated with multiwalled carbon nanotubes. The electrode exhibited a maximum specific capacitance of 1035 F g^?1 (91.7 mF cm^?2). Paper‐based symmetric and asymmetric capacitors were assembled, which gave a maximum specific energy density of 25.3 Wh kg^?1 and a power density of 81 kW kg^?1. The device could maintain a 98.9 % capacitance retention over 10 000 cycles at 4 A g^?1. The MnO₂ ink could be a versatile candidate for large‐scale production of flexible and printable electronic devices for energy storage and conversion.     

The kinetics of reaction between permanganate and chlorine ions in acid solutions

The reaction between MnO ₄ ^? and Cl^? was studied in acid media at room temperature and ionic strength 1 M. The stoichiometric equation of the reaction has the form MnO ₄ ^? + 8H⁺ + 4Cl^? = Mn³⁺ + 2Cl₂ + 4H₂O. The reaction proceeds in two stages. At the first stage, permanganate ions are consumed to produce one Cl₂ molecule per MnO ₄ ^? ion. At the second stage, the second Cl₂ molecule and the final MnO ₄ ^? reduction product (trivalent manganese) are formed. The first stage is a reaction first-order in MnO ₄ ^? and second-order in H⁺ and Cl^?; its rate constant is (9.8 ± 0.6) × 10^?2l⁴/(mol⁴ min). An analysis of the literature data leads to a value of 18–20 kcal/mol for its activation energy.     

Die Feinstruktur in den Schwingungs- und elektronischen Absorptionsspektren von [CrO4]2− und [MnO4]−

Finestructure in the Vibrational and Electronic Absorption Spectra of [CrO₄]^2? and [MnO₄]^? The ir and ra spectra of Tl₂[CrO₄] and (C₂H₅)₄N[MnO₄] are measured and assigned. Details of the preresonance- and resonance-Raman effect are discussed. The exact knowledge of the vibrational spectrum enables the understanding of the complicated vibrational finestructure in the electronic absorption spectrum of (C₂H₅)₄N[MnO₄]. For the states of the charge-transfer t₁ → e* bands are found at 15 000, 15 170 cm^?1 for ¹T₁(I), at 17 646, 17 708, 17 809 cm^?1 for ¹T₂(II) and at 17 920, 17 992 and 18 080 cm^?1 for ³T₂(III). The electronic origin for the states of the t₂ → e* chargetransfer is at 24 661 for ¹T₁(IV) and 30 230 cm^?1 for ¹T₂(V). The vibrational coupling is only with the totally symmetric Mn? O-stretching-vibration. Bands at 29 500 cm^?1 and 44 450 cm^?1 are assigned to the ¹T₂-states of the t₁, t₂ → t₂* charge-transfer.     

A Water‐Stable Terbium(III)–Organic Framework as a Chemosensor for Inorganic Ions,Nitro‐Containing Compounds and Antibiotics in Aqueous Solutions

Effective detection of organic/inorganic pollutants, such as antibiotics, nitro‐compounds, excessive Fe³⁺ and MnO₄^?, is crucial for human health and environmental protection. Here, a new terbium(III)–organic framework, namely [Tb(TATAB)(H₂O)]?2H₂O ( Tb‐MOF , H₃TATAB=4,4′,4′′‐s‐triazine‐1,3,5‐triyltri‐m‐aminobenzoic acid), was assembled and characterized. The Tb‐MOF exhibits a water‐stable 3D bnn framework. Due to the existence of competitive absorption, Tb‐MOF has a high selectivity for detecting Fe³⁺, MnO₄^?, 4‐nirophenol and nitroimidazole (ronidazole, metronidazole, dimetridazole, ornidazole) in aqueous through luminescent quenching. The results suggest that Tb‐MOF is a simple and reliable reagent with multiple sensor responses in practical applications. To the best of our knowledge, this work represents the first Tb^III‐based MOF as an efficient fluorescent sensor for detecting metal ions, inorganic anions, nitro‐compounds, and antibiotics simultaneously.     

Electronic absorption spectra of MnO4− ions in single crystals of alums

The electronic absorption spectra of MnO₄^? ions in the single crystals of KA1(SO₄)₂·12H₂O and NH₄A1(SO₄)₂·12H₂O at room temperature and liquid nitrogen temperature are reported. The assignments of the absorption bands observed at around 5200 Å, 3600 Å, 3000 Å and 2300 Å have been made in a consistent manner. The molecular orbital energy level scheme given by Johnson and Smith on the basis of a spin-unrestricted SCF Xα cluster model has been used in conjunction with Slater's transition state theory to interpret the optical absorption spectra.     

The resonance raman spectra of manganates (VII) with different counterions

As part of a study of the RR spectra of different manganates, the spectra of RbMnO₄, CsMnO₄, AgMnO₄, Sr(MnO₄)₂.3H₂O and La(MnO₄)₃.nH₂O were obtained and interpreted in comparison with those of other permanganates previously reported. The analysis of the corresponding X₁₁ anharmonicity constants and full-widths at half maxima of the members of the vν₁ progressions allowed a wider insight into the effects of the countercations on the vibrational properties of the MnO^?₄ ion.     

A Highly Oxidizing and Isolable Oxoruthenium(V) Complex [RuV(N4O)(O)]2+: Electronic Structure,Redox Properties,and Oxidation Reactions Investigated by DFT Calculations

The electronic structure and redox properties of the highly oxidizing, isolable Ru^V?O complex [Ru^V(N₄O)(O)]²⁺, its oxidation reactions with saturated alkanes (cyclohexane and methane) and inorganic substrates (hydrochloric acid and water), and its intermolecular coupling reaction have been examined by DFT calculations. The oxidation reactions with cyclohexane and methane proceed through hydrogen atom transfer in a transition state with a calculated free energy barrier of 10.8 and 23.8 kcal mol^?1, respectively. The overall free energy activation barrier (ΔG^≠=25.5 kcal mol^?1) of oxidation of hydrochloric acid can be decomposed into two parts: the formation of [Ru^III(N₄O)(HOCl)]²⁺ (ΔG=15.0 kcal mol^?1) and the substitution of HOCl by a water molecule (ΔG^≠=10.5 kcal mol^?1). For water oxidation, nucleophilic attack on Ru^V?O by water, leading to O? O bond formation, has a free energy barrier of 24.0 kcal mol^?1, the major component of which comes from the cleavage of the H? OH bond of water. Intermolecular self‐coupling of two molecules of [Ru^V(N₄O)(O)]²⁺ leads to the [(N₄O)Ru^IV? O₂? Ru^III(N₄O)]⁴⁺ complex with a calculated free energy barrier of 12.0 kcal mol^?1.     

Excited‐State Hydrogen Bonding Strengthening and Weakening with Intramolecular Charge Transfer in Resorufin‐Water Complexes: A TD‐DFT Study

The geometric structures, infrared spectra and hydrogen bond binding energies of the various hydrogen‐bonded Res^?‐water complexes in states S0 and S1 have been calculated using the density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT) methods, respectively. Based on the changes of the hydrogen bond lengths and binding energies as well as the spectral shifts of the vibrational mode of the hydroxyl groups, it is demonstrated that hydrogen bonds HB‐II, HB‐III and HB‐IV are strengthened while hydrogen bond HB‐I is weakened in the four singly hydrogen‐bonded Res^?‐Water complexes upon photoexcitation. When the four hydrogen bonds are formed simultaneously between one resorufin anion and four water molecules in the Res^?‐4Water complex, all the hydrogen bonds are weakened in both the ground and excited states compared with those in the corresponding singly hydrogen‐bonded Res^?‐Water complexes. Furthermore, in complex Res^?‐4Water, hydrogen bonds HB‐II and HB‐IV are strengthened while hydrogen bonds HB‐I and HB‐III are weakened after the electronic excitation. The hydrogen bond strengthening and weakening in the various hydrogen‐bonded Res^?‐water complexes should be due to the redistribution of the charges among the four heteroatoms (O_1‐3 and N₁) within the resorufin molecule upon the optical excitation.     

Complexes of Cu2(μ‐OAc)4(H2O)2 with 1,10‐Phenanthroline and Comparison with those of 2,2′‐Bipyridine. Crystal Structure of the Dimer [Cu(OAc)2(phen)](μ‐H2O)

The two complexes of composition Cu₂(OAc)₄(phen)(H₂O)₂ ( 1 ) andCu₂(OAc)₄(phen)₂(H₂O) ( 2 ) have been synthesized and characterized by chemical analysis and IR and electronic spectroscopies. Compound 2 has the structure of a dimer with a phenanthroline molecule and two monodentate acetate groups coordinated to each copper atom and a water molecule as the only bridging ligand between them. Each copper atom has a distorted square‐planar pyramidal coordination, determined by two oxygen atoms at 1.94(3) and 1.959(3) Å, two nitrogen atoms at 2.023(4) Å and the oxygen atom of the bridging water molecule at 2.289(2) Å. The distance between the two copper atoms is of 4.29 Å and the angle Cu(1)‐O(3)‐Cu(1A) 139.2(2)°. The water molecule is involved in two intramolecular hydrogen bonds with non coordinated oxygen atoms. The distance between the molecules of phenanthroline is 3.75 Å. Magnetic and EPR results for Cu₂(OAc)₄(phen)(H₂O)₂ ( 1 ), Cu₂(OAc)₄(phen)₂(H₂O) ( 2 ), Cu₂(OAc)₄(bipy) ( 3 ) and Cu₂(OAc)₄(bipy)₂(H₂O)₂ ( 4 ) have been analysed and compared. For 1 and 3 an antiferromagnetic dimer unit [Cu₂(μ‐OAc)₄] with 2J = ?325 and ?292 cm^?1, respectively, and other two copper atoms without significant magnetic interaction are present. Triplet signals are detected in the EPR spectra. In 2 and 4 there is no practically magnetic exchange and the orthorhombic signals are observed in the EPR spectra.     

Stokes/anti-stokes intensity ratio in the resonance region

Relative intensities of the Stokes and anti-Stokes Raman lines associated with the I-I stretching mode of I₂ and symmetric stretching mode of MnO^?₄ are presented. The data indicate that the maxima in the excitation profile of the anti-Stokes scattering are shifted from those of the Stokes scattering. The experimental Stokes/anti-Stokes intensity ratios agree with the theoretical values obtained with parameters from the electronic absorption spectra.     

Synthesis,crystal structure and spectroscopic properties of a chiral cyano-bridged heterobinuclear complex, (4 S ,11 S )-[Cu(1,7-CT)( μ -CN)Fe(CN)4NO] · H2O

The chiral complex, (4S,11S)-[Cu(1,7-CT)(μ-CN)Fe(CN)₄NO] ·?H₂O (1,7-CT =?5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-1,7-diene), and its enantiomer have been synthesized by reaction and conglomerate crystallization. They consist of heterobinuclear species in which the Cu and Fe centers are linked by a cyanide bridge and crystalline water. The Cu(II) is coordinated by five N atoms and exhibits a distorted square-pyramidal geometry, in which two hydrogen atoms on secondary amines lie in the inward side of the macrocyclic plane, while on the other moiety the Fe(II) is a slightly distorted octahedral structure. The binuclear molecules are linked through intermolecular O2–H2A···N1 and O2–H2B···N4 hydrogen bonds, forming two different waved chains that oriented the molecules for optical activity. IR spectrum shows the existence of bridging cyanide ligand. In methanol the specific rotations of enantiomers are ±205 deg ·?cm² ·?(10 g)^?1, the peak positions of their circular dichroism spectra are close to that of their UV-Vis spectra and present up and down symmetric signals.     

A Simple Electrochemical Approach Based on Inexpensive Wall‐Jet Screen‐Printed Ring Disk Electrode to Evaluate Oxygen Reduction Catalysts

A simple electrochemical approach to evaluate oxygen reduction catalysts using an inexpensive screen‐printed ring disk carbon electrode system, consisting of a ring electrode deposited with MnO₂ and a disk electrode modified with the catalysts for study, is developed in this study. The as‐prepared MnO₂ is selective and sensitive for H₂O₂ oxidation in the presence of O₂ and is crucial to the proposed approach. By coupling with a wall‐jet electrochemical cell, the product generated from the reduction reaction at the disk electrode can effectively be monitored at the MnO₂‐deposited ring electrode. Model catalysts of nano‐Au and nano‐Pd representing 2e^? reduction of O₂ to H₂O₂ and 4e^? reduction to H₂O, respectively, were evaluated as electrode materials in oxygen reduction reaction to demonstrate the applicability of the proposed method.     

Surface and Structural Investigation of a MnOx Birnessite‐Type Water Oxidation Catalyst Formed under Photocatalytic Conditions

Catalytically active MnO_x species have been reported to form in situ from various Mn‐complexes during electrocatalytic and solution‐based water oxidation when employing cerium(IV) ammonium ammonium nitrate (CAN) oxidant as a sacrificial reagent. The full structural characterization of these oxides may be complicated by the presence of support material and lack of a pure bulk phase. For the first time, we show that highly active MnO_x catalysts form without supports in situ under photocatalytic conditions. Our most active ⁴MnO_x catalyst (～0.84 mmol O₂ mol Mn^?1 s^?1) forms from a Mn₄O₄ bearing a metal–organic framework. ⁴MnO_x is characterized by pair distribution function analysis (PDF), Raman spectroscopy, and HR‐TEM as a disordered, layered Mn‐oxide with high surface area (216 m²g^?1) and small regions of crystallinity and layer flexibility. In contrast, the ^SMnO_x formed from Mn²⁺ salt gives an amorphous species of lower surface area (80 m²g^?1) and lower activity (～0.15 mmol O₂ mol Mn^?1 s^?1). We compare these catalysts to crystalline hexagonal birnessite, which activates under the same conditions. Full deconvolution of the XPS Mn2p_3/2 core levels detects enriched Mn³⁺ and Mn²⁺ content on the surfaces, which indicates possible disproportionation/comproportionation surface equilibria.     

Synthesis,Crystal Structure and Magnetic Behaviour of Two 1‐D Chain Manganese‐Nitroxide Complexes Bridged by Isophthalate Anions

Two one‐dimensional (1‐D) chain manganese‐nitroxide complexes {[Mn(NIT4Py)₂(ip)(H₂O)₂]·4H₂O}_n ( 1 ) and [Mn(IM4Py)₂(ip)(H₂O)₂]_n ( 2 ) (NIT4Py = 2‐(4′‐pyridinyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide, IM4Py = 2‐(4′‐pyridinyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl and ip = isophthalate anion) have been synthesized and characterized by elemental analyses, IR spectrum and electronic absorption spectra. Complex 1 was structurally characterized and it crystallizes in neutral 1‐D chains where Mn^II nitroxide units [Mn(NIT4Py)₂(H₂O)₂] are linked by isophthalate anions. The magnetic measurements show that complex 1 exhibits antiferromagnetic couplings, while complex 2 exhibits ferromagnetic interactions between the Mn^II ion and the nitroxide radicals.     

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 O^2? 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 MnO ₃ ^2? 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.     

Boosting Water Oxidation through In Situ Electroconversion of Manganese Gallide: An Intermetallic Precursor Approach

For the first time, the manganese gallide (MnGa₄) served as an intermetallic precursor, which upon in situ electroconversion in alkaline media produced high‐performance and long‐term‐stable MnO_x‐based electrocatalysts for water oxidation. Unexpectedly, its electrocorrosion (with the concomitant loss of Ga) leads simultaneously to three crystalline types of MnO_x minerals with distinct structures and induced defects: birnessite δ‐MnO₂, feitknechtite β‐MnOOH, and hausmannite α‐Mn₃O₄. The abundance and intrinsic stabilization of Mn^III/Mn^IV active sites in the three MnO_x phases explains the superior efficiency and durability of the system for electrocatalytic water oxidation. After electrophoretic deposition of the MnGa₄ precursor on conductive nickel foam (NF), a low overpotential of 291 mV, comparable to that of precious‐metal‐based catalysts, could be achieved at a current density of 10 mA cm^?2 with a durability of more than five days.