Weak Acidic Aqueous Solutions Research Articles

Closed-form expressions for monoprotic weak acid aqueous solutions

A general closed-form expression for {[textrm{H}_{3}textrm{O}^+]} of solutions of a weak acid and a weak acid buffer, as well as their titration with a strong base, has been obtained and mathematically analyzed with the aid of computer algebra systems. This expression is used to evaluate, without the use of numerical approximations, the precision and accuracy of different approximations commonly employed in general chemistry and chemical analysis courses. The closed-form expression for {{[textrm{H}_{3}textrm{O}^+]}} of a buffer solution is used to obtain an analytical expression for the pH stability when a strong base is added. Finally, it is shown that the {[textrm{H}_{3}textrm{O}^+]} expressions for all the systems under study can be obtained from a general closed-form expression in terms of an effective weak acid constant and an effective acid concentration. The formulas found in this work do not display numerical rounding errors and do not require the use of numerical or graphical methods for their evaluation.Graphical abstractGraphical TOC: A closed-form expression for the weak acid and weak acid buffersolutions and their titrations with a strong base

Rechargeable zinc-ion batteries with manganese dioxide cathode: How critical is choice of manganese dioxide polymorphs in aqueous solutions?

In this work, different MnO2 polymorphs are applied as cathodes in zinc-ion batteries (ZIBs). All the polymorphs result in similar electrochemical behavior in weak acidic (1 М) ZnSO4 aqueous solutions at comparable specific capacity (200–225 mAh g−1), similar charge–discharge curves, and temporal stability owing to an irreversible modification of the pristine positive electrode during battery charge and discharge. This irreversibility stems from the dissolution and re-deposition of MnO2 and the formation of new manganese and zinc compounds (basic salt deposits such as ZnMn2O4, Mn2O3, and MnOOH). The additional (new) MnO2 phase is formed via two routes: disproportionation of Mn+3 ions formed during the discharge process and anodic oxidation of Mn2+ ions in a solution. According to X-ray diffraction and Raman spectroscopy analyses, the re-deposited MnO2 is in an amorphous state. The amorphous MnO2 covers the surface of the initial crystalline particles and affects the electrochemical behavior of the ZIBs. The strong pH dependence of the electrochemical response of the MnO2 electrodes is related to the H+ concentration effect on ionic equilibria in this system, such as the formation of basic zinc and manganese salts and hydroxides as well as the disproportionation of Mn+3 and anodic oxidation of Mn+2.

Synthesis, Characterization and Kinetic Study of poly(vinyl acetate)-g-Chitosan and its Use in Removal of Cadmium (II) ions from Water

The grafted vinyl acetate copolymerization lying on chitosan in weak acidic aqueous solution was examined via using K2S2O8 as initiator. FTIR spectra, DSC, DTG and TGA were used for graft polymer characterizing. The monomer to chitosan ratio was tested and the optimal grafting conditions were affixed. the highest grafting percentage PG of production polymers have been applied to remove Cd(II) ions from water samples through adsorption experiments at pH=7. The amounts of adsorbed metal ion on the polymers was estimated using atomic absorption spectrophotometer. The temperature effect on Cd(II) adsorption was studied too. Langmuir and Freundlich isotherms as well as kinetic study equations were employed to fit the experimental data. The results of the adsorption equilibrium for Cd(II) fitted well to Langmuir isotherm and the removal percentage at 30°C after 5 min is 76.65 % and the thermodynamic parameters for the adsorption are ΔH= 96.87 kJ/mol ΔS= 339.19 J/mol K and ΔG= -5.11, -11.13 and -11.78 kJ/mol in different temperatures. The kinetic study of these adsorption isotherms showed that all these isotherms correlates well with the second order equation.

Preparation and Properties of Chitosan-Tranexamic Acid Salts

The solid chitosan-tranexamic acid salts were successfully prepared by the method of half-wet grinding with chitosan and tranexamic acid as raw materials. The physical properties including water solubility and stability of the prepared samples were tested, and their structures were characterized by Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). In addition, the in vitro pro-coagulant activity was evaluated by the test tube method. The results showed that the prepared chitosan-tranexamic acid salts could be dissolved in weak acidic, neutral and weak alkaline aqueous solutions, expanding the dissolution range. The characterization results indicated that the protonation reaction of the chitosan amino group was achieved without solvent and the crystallinity degree of chitosan-tranexamic acid salts decreased by comparison with chitosan. The hemostasis evaluation showed that chitosan-tranexamic acid salts with different mass ratios had pro-coagulant activities in vitro. In particular, the clotting time of chitosan acid salt with mass ratio of 1:2 was shorter than that of Yunnan Baiyao. This effort laid the foundation for the development of the promising chitosan-based hemostatic materials.

The synergistic effect of weak oxalic acid and thymol aqueous solutions on Varroa mites and honey bees

In this study, the effects of a weak oxalic acid (OA) water solution (0.5%) and a mixture of oxalic acid (0.5%) and thymol (0.12%) (OA/TH) on Varroa mites and honey bees were investigated by trickling method. Prior to the experiments, queens in colonies were caged for 21 days to prevent egg laying and hives were provided with screened bottom boards. In experiments with caged bees in laboratory and brood-free colonies in field conditions, mite mortality and bee tolerance were assessed. Trickling caged bees once with OA resulted in 46.8 ± 4.4% effectiveness, while OA/TH had an effectiveness of 91.6–98.7%. Aqueous thymol (TH) solution had no acaricidal effect, but if mixed with OA doubled the effectiveness. Sugar solutions with low concentrations of OA and OA/TH (1:1) were considerably less effective than aqueous solutions. OA/TH was more harmful to bees than OA alone: respectively 3.2 and 1.2% of bees perished in trials. In field conditions, trickling with OA/TH (25 mL/comb space) was highly effective in autumn experiments: 97.6–99.0% for single and 99.2–99.8% for double trickling. Trickling once in spring was considerably less effective (77.0 ± 3.0%). The acaricidal effect of OA double trickling in autumn appeared more slowly, but had similarly high effectiveness: 99.6–99.8%. OA/TH double trickling in autumn was shown to be toxic to bees: colonies weakened considerably the following winter. Water provision reduced weakening of colonies in winter. Trickling of colonies with OA/TH or OA at a lower dosage (15 and 20 mL/comb space, respectively) earlier in autumn ensured high effectiveness and good bee tolerance.

Homochiral MOF as Circular Dichroism Sensor for Enantioselective Recognition on Nature and Chirality of Unmodified Amino Acids.

Self-assembly of zinc salt with rationally designed chiral ligand, (1R,2R)-2-(pyridine-4-ylcarbamoyl) cyclohexanecarboxylic acid (RR-PCCHC) generated 2D homochiral metal-organic framework [Zn(RR-PCCHC)2] (HMOF-1) that is composed of DNA-like right-handed double-helix structure. HMOF-1 shows high solvent and thermal stability and is also stable in neutral, weak acidic and weak basic aqueous solution. Emulsified HMOF-1 shows strong inherent circular dichroism (CD) signal in aqueous solution, which can show regular intensity change by induction of amino acids. On the basis of the measuring of CD signal intensity, a chemosensor for unmodified amino acids is fabricated, which differ from reported those in which CD signal is amplified by a complicated chemical reaction of originally CD-silent molecule with probed amino acids. This chemosensor can be used for rapid, convenient and sensitive detection of micro amount of amino acids. Most remarkably, 3 × 10-8 mol of l-aspartic acid and 4 × 10-8 mol of d-aspartic acid in aqueous solution can completely quench CD signal of emulsified HMOF-1 in H2O. It is found that the difference of recognition ability between d- and l-proline is the largest in all probed amino acids. The LOD (limit of detection) of the proposed sensor for the determination of aspartic acid is 13.31 ppm. The recognition efficiency η = [Formula: see text] × 100% for l-aspartic acid is as high as 92.1%. The interacting mechanism of DNA-like HMOF-1 with probed amino acids is similar to that of groove binding of targeting drug with DNA.

A Cu‐Based Nanoparticulate Film as Super‐Active and Robust Catalyst Surpasses Pt for Electrochemical H2 Production from Neutral and Weak Acidic Aqueous Solutions

Electrocatalysts that are stable and highly active at low overpotential (η) under mild conditions as well as cost‐effective and scalable are eagerly desired for potential use in photo‐ and electro‐driven hydrogen evolution devices. Here the fabrication and characterization of a super‐active and robust Cu‐CuxO‐Pt nanoparticulate electrocatalyst is reported, which displays a small Tafel slope (44 mV dec−1) and a large exchange current density (1.601 mA cm−2) in neutral buffer solution. The catalytic current density of this catalyst film reaches 500 mA cm−2 at η = −390 ± 12 mV and 20 mA cm−2 at η = −45 ± 3 mV, which are significantly higher than the values displayed by Pt foil and Pt/C electrodes in neutral buffer solution and even comparable with the activity of Pt electrode in 0.5 m H2SO4 solution.

A water-soluble perylene derivative for live-cell imaging

Glutamic functionalized water-soluble perylene diimide, N, N'-di (L-glutamic amine)-perylene-3,4,9,10-tetracarboxylic diimide (GAPTCD) has three absorbance maxima at 469, 498, and 534 nm and two emission peaks at 550 and 587 nm. Owing to the highly negative electrostatic potential of the perylene plane, the perylene derivative showed good water solubility and strong fluorescence in alkali and neutral solutions. Both the absorbance and emission intensities decreased with the decreasing of pH from 9.66 to 5.92. This could be ascribed to the $\pi -\pi $ stacking produced by H$^{+}$ at the carboxyl group due to its electron accepting nature. Electrostatic potential maps also indicated that GAPTCD can exist stably in basic to weak acidic aqueous solution. Then GAPTCD was successfully applied as a high performance fluorochrome for imaging of living hela cells.

Effects of environment parameters on sol-gel transition and dry-spinnability of regenerated silk fibroin aqueous solution

Protein concentration, pH, the types and concentrations of metallic ions, and extensional flow are thought to be important environment parameters affecting the natural spinning process. In this study, we investigate the effects of the types and concentrations of metallic ions (Ca2+, Mg2+, and K+ ions), pH, and silk fibroin concentration on the sol-gel transition and the rheological behavior of a regenerated silk fibroin (RSF) aqueous solution. The results show that with an increase in the silk fibroin concentration, the weak acidic RSF aqueous solutions containing Mg2+ or Ca2+ ions undergo a phase transition to a weak gel state. Moreover, the rheological characterization of RSF aqueous solutions shows a dramatic change, and their apparent viscosities increase by almost three orders of magnitude and approach the apparent viscosity of the native dope in the silkworm gland. By using conventional pressure equipment, we investigate the dry-spinnability of weak gels. Further, we observe that the as-spun fibers exhibit a smooth surface and have inferior mechanical properties. The structure of the as-spun fibers is predominantly in a random coil or Silk I conformation.

Physical properties of N,N,N′,N′-tetramethyl diglycolamide and thermodynamic studies of its complexation with zirconium, lanthanides and actinides

The crystal structure, melting range, decomposition temperature, solubilities in aqueous and organic phase, and distribution ratio in biphase system of N,N,N′,N′-tetramethyl diglycolamide (TMDGA) have been studied in the present work. Water-soluble TMDGA with very low solubility in kerosene or 30 % trialkyl phosphine (TRPO)/kerosene meets the primary requirement to act as the stripping agent in TRPO process which has been developed for actinides partitioning from high level waste. Slope analysis, electrospray ionization mass spectrometry (ESI–MS) and spectrophotometric titration indicate that in weak and moderate acidic aqueous solution, up to three TMDGA molecules form complexes with Zr4+, trivalent lanthanides (Ln3+), trivalent actinides (An3+) or tetravalent actinides (An4+). Their complex formation constants determined by liquid–liquid extraction method follow the order predicted by the electrostatic model of 4f and 5f elements and the covalent model of 4d transition elements: Ln3+ ~ An3+ < An4+ ≪ Zr4+. Hydrolysis of actinide cations, especially An4+, in the media of low acidity, reduces the complexation stability. In addition, the effect of aqueous acidity and temperature has been investigated. No obvious influence of temperature on Np4+ complexes has been found. However, the influence on Am3+ and Pu4+, especially on their 1:1 or 1:2 complex species with TMDGA, is relatively considerable. Strong affinity of TMDGA to An3+ and An4+ implies that TMDGA has potential to strip An3+ and An4+ from TRPO.

Kinetics and mechanism of the reaction between chromium(III) and picolinic acid in weak acidic aqueous solution

The interaction between chromium(III) and picolinic acid in weak acid aqueous solution was studied, resulting in the formation of a complex upon substitution of water molecules in the chromium(III) coordination sphere. Experimental results show that the reaction takes place in multiple steps. The first step is the formation of an ion pair, the second step (two consecutive steps) is the slow one corresponding to substitution of the first water molecule from the chromium aqueous complex coordination sphere by a picolinic acid molecule via oxygen atom of the carboxylic acid group and substitution of the second water molecule via nitrogen of the pyridine ring forming an 1:1 complex. Both consecutive steps were independent of chromium concentration. The rate constants of the 1st and 2nd consecutive steps were increased by increasing picolinic acid concentration. The corresponding activation parameters are ∆H 1 * = 28.4 ± 4 kJ mol−1, ∆S 1 * = −202 ± 26 J K−1 mol−1, ∆H 2 * = 39.6 ± 5 kJ mol−1, and ∆S 2 * = −175 ± 19 J K−1 mol−1. The third step is fast, corresponding to formation of the final complex [Cr(pic)3]. The logarithms of the formation constants of 1:1 and 1:3 complexes were found to be 1.724 and 4.274, respectively.

A facile pollutant-free approach toward a series of nutritionally effective calcium phosphate nanomaterials for food and drink additives

Micronutrient malnutrition is widespread and constitutes one of the main nutritional problems worldwide. Vitamins, amino acids, carbohydrates and Ca-phosphate (CaP) minerals are important to human health and disease prevention. Herein we developed a simple wet-chemical method to prepare multinary nutrients-containing CaP nanomaterials in diluted apple, orange, and grape juices. The scanning electron microscopy observation shows that these nanomaterials are short plate-like CaP nanocrystals of ~500 nm in length. The X-ray photoelectron spectroscopy, nitrogen adsorption, thermogravimetric analyses confirm the different specific surface area and organic nutrient contents. The Fourier transform infrared and X-ray diffraction analyses indicate there exist similar organic groups (i.e., COO−, HN-CO) but different CaP species in the precipitates. The dissolution test in vitro simulated stomach juice pH condition indicates that these inorganic–organic nanohybrid materials are multidoped by micronutrients (such as Zn, Sr, Mg, K, vitamin c) and can be readily dissolved in the weak acidic aqueous solutions. This highly efficient utilization of fruit juice to produce CaP-based micronutrient composites may minimize the adverse side effect, so that the nanomaterials are promising as functional food/drink additives. Thus, this novel approach is environmentally and biologically friendly to produce edible nutrients while production cost is attained.

Concentration-Dependent Wet Etching Behaviors of Ga-Doped ZnO Films Sputter-Deposited at Room Temperature Using Formic and Citric Acids

Transparent conducting Ga-doped zinc oxide (GZO) thin films (150 nm thick) were sputter-deposited on glass substrate at room temperature. As-deposited GZO films were wet-patterned with weak organic acid aqueous solutions containing formic or citric acid. Wet etching behaviors of the films were influenced by the type and concentration of organic acids used. The concentrations of formic and citric acids were varied from 0.02–0.1 and 0.0008–0.02 M, respectively. The concentration-dependent different etching behaviors, i.e., diffusion- vs reaction-limited etching modes, were observed for each etchant. Different rate-limiting behaviors were also verified by the calculated activation energy data for vertical etching of the films as a function of concentration of each etchant. With the optimal etching conditions for the GZO films on glass substrate, the wet patterning of the films deposited on poly(ethylene terephthalate) was also attempted.

Kinetics and Mechanisms of the Chromium(III) Reactions with 2,4‐ and 2,5‐Dihydroxybenzoic Acids in Weak Acidic Aqueous Solutions

The reactions of 2,4- and 2,5-dihydroxybenzoic acids (dihydroxybenzoic acid, DHBA) with chromium(III) in weak acidic aqueous solutions have been shown to take place in at least two stages. The first stage of the reactions has an observed rate constant k 1(obs) = k 1[DHBA] + C and the corresponding activation parameters are ΔH1(2,4) ≠ = 49, 5 kJ/mol−1, ΔS 1(2,4) ≠ = −103, 7 J mol−1 K−1, ΔH1(2,5) ≠ = 60, 3 kJ/mol−1, and ΔS 1(2,5) ≠ = −68, 0 J mol−1 K−1. These are composite activation parameters and the breaking of the strong intramolecular hydrogen bonding in the two ligands is suggested to be the first step of the (composite) first stage of the reactions. The second stage is ligand concentration independent and is thus attributed to a chelation process. The corresponding activation parameters are ΔH2(2,4) ≠ = 45, 13 kJ/mol−1, ΔS 2(2,4) ≠ = −185, 9 J mol−1 K−1, ΔH2(2,5) ≠ = 54, 55 kJ/mol−1, and ΔS 2(2,5) ≠ = −154, 8 J mol−1 K−1. The activation parameters support an associative mechanism for the second stage of the reactions. The various substitution processes are accompanied by proton release, resulting in pH decrease.

Kinetics and Mechanism of the Reaction between Chromium(III) and 2,3‐Dihydroxybenzoic Acid in Weak Acidic Aqueous Solutions

The reaction between chromium(III) and 2,3-dihydroxybenzoic acid (2,3-DHBA) takes place in at least three stages, involving various intermediates. The ligand (2,3-DHBA)-to-chromium(III) ratio in the final product of the reaction is 1 : 1. The first stage is suggested to be the reaction of [Cr(H2O)5(OH)]2+ with the ligand in weak acidic aqueous solutions that follows an I d mechanism. The second and third stages do not depend on the concentrations of chromium(III), and their activation parameters are ΔH ≠ 2(obs) = 61.2 ± 3.1 kJmol−1, ΔS ≠ 2(obs) = −91.1 ± 11.0 JK−1mol−1, ΔH ≠ 3(obs) = 124.5 ± 8.7 kJmol−1, and ΔS ≠ 3(obs) = 95.1 ± 29.0 JK−1mol−1. These two stages are proposed to proceed via associative mechanisms. The positive value of ΔS ≠ 3(obs) can be explained by the opening of a four-membered ring (positive entropy change) and the breaking of a hydrogen bond (positive entropy change) at the associative step of the replacement of the carboxyl group by the hydroxyl group at the chromium(III) center (negative entropy change in associative mechanisms). The reactions are accompanied by proton release, as shown by the pH decrease.

Two new extended frameworks constructed from the sandwiching polytungstoarsenate clusters

Two new extended frameworks based on two different sandwich-type polytungstoarsenates have been synthesized under routine conditions. The reaction of Na 9[As IIIW 9O 33]·19.5H 2O, MnSO 4·H 2O and citric acid in a weak acidic aqueous solution at pH = 4.23 led to the isolation of a new extended sandwich-type compound {K 3Na 8[{Mn II(H 2O)} 2.5{(WO)(H 2O)} 0.5(AsW 9O 33) 2]·12.5H 2O} n ( 1). In compound 1, each sandwiching polyoxoanion [{Mn II(H 2O)} 2.5{(WO)(H 2O)} 0.5(AsW 9O 33) 2] 11− acts as a quadridentate ligand to connect with four neighbors via the mode of {W–O–Mn}, finally leading to an interesting 2D network. The reaction of Na 8[HAsW 9O 34]·11H 2O, CeCl 3·7H 2O and hexamethylenetetramine in an aqueous solution with pH = 5.07 resulted in the obtainment of a polytungstoarsenate-based extended compound [HMTA–CH 3] 2[HMTA]K 2Na 7[Ce(AsW 11O 39) 2]·19H 2O( 2) (HMTA–CH 3 = methyl-hexamethylenetetraamine; HMTA = hexamethylenetetraamine). In 2, the polyoxoanions [Ce(AsW 11O 39) 2] 11− construct a new extended structure through coordinating to the {KO 5(H 2O)[HMTA–CH 3]} and {KO 4(H 2O) 2[HMTA]} units. The two compounds are characterized by elemental analyses, IR, the diffuse reflectance UV–Vis spectra, PXRD and TG analyses. The electrochemical and electrocatalytical properties of 1 and 2, as well as the fluorescent property of 2 were also investigated.

Kinetics and Mechanism of the Reaction between Chromium(III) and 3,4‐Dihydroxy‐Phenyl‐Propenoic Acid (Caffeic Acid) in Weak Acidic Aqueous Solutions

Our study of the complexation of 3,4-dihydroxy-phenyl-propenoic acid by chromium(III) could give information on the way that this metal ion is available to plants. The reaction between chromium(III) and 3,4-dihydroxy-phenyl-propenoic acid in weak acidic aqueous solutions has been shown to take place by at least three stages. The first stage corresponds to substitution (I d mechanism) of water molecule from the Cr(H2O)5OH2+ coordination sphere by a ligand molecule. A very rapid protonation equilibrium, which follows, favors the aqua species. The second and the third stages are chromium(III) and ligand concentration independent and are attributed to isomerisation and chelation processes. The corresponding activation parameters are ΔH 2(obs) ≠ = 28.6 ± 2.9 kJ mol−1, ΔS 2(obs) ≠ = −220 ± 10 J K−1mol−1, ΔH 3(obs) ≠ = 62.9 ± 6.7 kJ mol−1 and ΔS 3(obs) ≠ = −121 ± 22 J K−1mol−1. The kinetic results suggest associative mechanisms for the two steps. The associatively activated substitution processes are accompanied by proton release causing pH decrease.

Reaction of Chromium(III) with 3,4‐Dihydroxybenzoic Acid: Kinetics and Mechanism in Weak Acidic Aqueous Solutions

The interactions between chromium(III) and 3,4-dihydroxybenzoic acid (3,4-DHBA) were studied resulting in the formation of oxygen-bonded complexes upon substitution of water molecules in the chromium(III) coordination sphere. The experimental results show that the reaction takes place in at least three stages, involving various intermediates. The first stage was found to be linearly dependent on ligand concentration k 1(obs)′ = k 0 + k 1(obs)[3, 4-DHBA], and the corresponding activation parameters were calculated as follows: ΔH 1(obs) ≠ = 51.2 ± 11.5 kJ mol−1, ΔS 1(obs) ≠ = −97.3 ± 28.9 J mol−1 K−1 (composite activation parameters) . The second and third stages, which are kinetically indistinguishable, do not depend on the concentrations of ligand and chromium(III), accounting for isomerization and chelation processes, respectively. The corresponding activation parameters are ΔH 2(obs) ≠ = 44.5 ± 5.0 kJ mol−1, ΔS 2(obs) ≠ = −175.8 ± 70.3 J mol−1 K−1. The observed stages are proposed to proceed via interchange dissociative (I d, first stage) and associative (second and third stages) mechanisms. The reactions are accompanied by proton release, as is shown by the pH decrease.

Laccase-catalyzed synthesis of optically active polyaniline

One step, simple and environmentally friendly enzymatic synthesis of optically active polyaniline in the bulk solution and on the surface of glass slides ( in situ deposition) was developed. Fungal laccase from Trametes hirsuta was used as the catalyst of the oxidative polymerisation of aniline. The reaction was carried out under aerobic condition in the weak acidic aqueous solution in the presence of the chiral dopant, such as ( S)- or ( R)-camphorsulfonic acid. The doping/de-doping procedure of optically active polyaniline was reversible. It was shown that a chiral conformation of the polyaniline was quite variable, and the optical activity of the polymer could be changed by the replacement of camphorsulfonic acid enantiomer in the polyaniline structure.

Synthesis, Characterization, and Solution Properties of a Novel Cross-Bridged Cyclam Manganese(IV) Complex Having Two Terminal Hydroxo Ligands

A novel monomeric tetravalent manganese complex with the cross-bridged cyclam ligand 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (Me2EBC), [Mn(IV)(Me2EBC)(OH)2](PF6)2, was synthesized by oxidation of Mn(II)(Me2EBC)Cl2 with H2O2 in the presence of NH4PF6)in aqueous solution. The X-ray crystal structure determination of this manganese(IV) compound revealed that it contains two rare terminal hydroxo ligands. EPR studies in dry acetonitrile at 77 K show two broad resonances at g = 1.96 and 3.41, indicating that the manganese(IV) exists as a high-spin d3 species. Resonance Raman (rR) spectra of this manganese(IV) species reveal that the dihydroxy moiety, Mn(IV)(OH)2, is also the dominant species in aqueous solution (pH < 7). pH titration provides two pK(a) values, 6.86(4) and 10.0(1), associated with stepwise removal of the last two oxygen-bound protons from [Mn(IV)(Me2EBC)(OH)2](2+). The cyclic voltammetry of this manganese(IV) complex in dry acetonitrile at 298 K demonstrates two reversible redox processes at +0.756 and -0.696 V (versus SHE) for the Mn4+/Mn3+ and Mn3+/Mn2+ couples, respectively. This manganese(IV) complex is relatively stable in weak acidic aqueous solution but easily degrades in basic solution to manganese(III) derivatives with an 88 +/- 1% yield.