Fluorimetric Detection of Phosphates in Water Using a Disassembly Approach: A Comparison of FeIII-, ZnII-, MnII- and MnIII-salen Complexes

Details of the reaction sequence used for the fluorimetric detection of phosphates by disassembly of transition metal Schiff base complexes were investigated for [Fe^III(salen)(H₂O)]⁺, [Zn^II(salen)], [Mn^II(salen)(H₂O)₂], and [Mn^III(salen)(H₂O)]⁺. The reactivity of these compounds towards phosphorus oxoanions of differing charge, number of donor atoms and steric hindrance was detected by UV/Vis and fluorescence spectroscopy in both aprotic organic and aqueous media. Selectivity of [Fe^III(salen)(H₂O)]⁺ towards pyrophosphate over all other tested phosphorus-containing analytes was strongly supported. [Zn^II(salen)] showed a faster reactivity but was much less selective. In contrast, [Mn^III(salen)(H₂O)]⁺ proved to be more stable than the iron complex but generally showed little reactivity towards phosphorus oxoanions. The influence of the charge of the central atom was investigated using the Mn^II analogue [Mn^II(salen)(H₂O)₂]. As expected, the reduced charge resulted in a reactivity comparable to the Zn^II complex in organic solution but lead to hydrolysis of the complex in water. Finally, the reaction products of [Fe^III(salen)(H₂O)]⁺ with phosphates were characterized by IR spectroscopy and mass spectrometry, providing further insights into the reaction mechanism of the disassembly process.     

Diverse Ligand‐Functionalized Mixed‐Valent Hexamanganese Sandwiched Silicotungstates with Single‐Molecule Magnet Behavior

Under hydrothermal conditions, replacement of the water molecules in the [Mn^III₄Mn^II₂O₄(H₂O)₄]⁸⁺ cluster of mixed‐valent Mn₆ sandwiched silicotungstate [(B‐α‐SiW₉O₃₄)₂Mn^III₄Mn^II₂O₄(H₂O)₄]^12? ( 1 a ) with organic N ligands led to the isolation of five organic–inorganic hybrid, Mn₆‐substituted polyoxometalates (POMs) 2 – 6 . They were all structurally characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis, diffuse‐reflectance spectroscopy, and powder and single‐crystal X‐ray diffraction. Compounds 2 – 6 represent the first series of mixed‐valent {Mn^III₄Mn^II₂O₄(H₂O)_4?n(L)_n} sandwiched POMs covalently functionalized by organic ligands. The preparation of 1 – 6 not only indicates that the double‐cubane {Mn^III₄Mn^II₂O₄(H₂O)_4?n(L)_n} clusters are very stable fragments in both conventional aqueous solution and hydrothermal systems and that organic functionalization of the [Mn^III₄Mn^II₂O₄(H₂O)₄]⁸⁺ cluster by substitution reactions is feasible, but also demonstrates that hydrothermal environments can promote and facilitate the occurrence of this substitution reaction. This work confirms that hydrothermal synthesis is effective for making novel mixed‐valent POMs substituted with transition‐metal (TM) clusters by combining lacunary Keggin precursors with TM cations and tunable organic ligands. Furthermore, magnetic measurements reveal that 3 and 6 exhibit single‐molecule magnet behavior.     

Synthèse et étude structurale d’un nouvel hétéropolytungstate substitué Na8〚H3XIIIMIIW17O59(H2O)〛·36 H2O (X = SbIII,BiIII et M = Mn2+, Co2+, Ni2+, Cu2+, Zn2+) de structure identique à celle de 〚H2XIIIW18O60〛7– (X = As,Bi)

By mixing an aqueous solution of antimonotungstate at pH = 4–5 and an aqueous solution of manganese(II) chloride, of cobalt(II) chloride, of nickel(II) chloride, or of zinc, a monosubstituted heteropolytungstate 〚H₃Sb^IIIM^IIW₁₇O₅₉(H₂O)〛^8– is obtained (M^II = Mn^II, Co^II, Ni^II, Zn^II). The crystallographic study, associated to EPR, XANES, EXAFS, and proton NMR spectrometries, leads to a structure identical to this of 〚H₂As^IIIW₁₈O₆₀〛^7–. There are two moieties Sb^IIIW₉O₃₀ and H₃M^IIW₈O₃₀. It is concluded that the M^II atom substitutes a tungsten atom of the belt of six octahedra perpendicular to the ternary axis of the polytungstate. The same type of compound was obtained starting from bismuth chloride and copper acetate, that is 〚H₃Bi^IIICu^IIW₁₇O₅₉(H₂O)〛^8–.     

Mechanistic studies on the oxidation of glyoxylic and pyruvic acids by a {Mn3O4}4+ core in aqueous media

In aqueous media, the Mn^IV trimer [Mn^IV₃(μ‐O)₄(phen)₄(H₂O)₂]⁴⁺ ( 1 , phen = 1,10‐phenanthroline) equilibrates with its deprotonated from [Mn₃(μ‐O)₄(phen)₄(H₂O)(OH)]³⁺ ( 2 ). Among the several synthetic multinuclear oxo‐ and/or carboxylato‐bridged manganese complexes known to date containing metal‐bound water, to the best of our knowledge, 1 is one of the rare examples that deprotonates ( 1 ? 2 + H⁺; pK_a = 4.00 (±0.15) at 25.0°C, I = 1.0 mol dm^?3, maintained with NaNO₃) at physiological pH. In aqueous media (pH 2–4), 1 oxidizes both glyoxylic and pyruvic acids to formic and acetic acid, respectively, along with the formation of CO₂, the end manganese state being Mn^II. Kinetic studies suggest that the species 1 , its deprotonated form 2 , the reducing acids (HA), and their conjugate bases (A^?) all take part in the reaction. The oxidant 1 is found to be more reactive than its conjugate base 2 , and HA reacts faster than A^? in reducing 1 or 2 . The gem‐diol form of the α‐oxo acids (especially for glyoxylic acid) is the possible reducing species. The Mn^IV₃ to Mn^II transition in the present observation proceeds through the intermediate generation of the spectrally characterized mixed‐valent Mn^IIIMn^IV dimer that quickly collapses to Mn^II. The observed rates of glyoxylic or pyruvic acid oxidation do not depend on the variation of 1,10‐phenanthroline content of the solution, indicating the absence of any phen‐releasing preequilibrium of the title complex in solution. The reactions rates were found to be lowered in media enriched with D₂O in comparison to that in H₂O and a rate‐limiting one electron one proton (1e, 1H⁺) electroprotic mechanism is proposed. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 323–335, 2010     

Synthesis and spectral studies on heterobimetallic complexes of manganese and ruthenium derived from N-(2-hydroxynaphthalen-1-yl)methylenebenzoylhydrazide

The complex [Mn^IV(napbh)₂] (napbhH₂ = N-(2-hydroxynaphthalen-1-yl)methylenebenzoylhydrazide) reacts with activated ruthenium(III) chloride in methanol in 1 : 1.2 molar ratio under reflux, giving heterobimetallic complexes, [Mn^IV(napbh)₂Ru^IIICl₃(H₂O)] · [Ru^III(napbhH)Cl₂(H₂O)] reacts with Mn(OAc)₂·4H₂O in methanol in 1 : 1.2 molar ratio under reflux to give [Ru^III(napbhH)Cl₂(H₂O)Mn^II(OAc)₂]. Replacement of aquo in these heterobimetallic complexes has been observed when the reactions are carried out in the presence of pyridine (py), 3-picoline (3-pic), or 4-picoline (4-pic). The molar conductances for these complexes in DMF indicates 1 : 1 electrolytes. Magnetic moment values suggest that these heterobimetallic complexes contain Mn^IV and Ru^III or Ru^III and Mn^II in the same structural unit. Electronic spectral studies suggest six coordinate metal ions. IR spectra reveal that the napbhH₂ ligand coordinates in its enol form to Mn^IV and bridges to Ru^III and in the keto form to Ru^III and bridging to Mn^II.     

The Interaction of Water‐Soluble Manganese Porphyrins with DNA Films and Their Electrocatalytic Properties with Hydrazine

The electrochemistry of water‐soluble manganese porphyrins (Mn(4‐TMPyP)) has been studied as an electrochemically‐active film on double‐stranded deoxyribonucleic acid (dsDNA) modified electrodes in solutions at various pH. An electrochemical quartz crystal microbalance and cyclic voltammetry were used to study the in situ deposition of DNA on gold disk electrodes, and Mn(4‐TMPyP) (manganese meso‐tetrakis‐(N‐methyl‐4‐pyridyl)porphyrin) deposition on DNA film modified electrodes. Mn^II(4‐TMPyP) (the reduced form) is more easily deposited on a DNA film than Mn^III(4‐TMPyP) (the oxidized form). Electrodeposition of Mn(4‐TMPyP) can be performed in strong basic aqueous solutions, and shows two redox couples with electrochemically active voltammograms. The films can also be produced on glassy carbon, platinum, gold, and transparent semiconductor tin (IV) oxide electrodes. The Mn(4‐TMPyP)/DNA film was electrocatalytically oxidative for hydrazine, hydroxylamine, and SO in a basic aqueous solution through a Mn(IV) species. The electrocatalytic efficiency of Mn^IV(O)(4‐TMPyP) was observed to be greater than (OH)Mn^IV(O)(4‐TMPyP). Electrocatalytic oxidation by a Mn(4‐TMPyP) film as a catalyst for hydrazine oxidation is also discussed. This shows a new anodic peak current in the second segment after the positive scan during electrocatalytic oxidation, and is pH dependent.     

Unusual stabilization of manganese(III) during the cooxidation of dimethylformamide and manganese(II) by chromium(VI)

The kinetics of the formation and decomposition of Mn^III have been investigated spectrophotometrically in acidic media at 25 °C. The complete rate law for Mn^III formation isCr^VI + DMF + Mn^II {H⁺} Mn^III + CO₂ + Me₂NH + Cr^III ... (1)Mn^III + DMF {H⁺} Mn^II + CO₂ + Me₂NH ... (2)expressed by k _obs1 = k ₁ k₁ K _a1[H⁺][DMFH⁺][Mn^II]/{1 + K _a1[H⁺]}. Mn^III reduction by DMF follows the rate law k _obs2 = k ₂ K _h[DMF][H⁺]²/{[H⁺] + K _h}. The above results are accounted for by a mechanism involving the intermediacy of Cr^IV.     

Autoxidation of cobalt(II) in azide containing medium in presence of sulfur (IV): an interpretative study

Summary The factors influencing the oxidation of Co^II by dissolved oxygen in aqueous azide buffers in the presence of sulfur (IV) are discussed. It is proposed that mixed complexes of Co^II, N ₃ ^– and O₂ are formed during an induction period with spontaneous oxidation of Co^II by the O₂, H⁺/ H₂O₂ system. Co^III azide complexes then oxidize sulfite according to a Bäckström mechanism to produce highly oxidized intermediate species. Secondary reactions as that leading to S₂O ₆ ^2– decrease the amount of Co^III formed. The role of Mn^II accelerating the reaction was considered on the basis of labile Mn^III formed as an intermediate, which oxidizes Co^II to Co^III.

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Autoxidation von Cobalt(II) in azidhaltigem Medium in Gegenwart von Schwefel(IV): Eine interpretierende Analyse

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Dedicated to Prof. Dr. F. Huber, University of Dortmund, on the occasion of his sixtieth birthday     

Electrochemical and Spectral Studies of Sterically Hindered Water-Soluble Iron Tetrakis(Sulfonatomesityl)Porphine

Sterically hindered water-soluble iron(III) tetrakis(sulfonatomesityl)porphine (FeTSMP) exists exclusively in its monomer form in neutral and basic aqueous solutions. The acid dissociation constant (pKa) for Fe^IIITSMP is 6.6. The Fe^III/IITSMP couple has a formal reduction potential at ?0.22 V (vs. Ag/AgCl) in an acidic buffer solution. The E°-pH diagram shows that E° is independent of pH until the pH is larger than the pKa. The acid dissociation constant for Fe^IITSMP is 11.7. The redox potential of Fe^III/IITSMP shifts positively when imidazole is present, indicating the ligation of imidazole to Fe^IITSMP. At pH 4.0 and 10.2 buffer solutions, two imidazoles are found to ligate at the iron(III) center with β₂ = 10^4.7 and 10^4.1, respectively. The E°-pH diagram indicates that the pKa of (ImH)₂Fe^IIITSMP is 11.3 at 0.03 M imidazole solution. The oxidation of Fe^IIITSMP could involve two one-electron transfer processes, namely, one electron oxidation at the iron center, while another at the porphyrin ring. The two one-electron oxidations are found to overlap at pH = 5.5 and separate as the pH increases by shifting of the potential at the iron center, which is pH dependent. The radical cation of porphyrin ring is not stable and decomposes rapidly in water.     

A Single‐Chain Magnet Tape Based on Hexacyanomanganate(III)

The tape‐like chain {[(tptz)Mn^II(H₂O)Mn^III(CN)₆]₂Mn^II(H₂O)₂}_n?4n MeOH?2n H₂O based on the anisotropic building block hexacyanomanganate(III) exhibits long‐range magnetic ordering below 5.1 K as well as single‐chain magnetic behavior at lower temperatures with an effective energy barrier of 40.5(7) K.     

Insertion of a Single‐Molecule Magnet inside a Ferromagnetic Lattice Based on a 3D Bimetallic Oxalate Network: Towards Molecular Analogues of Permanent Magnets

The insertion of the single‐molecule magnet (SMM) [Mn^III(salen)(H₂O)]₂²⁺ (salen^2?=N,N′‐ethylenebis‐(salicylideneiminate)) into a ferromagnetic bimetallic oxalate network affords the hybrid compound [Mn^III(salen)(H₂O)]₂[Mn^IICr^III(ox)₃]₂ ? (CH₃OH) ? (CH₃CN)₂ ( 1 ). This cationic Mn₂ cluster templates the growth of crystals formed by an unusual achiral 3D oxalate network. The magnetic properties of this hybrid magnet are compared with those of the analogous compounds [Mn^III(salen)(H₂O)]₂[Zn^IICr^III(ox)₃]₂ ? (CH₃OH) ? (CH₃CN)₂ ( 2 ) and [In^III(sal₂‐trien)][Mn^IICr^III(ox)₃] ? (H₂O)_0.25 ? (CH₃OH)_0.25 ? (CH₃CN)_0.25 ( 3 ), which are used as reference compounds. In 2 it has been shown that the magnetic isolation of the Mn₂ clusters provided by their insertion into a paramagnetic oxalate network of Cr^III affords a SMM behavior, albeit with blocking temperatures well below 500 mK even for frequencies as high as 160 kHz. In 3 the onset of ferromagnetism in the bimetallic Mn^IICr^III network is observed at T_c=5 K. Finally, in the hybrid compound 1 the interaction between the two magnetic networks leads to the antiparallel arrangement of their respective magnetizations, that is, to a ferrimagnetic phase. This coupling induces also important changes on the magnetic properties of 1 with respect to those of the reference compounds 2 and 3 . In particular, compound 1 shows a large magnetization hysteresis below 1 K, which is in sharp contrast with the near‐reversible magnetizations that the SMMs and the oxalate ferromagnetic lattice show under the same conditions.     

Binuclear Homoleptic Manganese(III,III) and Manganese(IV,III) Complexes with Deprotonated D-Mannose from Aqueous Solution

Just a “reducing” sugar —namely, D -mannose—is a starting material in the synthesis of a mixed-valence complex of manganese in the oxidation states +III and +IV . Ba₂[Mn^IIIMn^IV(β-D -ManfH₋₅)₂]Cl⋅14 H₂O (Manf=mannofuranose; the structure of the anion is shown on the right) is prepared in aqueous solution by oxidation of an analogous Mn₂^III complex with oxygen. In neutral solutions the Mn^IIIMn^IV binuclear complex is formed by disproportionation of the Mn₂^III precursor.     

A binuclear manganese(II) complex,deca­aqua(μ‐1,2,4,5‐benzene­tetra­carboxyl­ato‐O1:O4)­di­manganese(II) hydrate

In the title Mn^II complex, [Mn₂(C₁₀H₂O₈)(H₂O)₁₀]·H₂O, two independent binuclear mol­ecules bridged by the 1,2,4,5‐benzene­tetra­carboxyl anion exist in a unit cell, with each anion lying about an inversion centre. One of the Mn—O_water distances [2.2922 (13) Å] is significantly longer than the Mn^II—O_water distances reported so far for Mn^II complexes and very close to the Mn—O_water distances found in the axial direction of Mn^III complexes.     

Electrochemistry and Spectroscopy of Sulfate Complexes of (Tetraphenylporphyrinato)manganese

The electrochemical and spectroscopic properties of [Mn₂(tpp)₂(SO₄)] (H₂tpp=tetraphenylporphyrin=5,10,15,20‐tetraphenyl‐21H,23H‐porphine) were studied to characterize the stability of this compound as a function of solvent, redox state, and sulfate concentration. In non‐coordinating solvents such as 1,2‐dichloroethane, the dimer was stable, and two cyclic voltammetric waves were observed in the region for Mn^III reduction. These waves correspond to reduction of the dimer to [Mn^II(tpp)] and [Mn^III(tpp)(OSO₃)]^?, and reduction of [Mn^III(tpp)(OSO₃)]^? to [Mn^II(tpp)(OSO₃)]^2?, respectively. In the coordinating solvent DMSO, [Mn₂(tpp)₂(SO₄)] was unstable and dissociated to form [Mn^III(tpp)(DMSO)₂]⁺. A single voltammetric wave was observed for Mn^III reduction in this solvent, corresponding to formation of [Mn^II(tpp)(DMSO)]. In non‐coordinating solvent systems, addition of sulfate (as the bis(triphenylphosphoranylidene)ammonium (PPN⁺) salt) resulted in dimer dissociation, yielding [Mn^III(tpp)(OSO₃)]^?. Reduction of this monomer produced [Mn^II(tpp)(OSO₃)]^2?. In DMSO, addition of SO led to displacement of solvent molecules forming [Mn^III(tpp)(OSO₃)]^?. Reduction of this species in DMSO led to [Mn^II(tpp)(DMSO)].     

Kinetics of oxidation of thiocyanate ion by manganese(III) in pyrophosphate medium

Summary Mn^III is stabilized by pyrophosphate in weakly acidic solutions. The nature of the complex formed was elucidated spectrophotometrically. The kinetics of Mn^III oxidation of thiocyanate in pyrophosphate medium was investigated over the pH range 2–3. The oxidation followed first order kinetics with [Mn^III]. The effects of varying [Mn^III], [NCS^–], added Mn^II and metal ions, pH, total [P₂O _f7 ^p4– ] and added ClO _f4 ^p– , Cl^– and SO _f4 ^p2– were studied. The order in [NCS^–] was unity, and increasing [H⁺] increased the rate. Retardations with added P₂O _f7 ^p4– and Mn^II were observed. Complexation of NCS^– as K₂Zn(NCS)₄ decreased the reactivity without any change in overall mechanism. The dependence of the reaction rate on temperature was examined, and activation parameters were computed from Arrhenius and Eyring plots. A mechanism consistent with the results is proposed.     

Synthesis and Properties of Complexes with Unusual {MnIII4} and {MnII4} Cages

Two types of manganese complexes with [Mn₄] cores featuring the unusual distorted cube topology are presented, the first of which comprises new modifications of the reported complex [Mn^III₄(sao)₄(saoH)₄]·3CHCl₃: [Mn₄(sao)₄(saoH)₄]·1.32(C₄H₁₀O)·0.43(CH₄O) ( 1a ) and [Mn(sao)₄(saoH)₄]·0.5(CH₄O)·0.5(C₂H₃N) ( 1b ) sao = salicylaldoxime. The second, 0.55[Mn₄Cl₄(C₁₂H₉N₂O)₄(CH₃OH)₂(H₂O)₂]·0.45[Mn₄Cl₄(C₁₂H₉N₂O)₄(CH₃OH)₄] ( 2 ), is the first reported case of a {Mn^II₄} core of this topology besides known {Mn^III₄} compounds. Differences between the {Mn^II₄} and {Mn^III₄} situation are discussed, and so far overlooked differences in magnetic properties between different {Mn^III₄} compounds are pointed out.     

Synthesis,Crystal Structures,and Magnetic Properties of Two Tetrahedral MnIIMnIII3 Complexes

Two tetranuclear manganese complexes, [NaMn^IIMn₃^III(μ₄‐O^2–)(HL)₃(SCN)₄] ( 1 ) and [NaMn^IIMn₃^III(μ₄‐O^2–)(HL)₃Cl₄][NaMn^IIMn₃^III(μ₄‐O^2–)(HL)₃Cl₃(H₂O)]ClO₄ · 3.5H₂O ( 2 ) were obtained from the reaction of manganese perchlorate with a quadridentate Schiff base ligand, 3‐(2‐hydroxybenzylideneamino)propane‐1, 2‐diol (H₃L) derived from condensation of 2‐hydroxybenzaldehyde with 3‐amino‐1, 2‐propanediol, as well as the coligand KSCN or NaCl under basic conditions. Single‐crystal X‐ray studies reveal that those two complexes all have a mixed‐valent tetrahedral core, which contains an apical Mn^II ion and three basal Mn^III ions situated in the [Mn₃(μ₄‐O^2–)]⁷⁺ equilateral triangle plane. Fitting of the magnetic susceptibility data to the theoretical χ_mT vs. T expression, revealed that the presence of only antiferromagnetic interactions between the central metal atoms in 1 , while both antiferromagnetic and ferromagnetic interactions are present in 2 .     

Die Kristallstruktur der hydratisierten Cyanokomplexe NMe4MnII[(Mn, Cr)III(CN)6] · 3 H2O und NMe4Cd[MIII(CN)6] · 3 H2O (MIII = Fe,Co): Verwandte des Berliner Blaus

The Crystal Structure of the Hydrated Cyano Complexes NMe₄Mn^II[(Mn, Cr)^III(CN)₆] · 3 H₂O and NMe₄Cd[M^III(CN)₆] · 3 H₂O (M^III = Fe, Co): Compounds Related to Prussian Blue The crystal structures of the isotypic tetragonal compounds (space group I4, Z = 10) NMe₄Mn^II · [(Mn, Cr)^III(CN)₆] · 3 H₂O (a = 1653.2(4), c = 1728.8(6) pm), NMe₄Cd[Fe(CN)₆] · 3 H₂O (a = 1642.7(1), c = 1733.1(1) pm) and NMe₄Cd[Co(CN)₆] · 3 H₂O (a = 1632.1(2), c = 1722.4(3) pm) were determined by X‐rays. They exhibit ⊥ c cyanobridged layers of octahedra [M^III(CN)₆] and [M^IIN₄(OH₂)₂], which punctually are interconnected also || c to yield altogether a spaceous framework. The M^II atoms at the positions linking into the third dimension are only five‐coordinated and form square pyramids [M^IIN₅] with angles N–M^II–N near 104° and distances of Mn–N: 1 × 214, 4 × 219 pm; Cd–N: 1 × 220 resp. 222, 4 × 226 resp. 228 pm. Further details and structural relations within the family of Prussian Blue are reported and discussed.     

Synthesis and characterization of new aluminium and gallium heteropoly complexes with chromium,iron, cobalt or coppercentred undecatungstate ligand

Summary Eight aluminium and gallium heteropoly undecatungstometalate complexes of general formula K_n[M(H₂O)-XW₁₁O₃₉]·nH₂O, where M=Al^III, Ga^III, and X=Cr^III, Fe^III, Co^II or Cu^II, have been prepared and characterized by elemental analysis, cation exchange i.r., u.v., x-ray powder diffraction and by thermal analyis. The compounds are stable in acidic solution. I.r., u.v. spectra and x-ray diffraction studies show that the structure of the compounds derives from the Keggin structure. Their thermostability is higher than that of the homologous dodecatungstometalates.