Crystal-field spectra of MnII and FeIII in sodium phosphate glasses

Summary Electronic absorption spectra of Mn^II in sodium phosphate glasses have been measured in the energy range 15 000–42 000 cm^–1 at room temperature and 80 K. The positions of bands are in good agreement with those calculated using the free-atom representation of the crystal-field theory including a Trees' correction, assuming a parent cubic-field microsymmetry. By analogy to known spectra of Mn^II, results indicate that Mn^II is coordinated to six oxygens and that there is distortion from a regular octahedral symmetry. With decreasing P₂O₅/Na₂O molar ratio, there are slight decreases in the energies of the field-independent transitions. Spectra of Fe^III in the same host glasses are briefly considered.     

Zero-Field Splittings and Redox Potentials in an Isostructural Series of Dinuclear FeIITiIV,FeIIITiIV, and MnIITiIV Complexes with a Face-Sharing Bridging Motive

The ligand H₆ioan has been used to synthesize the three dinuclear complexes [(ioan)Mn^IITi^IV], [(ioan)Fe^IITi^IV], and [(ioan)Fe^IIITi^IV]⁺. The face-sharing bridging mode of the three phenolates provides short M-Ti^IV distances of ≈3.0 Å. Mössbauer spectra of [(ioan)Fe^IIITi^IV]⁺ show a magnetically split six-line spectrum at 3 K in zero magnetic field demonstrating a slow magnetic relaxation. Magnetic measurements provide a zero-field splitting of |D|=5 cm⁻¹ in [(ioan)Fe^IITi^IV]. EPR spectroscopy demonstrates sizable zero-field splittings of the S=5/2 spin systems of [(ioan)Mn^IITi^IV] (D=0.246 cm⁻¹) and [(ioan)Fe^IIITi^IV]⁺ (D<−1 cm⁻¹) that can be related to enforced covalency of the M-O^ph bonds. [(ioan)Fe^IIITi^IV]⁺ exhibits a reversible reduction at −0.26 V vs. Fc⁺/Fc demonstrating the facile accessibility of Fe^III and Fe^II. In contrast to an irreversible oxidation in [(ioan)Ni^IITi^IV] at 0.78 V vs. Fc⁺/Fc, the reversible oxidation at 0.25 V vs. Fc⁺/Fc in [(ioan)Mn^IITi^IV] indicates even the access of Mn^III. These results indicate that pentanuclear complexes [(ioan)FeM¹M²M¹Fe(ioan)]ⁿ⁺ are meaningful targets to access electron delocalization in mixed-valence systems over five ions due to the facile accessibility of both Fe^II and Fe^III in the terminal positions. This study provides important local spin-Hamiltonian and Mössbauer parameters that will be essential for the understanding of the potentially complicated electronic structure in the anticipated pentanuclear complexes.     

ESR spectroscopy of FeIII ions in sodium silicate glasses

The state of Fe^III ions doped in sodium silicate glasses of the composition (100 ? x)Na₂O-xSiO_2?y Fe₂O₃ (x = 75, 81 mol.%; y = 0.05?13 wt.%) was studied by electron spin resonance (ESR). X-band ESR spectra exhibited three resonance signals at g ≈ 2.0, 4.3, and 6. The computer simulation of ESR spectra was performed on the basis of spin-Hamiltonian of rhombic symmetry. The nature of observed signals was interpreted as a combination of five types of Fe^III complexes. Three of them were clustered iron ions and two other were isolated paramagnetic ones. The ratio of observed forms was found for different glass compositions and various total amounts of Fe^III ions in a matrix containing 0.55, 2.5, 4, 7, and 13 wt.% of Fe₂O₃.     

Complexes of 1-isonicotinoyl-4-benzoyl-3-thiosemicarbazide with manganese(II), iron(III), chromium(III), cobalt(II), nickel(II), copper(II) and zinc(II)

1-Isonicotinoyl-4-benzoyl-3-thiosemicarbazide (IBtsc) and its Cr^III, Mn^II, Fe^III, Co^II, Ni^II, Cu^II and Zn^II complexes have been prepared and characterized by elemental analyses, magnetic susceptibility measurements, u.v.–vis., i.r., n.m.r. and FAB mass spectral data. The room temperature e.s.r. spectra of the Cr^III, Fe^III and Cu^II complexes yield values, characteristic of octahedral, tetrahedral and square-planar complexes, respectively. The Mössbauer spectra of [Fe(IBtsc-H)Cl₂] at room temperature and at 78 K suggest the presence of high-spin Fe^III. The Ni^II, Cr^III and Cu^II complexes show semiconducting behaviour in the solid state, but the Zn^II complex is an insulator at room temperature. IBtsc and its soluble complexes have been screened against several bacteria, fungi and tumour cell lines.     

Electron Transfer in the Cs⊂{Mn4Fe4} Cubic Switch: A Soluble Molecular Model of the MnFe Prussian‐Blue Analogues

A mixed‐valence {Mn^II₃Mn^IIIFe^II₂Fe^III₂} cyanide‐bridged molecular cube hosting a caesium cation, Cs?{Mn₄Fe₄}, was synthesized and structurally characterized by X‐ray diffraction. Cyclic‐voltammetry measurements show that its electronic state can be switched between five different redox states, which results in a remarkable electrochromic effect. Magnetic measurements on fresh samples point to the occurrence of a spin‐state change near room temperature, which could be ascribed to a metal‐to‐metal electron transfer converting the {Fe^II?CN?Mn^III} pair into a {Fe^III?CN?Mn^II} pair. This feature was only previously observed in the polymeric MnFe Prussian‐blue analogues (PBAs). Moreover, this novel switchable molecule proved to be soluble and stable in organic solvents, paving the way for its integration into advanced materials.     

Complexes of N-phenyl-N′-2-furanthiocarbohydrazide with oxovanadium(IV), manganese(III), iron(III), cobalt(II), nickel(II), copper(II) and zinc(II)

A new ligand, N-phenyl-N -2-furanthiocarbohydrazide (HPhfth), and its complexes with VO^IV, Mn^III, Fe^III, Co^II, Ni^II, Cu^II and Zn^II have been prepared and characterized by elemental analyses, magnetic susceptibility measurements, i.r., n.m.r., u.v.–vis., mass and FAB mass spectral data. The room temperature e.s.r. spectra of the VO^IV, Fe^III and Cu^II complexes yield <g> values characteristic of square pyramidal VO^IV, octahedral Fe^III and square planar Cu^II, respectively. The Ni^II and Cu^II complexes semiconduct, but the Zn^II complex is an insulator at room temperature. However, the conductivity increases as the temperature increases from 303–383 K, with a band gap of 0.21–1.01 eV. HPhfth and its soluble complexes have been screened against several bacteria and fungi.     

Synthesis of new 14- and 16-membered macrocycles and their transition metal complexes

Summary Benzoylacetic acid (1 mol) interacts with ethylenediamine or with propanediamine (2 mol) to yield new N₄ macrocycles 1,5,8,12-tetraazacyclotetradeca-2,4,9,11-tetraphenyl-3, 10-dicarboxylic-4,11-diacetic acid- 1,8-diene (L¹) and 1,5,9,13-tetraazacyclohexadeca-2,4,10,12-tetraphenyl-3, 11-dicarboxylic-4,12-diacetic acid-1,9-diene (L²), respectively. These macrocycles have been successfully complexed with Cr^III, Fe^III, Mn^II, Co^II, Ni^II, Cu^II and Zn^II. The complexes of the divalent metal ions are non-electrolytes, while those of Fe^III and Cr^III are 1:1 electrolytes in DMSO. On the basis of ligand field spectra and magnetic moments an octahedral geometry has been proposed for all the complexes.     

Ambidenticity of a tridentate oxygen-nitrogen donor towards bivalent and trivalent transition metal ions

Summary N-salicylidene anthranilamide (H₂SAA) and its Cr^III, Mn^II, Fe^III, Co^II, Ni^II and Cu^II complexes were prepared and characterized by physicochemical and spectroscopic data. H₂SAA enolizes to give a dibasic ONO donor set in the divalent metal complexes. It also binds to the trivalent metal ions in a nonenolized form using a monobasic ONN donor set. Co^II is oxidized to Co^III during complexation. Octahedral geometries are proposed for Cr^III, Mn^II, Fe^III and Co^III complexes, while square planar geometries are suggested for the Ni^II and Cu^II complexes. Phenoxide bridging in the Cr^III and Fe^III complexes and enoxide bridging in the Ni^II and Cu^II complexes is proposed.     

Spectroscopic and thermal investigations of transition and non-transition metal complexes of penicillin G as potential biological active species

Seven types of complexes were obtained when penicillin G potassium (pin) was reacted with transition and non-transition metal ions in methanol/distilled water mixed solvent. Magnetic susceptibilities and ESR spectra (Cu^II complex) of powdered samples indicated that the monomeric form of the complexes in the solid state, and the paramagnetic nature of the Cu^II, Ni^II, Mn^II, Cr^III, Co^II, and Fe^III complexes is attributable to the octahedral ligitional behavior of the potassium G penicillinate ligand. The antibacterial activity of the metal complexes were tested against some kind of bacteria and fungi strains and compared with penicillin G potassium activity. The possible mechanism of antibacterial action is discussed.     

Low-spin Manganphthalocyanine: Darstellung,Eigenschaften und elektronisches Raman-Spektrum von Di(cyano)phthalocyaninatomanganat(III) und -(II)

Low Spin Manganese Phthalocyanines: Preparation, Properties and Electronic Raman Spectrum of Di(cyano)phthalocyaninatomanganate(III) and -(II) . Iodophthalocyaninatomanganese(III) reacts with cyanide in acetone to yield di(cyano)phthalocyaninatomanganate(II), in dichloromethane, however di(cyano)phthalocyaninatomanganate(III) is formed. Both complexes are isolated as (n-Bu₄N)-salts. In the cyclovoltammogram the redox couple Mn^II/Mn^III is attributed to E_1/2 = - 0.22 V and the first ringoxidation Pc(2 -)/Pc(1 -) to E_1/2 = 0.75 V. The paramagnetic salts have magnetic moments (μ_eff = 2.11 resp. 2.95 B.M.) typical for the low spin ground state of Mn^II resp. Mn^III (S = 1/2 resp. 1). The uv-vis-nir spectra are discussed. Comparison with the dicyano-complexes of Cr^III, Fe^II/III and Co^III indicates that the multiple “extra bands” between 4 and 23 kK should be assigned to spin allowed trip-multiplets. The vibrational spectra are discussed. ν_as(Mn? C)(a_2u) is found at 350 cm^?1, ν_as(C? N)(a_2u; cyanide) at 2 092 (Mn^II) and 2 114 cm^?1 (Mn^III). The Raman spectra are dominated by resonance Raman(RR) effects. With variable-wavelength excitation polarized, depolarized and anomalously polarized vibrations assigned to phthalocyanine skeletal modes are selectively RR-enhanced for the Mn^II complex. Intensive lines between 1 650 and 3 300 cm^?1 are due to combinations and overtones of the a_2g vibrations at 1 492 and 1 602 cm^?1. In the 10 K Raman spectrum of (n-Bu₄N)[Mn(CN)₂Pc(2 -)] intraconfigurational transitions Γ₁ → Γ₄ and Γ₁ → Γ₃, Γ₅ resulting from the splitting of the ³T_1g ground state of Mn^III (O_h symmetry) by spin-orbit coupling are observed as anomalously polarized and depolarized lines at 172 and 287 cm^?1.     

Quenching of the luminescence of upconverting luminescent nanoparticles by heavy metal ions

We report that the luminescence of upconverting luminescent nanoparticles (UCLNPs) is quenched by heavy metal ions and halide ions in aqueous solution. The UCLNPs consist of hexagonal NaYF₄ nanocrystals doped with trivalent rare earth ions and were synthesized by both the oleic acid (solvothermal) method and the ethylenediaminetetraacetic acid (co‐precipitation) method. Quenching was studied for the Cu^II, Hg^II, Pb^II, Cd^II, Co^II, Ag^I, Fe^III, Zn^II, bromide, and iodide ions and is found to be particularly strong for Hg^II. Stern–Volmer plots are virtually linear up to quencher concentrations of 10–25 mM , but deviate from linearity at higher quencher concentrations, because static quenching causes an additional effect. The UCLNPs display two main emission bands (blue, green, red or near‐infrared), and the quenching efficiencies for these are found to be different. The effect seems to be generally associated with UCLNPs because it was observed for all UCLNPs doped with trivalent lanthanide ions including Yb^III, Er^III, Ho^III, and Tm^III. The results are discussed in terms of quenching mechanisms and with respect to potential applications such as optical sensing.     

Electron Transfer in the Cs⊂{Mn4Fe4} Cubic Switch: A Soluble Molecular Model of the MnFe Prussian-Blue Analogues

A mixed-valence {Mn^II₃Mn^IIIFe^II₂Fe^III₂} cyanide-bridged molecular cube hosting a caesium cation, Cs⊂{Mn₄Fe₄}, was synthesized and structurally characterized by X-ray diffraction. Cyclic-voltammetry measurements show that its electronic state can be switched between five different redox states, which results in a remarkable electrochromic effect. Magnetic measurements on fresh samples point to the occurrence of a spin-state change near room temperature, which could be ascribed to a metal-to-metal electron transfer converting the {Fe^II−CN−Mn^III} pair into a {Fe^III−CN−Mn^II} pair. This feature was only previously observed in the polymeric MnFe Prussian-blue analogues (PBAs). Moreover, this novel switchable molecule proved to be soluble and stable in organic solvents, paving the way for its integration into advanced materials.     

8-Hydroxyquinoline and 8-hydroxyquinaldine as reagents for the colorimetric estimation of chromium

Summary A simple colorimetric method for the estimation of Cr^III ions, employing 8-hydroxyquinoline and 8-hydroxyquinaldine, has been described. It has been shown that upto a concentration ratio of 13, the presence of Al^III ions, does not interfere with the 8-hydroxyquinaldine reagent. The method has been further shown not to be interfered by the presence of Ce^III, Ni^II, W^VI, Mn^II, Th^IV, Zn^II, Tl^I, and Ba^IIions, but the presence of Fe^II, Fe^III, U^VI, Cu^II, Co^II and Mo^VIions affects the results. It is found to be necessary to heat the reaction mixture, before carrying out the extraction process.     

Darstellung und Charakterisierung einige Thiocyanat- und Selenocyanat-Komplexe von Übergangsmetallen

Some 6:1 thiocyanate complexes of Fe^III, Mo^III, Ru^III, Os^III, Ir^III and some 6:1 or 4:1 selenocyanate complexes of Fe^II, Fe^III, Mo^III, Rh^III, Pd^II, Pt^II, and Au^III have been prepared as salts of large organic cations. The compounds are characterized by their infra-red spectra and by conductance measurements. In particular the linkage property of the thiocyanate and selenocyanate ligand is discussed together with the consequences it has on the AHRLAND -CHATT -DAVIES -PEARSON classification of the central ions.     

Tunability of Fluorescence Property of a Terbium‐Complex‐Containing Polymer via Incorporation of a Transition‐Metal Complex

Summary: In this study, a terbium‐complex monomer and transition‐metal‐complex monomers (Fe^III, Mn^II, and Ni^II complex monomers) are synthesized, and novel acrylate copolymers are then obtained through covalent attachment of the terbium complex and the transition‐metal complex onto the macromolecular chain simultaneously. The copolymers developed herein present the characteristic fluorescence properties of the terbium(III ) ion, The incorporation of an Mn^II complex into a Tb^III‐containing polymer leads to greater fluorescence enhancement compared with the Ni^II complex, while the incorporation of the Fe^III complex results in fluorescence quenching, thus the incorporation of different transition‐metal complexes into the copolymers ensures tunability of the copolymer's fluorescence property.

Fluorescence emission spectra of the copolymer solid films. Solid: P‐Tb; dash‐dot: P‐Tb‐Mn^II; dash: P‐Tb‐Ni^II; and dot: P‐Tb‐Fe^III.     

Synthesis, structures, and magnetic properties of carboxylate-bridged trinuclear complexes based on low-spin manganese(III)/iron(III) building blocks

Four linear trinuclear transition metal complexes have been prepared and characterized. The complexes [M^II(MeOH)₄][Fe^III(L)₂]₂·2MeOH (M = Fe (1) or Ni (2)), [Co^II(EtOH)₂(H₂O)₂][Fe^III(L)₂]₂·2EtOH (3), and [Mn^II(phen)₂][Mn^III(L)₂]₂·4MeOH (4) (H₂L = ((2-carboxyphenyl)azo)-benzaldoxime, phen = 1,10-phenanthroline) possesses a similar syn–anti carboxylate-bridged structure. The terminal Fe(III) or Mn(III) ions are low spin, and the central M(II) ions are high spin. Magnetic measurements show that antiferromagnetic interactions were present between the adjacent metal ions via the syn–anti carboxylate bridges. The antiferromagnetic coupling between low-spin Fe(III) and Ni(II) is unusual, which has been tentatively assigned to the structural distortion of Fe(III).     

Bemerkungen zur chemischen Bestimmung von zweiwertigem Eisen und dreiwertigem Mangan in manganhaltigen Ferriten

Zusammenfassung Die Methode von Bonsels u. Linnemann [1] zur Bestimmung von Fe^II und Mn^III lieferte bei der Überprüfung falsche Ergebnisse. Die Ursache liegt darin, daß sich der Blindwert des Azides in Gegenwart von Mn^2ü-Ionen erheblich erhöht und in der Siedehitze eine Reaktion zwischen Mn^III und Cr^III abläuft. Da eine Auflösung selbst fein pulverisierter Ferrite in dem mitgeteilten Lösungsgemisch nur in der Siedehitze erfolgt, ist eine Bestimmung von Fe^II und Mn^III in Ferriten nach dieser Methode nicht möglich.

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Summary The method for the determination of Fe^II and Mn^III in manganese ferrites by Bonsels and Linnemann [1] was examined. It was found that the consumption of NaN₃, used for the reduction of Mn^III and effecting in a second (not wanted) reaction the reduction of Cr₂O₇ ^2–, is essentially increased by the presence of Mn^II and causes an error in the determination of Fe^II. The second error is the reaction between Mn^III and Cr^III at boiling temperature. On account of the necessity to dissolve the ferrites with the acid mixture at boiling temperature the determination of Mn^III and Fe^II is not possible.

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Herrn Dr. P. Kleinert vom Institut für Magnetische Werkstoffe danken wir an dieser Stelle für wertvolle Diskussionsbeiträge und das bei der Durchführung der Arbeit gezeigte Interesse.     

Die Bestimmung von zweiwertigem Eisen und dreiwertigem Mangan in Mangan-Zink-Ferriten

Zusammenfassung Es wird eine Methode beschrieben, mit der zweiwertiges Eisen und dreiwertiges Mangan in Ferriten nebeneinander ma\analytisch bestimmt werden können. Das wesentliche Problem dieser Methode, die Probe in Lösung zu bringen, ohne da\ sich Anteile von Fe^II und Mn^III chemisch miteinander umsetzen, wurde so gelöst, da\ Dichromat als Oxydationsmittel zugesetzt wurde, das sich wÄhrend des Lösungsvorganges vor dem Mn^III mit dem Fe^II umsetzt.

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Summary A method is described for the volumetric determination of divalent iron and trivalent manganese in presence of each other. In order to dissolve the samples without reaction between Fe^II and Mn^III (the essential problem of this method) dichromate is added which reacts with the divalent iron before Mn^III during the process of dissolution.

     

Paramagnetic Centres in Irradiated Ultraphosphate Glasses Containing Rare Earth Elements

Abstract

In this study three-component ultraphosphate glasses based on Nd, Gd, Ce penta-phosphates were investigated by the EPR method depending on their synthesis conditions. EPR spectra were recorded using a “Radiopan” (Poland) radiospectrometer with a-c-field frequency 9 GHz and modulation frequency 100 kXz at 77 K. The samples were irradiated at γ-⁶⁰Co source. EPR spectra of unirradiated ultraphosphate glasses synthesized in oxidizing conditions exhibit at broad nonstructural line with ΔH_1/2 = 100 mT which, probably, can be considered as a Gd³⁺ ion cluster. After gamma-irradiation no additive PMC (except nydrogen atoms) arise in these glasses. EPR spectra of nonirradiated glasses synthesized in reductive conditions do not exhibit paramagnetic centres. 4 types of PMC appear in EPR spectra after irradiation: hydrogen atoms doublet with A iso = 50 mT, anisotropic doublet with A_I = 3.7 mT, A_II = 4.6 mT and g_II = 2.004, g_I = 2.018 which was earlier considered as a phosphor-acid radical PO^2- ₄, and two doublets with A¹ _I = 75 mT, A¹ _II = 90 mT, g¹ _I = 2.036, g¹ _II = 2.033, and A² _I = 105 mT, A² _II = 150 mT and g² _I = 2.082, g² _II = 2.077, which can be considered as a hole PMC PO^2- ₃ in different environment. The maximum concentration of these centres does not exceed 10^l5 (absorbed dose 600 kGy/h), and the ratio changes according to glass synthesizing temperature. Thus, ultraphosphate glasses synthesized in oxidizing conditions have a big paramagnetic radiation stability in comparison to analogous glasses synthesized in reductive conditions.     

Simultispin: A versatile graphical user interface for the simulation of solid-state continuous wave EPR spectra

Solid-state continuous wave (cw) electronic paramagnetic resonance (EPR) spectroscopy is particularly suitable for metal complex analysis. Extracting magnetic parameters by simulation is often necessary to describe the electronic structure of the studied molecular compounds that can have various electronic spin states and characterized by different parameters like g-values, hyperfine coupling or zero field splitting values. Easyspin toolbox on MATLAB is a powerful tool, but for the user, it requires spending time with coding and could discourage nonexperts. Facing this context, we have developed a graphical user interface called Simultispin, dedicated to solid-state cw-EPR spectra simulation. Some examples of experimental spectra of metal complexes (mixture of low spin and high spin Fe^III complexes, dynamic disorder of a Cu^II complex, photogeneration of a Mn^III complex), highlighting specific solid-state functions, are described and analyzed based on simulations performed with Simultispin. We hope that its ergonomy and the ease to set up a complete set of parameters to get reliable simulations could help a large EPR community to improve the efficiency of their interpretations.