Electron Paramagnetic Resonance Of Mn2 Research Articles

Electron paramagnetic resonance of Mn 2+ in II–VI semiconductor alloys

The electron paramagnetic resonance spectrum from Mn 2+ ions has been measured as a function of composition in six different II–VI semiconductor alloys. Despite the overall cubic structure of the alloys, there is a large axial crystal field interaction D due to the lowered symmetry in the alloy environment. The variation of D with composition is explained in terms of the superposition model except in the Hg-based alloys where it is correlated with the band structure variation with composition.

Electron paramagnetic resonance of Mn 2+-doped KCo xMg 1−xF 3 crystals

The X-band EPR of Mn 2+-doped in KCo x Mg 1− x F 3 single crystals has been studied at 70–400K. The resolved Mn 2+ spectra were recorded for x<0.5 and high temperatures. A narrowing of EPR linewidths is considered as an effect of the random modulation of the magnetic interactions between the Mn 2+ and Co 2+ ions due to the spin-lattice relaxation processes of the Co 2+ ions. The Co 2+ spin-lattice relaxation time τ host has been estimated in these perovskite crystals using a modified Mitsuma theory.

ESR of Mn2+ reveals a crystal field reduction in AlCl3 upon intercalation in graphite

Electron spin resonance of Mn2+ in AlCl3 single-crystal and AlCl3-GICS reveals a reduction of about 30% in crystal field parameter (D) upon intercalation of AlCl3 in graphite.

Host spin-lattice relaxation narrowing and the electron paramagnetic resonance of Mn(II) in single crystals of hexakis(pyridineN-oxide)cobalt(II) complexes

The electron paramagnetic resonance spectra of Mn(C5H5NO)6. X2 (X ≡ ClO- 4, BF- 4 and NO- 3) doped in single crystals of isomorphous paramagnetic Co(C5H5NO)6. X2 are studied at various temperatures. Zero-field splitting in all three crystals is axially symmetric and the magnitude of D is unusually large for an octahedral coordination polyhedron with all ligands identical. The sharp resonance of Mn(II) in the paramagnetic host observed at high temperatures is interpreted in terms of random modulation of the dipolar interaction between the guest Mn(II) and host Co(II) ions by the rapid spin-lattice relaxation of Co(II). The spin-lattice relaxation times of Co(II) ions at 300 K, estimated from the temperature dependent linewidth of the Mn(II) resonance, are 24 × 10-12, 28 × 10-12 and 23 × 10-12 s in perchlorate, fluoborate and nitrate crystals respectively. The temperature dependence of the relaxation is of the form 1/(at + bt 5) and below 270 K the direct process dominates.

The manganese center of oxygen-evolving and calcium-depleted photosystem II: a pulsed EPR spectroscopy study

The environment of the multi-manganese center in the O2-evolving complex (OEC) of plant photosystem II (PS II) under conditions of Ca2+ depletion has been probed using pulsed electron paramagnetic resonance (EPR) spectroscopy, and the following results are reported: (1) In Ca(2+)-depleted PS II membranes treated with the chelator [ethylenebis(oxyethylenenitrilo)]tetraacetic acid (EGTA), the modified Mn EPR signal arising from the OEC in the S2 state and the split EPR signal from the S3 state could be detected in the absorption mode by recording the amplitude of a two-pulse echo as a function of the external magnetic field. The formation of the S3 signal (g approximately 2.004; delta Hpp = 164 G) is not accompanied by the disappearance of the Mn EPR signal, although the signal becomes difficult to detect in CW EPR. This result supports the previous interpretation of the split S3 EPR signal as arising from the interaction of an organic radical with the Mn cluster [Boussac, A., Zimmermann, J. L., Rutherford, A. W., & Lavergne, J. (1990) Nature 347, 303-306]. (2) The two-pulse electron spin echo envelope modulation (ESEEM) spectra of the S2 state formed in Ca(2+)-depleted PS II membranes obtained from 14N- and 15N-labeled material are different. This indicates that nitrogen nuclei from nitrogen-containing protein residues are coupled to the Mn center in the S2 state of the inhibited enzyme. In addition, comparison with the two-pulse ESEEM data obtained for the S2 state in the untreated enzyme suggests that the coupling may be altered by the Ca2+ depletion and/or EGTA treatment. (3) The treatment of Ca(2+)-depleted PS II membranes with sodium pyrophosphate also induced a stable S2 state characterized by a modified multiline EPR signal that is similar to that obtained in EGTA-treated PS II membranes. Comparison of the ESEEM data obtained for the pyrophosphate and 14N and 15N samples treated with EGTA suggests that the modification induced by the EGTA treatment is accompanied by the binding of (an) EGTA molecule(s) to or near the Mn center. (4) ESEEM data obtained for the S3 state formed in the pyrophosphate or EGTA-treated enzyme are quite similar to those obtained for the corresponding S2 state. The data are also compared with ESEEM data obtained on oxidized 4(5)-methylimidazole obtained by UV irradiation. These results are discussed with respect to the current assignment of the S3 radical as arising from oxidation of a histidine residue.

Magnetic and vibrational Raman scattering from II-VI magnetic quantum wells: ZnTe/Cd1-xMnxSe and ZnTe/MnSe.

In a type-II multiple quantum well consisting of ZnTe/Cd 1-x Mn x Se, the Raman shifts associated with the spin flip of donor-bound electrons in the Cd 1-x Mn x Se wells are significantly smaller than in bulk Cd 1-x Mn x Se of comparable x. This effect is ascribed to the decrease in the effective Mn 2+ concentration as a result of the penetration of the donor electron wave function into the nonmagnetic barrier. Raman electron paramagnetic resonance of Mn 2+ is also observed in these type-II quantum wells, whose resonance enhancement is associated with spatially direct interband transitions from states above the barrier for holes to the quantum confined electronic states

EPR of Mn2+‐Doped Tutton Salts. Role of Hydrogen Bonding

AbstractThe work deals with electron paramagnetic resonance of Mn2+‐doped zinc potassium selenate hexahydrate and zinc cobalt selenate hexahydrate Tutton salt single crystals. The different field parameters for the two hosts are evaluated from the observed z‐ and x‐axes spectra. The D parameters for the two hosts are compared with the corresponding reported values for hexahydrate. This parameter shows a systematic variation with the change in radii of the M′ ion in the series of salts ZnM′2(SeO4)2. 6H2O with M′ as K, Rb, and Cs. The case of M′ as NH4, however, does not show such a systematics. Similar behaviour is found for two other such series of Tutton salts, as well. Further it is found that D is, in general, negative for K, Rb, and Cs Tutton salts but is positive for NH4 Tutton salts. This unusual behavior of NH4 Tutton salts is attributed to two types of hydrogen bondings existing in such Tutton salts, in contrast to the only one type linking the H2O groups to the sulphate groups in all other Tutton salts. An attempt is also made to explain the unusual reported negative value of D in ammonium‐iron, ammonium‐cadmium, and ammonium‐nickel Tutton salts.

Electron Spin Resonance of Mn2+ in Hemimorphite

The Electron Spin Resonance of Mn2+ in natural crystals of hemimorphite was studied at RT, X-band. No fine structure other than the central M = | + 1/2 〉 ⇆ | −1/2 > transition with allowed (Δm = 0) and forbidden (Δm = ±1) hyperfine transitions were observed. The spectrum was fitted with the spin Hamiltonian parameters g = 2.001, A = −84.6 × 10−4 cm−1. The crystal field parameter D was estimated equal to (8 ± 2) × 10−3 cm−1. The most striking result is the size of the hyperfine splitting constant favoring occupancy of sixfold coordinated sites.

Electron Paramagnetic Resonance of Mn2+ in Orthorhombic and Higher Symmetry Crystals

Les spectres de ces ions sont etudies dans differents hotes paramagnetiques. On observe, a temperature ambiante, des spectres dus au retrecissement de la relaxation spin-reseau hote pour plusieurs cristaux. Les raies de Mn 2+ s'elargissent avec l'abaissement de la temperature jusqu'a 77 K

Electron paramagnetic resonance of Mn2+ in Sm2Zn3(NO3)12·24H2O single crystals

The X-band electron paramagnetic resonance of Mn2+ doped in Sm2Zn3(NO3)12·24H2O single crystals has been studied. Mn2+ substitutes at two inequivalent Zn2+ sites. The spin-Hamiltonian analysis of the EPR spectra is presented at 298 and 77 K.

A single crystal electron paramagnetic resonance study of manganese(II) doped cadmium maleate dihydrate

Electron paramagnetic resonance of Mn 2+ doped into cadmium maleate dihydrate single crystal was studied at X-band frequencies (~9.5 GHz) at room temperature. The spin-Hamiltonian parameters were calculated. It was found that Mn 2+ enters the lattice interstitially and only one type of complex was identified. Forbidden hyperfine transitions were studied in the central group. The doublet separations are in agreement with the calculated values.

Electron paramagnetic resonance of Mn 4+ in BaTiO 3

The Electron Paramagnetic Resonance (EPR) of Mn 4+ in the rhombohedral low- temperature phase of BaTiO 3 has been observed at 19.3 and 13.0 GHz. The spectra have axial symmetry along 〈111〉 directions. Intensity measurements prove that the Mn 4+ EPR reflects {111} domain orientation. The spin-Hamiltonian constants are g ‖=1.9968(19), g ‖=2.0015(5), A ‖=67.48(5)×10 −4 cm −1, A ‖=73.04(15)×10 −4cm −1, and D=0.65(1)cm −1 at 4.2 K. The very large D value is more than 20 times that found for the isoelectronic Cr 3+. The latter ion remains centered in its surrounding octahedral oxygen cage, whereas the Mn 4+ is off-center with similar coordinates as Ti 4+. This result is deduced from a superposition-model analysis.

Electron paramagnetic resonance of Mn2+ in Ce2 Zn3 (NO3)12.24H2O single crystals

Electron paramagnetic resonance of Mn2+ in Ce2 Zn3 (NO3)12.24H2O single crystals has been studied in X-band at 290 and 90K. Mn2+ substitutes for Zn2+ sites. The spin-Hamiltonian parameters are evaluated.

Synthesis and characterization of stoichiometric CdPS 3

Compounds from the system CdPS 3 xSe x (where x = 1, 2, and 3) have been synthesized by a variety of synthetic techniques and characterized by X-ray diffraction. The X-ray diffraction lines obtained from CdPSe 3 and from CdPSSe 2 could be indexed using the reported powder pattern for CdPSe 3. However, despite different synthetic attempts and reannealing, powder pattern data for the CdPS 3 samples, although reproducible from sample to sample, are not consistent with the C2/m structure previously reported. Luminescence data indicate the presence of neutral Cd atoms, Cd vacancies, and S vacancies in crystals annealed under selected conditions. Electron paramagnetic resonance of Mn(II) doped CdPS 3 and 113Cd solid state nuclear magnetic resonance of CdPS 3 spectrum are consistent with a single cadmium environment.

On the charge compensation effects in Mn(II) doped (NH4)2SbF5: EPR study

Electron paramagnetic resonance of Mn(II) ion doped in bis (ammonium) pentafluorostibnate is reported. Local charge compensation is proposed as the reason for the doubling of the expected single site. A ±20° rotation of the MnF3−5 moeity about the crystallographic a axis has been attributed to charge compensation processes. The D tensor is found to have the values Dzz=0.0358 cm−1, Dyy=−0.028 62 cm−1, Dxx=−0.007 26 cm−1; the Mn hyperfine coupling is found to be −0.0095 cm−1. The apical flourine does not give resolved hyperfine coupling, while the four basal flourine atoms give hyperfine couplings in the range amax=0.0018 cm−1, amin=0.0015 cm−1.

Electron Paramagnetic Resonance of Mn2+ in Double Nitrate Crystals

AbstractElectron paramagnetic resonance of Mn2+ in Ce2Mg3(NO3)12 · 24 H2O and Ce2Co3(NO3)12 · 24 H2O single crystals is studied in X‐band at 290 and 90 K. Mn2+ substitutes for Mg and Co sites. The spin‐Hamiltonian parameters are evaluated. The broadening of the resolved spectra of Mn2+ doped in Ce2Co3(NO3)12 · 24 H2O on lowering the temperature is discussed in terms of host spin‐lattice relaxation narrowing. An analysis in terms of the superposition theory shows that the intrinsic second order parameter for the ligand oxygen atoms of the site I probably falls within the normal range of oxygen.

Electron paramagnetic resonance of Mn2+, VO2+, Cu2+, and x-ray induced centers in Rb2C2O4 ⋅ H2O single crystals

The electron paramagnetic resonance spectra of Mn2+, VO2+, Cu2+, and x-ray induced centers in Rb2C2O4 ⋅ H2O single crystals are studied at 9.45 GHz and 290 K. The spectra at 77 K show no appreciable change. The ions appear to enter the lattice at interstitial sites. The doublet separations of forbidden hyperfine transitions (Δm=±1) are studied in Mn2+ doped crystals. The x-ray irradiated single crystals exhibit singlet spectrum and show saturation effect. The spin-Hamiltonian parameters are evaluated at 290 K.

Structural investigations of the Mg.ATP complex at the active site of porcine adenylate kinase using phosphorothioate analogs and electron paramagnetic resonance of Mn(II) with chiral 17O-labelled ATP analogs.

The interaction between ATP, divalent metal ions and the active site of adenylate kinase from muscle has been studied by two different methods. No reversal of the relative reaction rates of the two diastereomers of adenosine 5′‐([α‐thio]triphosphate) was observed on changing the metal ion from Mg2+ to Cd2+, suggesting that the α‐phosphate group is not coordinated to the divalent metal ion in the enzyme · metal · ATP complex. This interpretation is confirmed by the lack of influence of 17O incorporated into the α‐phosphate group of ATP on the electron paramagnetic resonance (EPR) spectrum of Mn2+ at the active site of the enzyme. The specificity for the Sp diastereomer thus appears to be due to an interaction of the enzyme active site with the pro‐R oxygen of the α‐phosphate group. In contrast, the specificity of adenylate kinase for the diastereomers of adenosine 5′([β‐thio]triphosphate) is reversed from Sp to Rp on replacing Mg2+ by Cd2+, indicating an interaction of the pro‐R oxygen of the β‐phosphate group of ATP with the metal ion in the enzyme · metal · ATP complex. In agreement with this, ATP which is regio‐specifically labelled with 17O on the β‐phosphate group causes a line‐broadening of the EPR spectrum of Mn2+ at the active site, demonstrating coordination of at least one of the β‐phosphate oxygens with the metal. Using stereospecifically labelled [β‐17O]ATPs, it was found that (Rp)‐[β‐17O]ATP but not (Sp)‐[β‐17O]ATP caused a line broadening in the Mn2+ EPR spectrum similar to that seen with regio‐labelled [β‐17O]ATP, further indicating that the pro‐R oxygen of the β‐phosphate group of ATP is coordinated to the metal ion at the active site of adenylate kinase. These results lead to a value of 0.22–0.25 mT for the superhyperfine coupling constant of a single 17O‐Mn2+ interaction in a manganese‐ATP‐enzyme complex. ATP labelled with 17O on the γ‐phosphate group has no effect on the spectrum of Mn2+ at the active site, leading to the conclusion that Mg · ATP exists predominantly as a β‐monodentate complex at the active site of adenylate kinase. From the effect of H217O on the EPR spectrum of Mn2+ in the Mn · ATP complex at the active site it appears most likely that three, four or five water molecules are bound to the metal ion.

Host Spin—Lattice Relaxation Narrowing in Sm2Co3(NO3)12 · 24 H2O:Mn2+, Gd3+ Single Crystals

AbstractThe electron paramagnetic resonance of Mn2+ and Gd3+ in single crystals of Sm2Co3(NO3)12 · 24 H2O is studied in the X‐band at 300 and 90 K. The spin‐Hamiltonian parameters are evaluated. The observation of resolved Mn2+ and Gd3+ spectra at 300 K and their broadening on lowering the temperature is discussed in terms of host spin—lattice relaxation narrowing.

EPR Study of Mn2+ in Hg(ClO4)2 · 6H2O Single Crystals

Abstract The electron paramagnetic resonance of Mn2+ in Hg(ClO4)2 · 6H2O has been studied at X-band at 298 K and 77 K. Mn2+ is found to substitute Hg 2+ . The spectra have been analysed using the spin-Hamiltonian appropriate for trigonal symmetry. From the unequal separations between the Δm = ± 1 doublets in M = + 1/2 → - 1/2 transitions, the value of the axial part of the quadrupole coupling constant is determined. The observed doublet separations of forbidden hyperfine transitions in M = + 1/2 → - 1/2 are in good agreement with those cal-culated.