Large Quadrupole Splitting Research Articles

Structural, Moessbauer, and EPR investigations on two oxidation states of a five-coordinate, high-spin synthetic heme. Quantitative interpretation of zero-field parameters and large quadrupole splitting

P2,/n. The five-coordinate iron atom is bonded to four porphyrinato nitrogens (Fe-N,) = 2.107 (14) A and to an oxygen atom of the acetate ion (FA,, = 2.034 (3) A), placed inside the molecular cavity of the picket-fence porphyrin. Mhsbauer spectra were recorded in the two oxidation states of the complex at temperatures varying from 1.5 to 200 K in fields of 0-6.21 T. The ferrous complex has a large quadrupole splitting, AEQ = 4.25 mm s-I, nearly independent of temperature. In the ferric species, the quadrupole splitting, AEQ = 1.1 mm s-', is as normally found in ferric high-spin iron porphyrins. The spin-Hamiltonian analysis of the spectra yields the zero-field parameters D = -0.9 cm-' and E/D = 0.33 and the magnetic hyperfine parameters A,, = -17 T and A, = -13.3 T in the ferrous complex (spin S = 2) and D = 7.5 cm-I, E/D = 0 and Ax,,= = -20 T in the ferric species (S = 5/2). The values of the zero-field parameters of the ferric species are confirmed by EPR analysis; the g values are g, = 1.960, g, = 2.017, and g, = 2.00. The zero-field splittings and effective g values in the ferric complex are interpreted in terms of a crystal-field model. Theoretical estimates of the quadrupole splitting and zero-field parameters in the ferrous complex are given on the basis of molecular-orbital calculations. The relation between the zero-field tensor (D) and electronic and X-ray structure in the ferrous species is discussed. Parallel to the discovery of the unusually large quadrupole splitting, PE - 4 mm s-', in the ferrous state of the prosthetic group term4 p460 of the multiheme enzyme hydroxylamine oxidoreductase from the bacterium Nitrosomonas europeae,'V2 comparably large splittings were observed in a number of synthetic five-coordinate porphyrins of the formula [Fe(X)(Porph)]-, where X is an anionic oxygen- or nitrogen-donor ligand or a halide ion.38 In order to gain more insight into the electronic structure of the iron ions in these complexes, field- and temperature-dependent MBssbauer measurements have been performed in the synthetic phenolato porphyrinato complex [ Fe(OC6H,)(TPP)]- by Lang et a1.* For the derivation of a set of zero-field parameters consistent with both the susceptibility and MBssbauer data in the phenolate complex, these authors introduced weak antiferromagnetic exchange coupling between the paramagnetic iron centers.8 Strong correlations between the sign and magnitude of the zero-field parameter D and the value of the exchange-coupling constant were found in the simulations of the magnetic susceptibility data. However, the spin-Hamiltonian parameters inferred from the Mbsbauer spectra are rather insensitive to the weak intermolecular couplings. The value of the zero-field parameter D obtained by Lang et al. is small and negative (see Table I). The principal components of the magnetic hyperfine tensor (A) in the complex are negative, which is characteristic of a dominant Fermi contact interaction. Furthermore, the A tensor shows anisotropy, lAll < IA, 1, originating from spin-dipolar interaction. The anisotropy ob the A tensor and the positive sign of the main component of the electric-field-gradient (EFG) tensor indicate that the iron(I1) ion in the phenolate complex possesses a half-filled subshell of spin-parallel electrons plus an excessn electron of opposite spin in an oblate orbital of d, ty~,~*,' The weak temperature dependence of the quadrupole sphttmg in the range 1-300 K shows that the ground orbital state is energetically well-separated from excited orbital states by energy gaps typically 1 order

Photochemical reactions of tetramethylstannane isolated in low temperature argon matrix

Photolytic products of tetramethylstannane in low temperature argon matrix were studied by Mossbauer, IR, and UV spectroscopy. At an early stage of the reaction, an unstable tin compound possibly with a tin-carbon double bond was formed in low temperature argon matrix, which might not exist in ordinary conditions. In subsequent reaction, cyclic tin compounds with large quadrupole splittings might be produced.

A study of the thermal decomposition of iron(II) and iron(III) rubidium oxalates using the Mössbauer effect

The thermal decompositions of Rb3Fe(ox)3 4 H2O and Rb2Fe(ox)2 6 H2O have been studied using Mossbauer spectroscopy and thermal analysis methods (TGA, DSC). It is shown that after dehydration, the ferric complex is reduced into a ferrous compound, with a large quadrupole splitting (3.84 mm/s), which corresponds to thc anhydrous form of Rb2Fe(ox)2 6 H2O.

Spectroscopic and structural investigations of the ferrous and ferric high-spin state of a “picket—fence” porphyrinato acetato iron complex. A refined model for the P460 center of hydroxylamine oxidoreductase

Mossbauer investigations were performed in the ferrous and ferric form of the ‘picket-fence’ porphyrinato acetato iron complex |Fe(CH3CO2) (TPpivP)|1−,0 at temperatures varying from 1.5–200K and in fields of 0–6.2T. The ferrous complex has an unusually large quadrupole splitting, ΔEQ=+4.25mms−1. The quadrupole splitting in the ferric species, ΔEQ=+1.1mms−1, is as normally found in ferric high-spin iron porphyrins. Spin-Hamiltonian analysis of the magnetic spectra yields zero-field parameters D=−0.9mms−1, E/D=0.33 and magnetic hyperfine parameters Ax,y=−17T, Az=−13.3T in the ferrous high-spin (S=2) complex, and D=7.5cm−1, E/D≈0 and Ax,y,z=20T in the ferric high-spin (S=5/2) species.

57Fe-Mössbauer study of the high-T c system GdBa2Cu3O7−x: local binding strength and oxygen coordination of the Fe sites

The GdBa2(Cu1−yFey)3O7−x system with y=0.005–0.01 and various oxygen concentrations was investigated in the temperature range 20 K to 300 K. The57Fe-Mossbauer spectra of the orthorhombic phase were analyzed with four quadrupole doublets. Three of them are attributed to substitutional Cu(1) sites and one (with the smallest quadrupole splitting) to the substitutional Cu(2) site. From an analysis of the temperature dependence of the relative site intensities, different local Debye temperatures for the Cu(1) sites were derived. Measurements of texturized absorbers at various angles give evidence for a vibrational anisotropy of the Cu(1) sites. The Cu(1) site with the largest quadrupole splitting exhibits the lowest Debye temperature and the largest vibrational anisotropy.

Irreducible tensor operators and selective/hard single and double resonance experiments in insulators: Applications to NMRON and MQ-NMR

Recently, pulsed NMRON experiments have been carried out on trace amounts of radioactive54Mn in the antiferromagnet MnCl24H2O at 500 MHz (Le Gros et al. [1]). In this compound, the quadrupole splitting between the two lowest NMR transitions is ≈3 MHz, which precludes the use of non-selective (hard) rf pulses. Yet within the restricted 2*2 manifold, associated with a given transition, the nuclear rotation is “hard”. In this paper, the theory of “selective-hard” NMRON and MQ-NMR experiments is developed within the framework of irreducible tensor operators. In essence, the theory extends the early work of Jaynes [4] to deal with the higher-order multipolar states created during the course of a given NMR experiment. Several new pulsed NMRON and MQ-NMR experiments are proposed. For example, it is demonstrated how “ouble resonance”, “selective-hard” experiments on the pseudo spin-1 manifold spanned by |±1> and |0> Zeeman states of any integer spinI could be used to extract small chemical shifts in the face of very large quadrupole splittings.

Mössbauer study of quadrupole interaction at the different Cu sites in the Bi-system superconductor

57Fe Mössbauer measurements have been performed on Fe-doped samples of Bi 1.6Pb 0.4Sr 2Ca 3Cu 4- x Fe x O y ( x=0.06 and 0.08) at room temperature. The Mössbauer spectra show three quadrupole doublets that can be related to different Cu sites. Two doublets (B and C) with larger quadrupole splitting (QS) are assigned with a 57Fe probe atom on the Cu-O square planar sites of the compound with different local charge environments. Another doublet A with smallest quadrupole splitting is associated with a Fe atom in a planar pyramid site. the doublet with smallest QS possesses relatively the smaller area indicating that the Fe atom preferentially occupies a square planar site rather than a pyramid site. To assure our assignment, we calculated the EFG (electric field gradient) on different Cu sites with the use of the point charge model and of the calculation of an effective ions valence.

Change in magnetic state of Fe+silica gel nanocomposites due to low temperature treatment in ammonia

Homogeneous gelled composites of iron and silica containing 11–40 wt. % Fe were prepared by room temperature polymerization of aqueous solutions of ferric nitrate, tetraethoxysilane, and ethanol (with an HF catalyst). Previous electron microscopy, x-ray diffraction, and Mössbauer effect data showed these bulk materials are comprised of nanometer-sized regions of iron compounds embedded in a silica gel matrix. They were also all paramagnetic below 300 K. Here the effect on the magnetic state of these nanocomposites following a low temperature (T&amp;lt;400 °C) treatment in 1 atm of ammonia (after a prior anneal in 1 atm of hydrogen) is presented, along with the dependence on the H2 pretreatment. In all cases the room temperature Mössbauer spectra for the material in the NH3-treated and H2-pretreated conditions were similar. However, when treated in H2 at 770 °C (2 h) the Mössbauer spectra also contained a significant component having a large isomer shift (∼1.3 mm/s) and quadrupole splitting (∼3.2 mm/s). This material was also slightly ferromagnetic at all temperatures below 300 K. For materials pretreated in hydrogen below 400 °C, a threefold enhancement in the magnetic susceptibility was measured following treatment in ammonia. In addition, both the field and temperature dependence of the susceptibility indicated the presence of spin-glass behavior at 10 K for NH3-treated samples containing up to 40% Fe. At room temperature, these latter ammonia-treated nanocomposites were either superparamagnetic (Fe contents, CFe, up to 25%) or ferromagnetic (CFe≳25%).

Triphenyltin derivatives of isothiazol-3(2 H)-one 1,1-dioxides. Synthesis, Mössbauer spectra, some fungitoxicity data, and crystal structure of triphenylstannyl 1,2-benziosthiazol-3-(2 H)-one 1,1-dioxide· N,N-dimethylformamide

The syntheses and tin-119m Mössbauer spectroscopic data are reported for two series of stannylimides, 2-triphenylstannyl 1,2-benziosithiazol-3(2 H)-one 1,1-dioxide·L (L = O-donor ligand) and 2-triphenylstannyl 4,5-substituted isothiazol-3(2 H)-one 1,1-dioxides, and for the stannylester, triphenyltin 1,2-benzisothiazol-3(2 H-onyl-2-acetate 1,1-dioxide. The observed quadrupole splitting (QS) values (3.12–3.25 mm s −1) are interpreted in terms of trans-C 3SnNo trigonal bipyramidal structures for the (C 6H 5) 3Sn NC(O)C 6H 4S O 2·L [ L = (C 6H 5) 2C 2CO, (CH 3) 2NCHO, C 9H 7NO, (C 6H 5CH 2) 2SO, (C 6H 5 3PO, (C 6H 5) 3AsO] adducts. A crystal structure determination of the N,N-dimethylformamide adduct confirms the Mössbauer assignment. The ipso-carbons [Sn-C 2.120(4), 2.120(5), 2.122(5) Å] comprise the equatorial girdle of the trigonal bipyramid, the apical positions being occupied by the imido nitrogen [Sn−N 2.242(5) Å] and amido oxygen [Sn–O 2.402(5) Å] atoms. A similar five-coordinate structure is assigned to (C 6H 5) 3Sn NC(O)C(R′)C(R″)S O 2 [Qs 2.95–3.32 mm s −1; R′ = R″ = CH 3; R′ = H, R″ = C 6H 5; = −(CH 2) 4−; R′R″ = −(CH 2) 5−], but for the R′ = CH 3, R″ = C 6H 5 derivative, the lower QS value (2.54 mm s −1) is more consistent with a four-coordinated tetrahedral structure. A trans-C 3SnO 2 trigonal bipyramidal structure for the (C 6H 5) 3SnO 2CCH 2 NC(O)C 6H 4S O 2 stannylester is indicated by its large QS (3.53 mm s −1). Results on fungitoxicity tests on some of the triphenyltin compounds are presented.

Nitrite-bound five-coordinate low-spin iron(II) model complex for the prosthetic group of nitrite reductase with an unusually large quadrupole splitting. Synthesis, Moessbauer properties, and molecular structure of the complex (nitro)(.alpha.,.alpha.,.alpha.,.alpha.-tetrakis(o-pivalamidophenyl)porphinato)iron(II)

Nitrite-bound five-coordinate low-spin iron(II) model complex for the prosthetic group of nitrite reductase with an unusually large quadrupole splitting. Synthesis, Moessbauer properties, and molecular structure of the complex (nitro)(.alpha.,.alpha.,.alpha.,.alpha.-tetrakis(o-pivalamidophenyl)porphinato)iron(II)

A Study on Magnetic Properties of Fe4N Powders

Magnetization and Mössbauer spectra were measured for three kinds of Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> N powders made from acicular α-FeOOH, α-Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and carbonyl iron powders. Except for the Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> N powder from carbonyl iron, the saturation magnetization was lower than the bulk value (190 emu/g). A large amount of oxygen and small amounts of Ni, Zn and Si were detected in the sample obtained from α-FeOOH. From the Mössbauer spectra, it was concluded that decreases in the saturation magnetization were mainly due to the coexistence of a paramagnetic phase. A large quadrupole splitting of the paramagnetic peak indicates that the paramagnetic phase may be an oxide consisting of Fe(II) ions, e.g. wustite. In addition, it is thought that Ni and Zn preferentially substitute for Fe at the corner sites of fcc Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> N, and also reduce the magnetization.

119Sn conversion electron Mössbauer spectrometric (CEMS) study on transparent conductive ITO and tin oxide films

Indium-tin oxides (ITO) films were prepared on glass by Ar ion sputtering, ion plating and electron beam melting in vacuum, and tin oxide films were prepared by chemical vapour deposition (CVD) of SnCl4 in methanol containing HF. The chemical state of samples prepared was analyzed by CEMS. ITO films, produced from ITO source materials with higher solubility of tin oxide, showed lower electric resistivity. Amorphous ITO films had larger quadrupole splitting than crystalline ones. The tin oxide films were exposed in hydrogen plasma and hydrogen gas and the change of these films was also assessed by CEMS.

Magnetic interactions in119Sn substituted for Cu in antiferromagnetic and superconducting lamellar cuprates

Mossbauer Spectroscopy (MS) studies of119Sn were carried out in antiferromagnetic La2(Cu0.99Sn0.01)O4 (214) and in superconducting GdBa2(Cu0.99Sn0.01)3O7(123). Non-magnetic Sn4+ substitutes for Cu if the right procedure for diffusing119SnO2 in CuO is carried out. Studies performed in 214 show a large quadrupole splitting (QS) down to 120 K followed by an onset of a magnetic interaction reaching a saturation internal field ofHeff=8.7(5) kOe atT=30K. From the combined magnetic-quadrupole interaction the angle θ formed byqzz andHeff, the η-parameter, and the sign ofQS were deduced and information on the local spin structure is derived. Studies conducted with the 123 material (Tc=90 K) reveal a broad unsplit line at temperatures down to 60 K followed by an abrupt onset of a magnetic interaction corresponding toHeff (Sn)=8.3(1) kOe. The hyperfine fielddecreases with decreasing temperature reaching 6.0(1) kOe at 16 K. The onset of the magnetic interaction at the119Sn nucleus is explained as due to a local depletion of holes following the Sn4+ doping and a consequent quenching of the magnetic fluctuations in its vicinity.

Ferrous porphyrins with an “unusually” large quadrupole splitting

High-spin ferrous metalloporphyrins FeII(NCH3TPP)Cl, FeII(NCH3TPP)Br, FeII(NCH3TPP)ClO4, and FeII(NCH3OEP)Cl(NCH3TPP-N-methyltetraphenylporphyrin, NCH3OEP-N-methyloctaethylporphyrin) have been characterized by Mossbauer spectroscopy. Values ofIS (0.8 mm/s versus α-Fe) typical for high-spin ferrous porphyrin and very large quadrupole splittings (≊4 mm/s) have been observed. Iron(II) N-methylporphyrins should be readily detected in proteins by means of Mossbauer spectroscopy. Such parameters are similar to those of symmetrical anionic five coordinate high-spin porphyrins [FeII(TPP)X]− (X-halide).

A Linear Relationship between the Glass Transition Temperature and Local Distortion of Calcium Gallate, Barium Gallate, and Calcium Aluminate Glasses

Abstract The isomer shift in the 57Fe-Mössbauer spectra of xCaO·(90−x)Ga2O3·10Fe2O3 (x=40–60) and xBaO ·(90−x)Ga2O3·10Fe2O3(x=65–70) glasses decreases gradually from 0.28 to 0.16 mm s−1 with increasing CaO or BaO contents. This indicates a formation of nonbridging oxygen atoms in the GaO4 and FeO4 tetrahedra. Large quadrupole splitting (Δ) values ranging from 0.98 to 1.24 mm s−1 indicate a noticeable distortion of the GaO4 and FeO4 tetrahedra. Mössbauer parameters of xCaO·(95−x)Al2O3·10Fe2O3 glasses (x=55–60) are comparable to those of the xCaO·(90−x)Ga2O3·10Fe2O3 glasses, suggesting that the local structures are essentially the same with each other. The glass transition temperatures (Tg) of the calcium gallate, barium gallate, and calcium aluminate glasses are 702–728, 580–583, and 750–773 °C, respectively. It is found that the Tg of several oxide glasses is proportional to the Δ, being expressed by Tg=aΔ+b, where “a” is 680 °C mm1 s and “b” is −180°C when the Fe3+ ions are present at substitutional sites of the network former (NWF). The “Tg–Δ rule” is also applicable to the Fe3+ ions present at interstitial sites, in which case “a” and “b” are 35°C mm−1 s and 260°C, respectively. These findings indicate that the Tg is primarily determined by the distortion of NWF–oxygen polyhedra.

Mössbauer spectra at 77 K of products formed during transformation of iron(II) hydroxide containing zinc(II) ion to Zn-bearing ferrite in aqueous suspension by air oxidation

At pH 7.0, lower crystalline iron (II) hydroxide, “green rust II” (the Fe II:Fe III mol ratios and the electron diffraction measurements do not indicate the tendency for Zn 2+ ion to be incorporated in place of the Fe 2+ ion) and Zn-bearing ferrite are formed from aqueous iron (II) hydroxide suspensions containing the zinc (II) ion at a Zn: Fe tot. mol ratio of 1.00:2.00. At pH 9.0 and 10.0, higher and lower crystalline iron (II) hydroxides and Zn-bearing ferrite are formed. The ratios of higher to lower crystalline iron (II) hydroxide are approximately constant during oxidation at pH 9.0. The oxidation reactions are divided into two classes according to the Zn: Fe tot. mol ratios. At pH 7.0, lower crystalline iron (II) hydroxide is formed at the early stages of oxidation and dissolved iron (II) species are formed during the oxidation at a Zn:Fe tot. mol ratio of 0.20:2.80. Iron (II) hydroxide is formed during oxidation and dissolved iron (II) species are formed at an early stage of the oxidation at Zn:Fe tot. mol ratios of 0.60:2.40 and higher. At pH 9.0 and 10.0, both higher and lower crystalline iron (II) hydroxides are formed at Zn: Fe tot. mol ratios of 0.60:2.40 and higher, and 1.00:2.00, respectively. However, at a Zn:Fe tot. mol ratio of 0.20:2.80, iron (II) hydroxide with a large quadrupole splitting value and dissolved iron (II) species with large isomer shifts and quadrupole splitting values are formed before and during oxidation at pH 7.0, and the formation of Zn-bearing ferrite is depressed (α-FeO(OH) is formed) at pH 10.0.

Ｆｅ４Ｎ微粒子の磁気特性に関する一考察

Magnetization and Mossbauer spectra were measured for three kinds of Fe4N powders made from acicular α-FeOOH, α-Fe2O3 and carbonyl iron powders. Except for the Fe4N powder from carbonyl iron, the saturation magnetization was lower than the bulk value (190 emu/g). A large amount of oxygen and a small amount of Ni, Zn and Si were detected in the sample from α-FeOOH. According to the Mossbauer spectra, it was concluded that the decreases in the saturation magnetization were mainly due to the coexistence of a paramagnetic phase. A large quadrupole splitting of the paramagnetic peak indicates that the paramagnetic phase may be an oxide consisting of Fe(II) ion, e. g., wustite. In addition, it is considered that Ni and Zn preferentially substitute Fe at the corner of fcc-Fe4N and also reduce the magnetization.

Phase structure of the Ti1Cu1− x Fe x system

The phase structures of Ti1Cu1−X Fe X withX=0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 were investigated by means of Mossbauer spectroscopy, X-ray diffraction, and microprobe. The Mossbauer spectral and X-ray diffraction data imply that the γ-TiCu and CsCl structure phases coexisted in theX=0.1 andX=0.2 alloys. The Mossbauer spectrum ofX=0.1 is a sum of two components, one quadrupole doublet with larger quadrupole splitting and one with smaller quadrupole splitting. Mossbauer spectra for alloys other thanX=0.1 are simple doublet. By comparison, Ti1Cu0.5Fe0.5 has smaller linewidth and higher isomer shift than Ti1Co0.5Fe0.5. This might be attributed to stronger interaction between Cu and Fe than that between Co and Fe. The solid solubility of Fe in the γ-TiCu lattice is very limited to about 1 at. pct. On the contrary, CsCl structure phase is homogeneous in the range of Ti1Cu1−X Fe X ,X=0.25 to maybeX=1. The lattice parameter of CsCl structurevs concentration of Cu is related linearly.

In-beam Mössbauer study of atomic jump processes

Interstitial jump processes are studied using “in-beam Mossbauer technique” combining Coulomb excitation and recoil implantation. After implantation of Coulomb-excited57Fe into metals (α-Zr, Al, Nb and Au) at low temperature, a relatively large part of the implanted atoms ends up on interstitial positions yielding large quadrupole splittings. Inα-Zr, the interstitial line shows a clear quadrupole relaxation accompanied by a sharp decrease of the resonance intensity between 40 K and 100 K. This effect is interpreted as localized fast jumps of57Fe atoms in the octahedral cage of the hep Zr lattice. A preliminary result from a time-differential measurement onZr57Fe is presented.

Tin Mössbauer spectroscopy of tin-rich iridium-tin alloys

Ir5Sn7, Ir3Sn7 and newly obtained IrSn4 /4/ exhibit complex Mossbauer spectra. The positions of the individual lines range from 0.82 to 3.0 mm/s and the average isomer shift\(\overline {IS} \) derived for each compound of Sn atomic percentage x follows the relationship:\(\overline {IS} = 0.60 + 0.0194 x\). Rather large quadrupole splittings are obtained. The f factors are about 0.20 at 295 K and 0.37 at 78 K, from which Debye temperatures of 200 to 300 K have been calculated.