Quadrupole Doublet Research Articles

A Planar Carboxylate-Rich Tetrairon(II) Complex and Its Conversion to Linear Triiron(II) and Paddlewheel Diiron(II) Complexes

We report a series of oligonuclear carboxylate-rich high-spin ironII complexes with three different [FeIIn(mu-O2Cbiph)2n(L)m] (n = 2-4; m = 2 or 4) structural motifs, where -O2Cbiph is 2-biphenylcarboxylate and L is an exogenous ligand bound to terminal iron atoms. Solid compounds were isolated and their structural, spectroscopic, and magnetic properties thoroughly investigated. The discrete tetranuclear complexes [Fe4(mu-O2Cbiph)8(L)2] crystallize in a planar tetraironII motif in which two diiron paddlewheel units are linked in an unprecedented manner involving a mu3-1,1,3-bridging mode. X-ray crystallography reveals average Fe-Oanti bond lengths of 2.081[2] A at the dimer-dimer interface. Terminal axial positions are capped by ligands L, where L is tetrahydrofuran (THF) (1), indazole (2), pyrazole (3), 3,5-dimethylpyrazole (4), or acetamide (5). Reaction of 1 with an excess of acetonitrile affords the linear compound [Fe3(mu-O2Cbiph)6(MeCN)4] (6). The acetonitrile ligands in 6 can be replaced by THF or dimethoxyethane at elevated temperatures with retention of the structure to afford 7 and 8, respectively. Reaction of 1 or 6 with pyridine or 1-methylimidazole results in the isolation of paddlewheel dimers 9 and 10, respectively, with [Fe2(mu-O2Cbiph)4(L)2] composition. Mössbauer spectroscopy confirms the presence of high-spin ferrous ions and indicates that the two iron sites of the dimer are geometrically indistinguishable. For the tri- and tetrairon compounds, two quadrupole doublets are observed, suggesting that the iron centers do not have identical geometries. Plots of magnetic susceptibility versus temperature reveal intramolecular antiferromagnetic exchange coupling for all complexes under study. The magnetic data were fit to a theoretical model incorporating exchange coupling, single-ion zero-field splitting, and g-tensor anisotropy. The resulting magnetic parameters reveal in most cases weak antiferromagnetic exchange coupling (J typically <3 cm(-1)) and dominant zero-field-splitting parameters.

Mossbauer Spectroscopy of Kerogen Isolated from Miocene Petroleum Source Rocks of Three Fields in the Area of Suez Gulf, Egypt

The method of using room temperature Mossbauer spectroscopy were applied to identify the iron species in kerogen is illustrated for a series of 22 subsurface core samples from three oil fields: July, GS315 and Esh El-Melaha in the Gulf of Suez region, Egypt. The Mossbauer spectra of kerogen showed only two central quadrupole doublets that would be attributed to the presence of iron in pyrite/Fe2+ (low spin) and in carbonates possible ankerite/Fe2+ (high spin). Possible explanation for the presence of ankerite is discussed and it is suggested that a high level of maturation is the most likely reason. This suggestion is corroborated by data of the total organic carbon and the vitrinite reflectance which is available for all the samples studied.

Optical and transport properties of lanthanum-doped stannate BaSnO3

BaSnO3 crystallizes in a cubic perovskite structure and exhibits insulating behaviour. It can be made conducting by reducing a small fraction of Sn4+ into Sn2+ under an O2-free atmosphere. This can be achieved through the solid solution Ba1−xLaxSnO3−δ which is a mixed phase for x > 0.02, behaviour readily understood in terms of the lone pair cation Sn2+. The magnetic susceptibility was measured down to 4.2 K and is less than 1.7 × 10−5 emu cgs mol−1 consistent with collective electron behaviour. The Mössbauer spectrum exhibits a wide unsplit peak with a quadrupole doublet of 3.18 mm s−1 and an isomer shift of 0.12 mm s−1 characteristic of Sn4+and corroborating the delocalization of the stereo chemical pair 5s2. The band gap Eg was found to be 3.12 eV; further indirectly allowed inter-band transition occurs at 2.85 eV. The transport properties of Ba0.98La0.02SnO3−δ indicate n-type conductivity (σ300 K = 4.03 Ω−1 cm−1), little temperature dependence, with an activation energy ΔE of ∼1 meV and an electron mobility μ300 K ∼ 0.1 cm2 V−1 s−1, thermally activated. The conduction occurs by small polaron hopping between mixed valence Sn4+/2+ ions. The observed conductivity is greater than that coming from La-substitution with one-electron doping implying the existence of oxygen vacancies. The electrons are believed to travel in the Sn-5s conduction band with an effective mass of 3.7 mo. The non-linear dependence of Ln σ versus T−1 at low temperatures could result from a predominant variable range hopping as suggested by the linear variation of log σ versus T−0.25. The electron localization may be attributed to the random distribution of lanthanum as well as oxygen vacancies.

Mössbauer study of 57Fe in CVD diamond following 57Mn implantation

57Fe Mossbauer spectroscopy, following the implantation of radioactive parent 57Mn+ ions, has been performed on two chemical vapour deposited diamond samples, one synthesized in 2003 (CVD03) and the other in 2005 (CVD05). The spectra of sample CVD05 were as observed previously in natural IIa diamonds: single lines corresponding to substitutional and interstitial Fe were superimposed on a broad quadrupole split doublet. The site fraction of Fei reached 30% at 90 K. The spectra of the CVD03 sample showed, in addition to the above features, a strong contribution (>30%) from a quadrupole doublet attributable to the presence of intrinsic amorphous inclusions in the crystallites. This observation has been confirmed by X-ray diffraction.

Electron paramagnetic resonance and Mössbauer spectroscopy of intact mitochondria from respiring Saccharomyces cerevisiae

Mitochondria from respiring cells were isolated under anaerobic conditions. Microscopic images were largely devoid of contaminants, and samples consumed O(2) in an NADH-dependent manner. Protein and metal concentrations of packed mitochondria were determined, as was the percentage of external void volume. Samples were similarly packed into electron paramagnetic resonance tubes, either in the as-isolated state or after exposure to various reagents. Analyses revealed two signals originating from species that could be removed by chelation, including rhombic Fe(3+) (g = 4.3) and aqueous Mn(2+) ions (g = 2.00 with Mn-based hyperfine). Three S = 5/2 signals from Fe(3+) hemes were observed, probably arising from cytochrome c peroxidase and the a(3):Cu(b) site of cytochrome c oxidase. Three Fe/S-based signals were observed, with averaged g values of 1.94, 1.90 and 2.01. These probably arise, respectively, from the [Fe(2)S(2)](+) cluster of succinate dehydrogenase, the [Fe(2)S(2)](+) cluster of the Rieske protein of cytochrome bc (1), and the [Fe(3)S(4)](+) cluster of aconitase, homoaconitase or succinate dehydrogenase. Also observed was a low-intensity isotropic g = 2.00 signal arising from organic-based radicals, and a broad signal with g (ave) = 2.02. Mössbauer spectra of intact mitochondria were dominated by signals from Fe(4)S(4) clusters (60-85% of Fe). The major feature in as-isolated samples, and in samples treated with ethylenebis(oxyethylenenitrilo)tetraacetic acid, dithionite or O(2), was a quadrupole doublet with DeltaE (Q) = 1.15 mm/s and delta = 0.45 mm/s, assigned to [Fe(4)S(4)](2+) clusters. Substantial high-spin non-heme Fe(2+) (up to 20%) and Fe(3+) (up to 15%) species were observed. The distribution of Fe was qualitatively similar to that suggested by the mitochondrial proteome.

Chiral Discrimination in the 13C and 2H NMR of the Crown and Saddle Isomers of Nonamethoxy-Cyclotriveratrylene in Chiral Liquid-Crystalline Solutions

We report 2H and 13C NMR spectra of the crown and saddle isomers of nonamethoxy-tribenzocyclononene (1), dissolved in lyotropic achiral and chiral liquid-crystalline solutions based on poly-gamma-benzyl-glutamate and poly-gamma-benzyl-L-glutamate (PBG and PBLG). The 2H-[1H] measurements include spectra of compound 1 deuterated in the ring methylene and in the aromatic sites as well as of the methyl groups in natural abundance. Carbon-13 spectra were recorded in natural abundance as well as in two isotopomers enriched in the ring methylene and one of the methoxy groups. The crown isomer (c-1) is rigid with C3 symmetry and can be separated into its enantiomers using a chiral high-performance liquid chromatography column. The NMR spectra of racemic c-1 in PBLG solutions exhibit two sets of lines due to the enantiomers. The peaks were identified by comparing the spectra with those of the neat enantiomers. Analysis of the 2H quadrupolar splittings and the 13C residual chemical shift anisotropies shows that the dominant factor determining the chiral discrimination is the difference in the ordering of the two enantiomers in the chiral liquid crystals. The saddle isomer (s-1) is highly flexible, undergoing fast pseudorotation between six conformers. The "frozen" conformers have C1 symmetry and are therefore chiral. Three of these comprise one enantiomer, and the other three the second one. However, the rapidly interconverting species has, on the average, a C3h symmetry and is therefore achiral. The methylene groups in the latter are, however, prostereogenic, and their hydrogen/deuterium-carbon bonds constitute enantiotopic pairs. The 2H NMR spectra of the s-1 methylene-deuterated in PBLG solutions exhibit, in fact, enantio-discrimination with two quadrupolar doublets. This is in contrast to rigid prochiral molecules with a threefold symmetry axis, which normally do not show such discrimination. A detailed analysis of the effect is presented, and it is argued that the discrimination observed for s-1 reflects the different ordering of its enantiomers during the pseudorotation cycle.

X-ray diffraction and Mössbauer spectrometry studies of molecular iron compounds

We have synthesized two new iron complexes that have been structural and magnetically characterized: diphenylguanidinium hexafluoroferrate and hexakisvaline-oxo-triiron(III) chloride. The former crystallizes as monomers with the fluoride ions six-coordinating the Fe(II) ion. Valine iron chloride is comprised of trinuclear complexes, with a well ordered oxo-centered carboxylate core and some disordered organic ligands. The magnetization curves show a paramagnetic behavior. The Mössbauer measurements as a function of temperature show a paramagnetic behavior at 300 K with two Fe sites (one quadrupolar doublet and a broad single line). At 4.2 K, besides the quadrupolar doublet there is a magnetic component which can be attributed to a slow relaxation phenomenon associated to these samples.

Further Insights into the Spectroscopic Properties, Electronic Structure, and Kinetics of Formation of the Heme−Peroxo−Copper Complex [(F8TPP)FeIII−(O22-)−CuII(TMPA)]+

In the further development and understanding of heme-copper O2-reduction chemistry inspired by the active-site chemistry in cytochrome c oxidase, we describe a dioxygen adduct, [(F8TPP)FeIII-(O22-)-CuII(TMPA)](ClO4) (3), formed by addition of O2 to a 1:1 mixture of the porphyrinate-iron(II) complex (F8TPP)FeII (1a) {F8TPP = tetrakis(2,6-difluorophenyl)porphyrinate dianion} and the copper(I) complex [(TMPA)CuI(MeCN)](ClO4) (1b) {TMPA = tris(2-pyridylmethyl)amine}. Complex 3 forms in preference to heme-only or copper-only binuclear products, is remarkably stable {t1/2 (RT; MeCN) approximately 20 min; lambda max = 412 (Soret), 558 nm; EPR silent}, and is formulated as a peroxo complex on the basis of manometry {1a/1b/O2 = 1:1:1}, MALDI-TOF mass spectrometry {16O2, m/z 1239 [(3 + MeCN)+]; 18O2, m/z 1243}, and resonance Raman spectroscopy {nu(O-O) = 808 cm-1; Delta16O2/18O2 = 46 cm-1; Delta16O2/16/18O2 = 23 cm-1}. Consistent with a mu-eta2:eta1 bridging peroxide ligand, two metal-O stretching frequencies are observed {nu(Fe-O) = 533 cm-1, nu(Fe-O-Cu) = 511 cm-1}, and supporting normal coordinate analysis is presented. 2H and 19F NMR spectroscopies reveal that 3 is high-spin {also muB = 5.1 +/- 0.2, Evans method} with downfield-shifted pyrrole and upfield-shifted TMPA resonances, similar to the pattern observed for the structurally characterized mu-oxo complex [(F8TPP)FeIII-O-CuII(TMPA)]+ (4) (known S = 2 system, antiferromagnetically coupled high-spin FeIII and CuII). Mössbauer spectroscopy exhibits a sharp quadrupole doublet (zero field; delta = 0.57 mm/s, |DeltaEQ| = 1.14 mm/s) for 3, with isomer shift and magnetic field dependence data indicative of a peroxide ligand and S = 2 formulation. Both UV-visible-monitored stopped-flow kinetics and Mössbauer spectroscopic studies reveal the formation of heme-only superoxide complex (S)(F8TPP)FeIII-(O2-) (2a) (S = solvent molecule) prior to 3. Thermal decomposition of mu-peroxo complex 3 yields mu-oxo complex 4 with concomitant release of approximately 0.5 mol O2 per mol 3. Characterization of the reaction 1a/1b + O2 --> 2 --> 3 --> 4, presented here, advances our understanding and provides new insights to heme/Cu dioxygen-binding and reduction.

A compact cost-effective beamline for a PET Cyclotron

Most commercial PET Cyclotrons have targets mounted on or near the main cyclotron vacuum chamber. There is often little or no system capability for centering or focusing the extracted beam on target to achieve maximum production. This paper describes the ion-optics, design and development of a compact cost-effective beamline comprised of low activation and radiation resistant materials. The beamline, complete with suitable diagnostic devices, permits the extracted proton beam to be centered (X–Y steering magnet), and focused (quadrupole doublet) on target eliminating unnecessary beamspill and ensuring high production.

Crystal Chemistry of Iron in Non-Metamict Chevkinite-(Ce): Valence State and Site Occupation Proportions

The ideal formula for chevkinite can be expressed as A 4BC 2D 2Si 4O 22. It is important to determine the valence state and site occupation proportions for Fe among the B, C, and D octahedral sites as it may help to identify different species in the chevkinite group. Non-metamict chevkinite-(Ce) from Mianxi alkali feldspar-granite, Sichuan Province, China, was investigated using Mössbauer spectroscopy. The Fe 3+/ΣFe ratio was 39.2%. A significant increase of Fe 3+ occured during metamictization and annealing for chevkinite-group minerals. In metamict samples Fe tended to lower coordination. According to the correlation between bond length and isomer shift ( IS), the quadrupole doublets with IS = 1.10 and 0.94 mm·s −1 can be assigned to Fe 2+ in the B and C octahedral sites, respectively. Based on the correlation between octahedral distortion and quadrupole splitting ( QS), the quadrupole doublets with QS = 0.86 and 0.77 mm·s −1 can be assigned to Fe 3+ in the C and D sites, respectively. The simplified formula can be revised as: Ce 4Fe 2+ (Ti, Fe 2+, Fe 3+) 2(Ti, Fe 3+) 2Si 4(O, OH) 22. It indicated that the non-metamict chevkinite-(Ce) belonged to Fe 2+ end member of the chevkinite group because Fe 2+ was the predominant component in the B site.

Magnetic characterization of maghemite nanoparticles dispersed in surface-treated polymeric template

Magnetic characterization of maghemite nanoparticles dispersed in a polymeric template and treated under different chemical processes is reported in this work. Particle size estimated from magnetic measurements, DM ≈ 10 nm, for the free-surfactant sample, is consistent with values determined from XRD analysis and TEM images. The magnetic collapse of sextets towards a quadrupole doublet as the temperature is increased reveals the thermal relaxation of smaller ψ-Fe203 nanoparticles. Magnetic measurements show a strong irreversibility between ZFC and FC curves suggesting the occurrence of particle-particle interaction.

Superparamagnetic relaxation evidences large surface contribution for the magnetic anisotropy of MnFe204 nanoparticles of ferrofluids

Manganese ferrite nanoparticles, in the size range 3.3–9.0 nm, are prepared by a hydrothermal coprecipitation process and peptized in aqueous solution. The magnetization curves recorded at room temperature on diluted colloidal sols allow characterizing the distribution of magnetic moment by using a simple Langevin formalism. Mossbauer spectroscopy measurements performed on powder samples at 77 K exhibit a quadrupolar doublet which intensity grows at the expense of the hyperfine sextet pattern as the nanoparticles mean size decreases. The magnetic dynamics behavior is then investigated by measurements of magnetic hysteretic properties at 5 K and temperature dependence of the zero field cooling (ZFC) susceptibility. The values found for the effective anisotropy constant and the dependence of the irreversibility field, inversely proportional to the reference size, clearly indicate that the magnetic anisotropy of our nanoparticles finds its origin on the disordered surface layer.

Multivariate analysis in provenance studies: Cerrillos obsidians case, Peru

We present the preliminary results of a provenance study of obsidians samples from Cerrillos (ca. 800–100 b.c.) using Mossbauer Spectroscopy. The Cerrillos archaeological site, located in the Upper Ica Valley, Peru, is the only Paracas ceremonial center excavated so far. The archaeological data collected suggest the existence of a complex social and economic organization on the south coast of Peru. Provenance research of obsidian provides valuable information about the selection of lithic resources by our ancestors and eventually about the existence of communication routes and exchange networks. We characterized 18 obsidian artifacts samples by Mossbauer spectroscopy from Cerrillos. The spectra, recorded at room temperature using different velocities, are mainly composed of broad asymmetric doublets due to the superposition of at least two quadrupole doublets corresponding to Fe2+ in two different sites (species A and B), one weak Fe3+ doublet (specie C) and magnetic components associated to the presence of small particles of magnetite. Multivariate statistical analysis of the Mossbauer data (hyperfine parameters) allows to defined two main groups of obsidians, reflecting different geographical origins.

Mössbauer study of incompletely alloyed nanocrystalline Fe100 − x Al x prepared by high energy ball milling

Mechanically alloyed Fe100 − x Al x powders, with 20≤ x ≤90, have been studied by X-ray diffraction and room temperature 57Fe Mossbauer spectroscopy. The milling time was chosen such that complete alloying does not take place. For a fixed milling time of 10 h, the rate of alloying was seen to increase exponentially with increase in Fe content. Mossbauer spectra of all the samples consist of a broad magnetic sextet and a quadrupole doublet. The isomer shifts and quadrupole splitting of the doublets are typical of Al-rich, Fe–Al alloys. The area under the quadrupole doublet is a maximum for x = 66. Analysis of the Mossbauer spectra indicates the formation off- stoichiometric Fe3Al phase for x < 66, while the formation of Fe clusters is largely responsible for the magnetic hyperfine component in x ≥ 66 compositions.

57Fe Mössbauer spectroscopy predicts superstructure for K0.08[CuII(N,N′app)Cl]2[FeIII(CN)6]·0.92H3O·3H2O

The compound [Cu(N,N'app)Cl](2)[Fe(CN)(6)].xH(2)O, with N,N'app being bis(N,N'-3-aminopropylpiperazine), was prepared and its structure determined by single crystal X-ray analysis, confirming a ratio of two copper complexes to one iron complex; (57)Fe Mössbauer spectra showed three quadrupole doublets typical of iron(iii) low spin species which call for the presence of a superstructure.

Particle optics of quadrupole doublet magnets in Spallation Neutron Source accumulator ring

The Spallation Neutron Source ring employs doublet quadrupoles and dipole correctors in its straight sections. The electromagnetic quadrupoles have a large aperture, small aspect ratio, and relatively short iron-to-iron distance. The corrector is even closer to one of the quads. There have been concerns on the magnetic fringe field and interference in the doublet magnets and their assemblies. We have performed 3D computing simulations to study magnetic field distributions in the doublet magnets. Further, we have analyzed the particle optics based on the $z$-dependent focusing functions of the quads. The effect of the magnetic fringe field and interference, including the third-order aberrations, on the particle motion are investigated. The lens parameters and the first-order hard edge models are derived and compared with the parameters used in the ring lattice calculations.

Interpretation of the nontronite-dehydroxylate Mossbauer spectrum using EFG calculations

Dehydroxylated Garfield nontronite has been studied using Mossbauer spectroscopy. According to literature, in dehydroxylated Fe 3+ -rich dioctahedral 2:1 phyllosilicates (celadonites, glauconites and nontronites), the octahedral cations migrate from cis -into trans -sites with the formation of five-fold coordination of the former cis- and trans- octahedra. Therefore, the two main fitted doublets with quadrupole splittings, Δ, of 0.906 and 1.392 mm/s are supposed to be related to Fe 3+ in the former cis- and trans -octahedra. To assign these doublets to this or that positions, analysis of Pauling’s bond strength (PBS), structural modeling and EFG calculations were performed. The calculated quadrupole splittings for Fe 3+ located in the former cis- and trans- octahedra in the nontronite-dehydroxylate structure are equal to 1.295 and 1.026 mm/s, respectively. On the basis of the calculation results, the quadrupole doublet with smaller Δ should be assigned to the former trans -octahedra whereas the doublet with larger Δ should be assigned to the former cis -octahedra. The calculated EFG parameters proved to be independent of the mode in the layer stacking, which confirms the major role of the Fe 3+ nearest environment in the formation of the different EFGs at Fe nuclei. Possible disruptions of two-dimensional continuity of dehydroxylated octahedral sheets that may be a reason for superparamagnetic effects in nontronite-dehydroxylates at low temperatures are discussed in terms of the structural model of dehydroxylated Fe-rich dioctahedral 2:1 phyllosilicates.

Transformation of low crystalline ferrihydrite to α-Fe 2O 3 in the solid state

Low crystalline ferrihydrite (2-XRD lines) was synthesized and thermally treated between 195 and 325 °C in air. The obtained products were characterized by XRD, FT-IR and 57Fe Mössbauer spectroscopies. XRD and FT-IR did not show the formation of α-Fe 2O 3 at 220 °C. The IR band at 330 cm −1 for the sample obtained after heating at 245 °C indicated that at this temperature some α-Fe 2O 3 has crystallized. XRD also showed the presence of α-Fe 2O 3 in the sample obtained at 245 °C. XRD and FT-IR spectra of the sample obtained after heating at 325 °C fully correspond to that of α-Fe 2O 3. The Mössbauer spectrum recorded at RT of the sample prepared at 220 °C showed a broadened quadrupole doublet, whereas hyperfine-field distributions are observed at 78 and 12 K, presumably due to non-uniform chemical environments for the Fe 3+ and/or to the shape and size distributions of the α-Fe 2O 3 clusters. The RT Mössbauer spectrum of the sample heated at 245 °C showed a superposition of a quadrupole doublet and a distributed sextet, the latter believed to be due to poorly crystalline α-Fe 2O 3. At 78 K, two sextets were resolved. The sharper one, with a hyperfine field H hf = 527 kOe and quadrupole shift 2 ε Q = −0.12 mm s −1, and fractional area of RA = 0.22, is due to α-Fe 2O 3, which possibly shows the coexistence of antiferromagnetic and weakly ferromagnetic spin states. The much broader magnetic component is assigned to ferrihydrite. At 12 K, hematite has H hf = 535 kOe and 2 ε Q = −0.03 mm s −1. The ferrihydrite sextet is still considerably broadened. Mössbauer spectra at RT and 78 K recorded for the sample obtained upon heating at 325 °C correspond only to α-Fe 2O 3 fraction. For the sample obtained by heating at 245 °C, a Mössbauer spectrum was recorded at 4.2 K in an applied field of 6 T. The ferrihydrite component clearly splits into a high- and low-field contribution. The heating of 2-line ferrihydrite caused a certain crystalline ordering and in the next stage the transformation to α-Fe 2O 3.

Mössbauer Spectroscopy Study of Macromolecular Complexes of Polycarbosilazane Coordinated with Fe(II), Fe(III) and Mixed Valence Fe(II-III) Chlorides

A series of iron-polyethylenediaminecarbosilazane (PEDCSZ-Fe) macromolecular chloride macromolecular complexes were prepared by the reaction of Fe(II), Fe(III), and mixed valence Fe(II-III) chlorides with polyethylenediaminecarbosilazane matrix in toluene under inert atmosphere. The mixed valence macromolecular complexes composed of three different ratios of Fe(II)/Fe(III) (1:2, 1:1, and 2:1). Mössbauer spectra were recorded for the samples at room temperature. The spectra of the PEDCSZ-Fe(II) and PEDCSZ-Fe(III) macromolecular complexes showed pure paramagnetic phase, whereas, the spectra for the mixed valence PEDCSZ-Fe(II-III) showed both magnetic and paramagnetic splitting. The magnetic splitting is so broad such that it was fitted with three magnetic sextets and one quadrupole doublet. The relative intensity of the magnetic phase was the highest for the PEDCSZ-Fe(II-III) with 1:1 ratio. The magnetic phase could be attributed to an iron oxide phase (Fe3O4 or FeOOH phase) in a fine powder form as it is clear from the Mössbauer parameters. The XRD patterns of the PEDCSZ-Fe(II-III) with 1:1 ratio contained additional diffraction peaks similar to those observed for Fe3O4 in a fine particle form.

Isolation of a singly oxo-bridged Fe(III) dinuclear complex: Synthesis, crystal structure, spectroscopic and magnetic studies

The μ-oxo dinuclear complex {Fe 2O(tptz) 2[N(CN) 2] 2(NO 3) 2} ( 1) (where tptz = 2,4,6-tris(2-pyridyl)-1,3,5-triazine) has been synthesised and characterised by elemental analysis, FT-IR, UV–vis, cyclic voltammetry, Mössbauer spectroscopy, and variable-temperature magnetic susceptibility measurements and single crystal X-ray diffraction. The iron centres have a pentagonal-bipyramidal geometry. The dimeric neutral complex exhibits typical Fe-μ-O bond lengths of 1.763(1) Å and a bridge angle of 180.00°. The Fe⋯Fe separation is 3.526(3) Å. The Mössbauer spectrum at room temperature consists of one quadrupole doublet with an isomer shift of 0.41 mm/s and a quadrupole splitting of 1.12 mm/s. Variable-temperature magnetic susceptibility measurements have been measured in the temperature range 300–2 K, revealing an intramolecular antiferromagnetic coupling ( J = −211.6 cm −1).