Whereas one-dimensional, 10-membered ring zeolites are typically used forhydroisomerization, Fe3+-containing SSZ-70 (Fe-SSZ-70) shows remarkable isomerizationselectivity for a zeolite containing 12- and partially blocked 14-membered rings, in addition to10-membered rings. Fe-SSZ-70 was compared to Al3+-containing SSZ-70 (Al-SSZ-70) inconstraint index andn-decane hydrocracking tests. Fe-SSZ-70 exhibited a 74% total isomeryield (64% yield of monobranched isomers and 10% cracking yield) at 85% conversioncompared to 49% total isomer yield (41% yield of monobranched isomers and 36% crackingyield) for Al-SSZ-70 at the same conversion. The selectivity to isomerization is attributed tothe weaker acid strength of Fe-SSZ-70 over Al-SSZ-70. Fe-SSZ-70 was directly synthesizedwith Fe3+isomorphously substituted in tetrahedral positions. The coordination environmentof the Fe3+was characterized using Mo??ssbauer, electron paramagnetic resonance, and diffusereflectance UV-vis spectroscopies. The physicochemical properties were further probed withinductively coupled plasma atomic emissionspectroscopy, temperature-programmeddesorption of isopropylamine, and nitrogen adsorption-desorption. The Fe3+was tetrahedrally coordinated in the as-madematerials and became partially octahedrally coordinated upon calcination; enough Fe3+remained in the framework after calcinationfor Fe-SSZ-70 to remain catalytically active.

In their earlier paper, Niraula et al. (ACS Appl. Nano Mater. 2021, 4, 3148-3158) described the morphological, compositional, and magnetic properties of three different magnetite/maghemite or Fe3O4/gamma-Fe2O3, hollow nanoparticles, referred to herein as nanorings, short-nanotubes, and long-nanotubes. Scanning electron microscopy indicates that these nanoparticles have lengths of 275 +/- 51, 411 +/- 92, and 515 +/- 98 nm and outer diameters of 201 +/- 55, 251 +/- 46, and 229 +/- 42 nm, respectively, dimensions that are all rather similar in view of their distributions, as is shown in a figure herein. Further, the lengths indicate that these nanoparticles are far larger than what are normally considered nanoparticles. Rietveld refinement of the powder X-ray diffraction patterns presumably reveals the presence of Fe3O4, gamma-Fe2O3, and small amounts of alpha-Fe2O3 in some of the nanoparticles; unfortunately, the lack of refinement details make the validity of these compositions at least problematic. The published iron-57 Mo''ssbauer spectral analysis is marginal. An alternative analysis of both the reported X-ray lattice parameters and the Mo''ssbauer spectral results for the three nanoparticles in terms of solid solutions of magnetite and maghemite, Fe-A(3+)[(Fe1-3 delta 2+Fe1+2)-Fe-B delta(3+)square(delta)]O-4, where represents square vacancy, delta = 0 corresponds to magnetite, Fe3O4, and delta = 0.333 corresponds to maghemite, gamma-Fe2O3, is proposed herein. In the presence of the expected magnetite Verwey transition, the Mossbauer spectral analysis is formulated with the stoichiometry Fe-A(3+)[Fe-B(2(1-3 delta))2.5+Fe-5 delta(3+)square(delta)]O-4, and as far as we can tell, this model is consistent with the Rietveld X-ray diffraction analysis. The values of delta = 0.28(2) and 0.30(1) obtained from the X-ray diffraction and Mo''ssbauer spectral analyses, respectively, indicate that the composition of the nanoparticles is very close to gamma-Fe2O3, in contrast to the earlier conclusion. During the course of this reformulation, numerous errors in the mathematical expressions, and in some cases their subsequent misuse, have been discovered and corrected herein whenever possible.

Over the past 50 years or so, the authors have written and reviewed many papers dealing with Mossbauer spectral research and have noticed many pitfalls, omissions, and marginal to poor practices in the literature. This paper first describes the best recommended practices and protocols for measuring, analyzing, and presenting MOssbauer spectra for publication. To illustrate these recommendations, the paper next presents a discussion of the techniques that ensure the best possible Mossbauer-effect spectrometer calibration, the best methods for minimizing the spectral line widths and thus obtaining the best possible spectral resolution, and the best spectral velocity ranges to use. A variety of iron containing compounds chosen from the fields of inorganic, organic, and material chemistry are used to illustrate the best practices and protocols that should be used. These materials include an organoiron carbonyl complex, iron phosphate compounds, two single molecule magnet compounds, and iron spin-state crossover complexes.

Based on the combined corrected chemical analysis, the single-crystal X-ray structural results, and the revised Mossbauer spectral analysis, the best formulation of Li1.4(1)[Fe4.4(1)IIFe0.6(1)III(H...

Herein, evidence for the long-sought finite hyperfine interaction in the high-pressure hexagonal close-packed epsilon-iron is gained through synchrotron radiation perturbed angular correlation spectroscopy. This method yields an energy splitting of 3.5(5) neV between the m(Ie) = +/- 1/2 and m(Ie) = +/- 3/2 nuclear sublevels of the iron-57 14.412-keV nuclear excited state at 30(1) GPa and room temperature. This energy splitting is related to a nuclear quadrupole hyperfine interaction with an electric field gradient of eq = 1.2(2) x 10(16) V/cm(2). However, there is still a possibility that the splitting of the iron-57 nuclear levels is related to a modest magnetic hyperfine interaction of ca. 0.40(5) T.

Iron is one of the most abundantelements in the environment and in the human body. As an essential nutrient,iron homeostasis is tightly regulated, and iron dysregulation is implicated innumerous pathologies, including neuro-degenerative diseases, atherosclerosis,and diabetes. Endogenous iron pool concentrations are directly linked to ironion uptake from environmental sources such as drinking water, providingmotivation for developing new technologies for assessing iron(II) and iron(III)levels in water. However, conventional methods for measuring aqueous iron poolsremain laborious and costly and often require sophisticated equipment and/oradditional processing steps to remove the iron ions from the originalenvironmental source. We now report a simplified and accurate chemical platformfor capturing and quantifying the iron present in aqueous samples through useof a post-synthetically modified porous aromatic framework (PAF). Theether/thioether-functionalized network polymer, PAF-1-ET, exhibits highselectivity for the uptake of iron(II) and iron(III) over other physiologicallyand environmentally relevant metal ions. Mössbauer spectroscopy, XANES, andEXAFS measurements provide evidence to support iron(III) coordination tooxygen-based ligands within the material. The polymer is further successfullyemployed to adsorb and remove iron ions from groundwater, including fieldsources in West Bengal, India. Combined with an 8-hydroxyquinoline colorimetricindicator, PAF-1-ET enables the simple and direct determination of the iron(II)and iron(III) ion concentrations in these samples, providing a starting pointfor the design and use of molecularly-functionalized porous materials forpotential dual detection and remediation applications.

The synthesis, characterization, structure and magnetic properties of a hexametallic mixed-metal iron(III)-cobalt(III) compound are described. The compound has been characterized by standard spectroscopic and analytical methods to determine its composition. Single-crystal X-ray diffraction has shown that the asymmetric unit consists of discrete dinuclear dicationic units of {(mu-oxido-mu-[sulfato-O1,O2])bis[tris(2-pyridyl-methyl)amineiron(III)]}(2+), herein designated as Fe12, and two half-dinuclear dianionic units of {(mu-oxido)bis[(mu-cyanido-kappa N-pentacyanidocobaltato(III))(tris(2-pyridyl-methyl)-amine)iron(III)]}(2-) units, herein designated as Fe33a and Fe44b, generating the overall composition Co2Fe4O2(C-N)(12)(tpa)(4), 1, where tpa is tris(2-pyridyl-methyl)amine. X-ray structural results and thermogravimetric and differential scanning calorimetry measurements also indicate that the compound, depending upon its history, may contain up to nine interstitial waters of hydration, herein designated as 1(H2O)(9). In the dinuclear dicationic unit, the bridging Fe-O-Fe bond in Fe12 is bent and there is also an FeOSOFe sulfato-based bridge with an angle of 132.8 degrees. In contrast, in the two dinuclear dianionic units, Fe33a and Fe44b, the Fe-O-Fe bond angle is crystallographically constrained to be 180 degrees. The Co-C-N-Fe bonds are almost co-linear, with Co-C-N angles of 176 degrees and C-N-Fe angles of 169 degrees. In each species the tpa ligand is tripodal tetradentate with the tertiary amine trans to the sulfato ligand or to the cyanide ligand in the dianions or the bridged oxido ligand in the dications. Bond lengths and angles are all in the typical range for Fe(III) and Co(III) compounds. The magnetic behavior of 1(H2O)(9), obtained upon cooling from 300 to 2 K, reveals a strong antiferromagnetic interaction between the Fe(III) ions in each dinuclear unit. Attempts to discriminate between the two Fe(III) dinuclear units in 1(H2O)(9) have in all cases led to two very different Heisenberg isotropic exchange coupling constants, namely J = -220(2) and -716(32) cm(-1) for 1(H2O)(9); i.e. one of the dinuclear units, probably the Fe12 unit, is so strongly antiferromagnetically coupled that it is close to diamagnetic between 2 and ca. 250 K and has a Heisenberg S = 0 ground state. (C) 2018 Elsevier Ltd. All rights reserved.

The size-dependent and shape-dependent characteristics that distinguish nanoscale materials from bulk solids arise from constraining the dimensionality of an inorganic structure1-3. As a consequence, many studies have focused on rationally shaping these materials to influence and enhance their optical, electronic, magnetic and catalytic properties4-6. Although a select number of stable clusters can typically be synthesized within the nanoscale regime for a specific composition, isolating clusters of a predetermined size and shape remains a challenge, especially for those derived from two-dimensional materials. Here we realize a multidentate coordination environment in a metal-organic framework to stabilize discrete inorganic clusters within a porous crystalline support. We show confined growth of atomically defined nickel(II) bromide, nickel(II) chloride, cobalt(II) chloride and iron(II) chloride sheets through the peripheral coordination of six chelating bipyridine linkers. Notably, confinement within the framework defines the structure and composition of these sheets and facilitates their precise characterization by crystallography. Each metal(II) halide sheet represents a fragment excised from a single layer of the bulk solid structure, and structures obtained at different precursor loadings enable observation of successive stages of sheet assembly. Finally, the isolated sheets exhibit magnetic behaviours distinct from those of the bulk metal halides, including the isolation of ferromagnetically coupled large-spin ground states through the elimination of long-range, interlayer magnetic ordering. Overall, these results demonstrate that the pore environment of a metal-organic framework can be designed to afford precise control over the size, structure and spatial arrangement of inorganic clusters.

The Mössbauer spectra of trigonal α-FePO4, measured between 4.2 and 300 K, exhibit hyperfine parameters characteristic of high-spin iron(III) in a pseudotetrahedral oxygen environment. Between 24.5 and 300 K, the spectra show a paramagnetic quadrupole doublet and at 24.0 K the spectrum reveals the onset of antiferromagnetic exchange. At 4.2 and 16 K, a single magnetic sextet is observed with hyperfine fields of 51.36(1) and 42.74(1) T, respectively, with an angle, θ, of 90° between the principal axis of the electric field gradient tensor in the basal plane of the trigonal unit cell and the hyperfine field along the c axis. The spectra obtained between 21 and 18 K have been fitted with two equal-area magnetic sextets with θ angles of 25 and 85°, angles which indicate that the iron(III) magnetic moments are canted away from the c axis. The reduced hyperfine field versus reduced temperature plot indicates a departure from a Brillouin S = 5/2 behavior, as a result of some magnetostriction at the Néel temperature. The Mössbauer spectra of class 1 mixed-valence SrFe3(PO4)3, measured between 4.2 and 300 K, exhibit hyperfine parameters characteristic of two high-spin iron(II) ions and one high-spin iron(III) ion in a pseudooctahedral oxygen environment. At and above 40 K, the spectra show two paramagnetic quadrupole doublets, whereas at 39.0 K the spectrum reveals the onset of ferrimagnetic exchange. Between 4.2 and 30 K, the spectra have been fitted with two magnetic sextets with θ angles of 85 and 10° for the iron(II) and iron(III) sites, respectively. The reduced hyperfine field versus reduced temperature plots for the iron(II) and iron(III) sites show a distinct departure from Brillouin S = 2 and S = 5/2 behavior, respectively, a departure that suggests a first-order magnetic transition at 39.5(5) K with differing magnetostrictions at the iron(II) and iron(III) sites.

Metal-organic frameworks are of interest for use in a variety of electrochemical and electronic applications, although a detailed understanding of their charge transport behavior, which is of critical importance for enhancing electronic conductivities, remains limited. Herein, we report isolation of the mixed-valence framework materials, Fe(tri)2(BF4) x (tri- = 1,2,3-triazolate; x = 0.09, 0.22, and 0.33), obtained from the stoichiometric chemical oxidation of the poorly conductive iron(II) framework Fe(tri)2, and find that the conductivity increases dramatically with iron oxidation level. Notably, the most oxidized variant, Fe(tri)2(BF4)0.33, displays a room-temperature conductivity of 0.3(1) S/cm, which represents an increase of 8 orders of magnitude from that of the parent material and is one of the highest conductivity values reported among three-dimensional metal-organic frameworks. Detailed characterization of Fe(tri)2 and the Fe(tri)2(BF4) x materials via powder X-ray diffraction, Mössbauer spectroscopy, and IR and UV-vis-NIR diffuse reflectance spectroscopies reveals that the high conductivity arises from intervalence charge transfer between mixed-valence low-spin FeII/III centers. Further, Mössbauer spectroscopy indicates the presence of a valence-delocalized FeII/III species in Fe(tri)2(BF4) x at 290 K, one of the first such observations for a metal-organic framework. The electronic structure of valence-pure Fe(tri)2 and the charge transport mechanism and electronic structure of mixed-valence Fe(tri)2(BF4) x frameworks are discussed in detail.

Conductive metal–organic frameworks are an emerging class of three-dimensional architectures with degrees of modularity, synthetic flexibility and structural predictability that are unprecedented in other porous materials. However, engendering long-range charge delocalization and establishing synthetic strategies that are broadly applicable to the diverse range of structures encountered for this class of materials remain challenging. Here, we report the synthesis of K x Fe 2 (BDP) 3 (0 ≤ x ≤ 2; BDP 2− = 1,4-benzenedipyrazolate), which exhibits full charge delocalization within the parent framework and charge mobilities comparable to technologically relevant polymers and ceramics. Through a battery of spectroscopic methods, computational techniques and single-microcrystal field-effect transistor measurements, we demonstrate that fractional reduction of Fe 2 (BDP) 3 results in a metal–organic framework that displays a nearly 10,000-fold enhancement in conductivity along a single crystallographic axis. The attainment of such properties in a K x Fe 2 (BDP) 3 field-effect transistor represents the realization of a general synthetic strategy for the creation of new porous conductor-based devices.

The stabilization of isolated grafted Fe3+ sites on siliceous supports is investigated by a comparative study of crystalline versus amorphous materials. Our synthetic approach treats crystalline delaminated zeolite DZ-1 and amorphous silica (SiO2) with an aqueous NaFeEDTA cation precursor complex, to result in grafting of isolated Fe3+ sites via covalent attachment to support hydroxyl groups. Thermogravimetric analysis and UV-visible spectroscopy demonstrate;the complete detachment of chelating EDTA ligand upon Fe3+ grafting on both supports. Before calcination treatment, both Fe/DZ-1 and Fe/SiO2 have similar UV-visible spectral features, with absorption bands at 208-225 and 257 nm, characteristic of framework Fe3+ sites in zeolites. Calcination does not affect the UV-visible spectroscopic characteristics of Fe/DZ-1 but changes the spectrum of Fe/SiO2 to a single absorption band at 260 nm, indicating better thermal stability of Fe3+ sites in Fe/DZ-1 as compared to Fe/SiO2. This stability persists for Fe/DZ-1 even during alkane oxidation catalysis in the presence of hydrogen peroxide, which causes aggregation of Fe3+ into oxide oligomers for Fe/SiO2. Fe-57 Mossbauer spectroscopy of calcined materials indicates a more uniform distribution of sites in Fe/DZ-1 relative to Fe/SiO2. We thus attribute the greater robustness and site uniformity of Fe/DZ-1 to the chelation of Fe3+ by the rigid crystalline silicate DZ-1 framework, engendered by the spatial preorganization of grafting hydroxyls groups within its uniform defect sites, which are templated by framework B3+ removal during delamination. Such preorganization enables cooperativity between neighboring hydroxyl groups. This contrasts with more randomly distributed hydroxyl groups on SiO2, which lack such preorganization, leading to decreased hydrothermal stability and an Fe3+ grafting density that is similar to 7-fold lower for Fe/SiO2 relative to Fe/DZ-1. These observations reveal how the silicate surface onto which a cation is grafted can act as a relevant ligand, capable of controlling material synthesis and functionality akin to ligands in homogeneous metal complexes, and demonstrate the advantages of support crystallinity in having this ligand be hydrothermally stable and tunable via templating.

This review deals with our long-range goal of determining why the Prussian blue pigments, typically either the "soluble" KFeIII[FeII(CN)6]·xH2O or the alternative "insoluble" Fe[FeII(CN)6]3·xH2O compounds, used by artists from shortly after the discovery of Prussian blue in 1704 and well into the early twentieth century, often fade when exposed to light. In order to achieve this goal it was decided that first, for comparison purposes, we had to prepare and fully characterize Prussian blues prepared by various, often commercially successful, synthetic methods. The characterization has employed a large variety of modern methods to determine both the stoichiometry of the Prussian blues and the arrangement of the voids found in the latter "insoluble" Prussian blues. The refinement of synchrotron radiation derived X-ray powder diffraction data obtained for a formally soluble and an insoluble Prussian blue required refinement in the Pm3[combining macron]m space group and lead to the K1.9[FeFe(CN)18]·{1.9 OH + 7.0H2O}, 1, and FeFe(CN)18·11.0H2O, 2, stoichiometries. The former compound, 1, exhibits an apparently random iron(ii) long-range void arrangement, whereas 2 exhibits a more non-random long-range arrangement, however, a pair distribution function analysis indicates a short-range ordering of the voids in both compounds. After further detailed characterization of many Prussian blue samples, painted samples on linen canvas, were subjected to accelerated light exposure for up to 800 hours either as pure Prussian blues or mixed with (PbCO3)2Pb(OH)2, ZnO or TiO2, the white pigments often used by artists to lighten the intense Prussian blue colour. The results indicate that the first two of these white pigments play a significant role in the fading of the colour of Prussian blues. In order to achieve our long-range goal, several Prussian blue samples were prepared from "ancient" recipes published in 1758 and 1779. These so-called "ancient" samples, painted in a dark and a pale blue shade, were also subjected to accelerated light exposure. The colorimetric results, in conjunction with X-ray powder diffraction refinements, pair distribution analysis and Mössbauer spectral results, indicate that, depending on the exact method of ancient preparation, the Prussian blue pigments were sometimes badly contaminated with alumina hydrate and/or ferrihydrite, a contamination which leads to extensive fading or decolourization of the Prussian blue pigments. The presence of ferrihydrite was subsequently confirmed in the study of a surface paint fragment from an eighteenth-century polychrome sculpture.

The proportionality constant, α, between the observed isomer shifts and the calculated electron probability density at the iron nucleus has been reevaluated in terms of the correct experimental isomer shifts relative to α-iron and their corresponding accuracy, which should be considered in the linear regression fit yielding α. The iron-57 excited state nuclear quadrupole moment, Q, is not a "relative" value and its widely accepted experimental value is 0.16(1) × 10-28 m2 as also confirmed by nuclear model calculations.

Several high-resolution Mössbauer spectra of yttrium iron garnet, Y3Fe5O12, have been fit as a function of temperature with a new model based on a detailed analysis of the spectral changes that result from a reduction from the cubic Ia3̅d space group to the trigonal R3̅ space group. These spectral fits indicate that the magnetic sextet arising from the 16a site in cubic symmetry is subdivided into three sextets arising from the 6f, the 3d, 3d, and the 1a, 1b, 2c sites in rhombohedral-axis trigonal symmetry. The 24d site in cubic Ia3̅d symmetry is subdivided into four sextets arising from four different 6f sites in R3̅ rhombohedral-axis trigonal symmetry, sites that differ only by the angles between the principal axis of the electric field gradient tensor and the magnetic hyperfine field assumed to be parallel with the magnetic easy axis. This analysis, when applied to the potential nuclear waste storage compounds Y(3-x)Ca(0.5x)Th(0.5x)Fe5O12 and Y(3-x)Ca(0.5x)Ce(0.5x)Fe5O12, indicates virtually no perturbation of the structural, electronic, and magnetic properties upon substitution of small amounts of calcium(II) and thorium(IV) or cerium(IV) onto the yttrium(III) 24c site as compared with Y3Fe5O12. The observed broadening of the four different 6f sites derived from the 24d site results from the substitution of yttrium(III) with calcium(II) and thorium(IV) or cerium(IV) cations on the next-nearest neighbor 24c site. In contrast, the same analysis applied to Y(2.8)Ce(0.2)Fe5O12 indicates a local perturbation of the magnetic exchange pathways as a result of the presence of cerium(IV) in the 24c next-nearest neighbor site of the iron(III) 24d site.