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In nature, nonheme iron enzymes use dioxygen to generate high-spin iron(IV)=O species for a variety of oxygenation reactions. Although synthetic chemists have long sought to mimic this reactivity, the enzyme-like activation of O2 to form high-spin iron(IV) = O species remains an unrealized goal. Here, we report a metal-organic framework featuring iron(II) sites with a local structure similar to that in α-ketoglutarate-dependent dioxygenases. The framework reacts with O2 at low temperatures to form high-spin iron(IV) = O species that are characterized using in situ diffuse reflectance infrared Fourier transform, in situ and variable-field Mössbauer, Fe Kβ x-ray emission, and nuclear resonance vibrational spectroscopies. In the presence of O2, the framework is competent for catalytic oxygenation of cyclohexane and the stoichiometric conversion of ethane to ethanol.

Iron is one of the most abundant elements in the environment and in the human body. As an essential nutrient, iron homeostasis is tightly regulated, and iron dysregulation is implicated in numerous pathologies, including neuro-degenerative diseases, atherosclerosis, and diabetes. Endogenous iron pool concentrations are directly linked to iron ion uptake from environmental sources such as drinking water, providing motivation for developing new technologies for assessing iron(ii) and iron(iii) levels in water. However, conventional methods for measuring aqueous iron pools remain laborious and costly and often require sophisticated equipment and/or additional processing steps to remove the iron ions from the original environmental source. We now report a simplified and accurate chemical platform for capturing and quantifying the iron present in aqueous samples through use of a post-synthetically modified porous aromatic framework (PAF). The ether/thioether-functionalized network polymer, PAF-1-ET, exhibits high selectivity for the uptake of iron(ii) and iron(iii) over other physiologically and environmentally relevant metal ions. Mössbauer spectroscopy, XANES, and EXAFS measurements provide evidence to support iron(iii) coordination to oxygen-based ligands within the material. The polymer is further successfully employed to adsorb and remove iron ions from groundwater, including field sources in West Bengal, India. Combined with an 8-hydroxyquinoline colorimetric indicator, PAF-1-ET enables the simple and direct determination of the iron(ii) and iron(iii) ion concentrations in these samples, providing a starting point for the design and use of molecularly-functionalized porous materials for potential dual detection and remediation applications.

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 Fe2(BDP)3 (0 ≤ x ≤ 2; BDP2- = 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 Fe2(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 Fe2(BDP)3 field-effect transistor represents the realization of a general synthetic strategy for the creation of new porous conductor-based devices.

Author(s): Miguel I. Gonzalez [sup.1] , Ari B. Turkiewicz [sup.1] , Lucy E. Darago [sup.1] , Julia Oktawiec [sup.1] , Karen Bustillo [sup.2] , Fernande Grandjean [sup.3] , Gary J. [...], The size-dependent and shape-dependent characteristics that distinguish nanoscale materials from bulk solids arise from constraining the dimensionality of an inorganic structure.sup.1-3. As a consequence, many studies have focused on rationally shaping these materials to influence and enhance their optical, electronic, magnetic and catalytic properties.sup.4-6. 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 pore space in the metal-organic framework Zr.sub.6O.sub.4(OH).sub.4(bpydc).sub.6 can be used as a scaffold to grow precisely defined atomically thick sheets of metal halide materials, taking advantage of multiple binding sites to direct complexation of the metal ions; these metal halide nanosheets fill the size gap between discrete molecular magnets and bulk magnetic materials, with potentially unusual magnetic properties arising from this size regime.

Eu3InP3 has been prepared as large single crystals with an indium flux reaction. The structure of the new compound is isotypic to Sr3InP3 and crystallizes in the orthorhombic space group Pnma with unit cell dimensions of a = 12.6517(15) A, b = 4.2683(5) A, and c = 13.5643(14) A (Z = 4, T = 140 K, R1 = 0.0404, wR2 = 0.0971 for all data). The structure consists of one-dimensional chains of corner-shared distorted [InP2P2/2]6- tetrahedra separated by rows of Eu2+ ions. Two of the three crystallographically distinct europium sites have a short Eu(1)-Eu(2) distance of 3.5954(7) A, which yields Eu-Eu dimers. The Eu-P bond distances range from 2.974(2) to 3.166(2) A. The temperature dependence of the conductivity indicates that Eu3InP3 is a small band gap semiconductor. Both magnetization and Eu-151 Mossbauer spectral measurements indicate that the europium in Eu3InP3 is divalent and that at least two magnetic transitions occur. Magnetization studies reveal magnetic transitions at 14, 10.4, and approximately 5 K. These transitions are also observed in heat capacity studies of Eu3InP3. The Mossbauer spectra indicate that the two europium sites are ordered at 12 K and that all three europium sites are ordered at 8 K.

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/γ-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, γ-Fe2O3, and small amounts of α-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 Mössbauer spectral analysis is marginal. An alternative analysis of both the reported X-ray lattice parameters and the Mössbauer spectral results for the three nanoparticles in terms of solid solutions of magnetite and maghemite, AFe3+[BFe1–3δ2+Fe1+2δ3+□δ]-O4, where □ represents a vacancy, δ = 0 corresponds to magnetite, Fe3O4, and δ = 0.333 corresponds to maghemite, γ-Fe2O3, is proposed herein. In the presence of the expected magnetite Verwey transition, the Mössbauer spectral analysis is formulated with the stoichiometry AFe3+[BFe2(1–3δ)2.5+Fe5δ3+□δ]-O4, and as far as we can tell, this model is consistent with the Rietveld X-ray diffraction analysis. The values of δ = 0.28(2) and 0.30(1) obtained from the X-ray diffraction and Mössbauer spectral analyses, respectively, indicate that the composition of the nanoparticles is very close to γ-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. [ABSTRACT FROM AUTHOR]

We present a study of the magnetic properties and the [sup.57]Fe Mossbauer spectra of the [Hf.sub.1-x][R.sub.x][Fe.sub.6][Ge.sub.6], R = Gd and Dy, series. The macroscopic magnetic measurements are consistent with the magnetic independence of the R and Fe sublattices. However, the [sup.57]Fe Mossbauer study reveals a more complex magnetic behavior. Specifically, below [T.sub.t] [approximately equal to] 100 K a spin reorientation takes place in Hf[Fe.sub.6][Ge.sub.6]. The analysis of the corresponding Mossbauer spectra shows that below [T.sub.t] a fraction of the iron moments is canted from the c-axis. The substitution of Hf by Gd or Dy reduces the fraction of canted iron moments. The hyperfine magnetic fields are found to decrease upon the R = Gd or Dy substitution. This effect can be qualitatively explained as a result of the decrease in the hybridization between the d valence states of the R element with the 3d iron states. Index Terms--1-6-6 compounds, magnetic materials, Mossbauer spectroscopy.

The di-mixed-valence complex [{(eta(super 5)-C5H5)Fe(eta(super 5)-C5H4)}4(eta(super 4)-C(super 4))Co(eta(super 5)-C5H5)](super 2+), 1(super 2+) is evaluated as a molecular four-dot cell for the quantum cellular automata paradigm for electronic devices. In the solid state 1(super 2+) is a valence-trapped Robin and Day class II compound on the 10(super -12)s infrared time-scale, the fastest technique used, while an unambiguous evidence for two Fe(super II) and two Fe(super III) sites is observed.

Several compounds of the [Na.sub.2][([Mn.sub.1-x][Fe.sup.2+.sub.x]).sub.2] [Fe.sup.3+][([PO.sub.4]).sub.3] solid solution have been hydrothermally synthesized at 400 [degrees]C and 1 kbar: pure alluaudite-like compounds have been obtained for x = 0.00, 0.25, 0.50, 0.75, and 1.00. Rietveld refinements of the powder X-ray diffraction patterns indicate the presence of [Na.sup.+] at the A1 and A2' sites, [Mn.sup.2+] and [ Fe.sup.2+] at the M1 site, and [Mn.sup.2+], [Fe.sup.2+], and [Fe.sup.3+] at the M2 site. The presence of small amounts of [Na.sup.+] at the MI site and [Mn.sup.2+] at the AI sits indicates a partially disordered distribution of these cations. An excellent linear correlation has been established between the M1-M2 distance and the energy of the infrared band attributed to the [M.sup.2+]-O vibrations. The Mossbauer spectra, measured between 85 and 295 K, were analyzed in terms of a model which includes the next-nearest neighbor interactions at the M2 and M I crystallographic sites. [Fe.sup.2+] and [Fe.sup.3+] isomer shifts are typical of the alluaudite structure and exhibit the expected second-order Doppler shift. The derived iron vibrating masses and Mossbauer lattice temperatures are within the range of values expected for iron cations in an octahedral environment. The [Fe.sup.2+] and [Fe.sup.3+] quadrupole splittings are typical of the alluaudite structure, and the temperature dependence of the [Fe.sup.2+] quadrupole splitting was fit with the Ingalls model, which yielded a ground state orbital splitting of ca. 460 to 735 [cm.sup.-1] for the [Fe.sup.2+] sites. The isomer shifts and quadrupole splittings of [Fe.sup.2+] at the M1 site are larger than those of [Fe.sup.2+] at M2, indicating that the M1 site is both larger and more distorted than the M2 site.

The new ligands Na[(p-IC6H4)B(3-Rpz)3] (R = H, Me) react with FeBr2 to give either purple, low-spin Fe[(p-IC6H4)B(pz)3]2 or colorless, high-spin Fe[(p-IC6H4)B(30-Mepz)3]2. Depending upon the crystallization conditions, Fe[(p-IC6H4)B(30-Mepz)3]2 can exist both as two polymorphs and as a methylene chloride solvate.

The Einstein model of a solid usually lacks a clear illustration in introductory solid-state physics courses because most solids are much better described by the Debye model. Filled antimony skutterudites, materials that have recently attracted much attention because of their potential for thermoelectric applications, provide a canonical illustration of the Einstein model. The filling atoms are loosely bound in the atomic cage formed by their neighbors, and hence their description as independent harmonic oscillators is adequate. Simple models for the heat capacity and thermal conductivity of a solid are introduced, with emphasis on the density of vibrational states. These models are used in conjunction with experimental results obtained from heat capacity and inelastic neutron scattering measurements to demonstrate the applicability of the concept of the Einstein oscillator to the filling guests in antimony skutterudites. The importance of these Einstein oscillators for impeding thermal transport is discussed and some simple problems involving the heat capacity, thermal conductivity, and inelastic neutron scattering are proposed.

Europium-151 Mossbauer spectral study of Eu14MnP11 and Eu14MnAs11 has been analyzed by using two models. However, the second model in which the spectra are fit with a three-dimensional relaxation of the europium (I) and europium (III) hyperfine fields is preferred for its physical meaning and its reduced number of fitted parameters.

Magnetic susceptibility, ytterbium L(sub III)-edge x-ray absorption and tin-119 Mossbauer spectral measurements have been carried out to probe the electronic structure of ytterbium and tin in the filled or partially filled skutterudite compounds, Yb(sub y)Co4Sb(sub 12-x)Sn(sub x), over a range of x and y values. The tin electronic configuration is both very similar to that of the antimony in the structure and insensitive to the ytternium, y.

Several compounds of the NaMn [([Fe.sub.1-x][In.sub.x]).sub.]2[(P[O.sub.4]).sub.3] solid solution were synthesized by solid state reaction in air; pure alluaudite-like compounds were obtained for x = 0.00 to 1.00. X-ray Rietveld refinements indicate the presence of [Na.sup.+] at the A1 and A2' sites, [Mn.sup.2+] at the M1 site, and [Fe.sup.2+], [Fe.sup.3+], and [In.sup.3+] at the M2 site. The presence of small amounts of [In.sup.3+] at the M1 site, and [Mn.sup.2+] at the M2 site, indicates a partially disordered distribution between these cations. A good correlation was also established between the M1-M2 bond distance and the [beta] angle of the alluaudite-like compounds. The disordered distribution of [Fe.sup.2+], [Fe.sup.3+], and [In.sup.3+] at the M2 site is confirmed by the broadness of the infrared absorption bands. The Mossbauer spectra, measured between 90 and 295 K, were analyzed in terms of a model that takes into account the next-nearest neighbor interactions around the M2 crystallographic site. In all cases these spectra reveal the unexpected presence of small amounts of [Fe.sup.2+] at the M2 site, an amount that decreases as the [In.sup.3+] content increases. The [Fe.sup.2+] and [Fe.sup.3+] isomer shifts are typical of the alluaudite structure and vary with temperature, as expected from a second-order Doppler shift. The derived iron vibrating masses and Mossbauer lattice temperatures are within the expected range of values for iron cations in an octahedral environment. The [Fe.sup.2+] and [Fe.sup.3+] quadrupole splittings are also typical of the alluaudite structure and the temperature dependence of the [Fe.sup.2+] quadrupole splitting was fit with the model of Ingalls (1964), which yielded a ground state orbital splitting of ca. 380 to 570 [cm.sup.-1] for the [Fe.sup.2+] sites.

Research has been conducted on the Ba (sub)2 FeO (sub)4 and Ba (sub)3 FeO (sub)5 crustals. The characterization of these crystals carried out via the use of the single-crystal X-ray diffraction, magnetic measurements and Mossbauer spectroscopy is described.

Research demonstrates correlation between the K-edge X-ray specific absorption near-edge spectral lines to scattering by specific near-neighbor shells of the low- and high-spin complexes of iron(II) and the analogous low-spin methane trispyrazolylborate and trispyrazolylmethane complexes. Data indicate that the absorption profiles result from the medium-range scattering processes.