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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 pore space in the metal–organic framework Zr6O4(OH)4(bpydc)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.

The Mossbauer 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 Neel temperature. The Mossbauer 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.

International audience; Based on the combined corrected chemical analysis, the single-crystal X-ray structural results, and the revised Mössbauer spectral analysis, the best formulation of Li1.4(1)[Fe4.4(1)IIFe0.6(1)III(HPO3)6]·1.47(3) H2O, 1b, has been obtained; also, from a revised Mössbauer spectral analysis, a revised formulation of K0.95(5)[Fe3.95(5)IIFe1.05(5)III(HPO3)6]·0.5 H2O, 2m, has been obtained. The revised analysis of the room-temperature Mössbauer spectral parameters for both compounds is consistent with their crystallographic structures and the different nature and occupancies of the Li+ and K+ crystallographic sites. From a detailed analysis of the impedance spectroscopy measurements of Li1.43[Fe4.43IIFe0.57III(HPO3)6]·1.5 H2O, 1, between 123 and 189 °C, two processes involving the electric charge response to the ac electric field have been identified. An activation energy for the charge transfer in 1 of 0.91(2) eV or 7340(160) cm–1 has been obtained; the charge transfer may involve a correlated hopping of the Li+ ion and an electron between the iron(II) and iron(III) ions.

Herein, evidence for the long-sought finite hyperfine interaction in the high-pressure hexagonal close-packed $\ensuremath{\epsilon}$-iron is gained through synchrotron radiation perturbed angular correlation spectroscopy. This method yields an energy splitting of $3.5(5)\phantom{\rule{4.pt}{0ex}}\text{neV}$ between the ${m}_{{I}_{\text{e}}}=\ifmmode\pm\else\textpm\fi{}1/2$ and ${m}_{{I}_{\text{e}}}=\ifmmode\pm\else\textpm\fi{}3/2$ nuclear sublevels of the iron-57 $14.412\text{-keV}$ nuclear excited state at $30(1)\phantom{\rule{4.pt}{0ex}}\text{GPa}$ and room temperature. This energy splitting is related to a nuclear quadrupole hyperfine interaction with an electric field gradient of $eq=1.2(2)\ifmmode\times\else\texttimes\fi{}{10}^{16}{\phantom{\rule{0.16em}{0ex}}\mathrm{V}/\mathrm{cm}}^{2}$. 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. $0.40(5)\phantom{\rule{4.pt}{0ex}}\text{T}$.

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, Mossbauer spectrosco...

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/D...

The size-dependent and shape-dependent characteristics that distinguish nanoscale materials from bulk solids arise from constraining the dimensionality of an inorganic structure

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.

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” FeIII4[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 Pmm space group and lead to the K1.9[FeIII4FeII3(CN)18]·{1.9 OH + 7.0H2O}, 1, and FeIII4FeII3(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 Mossbauer 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.

The authors are in debt to the Algerian DG-RSDT (Direction Générale de la Recherche Scientifique et du Développement Technologique) and Université Ferhat Abbas Sétif 1 for financial support. SZ thanks Dr Ewa Juszyńska-Gałązka, from the Institute of Nuclear Physics Polish Academy of Sciences, for performing FT-IR measurements using EXCALIBUR FTS-3000 spectrometer. The magnetic part was supported by the Generalitat Valenciana (PrometeoII/2014/076 project) and the Spanish MINECO (project CTQ2017-87201-P AEI/FEDER, UE). 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 {(µ-oxido-µ-[sulfato–O1,O2])bis[tris(2-pyridyl-methyl)amineiron(III)]}2+, herein designated as Fe12, and two half-dinuclear dianionic units of {(µ-oxido)bis[iron(III)]}2– units, herein designated as Fe33a and Fe44b, generating the overall composition Co2Fe4O2(CN)12(tpa)4, 1 , where tpa is tris(2-pyridylmethyl)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 Fe-O-S-O-Fe sulfato-based bridge with an angle of 132.8°. In contrast, in the two dinuclear dianionic units, Fe33a and Fe44b, the Fe–O–Fe bond angle is crystallographically constrained to be linear. The Co–CN–Fe bonds are almost co-linear, with Co–C–N angles of 176° and C–NFe angles of 169°–. 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. Postprint

The bis(μ-oxo) dimeric complexes {AriPr8OM(μ-O)}2 (AriPr8 = C6H-2,6-(C6H2-2,4,6-iPr3)2-3,5-iPr2; M = Fe (1), Co (2)) were prepared by oxidation of the M(I) half-sandwich complexes {AriPr8M(η6-arene)} (arene = benzene or toluene). Iron species 1 was prepared by reacting {AriPr8Fe(η6-benzene)} with N2O or O2, and cobalt species 2 was prepared by reacting {AriPr8Co(η6-toluene)} with O2. Both 1 and 2 were characterized by X-ray crystallography, UV–vis spectroscopy, magnetic measurements, and, in the case of 1, Mossbauer spectroscopy. The solid-state structures of both compounds reveal unique M2(μ-O)2 (M = Fe (1), Co(2)) cores with formally three-coordinate metal ions. The Fe···Fe separation in 1 bears a resemblance to that in the Fe2(μ-O)2 diamond core proposed for the methane monooxygenase intermediate Q. The structural differences between 1 and 2 are reflected in rather differing magnetic behavior. Compound 2 is thermally unstable, and its decomposition at room temperature resulted in the oxidation of the A...

The iron-57 Mössbauer spectra of the eight-coordinate complex, [Fe(L(N4))2](BF4)2, where L(N4) is the tetradentate N(1)(E),N(2)(E)-bis[(1-methyl-1H-imidazol-2-yl)methylene]-1,2-benzenediimine ligand, have been measured between 4.2 and 295 K and fit with a quadrupole doublet. The fit at 4.2 K yields an isomer shift, δ(Fe), of 1.260(1) mm/s and a quadrupole splitting, ΔE(Q), of 3.854(2) mm/s, values that are typical of a high-spin iron(II) complex. The temperature dependence of the isomer shift yields a Mössbauer temperature, Θ(M), of 319(27) K and the temperature dependence of the logarithm of the Mössbauer spectral absorption area yields a Debye temperature, Θ(D), of 131(6) K, values that are indicative of high-spin iron(II). Nonrelativistic single point density functional calculations with the B3LYP functional, the full 6-311++G(d,p) basis set, and the known X-ray structures for [Mn(L(N4))2](2+), [Mn(L(N4))2](ClO4)2, 1, [Fe(L(N4))2](2+), and [Fe(L(N4))2](BF4)2, 2, yield small electric field gradients for the manganese(II) complexes and electric field gradients and s-electron densities at the iron-57 nuclide that are in good to excellent agreement with the Mössbauer spectral parameters. The structure of 2 with a distorted square-antiprism C1 iron(II) coordination symmetry exhibits four different Fe-N(imid) bonds to the imidazole nitrogens with an average bond distance of 2.253(2) Å and four different Fe-N(imine) bonds to the benzenediimine nitrogens, with an average bond distance of 2.432(2) Å; this large difference yields the large observed ΔE(Q). An optimization of the [Fe(L(N4))2](2+) structure leads to a highly symmetric eight-coordination environment with S4 symmetry and four equivalent Fe-N(imid) bond distances of 2.301(2) Å and four equivalent Fe-N(imine) bond distances of 2.487(2) Å. In contrast, an optimization of the [Mn(LN4)2](2+) structure leads to an eight-coordination manganese(II) environment with D(2d) symmetry and four equivalent Mn-N(imid) bond distances of 2.350(3) Å and four equivalent Mn-N(imine) bond distances of 2.565(3) Å.

Two isostructural europium(II) quaternary chalcogenides, Na8Eu2(Si2S6)2, 1, and Na8Eu2(Ge2S6)2, 2, containing an ethane-like (Si2S6)6− or (Ge2S6)6− moiety have been synthesized by employing the polychalcogenide molten flux method. Single-crystal X-ray diffraction reveals that both compounds crystallize in the C2/m space group, and their structures contain layers of {[Na2Eu2(Si2S6)2]6−}∞ or {[Na2Eu2(Ge2S6)2]6−}∞ anions held together by six interlayer sodium cations to yield {Na6[Na2Eu2(Si2S6)2]}∞ and {Na6[Na2Eu2(Ge2S6)2]}∞. Compound 2 is a semiconductor with an optical band gap of 2.15(2) eV. The temperature dependence of the magnetic susceptibility indicates that compounds 1 and 2 are paramagnetic with μeff=7.794(1) μB per Eu and g=1.964(1) for 1 and μeff=8.016(1) μB per Eu and g=2.020(1) for 2, moments that are in good agreement with the europium(II) spin-only moment of 7.94 μB. The europium-151 Mossbauer isomer shift of 2 confirms the presence of europium(II) cations with an electronic configuration between [Xe]4f6.81 and 4f76s0.32.

The 2 to 300 K magnetic susceptibilities of Fe{N(SiMe2Ph)2}2, 1, Fe{N(SiMePh2)2}2, 2, and the diaryl complex Fe(Ar(Pr(i)4))2, 3, where Ar(Pr(i)4) is C6H3-2,6(C6H3-2,6-Pr(i)2)2 have been measured. Initial fits of these properties in the absence of an independent knowledge of their ligand field splitting have proven problematic. Ab initio calculations of the CASSCF/RASSI/SINGLE-ANISO type have indicated that the orbital energies of the complexes, as well as those of Fe(Ar(Me6))2, 4, where Ar(Me6) is C6H3-2,6(C6H2-2,4,6-Me3)2), are in the order d(xy)≈ d(x(2)-y(2))d(xz) ≈ d(yz)d(z(2)), and the iron(II) complexes in this ligand field have the (d(xy), d(x(2)-y(2)))(3)(d(xz), d(yz))(2)(d(z(2)))(1) ground electronic configuration with a substantial orbital contribution to their effective magnetic moments. An ab initio-derived ligand field and spin-orbit model is found to yield an excellent simulation of the observed magnetic properties of 1-3. The calculated ligand field strengths of these ligands are placed in the broader context of common coordination ligands in hypothetical two-coordinate linear iron(ii) complexes. This yields the ordering I(-)H(-)Br(-)≈ PMe3CH3(-)Cl(-)≈ C(SiMe3)3(-)CN(-)≈ SAr(Pr(i)6-)Ar(Pr(i)4-)Ar(Me6-)≈ N3(-)NCS(-)≈ NCSe(-)≈ NCBH3(-)≈ MeCN ≈ H2O ≈ NH3NO3(-)≈ THF ≈ CO ≈ N(SiMe2Ph)2(-)≈ N(SiMePh2)2(-)F(-)≈ N(H)Ar(Pr(i)6-)≈ N(SiMe3)Dipp(-)OAr(Pr(i)4-). The magnetic susceptibility of the bridged dimer, [Fe{N(SiMe3)2}2]2, 5, has also been measured between 2 and 300 K and a fit of χMT with the isotropic Heisenberg Hamiltonian, Ĥ = -2JŜ1·Ŝ2 yields an antiferromagnetic exchange coupling constant, J, of -131(2) cm(-1).

The structural and magnetic data for the Mn(i) dialkyl anionic salts [K2(18-crown-6)3][Mn{C(SiMe3)3}2]2 and [K(15-crown-5)2][Mn{C(SiMe3)3}2] are presented, indicating that these complexes possess a non-degenerate S = 2 ground state owing to 4s–3dz2 mixing upon reduction from the Mn(ii) parent complexes.

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. A conducting metal–organic framework with charge delocalization by reductive potassium insertion is demonstrated. Integration into a field-effect transistor shows similar mobilities to semiconductors, with a mobility estimated to be at least 0.84 cm2 V–1 s–1.

Oxidation of the non-mesomorphic ferrocene derivative 1 with silver toluene-4-sulfonate gave the ferrocenium derivative 2, which showed a monotropic columnar phase. The latter two-dimensional phase is composed of ribbons, in which derivative 2 is organized into bilayers, and has a centered rectangular symmetry with a = 318.3 Å and c = 94.9 Å. The Mössbauer spectra of the ferrocene derivative 1 yields hyperfine parameters that are typical of these derivatives and are, as expected, virtually independent of temperature. In a similar fashion, the hyperfine parameters of the ferrocenium derivative 2 are typical of these derivatives, but in this case at both 78 and 4.2 K slow paramagnetic relaxation of the magnetic moment associated with the rather well isolated paramagnetic ferrocenium ion is observed. The temperature-dependent magnetic susceptibilities of 2 are in agreement with those expected for weakly interacting ferrocenium cores. No magnetic-field-induced orientation was observed upon cooling the sample from the isotropic phase down to the columnar phase. Ferrocene and ferrocenium are valuable units for the design of liquid-crystalline switches.

K

K3Fe(CN)6 reacts with the viologen 1,1′-bis(2,4-dinitrophenyl)-4,4′-bipyridinium dication, (DNP)2+, to form a supramolecular complex, (DNP)3[Fe(CN)6]2·10H2O (1). The crystal structure of 1 reveals that there are two [Fe(CN)6]3– anions within an organic framework of three (DNP)2+ cations with the shortest Fe(III)···Fe(III) distances of ca. 9.8 Å, distances that minimize extensive long-range magnetic exchange coupling interactions between the [Fe(CN)6]3– anions, and, thus, 1 is paramagnetic above ca. 17 K and exhibits weak ferromagnetic coupling between 17 and 3 K and antiferromagnetic coupling between 3 and 1.8 K. The long Fe(III)···Fe(III) distances permit slow spin–spin and slow spin–lattice paramagnetic relaxation, relative to the iron-57 Larmor precession frequency, as is evidenced by the Mössbauer spectra measured between 3 and 60 K; between 85 and 295 K, rapid paramagnetic relaxation is observed. Both the slow spin–spin and slow spin–lattice relaxation are mediated by the organic, π-conjugated viologen cations. The Fe–C distances, the Mössbauer isomer shifts, the temperature dependence of the magnetic susceptibility, and the 3 K magnetization results all indicate the presence of low-spin Fe(III) ions in the [Fe(CN)6]3– anions in 1. There is no unequivocal indication of the presence of any formal electron delocalization or transfer from the [Fe(CN)6]3– anion to the (DNP)2+ cations in the results obtained from X-ray crystallography, magnetic measurements, and Mössbauer spectra. Because of enhancement of the spin–orbit coupling by the heavy-atom or -ion effect, the Fe(III) ions in the [Fe(CN)6]3– anions interact with the (DNP)2+ cations, causing them to fluoresce with increasing intensity upon cooling from 90 to 25 K when excited at 300 nm. The resulting luminescence of the viologen (DNP)2+ cation induced by the [Fe(CN)6]3– anions indicates the presence of significant mixing of the molecular orbitals derived from the [Fe(CN)6]3– anions and the molecular orbitals associated with the (DNP)2+ cations to yield bonding supramolecular orbitals in 1, a mixing that is also observed between 50 and 3 K in the temperature dependence of the isomer shift of 1.

The 3,5-dichlorobenzoate anion, L–, serves as a bridging ligand and 2,2′-bipyridine, bipy, as a terminal bidentate ligand to yield, through hydrothermal syntheses, the tetranuclear clusters Dy2Co2L10(bipy)2, 1, and Ln2Ni2L10(bipy)2, where Ln is the trivalent La, 2, Gd, 3, Tb, 4, Dy, 5, or Ho, 6, ion. Single-crystal X-ray diffraction reveals that the six complexes are all isomorphous with the monoclinic P21/c space group and with lattice parameters that decrease with the lanthanide contraction. The two cobalt(II) or nickel(II) and two Ln(III) cations are linked by the 10 L– anions to generate Dy2Co2 or Ln2Ni2 3d–4f cationic heteronuclear clusters with a slightly bent Co···Dy···Dy···Co or Ni···Ln···Ln···Ni arrangement. Direct current magnetic susceptibility studies reveal that the complexes are essentially paramagnetic, with room-temperature χMT values close to the expected values for two cobalt(II) or nickel(II) and two Ln(III) cations. The temperature dependence of χMT for 1 and 5 is well reproduced by ab...

Three potassium crown ether salts, [K(Et2O)2(18-crown-6)][Fe{N(SiMe3)Dipp}2] (1a; Dipp = C6H3-2,6-Pr(i)2), [K(18-crown-6)][Fe{N(SiMe3)Dipp}2]·0.5PhMe (1b), and [K(18-crown-6)][M{N(SiMe3)Dipp}2] (M = Co, 2; M = Ni, 3), of the two-coordinate linear or near-linear bis-amido monoanions [M{N(SiMe3)Dipp}2](-) (M = Fe, Co, Ni) were synthesized by one-electron reduction of the neutral precursors M{N(SiMe3)Dipp}2 with KC8 in the presence of 18-crown-6. They were characterized by X-ray crystallography, UV-vis spectroscopy, cyclic voltammetry, and magnetic measurements. The anions feature lengthened M-N bonds in comparison with their neutral precursors, with slightly bent coordination (N-Fe-N = ca. 172°) for the iron(I) complex, but linear coordination for the cobalt(I) and nickel(I) complexes. Fits of the temperature dependence of χMT of 1 and 2 reveal that the iron(I) and cobalt(I) complexes have large negative D zero-field splittings and a substantial orbital contribution to their magnetic moments with L = 2, whereas the nickel(I) complex has at most a small orbital contribution to its magnetic moment. The magnetic results have been used to propose an ordering of the 3d orbitals in each of the complexes.

The homoleptic cobalt(I) alkyl [Co{C(SiMe2Ph)3}]2 (1) was prepared by reacting CoCl2 with [Li{C(SiMe2Ph)3}(THF)] in a 1:2 ratio. Attempts to synthesize the corresponding iron(I) species led to the iron(II) salt [Li(THF)4][Fe2(μ-Cl)3{C(SiMe2Ph)3}2] (2). Both 1 and 2 were characterized by X-ray crystallography, UV–vis spectroscopy, and magnetic measurements. The structure of 1 consists of dimeric units in which each cobalt(I) ion is σ-bonded to the central carbon of the alkyl group −C(SiMe2Ph)3 and π-bonded to one of the phenyl rings of the −C(SiMe2Ph)3 ligand attached to the other cobalt(I) ion in the dimer. The structure of 2 features three chlorides bridging two iron(II) ions. Each iron(II) ion is also σ-bonded to the central carbon of a terminal −C(SiMe2Ph)3 anionic ligand. The magnetic properties of 1 reveal the presence of two independent cobalt(I) ions with S = 1 and a significant zero-field splitting of D = 38.0(2) cm–1. The magnetic properties of 2 reveal extensive antiferromagnetic exchange coupli...

The titanium bisamido complex Ti{N(H)AriPr6}2 (AriPr6 = C6H3-2,6-(C6H2-2,4,6-iPr3)2 (2), along with its three-coordinate titanium(III) precursor, TiCl{N(H)AriPr6}2 (1), have been synthesized and characterized. Compound 1 was obtained via the stoichiometric reaction of LiN(H)AriPr6 with the Ti(III) complex TiCl3·2NMe3 in trimethylamine. Reduction of 1 with 1 equiv of KC8 afforded Ti{N(H)AriPr6}2 (2) in moderate yield. Both 1 and 2 were characterized by X-ray crystallography, NMR, and IR spectroscopy, magnetic studies, and by density functional theory (DFT) computations. The precursor 1 has quasi-four-coordinate coordination at the titanium atom, with bonding to two amido nitrogens and a chlorine as well as a secondary interaction to a flanking aryl ring of a terphenyl substituent. Compound 2 displays a very distorted four-coordinate metal environment in which the titanium atom is bound to two amido nitrogens and to two carbons from a terphenyl aryl ring. This structure is in sharp contrast to the expected ...

A series of high spin, two-coordinate first row transition metal-amido complexes, M{N(SiMe3)Dipp}2 {M = Fe (1), Co (2), or Ni (3); Dipp = C6H3-2,6-Pr(i)2} and a tetranuclear C-H activated chromium amide, [Cr{N(SiMe2CH2)Dipp}2Cr]2(THF) (4), were synthesized by reaction of their respective metal dihalides with 2 equiv of the lithium amide salt. They were characterized by X-ray crystallography, electronic and infrared spectroscopy, SQUID magnetic measurements, and computational methods. Contrary to steric considerations, the structures of 1-3 display planar eclipsed M{NSiC(ipso)}2 arrays and short M-N distances. DFT calculations, corrected for dispersion effects, show that dispersion interactions involving C-H-H-C moieties likely stabilize the structures by 21.1-29.4 kcal mol(-1), depending on the level of the calculations employed. SQUID measurements confirm high spin electron configurations for all the complexes and substantial orbital contributions for 1 and 2.

The synthesis, magnetic, and spectroscopic characteristics of the synthetically useful dimeric cobalt(II) silylamide complex [Co{N(SiMe3)2}2]2 (1) and several of its Lewis base complexes have been investigated. Variable-temperature nuclear magnetic resonance (NMR) spectroscopy of 1 showed that it exists in a monomer–dimer equilibrium in benzene solution and has an association energy (ΔGreacn) of −0.30(20) kcal mol–1 at 300 K. Magnetic data for the polycrystalline, red-brown [Co{N(SiMe3)2}2]2 (1) showed that it displays strong antiferromagnetic exchange coupling, expressed as −2JexS1S2, between the two S = 3/2 cobalt(II) centers with a Jex value of −215(5) cm–1, which is consistent with its bridged dimeric structure in the solid state. The electronic spectrum of 1 in solution is reported for the first time, and it is shown that earlier reports of the melting point, synthesis, electronic spectrum, and magnetic studies of the monomer “Co{N(SiMe3)2}2” are consistent with those of the bright green-colored tetr...

Two new isostructural cobalt(II) and nickel(II) polynuclear complexes with 2-(phosphonomethyl)aminosuccinic acid, H4PMAS, namely, Na[Co12(PMAS)6(H2O)17(OH)]·x2H2O, 1·x2H2O, and Na[Ni12(PMAS)6(H2O)17(OH)]·xH2O, 2·xH2O, have been synthesized for the first time from aqueous solutions and studied by single crystal X-ray diffraction, infrared, and UV-visible diffuse reflectance spectroscopy; TG/DTA analysis; and magnetochemistry. Both 1 and 2 crystallize in the rhombohedral crystal system with the R3[overline] space group with 1/6 of the Co12(PMAS)6 or Ni12(PMAS)6 moieties in the asymmetric unit. The X-ray refinements reveal the presence of 18 water sites, but unit cell charge balance requires that one water molecule must be an OH(-) anion, an anion which is disordered over the 18 sites. The PMAS(4-) ligand forms two five-membered and one six-membered chelation ring. Both 1 and 2 contain 24-membered metallacycles as a result of the bridging nature of the PMAS(4-) ligands. The resulting three-dimensional structures have one-dimensional channels with a sodium cation at the center of symmetry. The temperature dependence of the magnetic susceptibility reveals the presence of weak antiferromagnetic exchange coupling interactions in both 1 and 2. Two exchange coupling constants, J1 = -15.3(7) cm(-1) and J2 = -1.06(2) cm(-1) with S1 = S2 = 3/2 for the Co(1)···Co(1) and Co(1)···Co(2) exchange pathways, respectively, are required for 1, and J1 = -1.17(6) cm(-1) and J2 = -4.00(8) cm(-1) with S1 = S2 = 1 for the Ni(1)···Ni(1) and Ni(1)···Ni(2) exchange pathways, respectively, are required for 2, in order to fit the temperature dependence of the observed magnetic susceptibilities.

Prussian blue pigments, highly insoluble mixed-valence iron(III) hexacyanoferrate(II) complexes of typical stoichiometry Fe-4(III)[Fe-II(CN)(6)](3)center dot xH(2)O or KFeIII[Fe-II(CN)(6)]center do ...

Single-molecule magnets that contain one spin centre may represent the smallest possible unit for spin-based computational devices. Such applications, however, require the realization of molecules with a substantial energy barrier for spin inversion, achieved through a large axial magnetic anisotropy. Recently, significant progress has been made in this regard by using lanthanide centres such as terbium(III) and dysprosium(III), whose anisotropy can lead to extremely high relaxation barriers. We contend that similar effects should be achievable with transition metals by maintaining a low coordination number to restrict the magnitude of the d-orbital ligand-field splitting energy (which tends to hinder the development of large anisotropies). Herein we report the first two-coordinate complex of iron(I), [Fe(C(SiMe3)3)2](-), for which alternating current magnetic susceptibility measurements reveal slow magnetic relaxation below 29 K in a zero applied direct-current field. This S = complex exhibits an effective spin-reversal barrier of Ueff = 226(4) cm(-1), the largest yet observed for a single-molecule magnet based on a transition metal, and displays magnetic blocking below 4.5 K.

Prussian blue, a hydrated iron(III) hexacyanoferrate(II) complex, is a synthetic pigment discovered in Berlin in 1704. Because of both its highly intense color and its low cost, Prussian blue was widely used as a pigment in paintings until the 1970s. The early preparative methods were rapidly recognized as a contributory factor in the fading of the pigment, a fading already known by the mid-eighteenth century. Herein two typical eighteenth-century empirical recipes have been reproduced and the resulting pigment analyzed to better understand the reasons for this fading. X-ray absorption and Mössbauer spectroscopy indicated that the early syntheses lead to Prussian blue together with variable amounts of an undesirable iron(III) product. Pair distribution functional analysis confirmed the presence of nanocrystalline ferrihydrite, Fe10O14(OH)2, and also identified the presence of alumina hydrate, Al10O14(OH)2, with a particle size of ∼15 Å. Paint layers prepared from these pigments subjected to accelerated light exposure showed a tendency to turn green, a tendency that was often reported in eighteenth- and nineteenth-century books. The presence of particles of hydrous iron(III) oxides was also observed in a genuine eighteenth-century Prussian blue sample obtained from a polychrome sculpture.

Reaction of K2COT (COT = 1,3,5,7-cyclooctatetraene, C8H8) with the aryl chromium(II) halide [AriPr4Cr(μ-Cl)]2 (AriPr4 = C6H3-2,6-(C6H3-2,6-iPr2)2) gave (CrAriPr4)2(μ2-η3:η4-COT) (1), in which a non...

The structure proposed for Li(11)Nd(18)Fe(4)O(39-δ) (Chen et al. Inorg. Chem. 2012, 51, 8073) on the basis of diffraction and Mössbauer spectral data is compared to that determined previously for Nd(18)Li(8)Fe(5)O(39) (Dutton et al. Inorg. Chem.200847, 11212) using the same techniques. The Mössbauer spectrum reported by Chen et al. has been reinterpreted. The newly refined spectral parameters differ significantly from the published values but are similar to those reported for Nd(18)Li(8)Fe(5)O(39). The relative areas of the three components indicate that iron cations occupy the 2a, 8e, and 16i sites in space group Pm3n, in disagreement with the model determined from neutron diffraction by Chen et al. in which only the 2a and 8e sites are so occupied. The relationship between Li(11)Nd(18)Fe(4)O(39-δ) and Nd(18)Li(8)Fe(5)O(39) is discussed, and it is proposed that the sample prepared by Dutton et al. is a kinetic product whereas the sample prepared by Chen et al. is the thermodynamically preferred product.

A polycrystalline sample of Pr{sub 18}Li{sub 8}Fe{sub 4}RuO{sub 39} has been synthesized by a solid state method and characterized by neutron powder diffraction, magnetometry and Moessbauer spectroscopy; samples of Pr{sub 18}Li{sub 8}Fe{sub 5-x}Mn{sub x}O{sub 39} and Pr{sub 18}Li{sub 8}Fe{sub 5-x}Co{sub x}O{sub 39} (x=1, 2) have been studied by magnetometry. All these compounds adopt a cubic structure (space group Pm3-barn, a{sub 0}{approx}11.97 A) based on intersecting chains made up of alternating octahedral and trigonal-prismatic coordination sites. These chains occupy channels within a Pr-O framework. The trigonal-prismatic site in Pr{sub 18}Li{sub 8}Fe{sub 4}RuO{sub 39} is occupied by Li{sup +} and high-spin Fe{sup 3+}. The remaining transition-metal cations occupy the two crystallographically-distinct octahedral sites in a disordered manner. All five compositions adopt a spin-glass-like state at 7 K (Pr{sub 18}Li{sub 8}Fe{sub 4}RuO{sub 39}) or below. - Graphical abstract: Pr{sub 18}Li{sub 8}Fe{sub 5-x}M{sub x}O{sub 39} (M=Ru, Mn, Co) have been studied by neutron diffraction, Moessbauer spectroscopy and magnetometry, allowing the distribution of the different cation species over the octahedral and trigonal-prismatic coordination sites within the structure to be determined. All the compositions studied undergo a transition to a spin-glass-like phase on cooling below {approx}5 K.

Powder neutron diffraction data have been used to refine the crystal structure of KBaFe2(PO4)3 at 4.2 K; space group P213, a0 = 9.8732(1) A. The material is isostructural with the mineral langbeinite, having two crystallographically distinct, octahedrally coordinated Fe3+ ions in the asymmetric unit. Mossbauer effect spectroscopy and magnetic susceptibility measurements show that KBaFe2(PO4)3 orders as an L-type ferrimagnet with 3.9 < TC < 4.2 K. The variation of Hint has been monitored by Mossbauer spectroscopy in the temperature range 1.3 < T < 4.2 K.

A powder neutron-diffraction study and subsequent line-profile analysis of the nuclear and magnetic structure at 4.2 K of monoclinic anhydrous iron(III) sulfate indicate that it is a two-sublattice antiferromagnet. Each sublattice is made up of crystallographically distinct iron atoms in the space group P21/n (b-unique). The nuclear structure at 4.2 K is essentially the same as that found at room temperature by single-crystal X-ray analysis. An analysis of covalency in the material indicates that the degree of covalency is consistent with that found for other iron(III) ions octahedrally coordinated by oxygen. A Mössbauer effect study indicates that above 28.8 K this compound is paramagnetic with parameters typical of an octahedral high-spin iron(III) compound. Below 28.7 K the Mössbauer spectrum reveals the presence of spontaneous magnetic ordering with nonequivalent internal hyperfine fields on the two sublattices. The difference between these fields reaches a maximum at 23 K and decreases until, at 4.2 K, the field on each sublattice is essentially the same at ca. 550 kOe. The two sublattices have essentially the same isomer shifts while the quadrupole shifts are similar in magnitude but opposite in sign. Applied-field Mössbauer effect studies further support an antiferromagnetic coupling model. Magnetic susceptibility studies confirm that the material is paramagnetic with an effective magnetic moment of ca. 5.92 μB between 298 and 40 K. Below this temperature the magnetic susceptibility increases sharply to a maximum at 23 K and then decreases rapidly. This behavior results because of the nonequivalent magnitude of the spontaneous magnetization on each sublattice between 28 and 4.2 K. A magnetic superexchange coupling model is proposed to explain the magnetic nonequivalence of the two sublattices over this temperature range. © 1979 American Chemical Society.

Compositions in the series Ni(2-x)Co(x)GeMo(3)N (0 < or = x < or = 2), Co(2)Ge(1-x)Ga(x)Mo(3)N (0 < x < or = 0.7), Co(2-x)Fe(x)GeMo(3)N (0 < or = x < or = 2), and Co(2-x)Fe(x)Ge(0.5)Ga(0.5)Mo(3)N (0 < or = x < or = 0.8) have been synthesized by the reductive nitridation of binary oxides and studied by appropriate combinations of magnetometry, transport measurements, neutron diffraction, and Mossbauer spectroscopy. All of these compositions adopt the cubic eta-carbide structure (a approximately 11.11 A) and show a resistivity of approximately 10(-3) Omega cm. No long-range magnetic order was observed in Ni(2-x)Co(x)GeMo(3)N, although evidence of spin freezing was observed in Co(2)GeMo(3)N. The introduction of gallium into this composition leads to the onset of antiferromagnetic ordering at 90 K in Co(2)Ge(0.3)Ga(0.7)Mo(3)N. The magnetic structure consists of an antiferromagnetic arrangement of ferromagnetic Co(4) groups, with an ordered magnetic moment of 0.48(9) micro(B) per cobalt atom. The same magnetic structure is found in Co(0.5)Fe(1.5)GeMo(3)N and Co(1.2)Fe(0.8)Ge(0.5)Ga(0.5)Mo(3)N. The former orders above room temperature with an average moment of 1.08(3) mu(B) per transition-metal site, and the latter at 228 K with an average moment of 1.17(4) micro(B) per site. The magnetic behavior of these compounds is discussed in terms of the electron count within each series.

Magnetic susceptibility, Mossbauer spectroscopy and powder neutron diffraction experiments have shown that iron(III) phosphate, FePO4, undergoes a novel spin reorientation transition at 17K between two antiferromagnetic phases. The ordered magnetic moments lie in the basal plane of the trigonal unit cell between the Neel temperature (24K) and 17K, below which temperature the spins align along the unique (c) axis.

Nd 18Li 8Fe 4TiO 39 has been synthesised and characterised by neutron powder diffraction, X-ray absorption spectroscopy, Mössbauer spectroscopy and magnetometry. The cubic structure (Pm3n, a=11.97227(8) Å) is based on intersecting 〈1 1 1〉 chains comprised of alternating octahedral and trigonal-prismatic coordination sites. These chains lie within hexagonal-prismatic cavities formed by a NdO framework. The larger of the two crystallographically distinct octahedral sites, 8e, is occupied by iron, titanium and lithium in a ratio of 76:20:4; the smaller, 2a, is occupied by iron and titanium in a ratio of 79:21. The trigonal-prismatic site, 16i, is occupied by lithium and iron in a ratio of 98:2. The cations on the 2a sites are assigned as Ti 4and low-spin Fe 4, and those on the 16i sites as Li and Fe 3. The 8e sites are thought to be occupied by Li, Fe 3 and Ti 3. Nd 18Li 8Fe 4TiO 39 undergoes a transition to a spin-glass state at 4.25(5) K. © 2012 Elsevier Inc. © 2012 Elsevier Inc. All rights reserved.

Nd{sub 18}Li{sub 8}Co{sub 3}FeO{sub 39-y}, Nd{sub 18}Li{sub 8}CoFe{sub 3}O{sub 39-y} and Nd{sub 18}Li{sub 8}Co{sub 3}TiO{sub 39-y} have been synthesised and characterised by neutron powder diffraction, magnetometry and Moessbauer spectroscopy. Their cubic structure (Pm3-bar n, a{approx}11.9 A) is based on intersecting chains comprised of alternating octahedral and trigonal-prismatic coordination sites. These chains lie within hexagonal-prismatic cavities formed by a Nd-O framework. Each compound has an incomplete oxide sublattice (y{approx}1), with vacancies located around the octahedral sites that lie at the points of chain intersection. These sites are fully occupied by a disordered arrangement of transition-metal cations but only 75% of the remaining octahedral sites are occupied. The trigonal-prismatic sites are fully occupied by lithium except in the case of Nd{sub 18}Li{sub 8}CoFe{sub 3}O{sub 39-y} where some iron is present. Antiferromagnetic interactions are present on the Nd sublattice in each composition, but a spin glass forms below 5 K when a high concentration of spins is also present on the octahedral sites. - Graphical Abstract: Cation and anion vacancies are found to coexist in mixed-metal oxides that adopt the La{sub 18}Li{sub 8}Rh{sub 5}O{sub 39} structure. Highlights: > Coexistence of anion and cation vacancies in compounds adopting the La{sub 18}Li{submore » 8}Rh{sub 5}O{sub 39} structure. > Variation of the degree of magnetic frustration with the chemical composition in the La{sub 18}Li{sub 8}Rh{sub 5}O{sub 39} structure. > Controlling influence of the magnetic properties of the lanthanide cation becomes clear.« less

The air-free reaction between FeCl(2) and H(4)dobdc (dobdc(4-) = 2,5-dioxido-1,4-benzenedicarboxylate) in a mixture of N,N-dimethylformamide (DMF) and methanol affords Fe(2)(dobdc)·4DMF, a metal-organic framework adopting the MOF-74 (or CPO-27) structure type. The desolvated form of this material displays a Brunauer-Emmett-Teller (BET) surface area of 1360 m(2)/g and features a hexagonal array of one-dimensional channels lined with coordinatively unsaturated Fe(II) centers. Gas adsorption isotherms at 298 K indicate that Fe(2)(dobdc) binds O(2) preferentially over N(2), with an irreversible capacity of 9.3 wt %, corresponding to the adsorption of one O(2) molecule per two iron centers. Remarkably, at 211 K, O(2) uptake is fully reversible and the capacity increases to 18.2 wt %, corresponding to the adsorption of one O(2) molecule per iron center. Mössbauer and infrared spectra are consistent with partial charge transfer from iron(II) to O(2) at low temperature and complete charge transfer to form iron(III) and O(2)(2-) at room temperature. The results of Rietveld analyses of powder neutron diffraction data (4 K) confirm this interpretation, revealing O(2) bound to iron in a symmetric side-on mode with d(O-O) = 1.25(1) Å at low temperature and in a slipped side-on mode with d(O-O) = 1.6(1) Å when oxidized at room temperature. Application of ideal adsorbed solution theory in simulating breakthrough curves shows Fe(2)(dobdc) to be a promising material for the separation of O(2) from air at temperatures well above those currently employed in industrial settings.

We present a new structurally determined seven-coordinate iron platform supported by the tris(2-picolyl)amine ligand 6,6′-(pyridin-2-ylmethylazanediyl)bis(methylene)bis(N-tert-butylpicolinamide) (TPA2C(O)NHtBu, 3) and its reactivity with oxo and nitrene transfer agents. Oxidation of the pentagonal bipyramidal, seven-coordinate iron(II)–triflate complex [TPA2C(O)NHtBuFeII(OTf)][OTf] (4) with PhIO produces the corresponding diiron(III) μ-oxo complex [(TPA2C(O)NHtBuFeIII)2(O)][OTf]4 (5). Mossbauer and magnetic measurements on 5 in the solid-state establish antiferromagnetic coupling between its two Fe(III) centers. Reactions of 4 with the nitrene transfer agents PhINTs (Ts = p-MeC6H4SO2) and PhINNs (Ns = p-NO2C6H4SO2) provide the corresponding iron(III)-amide congeners [TPA2C(O)NHtBuFeIII(NHTs)][OTf]2 (6) and [TPA2C(O)NHtBuFeIII(NHNs)][OTf]2 (7), respectively, affording a rare pair of isolable Fe(III)-amide compounds formed from nitrene transfer. By characterizing well-defined products in the crystalline form, derived from atom and group transfer to seven-coordinate iron, the collective data provide a starting point for the exploration of high-valent and metal–ligand multiply bonded species supported by approximate pentagonal-type ligand fields.