Implementing Mesoporosity in Zeolitic Imidazolate Frameworks through Clip-Off Chemistry in Heterometallic Iron-Zinc ZIF-8

Bond breaking has emerged as a new tool to postsynthetically modify the pore structure in metal-organic frameworks since it allows us to obtain pore environments in structures that are inaccessible by other techniques. Here, we extend the concept of clip-off chemistry to archetypical ZIF-8, taking advantage of the different stabilities of the bonds between imidazolate and Zn and Fe metal atoms in heterometallic Fe-Zn-ZIF-8. We demonstrate that Fe centers can be removed selectively without affecting the backbone of the structure that is supported by the Zn atoms. This allows us to create mesopores within the highly stable ZIF-8 structure. The strategy presented, combined with control of the amount of iron centers incorporated into the structure, permits porosity engineering of ZIF materials and opens a new avenue for designing novel hierarchical porous frameworks.

The influence of strontium deficiency on thermodynamics of defect formation, structural stability and electrical transport of SrFe0.5Ta0.5O3-δ-based solid solutions with an excess tantalum content

The crystalline and electronic band structures, thermodynamic stability, oxygen non-stoichiometry and high-temperature transport properties of perovskite-like solid solutions with a general formula Sr1-yFe0.5-xTa0.5+xO3-δ, where x, y ≥ 0, are thoroughly studied using a combination of experimental and theoretical methods. It is argued that the basic compound SrFe0.5Ta0.5O3-δ possesses an orthorhombic lattice symmetry, while its tantalum-doped derivatives belong to a tetragonal space group. Importantly, the purposeful addition of a certain deficiency in a strontium sublattice is shown to be a valid method for stabilizing the Sr1-yFe0.5-xTa0.5+xO3-δ oxides with an excess tantalum content. Detailed studies of charge states in an iron sublattice suggest the predominance of Fe3+ ions even in tantalum-enriched materials. Also, the band structure calculations support the semiconducting nature of electrical transport with localized n-type conductivity provided by small polarons represented by Fe2+ ions. The overall defect structure of Sr1-yFe0.5-xTa0.5+xO3-δ compounds is proved to heavily rely on oxygen vacancy (VO) formation processes; in turn, the presence of strontium vacancies is shown to be an important factor that can decrease the respective energy penalties to introduce VO defects in the lattice. As a result, the experimentally measured oxygen non-stoichiometry for Sr0.95Fe0.45Ta0.55O3-δ at elevated temperatures appears to be sufficiently enlarged as compared to pristine SrFe0.5Ta0.5O3-δ. Similar to that, the conductive properties of tantalum-enriched phase Sr0.95Fe0.45Ta0.55O3-δ are shown to be improved. On the basis of the obtained results, it is argued that cation non-stoichiometry is a valuable tool for enhancing thermodynamic and transport characteristics of perovskite-like compounds, which are currently viewed as promising materials for high-temperature applications.

Investigation of Charge-Ordered Barium Iron Fluorides with One-Dimensional Structural Diversity and Complex Magnetic Interactions

Three mixed-valence barium iron fluorides, Ba7Fe7F34, Ba2Fe2F9, and BaFe2F7, were prepared through hydrothermal redox reactions. The characteristic structures of these compounds feature diverse distributions of FeIIF6 octahedra and FeIIIF6 groups. Ba7Fe7F34 contained one-dimensional infinite ∞[FeIIFeIII6F34]14- double chains, comprising cis corner-sharing octahedra along the b direction; Ba2Fe2F9 contained one-dimensional ∞[Fe2F9]4- double chains, consisting of cis corner-sharing octahedra along the chain (a-axis direction) and trans corner-sharing octahedra vertical to the chain, while BaFe2F7 revealed three-dimensional (3D) frameworks that consist of isolated edge-sharing dinuclear FeII2F10 units linked via corners by FeIIIF6 octahedra. Magnetization and Mössbauer spectroscopy measurements revealed that Ba7Fe7F34 exhibits an antiferromagnetic phase transition at ∼11 K, where ferrimagnetic ∞[FeIIFeIII6F34]14- double chains are arranged in a paralleling manner, while Ba2Fe2F9 shows canted antiferromagnetic ordering at ∼32.5 K, leading to noncollinear spin ordering.

Ultramicroporous iron-isonicotinate MOFs combining size-exclusion kinetics and thermodynamics for efficient CO2/N2 gas separation

Two ultramicroporous 2D and 3D iron-based Metal-Organic Frameworks (MOFs) have been obtained by solvothermal synthesis using different ratios and concentrations of precursors. Their reduced pore space decorated with pendant pyridine from tangling isonicotinic ligands enables the combination of size-exclusion kinetic gas separation, due to their small pores, with thermodynamic separation, resulting from the interaction of the linker with CO₂ molecules. This combined separation results in efficient materials for dynamic breakthrough gas separation with virtually infinite CO₂/N₂ selectivity in a wide operando range and with complete renewability at room temperature and ambient pressure.

Controlled modulation of the dynamics of the Deinococcus grandis Dps N-terminal tails by divalent metals

DNA-binding proteins from starved cells (Dps) are small multifunctional nanocages expressed by prokaryotes in acute oxidative stress conditions or during the starvation-induced stationary phase, as a bacterial defense mechanism. Dps proteins protect bacterial DNA from damage by either direct binding or by removing precursors of reactive oxygen species from solution. The DNA-binding properties of most Dps proteins studied so far are related to their unordered, flexible, N- and C-terminal extensions. In a previous work, we revealed that the N-terminal tails of Deinoccocus grandis Dps shift from an extended to a compact conformation depending on the ionic strength of the buffer and detected a novel high-spin ferrous iron center in the proximal ends of those tails. In this work, we further explore the conformational dynamics of the protein by probing the effect of divalent metals binding to the tail by comparing the metal-binding properties of the wild-type protein with a binding site-impaired D34A variant using size exclusion chromatography, dynamic light scattering, synchrotron radiation circular dichroism, and small-angle X-ray scattering. The N-terminal ferrous species was also characterized by Mössbauer spectroscopy. The results herein presented reveal that the conformation of the N-terminal tails is altered upon metal binding in a gradual, reversible, and specific manner. These observations may point towards the existence of a regulatory process for the DNA-binding properties of Dps proteins through metal binding to their N- and/or C-terminal extensions.

Two-dimensional magnetic behaviour in hybrid NiFe-layered double hydroxides by molecular engineering

Layered double hydroxides (LDHs) are a class of two-dimensional (2D) anionic materials that exhibit remarkable chemical versatility, making them ideal building blocks in the design of complex multifunctional materials. In this line, a NiFe-LDH is probably one of the most important LDHs due to its interesting electrochemical and magnetic properties. However, no direct magnetic measurements of exfoliated NiFe-LDH nanosheets have been reported so far. Herein, we synthesize a hybrid NiFe-LDH family through anion exchange reactions using surfactant molecules in order to increase the interlayer space (ranging from 8 to 31.6 Å), minimizing the interlayer dipolar interactions. By intercalation with octadecylsulphate, we have managed to obtain the largest interlayer space reported for a NiFe-LDH while keeping a similar size, morphology and composition. This wide interlayer separation results in a decrease in temperatures at which spontaneous magnetization (T_M) occurs and the blocking temperature (T_B), as well as a decrease in the coercive fields (H_C). In fact, an abrupt drop in all these magnetic parameters above 30 Å interlayer distance is observed, evidencing complete magnetic decoupling of the layers. We have further validated our molecular engineering approach by characterizing the hybrid materials by Mössbauer spectroscopy and comparing the magnetic analysis results with those for a liquid phase exfoliated NiFe-LDH sample. Overall, this work provides fundamental insights into the magnetism of NiFe-LDHs, showing the potential of molecular engineering for designing hybrid layered magnetic materials approaching the 2D magnetic limit.

Exploiting the Redox Activity of MIL-100(Fe) Carrier Enables Prolonged Carvacrol Antimicrobial Activity

The design of efficient food contact materials that maintain optimal levels of food safety is of paramount relevance to reduce the increasing number of foodborne illnesses. In this work, we develop a smart composite metal-organic framework (MOF)-based material that fosters a unique prolonged antibacterial activity. The composite is obtained by entrapping a natural food preserving molecule, carvacrol, into a mesoporous MIL-100(Fe) material following a direct and biocompatible impregnation method, and obtaining particularly high payloads. By exploiting the intrinsic redox nature of the MIL-100(Fe) material, it is possible to achieve a prolonged activity against Escherichia coli and Listeria innocua due to a triggered two-step carvacrol release from films containing the carvacrol@MOF composite. Essentially, it was discovered that based on the underlying chemical interaction between MIL-100(Fe) and carvacrol, it is possible to undergo a reversible charge-transfer process between the metallic MOF counterpart and carvacrol upon certain chemical stimuli. During this process, the preferred carvacrol binding site was monitored by infrared, Mössbauer, and electron paramagnetic resonance spectroscopies, and the results are supported by theoretical calculations.

Cyclam-based iron(iii) and copper(ii) complexes: synthesis, characterization and application as antifungal agents

Cyclam-based complexes of formulae [{H2(4-CF3PhCH2)2Cyclam}FeCl2]Cl and [{H2(4-CF3PhCH2)2Cyclam}Cu](CH3COO)2·2H2O reveal antifungal activity against diverse unicellular and multicellular fungal species.

Temperature dependence of desolvation effects in hydrogen-bonded spin crossover complexes

The synthesis, crystal structure and (photo)magnetic properties of the anhydrous spin crossover salt of formula [Fe(bpp)₂](C₆H₈O₄) (1) (bpp = 2,6-bis(pyrazol-3-yl)pyridine; C₆H₈O₄ = adipate dianion), obtained by desolvation at 400 K of the original tetrahydrate in a single-crystal-to-single-crystal (SC-SC) transformation, are reported. This work offers a comparison between this compound and the previously reported hydrated material ([Fe(bpp)₂](C₆H₈O₄)·4H₂O, 1·4H₂O), highlighting the significance of the thermal conditions used in the dehydration-rehydration processes. In both compounds, a hydrogen-bonded network between iron(ii) complexes and adipate anions is observed. The original tetrahydrate (1·4H₂O) is low-spin and desolvation at 450 K triggers a low-spin (LS) to high-spin (HS) transition to an amorphous phase that remains stable over the whole temperature range of study. Surprisingly, the dehydrated compound at 400 K (1) keeps the crystallinity, undergoes a partial spin crossover (T_1/2 = 180 K) and a quantitative LS to HS photomagnetic conversion at low temperatures, with a T(LIESST) value of 61 K.

Fundamental Insights into the Covalent Silane Functionalization of NiFe Layered Double Hydroxides

Layered double hydroxides (LDHs) are a class of 2D anionic materials exhibiting wide chemical versatility and promising applications in different fields, ranging from catalysis to energy storage and conversion. However, the covalent chemistry of this kind of 2D materials is still barely explored. Herein, the covalent functionalization with silanes of a magnetic NiFe-LDH is reported. The synthetic route consists of a topochemical approach followed by anion exchange reaction with surfactant molecules prior to covalent functionalization with the (3-aminopropyl)triethoxysilane (APTES) molecules. The functionalized NiFe-APTES was fully characterized by X-ray diffraction, infrared spectroscopy, electron microscopy, thermogravimetric analysis coupled with mass spectrometry and ²⁹ Si solid-state nuclear magnetic resonance, among others. The effect on the electronic properties of the functionalized LDH was investigated by a magnetic study in combination with Mössbauer spectroscopy. Moreover, the reversibility of the silane-functionalization at basic pH was demonstrated, and the quality of the resulting LDH was proven by studying the electrochemical performance in the oxygen evolution reaction in basic media. Furthermore, the anion exchange capability for the NiFe-APTES was tested employing Cr^VI , resulting in an increase of 200 % of the anion retention. This report allows for a new degree of tunability of LDHs, opening the door to the synthesis of new hybrid architectures and materials.

Role of Structure and Composition on the Performances of P-Type Tin Oxide Thin-Film Transistors Processed at Low-Temperatures

This work reports on the role of structure and composition on the determination of the performances of p-type SnO_x TFTs with a bottom gate configuration deposited by rf magnetron sputtering at room temperature, followed by a post-annealed step up to 200 °C at different oxygen partial pressures (O_pp) between 0% and 20% but where the p-type conduction was only observed between in a narrow window, from 2.8% to 3.8%. The role of structure and composition were evaluated by XRD and Mössbauer spectroscopic studies that allows to identify the best phases/compositions and thicknesses (around 12 nm) to be used to produce p-type TFTs with saturation mobility of 4.6 cm² V⁻¹ s⁻¹ and on-off ratio above 7 × 10⁴, operating at the enhancement mode with a saturation voltage of −10 V. Moreover, a brief overview is also presented concerning the present state of the existing developments in processing SnO_x TFTs with different methods and using different device configurations.

Hydroboration of terminal olefins with pinacolborane catalyzed by new 2-iminopyrrolyl iron(ii) complexes

New Fe(ii) mono(2-iminopyrrolyl) complexes catalyze the hydroboration of terminal olefins with pinacolborane via a borane oxidative addition pathway.

Iron(ii) complexes of tris(2-pyridylmethyl)amine (TPMA) and neutral bidentate ligands showing thermal- and photo-induced spin crossover

Three new mononuclear Fe(ii) complexes have been prepared and characterized by the combination of tetradentate tris(2-pyridylmethyl)amine (TPMA) with three neutral bidentate ligands, such as ethylenediamine (en), 1,2-diaminopropane (pn) and 2-picolylamine (2-pic), in compounds [FeII(TPMA)(en)](ClO4)2 (1), [FeII(TPMA)(2-pic)](ClO4)2 (2) and [FeII(TPMA)(pn)](ClO4)2 (3). Structural and magnetic characterization demonstrates that the three compounds present a complete SCO behavior. The absence of strong intermolecular interactions and solvent molecules leads to reversible and gradual spin transitions. The different ligands allow tuning T1/2 from 130 K (2) to 325 K (3). The compound with the lowest T1/2 (2) shows the LIESST effect with a TLIESST of 43 K. Interestingly, the use of these relatively small bidentate ligands leads to the crystallization in non-centrosymmetric space groups in contrast with previous studies using other bidentate ligands.

A highly stable and hierarchical tetrathiafulvalene-based metal-organic framework with improved performance as a solid catalyst

A highly stable Metal–Organic Framework with a hierarchical structure based on the Fe₃O cluster and a TTF-based ligand is presented.

Herein we report the synthesis of a tetrathiafulvalene (TTF)-based MOF, namely MUV-2, which shows a non-interpenetrated hierarchical crystal structure with mesoporous one-dimensional channels of ca. 3 nm and orthogonal microporous channels of ca. 1 nm. This highly stable MOF (aqueous solution with pH values ranging from 2 to 11 and different organic solvents), which possesses the well-known [Fe₃(μ₃-O)(COO)₆] secondary building unit, has proven to be an efficient catalyst for the aerobic oxidation of dibenzothiophenes.

Magnetic and structural correlations in [Fe(nsal2trien)] salts: the role of cation–anion interactions in the spin crossover phenomenon

Cation–anion and cation–solvent–anion interactions determine the SCO behaviour of six [Fe^III(nsal₂trien)] salts.

Synthesis, structure and physical properties of a low dimensional compound

The crystal structure of (μ₃-oxo)hexakis(cyanoacetato-κO,O')(cyanoacetato-κO)diaquatriiron(III) cyanoacetic acid shows the formation of trinuclear complexes in a hydrogen-bond network that bonds all the molecules in a 3D arrangement. For this complex, within whose clusters the whole magnetic interaction takes place, ⁵⁷Fe Mössbauer spectroscopy shows that the Fe cations are in the S=5/2 state in the temperature range 2-295K. The asymmetric broadening of the absorption peaks below 80K is consistent with strong antiferromagnetic interactions between the metal spins. The magnetization measurements also show the antiferromagnetic character of the spin ensemble and an S_T=1/2 magnetic ground state typical of triangular systems with similar J between Fe-Fe pairs.

Light-induced decarboxylation in a photo-responsive iron-containing complex based on polyoxometalate and oxalato ligands

A new iron-oxalato polyoxometalate exhibits a remarkable photocoloration effect in the solid state based entirely on an intramolecular process.

A new photoresponsive molecular polyanion in which two Fe(iii) ions are simultaneously coordinated by two [A-α-PW₉O₃₄]^9– polyoxometalate units and two oxalato ligands has been obtained. When irradiated with UV light its potassium salt, 1, exhibits a remarkable photocoloration effect, attributable to the partial reduction of the POM units to give rise to a mixed-valence species. The photoinduced process is intramolecular and involves electron transfer from the oxalato ligands, which partially decompose releasing CO₂, towards the Fe(iii) and the POM. This mechanism has been confirmed by DRS, IR, XPS and Mössbauer spectroscopy, magnetism and elemental analysis. An analogous derivative of 1 containing malonato ligands does not exhibit such photoactive behaviour, which is evidence that the oxalate ligand is essential for the photoactivity of 1. To our knowledge, 1 represents the first POM-based compound in which the photocoloration effect does not require the presence of intermolecular short interactions.

Magnetic properties of binary and ternary mixed metal oxides NiFe2O4 and Zn0.5Ni0.5Fe2O4 doped with rare earths by sol—gel synthesis

The spinel-type ferrites NiFe

Spin-crossover complex encapsulation within a magnetic metal–organic framework

We report the solid-state incorporation of a mononuclear iron(iii) spin-crossover (SCO) complex within the pores of a magnetic metal–organic framework (MOF).

Synthesis and structural/physical properties of U3Fe2Ge7: a single-crystal study

A single crystal of U3Fe2Ge7 was synthesized by the tin-flux method, and its structural and electronic properties were studied. The compound crystallizes in the orthorhombic crystal structure of La3Co2Sn7 type with two Wyckoff sites for the U atoms. U3Fe2Ge7 displays a ferromagnetic order below TC = 62 K. Magnetization measurements in static (up to 14 T) and pulsed (up to 60 T) magnetic fields revealed a strong two-ion uniaxial magnetic anisotropy. The easy magnetization direction is along the c axis and the spontaneous magnetic moment is 3.3 μB per formula unit at 2 K. The moment per Fe atom is 0.2 μB, as follows from Mössbauer spectroscopy. The magnetic moments are oriented perpendicular to the shortest inter-uranium distances that occur within the zigzag chains in the ab plane, contrary to other U-based isostructural compounds. The magnetization along the a axis reveals a first-order magnetization process that allows for a quantitative description of the magnetic anisotropy in spite of its enormous energetic strength. The strong anisotropy is reflected in the specific heat and electrical resistivity that are affected by a gap in magnon spectrum.

Unusual 5f magnetism in the U2Fe3Ge ternary Laves phase: a single crystal study

Magnetic properties of the intermetallic compound U(2)Fe(3)Ge were studied on a single crystal. The compound crystallizes in the hexagonal Mg(2)Cu(3)Si structure, an ordered variant of the MgZn(2) Laves structure (C14). U(2)Fe(3)Ge displays ferromagnetic order below the Curie temperature T(C) = 55 K and presents an exception to the Hill rule, as the nearest inter-uranium distances do not exceed 3.2 Å. Magnetic moments lie in the basal plane of the hexagonal lattice, with the spontaneous magnetic moment M(s) = 1.0 μ(B)/f.u. at T = 2 K. No anisotropy within the basal plane is detected. In contrast to typical U-based intermetallics, U(2)Fe(3)Ge exhibits very low magnetic anisotropy, whose field does not exceed 10 T. The dominance of U in the magnetism of U(2)Fe(3)Ge is suggested by the (57)Fe Mössbauer spectroscopy study, which indicates very low or even zero Fe moments. Electronic structure calculations are in agreement with the observed easy-plane anisotropy but fail to explain the lack of an Fe contribution to the magnetism of U(2)Fe(3)Ge.

Trapping of anionic organic radicals by (TpMe2)2Ln (Ln = Sm, Eu)

Stoichiometric reaction of [ Sm(Tp(Me2))2 ], 1, with a variety of reducible ketone- and quinone-type substrates gave thermally stable, isolable radical anions/ketyls in moderate to good yields. Thus reaction with benzophenone gave [Sm(Tp(Me2))2(OCPh2)], 2, with fluorenone [Sm(Tp(Me2))2(eta1-OC13H8)], 3, and di-tert-butylparaquinone [Sm(Tp(Me2))2(eta1-OC6H2(tBu)2O)], 4, each of which was structurally characterized. In the case of the less-hindered benzoquinone, an unimetallic semiquinone [Sm(Tp(Me2))2(OC6H4O)], 5, could be isolated, although it was unstable with respect to formation of the dimetallic complex [Sm(Tp(Me2))2]2(mu-OC6H4O), 6. Compound 6 was structurally characterized, as was its anthraquinone analogue [Sm(Tp(Me2))2]2(mu-OC14H8O), 7. When the analogous reaction was carried out between the less-reducing [Eu(Tp(Me2))2] and benzoquinone, only the europium analogue of the semiquinone 5, [Eu(Tp(Me2))2(OC6H4O)], 8, could be isolated. The use of the sterically hindered 3,5-di-tert-butyl-o-benzoquinone allowed isolation of [Sm(Tp(Me2))2(DTBSQ)], 9.