Iron(II) Formate [Fe(O2CH)2]·1/3HCO2H: A Mesoporous Magnet − Solvothermal Syntheses and Crystal Structures of the Isomorphous Framework Metal(II) Formates [M(O2CH)2]·n(Solvent) (M = Fe, Co, Ni, Zn, Mg)

On the Demise of PPP-Ligated Iron Catalysts in the Formic Acid Dehydrogenation Reaction

The PPP-ligated iron complexes, cis-(iPrPPRP)FeH2(CO) [iPrPPRP = (o-iPr2PC6H4)2PR (R = H or Me)], catalyze the dehydrogenation of formic acid to carbon dioxide but lose their catalytic activity over time. This study focuses on the analysis of the species formed from the degradation of cis-(iPrPPMeP)FeH2(CO) over its course of catalyzing the dehydrogenation reaction. These degradation products include species both soluble and insoluble in the reaction medium. The soluble component of the decomposed catalyst is a mixture of cis-[(iPrPPMeP)FeH(CO)2][(HCO2)(HCO2H)x], protonated iPrPPMeP, and oxidation products resulting from adventitious O2. The precipitate is solvated Fe(OCHO)2. Further mechanistic investigation suggests that cis-[(iPrPPMeP)FeH(CO)2][(HCO2)(HCO2H)x] displays diminished but measurable catalytic activity, likely through the displacement of a CO ligand by the formate ion. The formation of Fe(OCHO)2 along with the dissociation of iPrPPMeP is responsible for the eventual loss of catalytic activity.

Overcoming challenges in 67Zn NMR: a new strategy of signal enhancement for MOF characterization

67 Zn solid-state NMR suffers from low sensitivity, limiting its ability to probe the Zn2+ surroundings in MOFs. We report a breakthrough in overcoming challenges in 67Zn NMR. Combining new cryogenic MAS probe technology and performing NMR experiments at a high magnetic field results in remarkable signal enhancement, yielding enhanced information for MOF characterization.

Emission of Toxic HCN During NOx Removal by Ammonia SCR in the Exhaust of Lean-Burn Natural Gas Engines

Reducing greenhouse gas and pollutant emissions is one of the most stringent priorities of our society to minimize their dramatic effects on health and environment. Natural gas (NG) engines, in particular at lean conditions, emit less CO2 in comparison to combustion engines operated with liquid fuels but NG engines still require emission control devices for NOx removal. Using state-of-the-art technologies for selective catalytic reduction (SCR) of NOx with NH3 , we evaluated the interplay of the reducing agent NH3 and formaldehyde, which is always present in the exhaust of NG engines. Our results show that a significant amount of highly toxic hydrogen cyanide (HCN) is formed. All catalysts tested partially convert formaldehyde to HCOOH and CO. Additionally, they form secondary emissions of HCN due to catalytic reactions of formaldehyde and its oxidation intermediates with NH3 . With the present components of the exhaust gas aftertreatment system the HCN emissions are not efficiently converted to non-polluting gases. The development of more advanced catalyst formulations with improved oxidation activity is mandatory to solve this novel critical issue.

Metal-Organic Framework Magnets

Metal-organic frameworks represent the ultimate chemical platform on which to develop a new generation of designer magnets. In contrast to the inorganic solids that have dominated permanent magnet technology for decades, metal-organic frameworks offer numerous advantages, most notably the nearly infinite chemical space through which to synthesize predesigned and tunable structures with controllable properties. Moreover, the presence of a rigid, crystalline structure based on organic linkers enables the potential for permanent porosity and postsynthetic chemical modification of the inorganic and organic components. Despite these attributes, the realization of metal-organic magnets with high ordering temperatures represents a formidable challenge, owing largely to the typically weak magnetic exchange coupling mediated through organic linkers. Nevertheless, recent years have seen a number of exciting advances involving frameworks based on a wide range of metal ions and organic linkers. This review provides a survey of structurally characterized metal-organic frameworks that have been shown to exhibit magnetic order. Section 1 outlines the need for new magnets and the potential role of metal-organic frameworks toward that end, and it briefly introduces the classes of magnets and the experimental methods used to characterize them. Section 2 describes early milestones and key advances in metal-organic magnet research that laid the foundation for structurally characterized metal-organic framework magnets. Sections 3 and 4 then outline the literature of metal-organic framework magnets based on diamagnetic and radical organic linkers, respectively. Finally, Section 5 concludes with some potential strategies for increasing the ordering temperatures of metal-organic framework magnets while maintaining structural integrity and additional function.

Exploring Host-Guest Interactions in the α-Zn3(HCOO)6 Metal-Organic Framework

Metal-organic frameworks (MOFs) are promising gas adsorbents. Knowledge of the behavior of gas molecules adsorbed inside MOFs is crucial for advancing MOFs as gas capture materials. However, their behavior is not always well understood. In this work, carbon dioxide (CO₂) adsorption in the microporous α-Zn₃(HCOO)₆ MOF was investigated. The behavior of the CO₂ molecules inside the MOF was comprehensively studied by a combination of single-crystal X-ray diffraction (SCXRD) and multinuclear solid-state magnetic resonance spectroscopy. The locations of CO₂ molecules adsorbed inside the channels of the framework were accurately determined using SCXRD, and the framework hydrogens from the formate linkers were found to act as adsorption sites. ⁶⁷Zn solid-state NMR (SSNMR) results suggest that CO₂ adsorption does not significantly affect the metal center environment. Variable-temperature ¹³C SSNMR experiments were performed to quantitatively examine guest dynamics. The results indicate that CO₂ molecules adsorbed inside the MOF channel undergo two types of anisotropic motions: a localized rotation (or wobbling) upon the adsorption site and a twofold hopping between adjacent sites located along the MOF channel. Interestingly, ¹³C SSNMR spectroscopy targeting adsorbed CO₂ reveals negative thermal expansion (NTE) of the framework as the temperature rose past ca. 293 K. A comparative study shows that carbon monoxide (CO) adsorption does not induce framework shrinkage at high temperatures, suggesting that the NTE effect is guest-specific.

Redetermination of nickel(II) formate dihydrate

In comparison with the previous structure determination of poly[diaquadi-μ-formato-nickel(II)], [Ni(HCOO)2(H2O)2]n, based on Weissenberg film data [Krogmann & Mattes (1963).Z. Kristallogr.118, 291–302], the current redetermination from modern CCD data revealed the positions of the H atoms, thus making a detailed description of the hydrogen-bonding pattern possible. Both Ni2+cations in the crystal structure are located on inversion centres and are octahedrally coordinated. One Ni2+cation is bound to six O atoms of six formate anions whereas the other Ni2+cation is bound to four O atoms of water molecules and to two formate O atoms. In this way, the formate anions bridge the two types of Ni2+cations into a three-dimensional framework. O—H...O hydrogen bonds of medium strength between water molecules and formate O atoms consolidate the packing.

Magnetic functionalities in MOFs: from the framework to the pore

In this review, we show the different approaches developed so far to prepare metal-organic frameworks (MOFs) presenting electronic functionalities, with particular attention to magnetic properties. We will cover the chemical design of frameworks necessary for the incorporation of different magnetic phenomena, as well as the encapsulation of functional species in their pores leading to hybrid multifunctional MOFs combining an extended lattice with a molecular lattice.

“Explosive” synthesis of metal-formate frameworks for methane capture: an experimental and computational study

We present an ultrafast “explosive” synthesis of nickel-formate frameworks, which show prominent performance for methane capture from nitrogen, proved using experiments and simulations.

A magnetisation and Mössbauer study of triazole (M1−x2+Mx3+)M3+F5(Htaz)1−x(taz)x weberites (M = Fe, Co, Mn, Zn, Ga, V)

Several (M_1−x²⁺M_x³⁺)M³⁺F₅(Htaz)_1−x(taz)_x weberites, magnetically frustrated, exhibit negative magnetisations. ⁵⁷Fe Mössbauer spectrometry evidences a significant decrease of T_N for vacuum-treated samples.

Oriented Nano-Microstructure-Assisted Controllable Fabrication of Metal-Organic Framework Membranes on Nickel Foam

Oriented nano-microstructure-assisted controllable fabrication, a facile and versatile preparation strategy, is developed to fabricate metal-organic framework (MOF) membranes. With this method, several MOF membranes with tailored structures are prepared, including HKUST-1 (with 3D pores) and M3 (HCOO)6 (with 1D pores; M = Co, Mn, and Mg) membranes, which demonstrate good performances in gas separations.

NH4FeCl2(HCOO): synthesis, structure, and magnetism of a novel low-dimensional magnetic material

Solvothermal synthesis was used to create a low-dimensional iron(II) chloride formate compound, NH4FeCl2(HCOO), that exhibits interesting magnetic properties. NH4FeCl2(HCOO) crystallizes in the monoclinic space group C2/c (No. 15) with a = 7.888(1) Å, b = 11.156(2) Å, c = 6.920(2) Å, and β = 108.066(2)°. The crystal structure consists of infinite zigzag chains of distorted Fe(2+)-centered octahedra linked by μ2-Cl and syn-syn formate bridges, with interchain hydrogen bonding through NH4(+) cations holding the chains together. The unique Fe(2+) site is coordinated by four equatorial chlorides at a distance of 2.50 Å and two axial oxygens at a distance of 2.08 Å. Magnetic measurements performed on powder and oriented single-crystal samples show complex anisotropic magnetic behavior dominated by antiferromagnetic interactions (TN = 6 K) with a small ferromagnetic component in the direction of chain propagation. An anisotropic metamagnetic transition was observed in the ordered state at 2 K in an applied magnetic field of 0.85-3 T. (57)Fe Mössbauer spectroscopy reveals mixed hyperfine interactions below the ordering temperature, with strong electric field gradients and complex noncollinear arrangement of the magnetic moments.

Synthesis optimization of the ultra-microporous [Ni3(HCOO)6] framework to improve its CH4/N2separation selectivity

The adsorptive separation selectivities of CH₄/N₂were successfully improved from 4.0–4.8 to 7.0–7.5viasynthesis optimization of ultra-microporous [Ni₃(HCOO)₆] frameworks.

The Chemistry and Applications of Metal-Organic Frameworks

Crystalline metal-organic frameworks (MOFs) are formed by reticular synthesis, which creates strong bonds between inorganic and organic units. Careful selection of MOF constituents can yield crystals of ultrahigh porosity and high thermal and chemical stability. These characteristics allow the interior of MOFs to be chemically altered for use in gas separation, gas storage, and catalysis, among other applications. The precision commonly exercised in their chemical modification and the ability to expand their metrics without changing the underlying topology have not been achieved with other solids. MOFs whose chemical composition and shape of building units can be multiply varied within a particular structure already exist and may lead to materials that offer a synergistic combination of properties.

Dynamic magnetic MOFs

In this review we combine the use of coordination chemistry with the concepts of molecular magnetism to design magnetic Metal-Organic Frameworks (MOFs) in which the crystalline network undergoes a dynamic change upon application of an external stimulus. The various approaches so far developed to prepare these kinds of chemically or physically responsive MOFs with tunable magnetic properties are presented.

Synthesis, crystal structure and thermal properties of Ca6(C12H14O4)4(CO3)(OH)2(H2O)x--a 3D inorganic hybrid material

The inorganic-organic compound Ca(6)(1,3-adamantanedicarboxylate)(4)(CO(3))(OH)(2)(H(2)O)(x) with 0 < x < 15.2 was synthesized by hydrothermal methods. The crystal structure was determined on the basis of high resolution synchrotron powder diffraction data and poly-crystal measurements. The crystal structure of Ca(6)(C(12)H(14)O(4))(4)(CO(3))(OH)(2)(H(2)O)(14) is tetragonal, space group I4(1)/amd (141) with a = 29.12 Å, c = 15.85 Å, V = 13,440 Å(3) and Z = 8. The compound is classified as a 3D inorganic hybrid material with a 3-dimensional inorganic framework consisting of Ca and O, connected to 1,3-adamantanedicarboxylate anions. The structure shows hydrophilic channels in a diamond-like network. In between the channels there exist hydrophobic pores with surfaces defined by adamantane cages. The shortest distance between hydrogen atoms from different molecules in these pores is 3.6 Å. The largest hydrophilic cavity has a diameter of 10 Å and the pores connecting the channels have a diameter of 5 Å. In the as-synthesised state these channels are filled with water molecules. Reversible dehydration-rehydration occurs. The dehydrated compound easily takes up water from ambient air.

Hydrogen uptake by {H[Mg(HCOO)3]⊃NHMe2}∞ and determination of its H2 adsorption sites through Monte Carlo simulations

A detailed analysis of the solvothermal synthesis in DMF of the polymeric magnesium formate {H[Mg(HCOO)(3)]⊃NHMe(2)}(∞) (1) from Mg(ClO(4))(2)·6H(2)O revealed that the final crystalline product is formed after an acid-catalyzed DMF hydrolysis, producing formic acid and dimethylamine. The former bridges magnesium(II) centers, creating the 3D scaffold, while the latter is trapped inside the cubic cavities of the polymer, engaging in strong hydrogen bonding with the formate ions of the cage. After thermal activation and guest removal, the material was tested for hydrogen uptake at T = 77 K over the 0-80 bar pressure range, and the existence of preferred H(2) adsorption sites was assessed through grand canonical Monte Carlo (GCMC) simulations. No specific low-energy site was found, and the H(2) molecules positions within the framework cavities are mainly dependent on packing effects. Thus, at low H(2) loadings the most populated site is the center of the cubic cavities, even though, at higher pressures, two more "localized" positions have been found by the simulation because of the reduced freedom of movement. The maximum experimental H(2) uptake corresponds to 8.8 mg/g or 13.5 mg/cm(3).

Formate-based magnetic metal-organic frameworks templated by protonated amines

A systematic study has been carried out on the 3d divalent metal formate 3D magnetic frameworks templated by protonated amines, and the achievements have revealed that metal formate frameworks are very malleable, and their structures depend on the size, shape, charge, and hydrogen bonding geometries of the templating cations. Six kinds of metal formate frameworks have been created. They are chiral frameworks with a (4(9) . 6(6)) topology, perovskite ones with a (4(12) . 6(3)) topology, bi-nodal frameworks of (4(12) . 6(3))(4(9) . 6(6))(n) (n = 1, 2, 3) topologies, and porous diamond frameworks with 6(6) topology. These materials display promising and abundant magnetic, dielectric, porous, and optical properties and the possible combination of them. Therefore, they are of great interest for the study of molecule-based materials. It has been demonstrated that formate, being the smallest and simplest carboxylate, cheap and with low toxicity, thus more biocompatible and environmentally friendly, and having been more or less ignored, will find an important role in the construction of molecule-based materials and provide new materials with interesting properties.