Synthesis and Characterization of a Porous Magnetic Diamond Framework, Co3(HCOO)6, and Its N2 Sorption Characteristic

Phenylalanine-Based Co2+ and Cd2+ 1D Coordination Polymers: Structural Properties and Catalytic Application for Solvent-Free Aerobic Oxidation of Cycloalkene

Two 1D coordination polymers (CPs) with general formula [M(L)(H2O)(AcO)]n, (M = Co (1) or Cd (2), AcO = acetate anion and L denotes l-phenylalanine based ligand), were synthesized and fully characterized by various spectroscopies (UV-vis, FTIR, and NMR), thermal techniques, magnetic measurements (for 1), and single-crystal and powder X-ray diffraction studies. They can be described as "ribbon-like" 1D polymers constructed through a zigzag arrangement. The polymeric structure is developed due to the coordination mode adopted by the amino acid ligand, classified as μ3-N1O1:O1:O2, which simultaneously links three metal centers. This moiety also plays an important role as a magnetic coupler between metal centers in the cobalt system, which shows a weak antiferromagnetic interaction. Both CPs have also been used in the catalytic oxidation of cyclohexene with molecular oxygen (O2) as an oxidant. Under mild conditions, both compounds demonstrated remarkable catalytic activity, with the cobalt system being more efficient than the cadmium analogue (conversion: 73 and 58% and selectivity for the major product, 2-cyclohexanone: 63 and 55%, for 1 and 2, respectively). Leaching experiments and the results obtained using a radical quencher are consistent with a radical-mediated mechanism for the Co compound. The presence of the superoxide radical was also confirmed using EPR spectroscopy and DMPO as a spin trap, which was further validated by DFT calculations. The activity observed for the Cd analogue is attributed to the organic scaffold assisted by the templating effect of the metal ion.

[Ba4Cl] Cations Directed Perovskite-like Polar Metal Formate Frameworks {[Ba4Cl][M3(HCO2)13]}n (M = Mn, Co, and Mg): Microwave-Assisted Synthesis, Structures, and Properties

Novel 3D metal formate frameworks {[Ba₄Cl][M₃(HCO₂)₁₃]}_n (M = Mn for 1, Co for 2, and Mg for 3) were successfully assembled via microwave-assisted synthesis. The complexes are rare coordination polymers crystallized at space group P4cc with the polar point group C_4v. In the structure, the M^II ions are bridged by two types of anti-anti formate in forming a 3D pcu framework, and additional formates coordinate to the unsaturated sites of the M^II ions in the framework, giving an anionic M-formate net. Ba₄Cl clusters take the cavities of the net as charge balance, in which the chloride ion deviates from the center of the barium ions. The asymmetric Ba₄Cl structure is transmitted throughout the crystal resulting in polar structure, which is further confirmed by nonlinear optical and piezoelectric test. Nonlinear optical activity tests of 1 and 3 show SHG signals 0.32 and 0.28 times that of KDP, while 2 has a piezoelectric coefficient d₃₃ of 6.8 pC/N along polar axis. Magnetic studies reveal antiferromagnetic coupling between M^II ions in 1 and 2. Spin canting was found only in 2 with anisotropic Co^II ions, and 2 is a canted antiferromagnetically with T_N = 5 K. Further field-induced spin flop was also found in 2 with a critical field 0.9 T.

Exploiting the Specific Isotope-Selective Adsorption of Metal-Organic Framework for Hydrogen Isotope Separation

Adsorptive separation using narrow-micropore adsorbents has demonstrated the potential to separate hydrogen isotopes. In this work, we employed an isotope-responsive separation using cobalt formate. A D₂-responsive third sorption step was revealed, and consequently, a noticeable difference was observed in the uptakes of D₂ and H₂. This may have resulted from the additional space created for D₂ due to its dense packing, as DFT calculations revealed that cobalt formate possesses 2.26 kJ/mol higher binding strength for D₂ than for H₂. The exploitation of this D₂-responsive third sorption step renders a promising separation performance, with a D₂/H₂ selectivity of up to 44 at 25 K/1 bar. Lastly, cobalt formate was synthesized on a gram scale here, which makes it a prospect for commercialization.

High-throughput screening of metal-organic frameworks for kinetic separation of propane and propene

We apply molecular simulations to screen a database of reported metal-organic framework structures from the computation-ready, experimental (CoRE) MOF database to identify materials potentially capable of separating propane and propene by diffusion. We report a screening workflow that uses descriptor analysis, conventional molecular dynamics (MD), and Nudged Elastic Band (NEB) energy barrier calculations at both classical force field and Density Functional Theory (DFT) levels. For the first time, the effects of framework flexibility on guest transport properties were fully considered in a screening process and led to the identification of candidate MOFs. The hits identified by this proof-of-concept workflow include ZIF-8 and ZIF-67 previously shown to have large differences in propane and propene diffusivities as well as two other materials that have not been tested experimentally yet. This work emphasises the importance of taking into account framework flexibility when studying guest transport in porous materials, demonstrates the potential of the data-driven identification of high-performance materials and highlights the ways of improving the predictive power of the screening workflow.

Phenothiazine-chitosan based eco-adsorbents: A special design for mercury removal and fast naked eye detection

The aim of the paper was to investigate the ability of an eco-friendly luminescent xerogel prepared by chitosan crosslinking with a phenothiazine luminogen to detect and remove heavy metals. Its ability to give a divergent morphological and optical response towards fifteen environmental relevant metals was investigated by naked eye and UV lamp, fluorescence spectroscopy and scanning electron microscopy. A distinct response was noted for mercury, consisting in the transformation of the xerogel into a rubber-like material accompanied by the red shifting of the color of emitted light from yellow-green to greenish-yellow domain. The particularities of the metals anchoring into the xerogel were analyzed by FTIR spectroscopy and X-ray diffraction. The morphological changes and the metal uptake were analyzed by SEM-EDAX, swelling and gravimetric methods. It was concluded that mercury has a superior affinity towards this heteroatoms rich system, leading to a secondary crosslinking. This directed a great absorption capacity of 1673 mg/g and a specific morphological response for mercury ion concentrations up to 0.001 ppm.

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.

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.

Anion-Controlled Architecture and Photochromism of Naphthalene Diimide-Based Coordination Polymers

Three new cadmium coordination polymers, namely [Cd(NO₃)₂(DPNDI)(CH₃OH)]·CH₃OH (1), [Cd(SCN)₂(DPNDI)] (2), and [Cd(DPNDI)₂(DMF)₂]·2ClO₄ (3) (DPNDI = N,N-di(4-pyridyl)-1,4,5,8-naphthalene diimide, DMF = N,N-dimethylformamide) have been synthesized by reactions of DPNDI with Cd(NO₃)₂, Cd(SCN)₂, and Cd(ClO₄)₂, respectively. Compound 1 is a one-dimensional coordination polymer with strong lone pair-π interactions between the coordinated NO₃⁻ anions and the imide ring of DPNDI; while 2 is a two-dimensional network with a (4, 4) net topology. In the case of 3, due to the presence of uncoordinated perchlorate counter ions, it exhibits a non-interpenetrated square-grid coordination polymer containing one-dimensional rhomboid channels. The structural diversity in these compounds is attributed to different coordination abilities and geometries of counter anions. Due to the presence of electron-deficient NDI moiety, the photochromic behavior of these compounds was studied. Interestingly, only compounds 1 and 3 exhibit color changes under light irradiation. The influence of the anions on the photochromism process of the NDI-based materials has been discussed.

“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.

Solvent effects on the structures and magnetic properties of two doubly interpenetrated metal-organic frameworks

Two doubly interpenetrated coordination polymers [Co2(BDC)2(bpt)2]·nSolvent based on dimeric secondary building units and crystallizing with distinct solvent molecules (-H2O and -MeOH for nSolvent = 2H2O and MeOH·H2O, respectively) were obtained by employing 1,4-benzenedicarboxylate (BDC) and 1H-3,5-bis(4-pyridyl)-1,2,4-triazole) (bpt) as linkers. The structures consist of a square grid of dimers bridged by BDC and pillared by bpt. Thermogravimetry and PXRD indicate that the frameworks are stable and are retained up to 400 °C, but the structures are modified irreversibly. -H2O, high-symmetry Pna21, exhibits antiferromagnetic coupling within the dimer, while -MeOH, low-symmetry P21/n, exhibits ferromagnetic coupling. Upon desolvation, the -de and -de couplings are antiferromagnetic but reduced. Subsequent resolvation to -H2O and -MeOH resulted in a slight increase of the antiferromagnetic coupling without attaining the virgin states. The interesting difference of magnetic properties between -H2O and -MeOH, the solvated/desolvated phases, particularly at low temperature, indicates that there is a prominent solvent effect.

Solvent-controlled structural diversity observed in three Cu(ii) MOFs with a 2,2′-dinitro-biphenyl-4,4′-dicarboxylate ligand: synthesis, structures and magnetism

Three solvent-dependent 3D Cu^II-based MOFs with diverse topology net have been successfully separated under controllable solvothermal conditions and magnetic studies suggest homo-spin topological ferrimagnetic and antiferromagnetic interactions.

Novel layered crystalline organic polymer-inorganic hybrid material comprising calcium phosphate with unique architectures for superior performance catalyst support

Various pores or channels produced by the modification of PS-PVPA chain could contribute to significant impact on the excellent catalytic activity.

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.

A rare phenoxido/acetato/azido bridged trinuclear and an unprecedented phenoxido/azido bridged one-dimensional polynuclear nickel(II) complexes: synthesis, crystal structure, and magnetic properties with theoretical investigations on the exchange mechanism

The reaction of a tridentate Schiff base ligand HL (2-[(3-dimethylaminopropylimino)-methyl]-phenol) with Ni(II) acetate or perchlorate salts in the presence of azide as coligand has led to two new Ni(II) complexes of formulas [Ni(3)L(2)(OAc)(2)(μ(1,1)-N(3))(2)(H(2)O)(2)]·2H(2)O (1) and [Ni(2)L(2)(μ(1,1)-N(3))(μ(1,3)-N(3))](n)(2). Single crystal X-ray structures show that complex 1 is a linear trinuclear Ni(II) compound containing a μ(2)-phenoxido, an end-on (EO) azido and a syn-syn acetato bridge between the terminal and the central Ni(II) ions. Complex 2 can be viewed as a one-dimensional (1D) chain in which the triply bridged (di-μ(2)-phenoxido and EO azido) dimeric Ni(2) units are linked to each other in a zigzag pattern by a single end-to-end (EE) azido bridge. Variable-temperature magnetic susceptibility studies indicate the presence of moderate ferromagnetic exchange coupling in complex 1 with J value of 16.51(6) cm(-1). The magnetic behavior of 2 can be fitted in an alternating ferro- and antiferromagnetic model [J(FM) = +34.2(2.8) cm(-1) and J(AF) = -21.6(1.1) cm(-1)] corresponding to the triple bridged dinuclear core and EE azido bridge respectively. Density functional theory (DFT) calculations were performed to corroborate the magnetic results of 1 and 2. The contributions of the different bridges toward magnetic interactions in both compounds have also been calculated.

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).