A Robust Nanoporous Supramolecular Metal-Organic Framework Based on Ionic Hydrogen Bonds

A three-component hydrogen bonded framework

A porous three-component hydrogen bonded framework, 1⋅biphen⋅TP, was prepared from a tetra-amidinium component (14+) and two different dianions, benzene-1,4-dicarboxylate (terephthalate, TP2-) and biphenyl-4,4'-dicarboxylate (biphen2-). Interestingly, when the framework was prepared in ethanol/water, 1⋅biphen⋅TP forms even when an excess of either dicarboxylate is present. However, when only water is used as solvent, only two-component frameworks are formed.

Hydrogen-bonded frameworks containing aliphatic 3D linkers show high-capacity water vapour sorption

Hydrogen-bonded frameworks were prepared from a tetra-amidinium component and three-dimensional cubane and bicyclopentane dicarboxylate linkers. Despite the incorporation of aliphatic components, the frameworks demonstrate strong and reversible uptake of water vapour, with one of the frameworks showing water uptake at very low relative humidity.

Correspondence on "Crystalline Porous Organic Salt for Ultrarapid Adsorption/Desorption-Based Atmospheric Water Harvesting by Dual Hydrogen Bond System"

In a recent Research Article, Ben and co-workers reported a hydrogen-bonded framework prepared from a 4⁺ tetra-amidinium component and a 4^- tetra-sulfonate component, termed CPOS-6. They showed that CPOS-6 could reversibly adsorb and desorb water over a narrow humidity window, and that this material offered potential for applications in atmospheric water harvesting. This conclusion was supported by experiments that showed the material was stable over 50 adsorption/desorption cycles and that the kinetics of these cycles were very rapid. In this Correspondence we present additional structural data regarding this framework in both its hydrated and dehydrated states and thus discern the mechanism of water binding. These data do not disagree with Ben and co-workers' findings: rather they emphasise how remarkable the cyclability and rapid kinetics of adsorption/desorption are, as these processes involve a complete crystal-to-crystal rearrangement of the framework.

Modulation of the Sorption Characteristics for an H-bonded porous Architecture by Varying the Chemical Functionalization of the Channel Walls

Five isostructural microporous supramolecular architectures prepared by H-bonded assembly between the hexa-anionic complex [Zr₂ (Ox)₇ ]^6- (Ox=oxalate, (C₂ O₄ )^2- ) and tripodal cations (H₃ -TripCH₂ -R)³⁺ with R=H, CH₃ , OH and OBn (Bn=CH₂ Ph) are reported. The possibility to obtain the same structure using a mixture of tripodal cations with different R group (R=OH and R=CH₃ ) has also been successfully explored, providing a unique example of three-component H-bonded porous framework. The resulting SPA-1(R) materials feature 1D pores decorated by R groups, with apparent pore diameters ranging from 3.0 to 8.5 Å. Influence of R groups on the sorption properties of these materials is evidenced through CO₂ and H₂ O vapor sorption/desorption experiments, as well as with I₂ capture/release experiments in liquid media. This study is one of the first to demonstrate the possibility of tuning the porosity and exerting precise control over the chemical functionalization of the pores in a given H-bonded structure, without modifying the topology of the reference structure, and thus finely adjusting the sorption characteristics of the material.

Hydrogen-Bonded Framework of a Cobalt(II) Complex Showing Superior Stability and Field-Induced Slow Magnetic Relaxation

A unique hydrogen-bonded organic-inorganic framework (HOIF) constructed from a mononuclear cobalt(II) complex, [Co(MCA)₂·(H₂O)₂] (HMCA = 4-imidazolecarboxylic acid), via multiple hydrogen-bonding interactions was synthesized and structurally characterized. The Co(II) center in the HOIF features a highly distorted octahedral coordination environment. Remarkably, the Co^II HOIF showed permanent porosity with superior stability as established by combined thermogravimetric analysis (TGA), variable-temperature infrared spectra (IR), variable-temperature powder X-ray diffraction data (PXRD), and a CO₂ isotherm. Structural studies reveal that short multiple hydrogen bonds should be responsible for the superior thermal and chemical stability of a HIOF. Magnetic investigations reveal the large easy-plane magnetic anisotropy of the Co²⁺ ions with the fitted D values being 22.1 (magnetic susceptibility and magnetization data) and 29.1 cm^-1 (reduced magnetization data). In addition, the HOIF exhibits field-induced slow magnetic relaxation at low temperature with an effective energy barrier of U_eff = 45.2 cm^-1, indicative of a hydrogen-bonded framework single-ion magnet of the compound. The origin of the significant magnetic anisotropy of the complex was also understood from computational studies. In addition, BS-DFT calculations indicate that the superexchange interactions between the neighboring Co^II ions are non-negligible antiferromagnetism with J_Co-Co = -0.5 cm^-1. The foregoing results provide not only a carboxylate-imidazole ligand approach toward a stable HOIF but also a promising way to build a robust single-ion magnet via hydrogen-bond interactions.

Towards hydrogen and halogen bonded frameworks based on 3,5-bis(triazolyl)pyridinium motifs

Construction of supramolecular assemblies using hydrogen and halogen bonding between anions and the 3,5-bis(triazolyl)pyridinium motif was investigated.

Crystal Structure Transformation in Hydrogen-bonded Organic Frameworks via Ion Exchange

Hydrogen-bonded organic frameworks (HOFs) have emerged as rapidly growing porous materials while established permanent porosities are very fragile and difficult to stabilize due to weak hydrogen-bonding interactions among building units. Herein, we report a stable hydrogen-bonded metallotecton framework (termed as HOF-ZJU-102) that was constructed through hydrogen-bonding networks between cationic metal-organic complexes [Cu₂ (Hade)₄ (H₂ O)₂ ]⁴⁺ (Hade=adenine) and GeF₆ ^2- anions. The framework not only shows permanent porosity, but also exhibits efficient separation performance of C₂ H₂ /C₂ H₄ at room temperature. More interestingly, its crystal structure could be irreversibly transformed into isostructural counterpart HOF-ZJU-101 by ion exchange in the SiF₆ ^2- containing solution, evidenced by multiple characterization techniques including gas sorption measurements, ¹⁹ F NMR spectra, FTIR and EDS. Utilizing such an ion exchange mechanism, the collapsed HOF-ZJU-102 could be restored into HOF-ZJU-101 by simply soaking in the salt solution.

Amidinium⋯carboxylate frameworks: predictable, robust, water-stable hydrogen bonded materials

In the last few years, the amidinium⋯carboxylate interaction has emerged as a powerful tool for the relatively predictable construction of families of three dimensional hydrogen bonded organic frameworks. These frameworks can be prepared in water and are surprisingly stable, including to heating in polar organic solvents and water. This feature article describes the design and synthesis of these materials, discusses their structures and stability, and highlights their recent applications for enzyme encapsulation and as precursors for the synthesis of molecularly thin hydrogen bonded 2D nanosheets.

Self-Assembled Microporous M-HOFs Based on an Octahedral Rhenium Cluster with Benzimidazole

Substitution of apical halide ligands in [{Re₆Seⁱ₈}X^a₆]^3- (X = Cl, Br) by benzimidazole (bimzH) accompanied by a self-assembly process leads to the formation of microporous Re₆-based hydrogen-bonded organic frameworks (Re₆-HOFs) constructed on N-H···X hydrogen bonds and π-π-stacking interactions between bimzH ligands. Re₆-HOFs demonstrate sorption properties with a Brunauer-Emmett-Teller surface area of up to 443 m² g^-1 and luminescence with a quantum yield and an emission lifetime of up to 0.16 and 16 μs, respectively. The compounds obtained complement small groups of transition-metal cluster-based HOFs, which are a perspective for the development of multifunctional frameworks.

Metal hydrogen-bonded organic frameworks: structure and performance

Although great progress has been made in the design, synthesis, and performance expansion of porous materials, new porous materials with stable structures still need to be explored further. In recent years, porous molecular crystals formed by intermolecular interactions have attracted wide attention from chemists, especially metal hydrogen-bonded organic frameworks (M-HOFs) formed by connecting metal complexes through hydrogen bonds. Metal complexes with specific properties (e.g., magnetism, luminescence, sensing, and catalysis) can expand and develop the application of M-HOFs further. However, the huge volume, irregular shape, complex coordination modes, and interference of coordination bonds pose certain challenges in the synthesis and performance expansion of M-HOFs. In this frontier, we summarize the latest progress in the use of 3d, 4d, and 4f metal complexes for the synthesis of M-HOFs, and briefly introduce the performance expansion of these M-HOFs, which is expected to help expand new porous materials with stable structures and specific functions.

Controlled Growth of Ag Nanocrystals in a H-Bonded Open Framework

A procedure that enabled rational access to the first example of hybrid material made of NPs grown within a H-bonded framework is reported. To avoid competitive reactions with the framework units, the metal precursor was chemically trapped in the porous structure and subsequently photo-reduced to afford the hybrid material Ag@SPA-2, which consists of Ag NPs of nanometric sizes (<15 nm) homogeneously distributed in the crystals of the host material. In a subsequent step, taking advantage of the porous matrix the silver NPs have been transformed in situ to Ag₂ S NP by simple infiltration of H₂ S. The supramolecular network is shown to play an important role in stabilizing the inorganic nanomaterials and thus in controlling their growth.

Recent advances in self-assembled amidinium and guanidinium frameworks

Recent advances in amidinium and guanidinium-containing hydrogen-bonded framework materials are highlighted.

Non-covalent interactions observed in nevirapinium pentaiodide hydrate which include the rare I4–I−···O=C halogen bonding

In the course of screening for novel crystalline forms of antiviral drug nevirapine, co-crystallization of the latter with molecular iodine was attempted. This resulted in the formation of a hydrate salt form composed of the protonated nevirapinium cation and pentaiodide anion. In the X-ray structure of NVPH+I5 −·H2O, halogen and hydrogen bonding interactions were identified and studied by DFT calculations and topological analysis of the electron density distribution within the framework of QTAIM method at the B3LYP/DZP-DKH and M06/DZP-DKH levels of theory. Estimated energies of these contacts are 1.3–9.4 kcal/mol.

Fine Tuning and Specific Binding Sites with a Porous Hydrogen-Bonded Metal-Complex Framework for Gas Selective Separations

Research on hydrogen-bonded organic frameworks (HOFs) has been developed for quite a long time; however, those with both established permanent porosities and functional properties are extremely rare due to weak hydrogen-bonding interactions among molecular organic linkers, which are much more fragile and difficult to stabilize. Herein, through judiciously combining the superiority of both the moderately stable coordination bonds in metal-organic frameworks and hydrogen bonds, we have realized a microporous hydrogen-bonded metal-complex or metallotecton framework HOF-21, which not only shows permanent porosity, but also exhibits highly selective separation performance of C₂H₂/C₂H₄ at room temperature. The outstanding separation performance can be ascribed to sieving effect confined by the fine-tuning pores and the superimposed hydrogen-bonding interaction between C₂H₂ and SiF₆^2- on both ends as validated by both modeling and neutron powder diffraction experiments. More importantly, the collapsed HOF-21 can be restored by simply immersing it into water or salt solution. To the best of our knowledge, such extraordinary water stability and restorability of HOF-21 were observed for the first time in HOFs, underlying the bright perspective of such new HOF materials for their industrial usage.

Supramolecular frameworks based on 5,10,15,20-tetra(4-carboxyphenyl)porphyrins

Hydrogen bonding is used to prepare porphyrin-containing supramolecular frameworks.

Construction of half-sandwich multinuclear complexes including tunnel architectures via C–H-activation-directed assembly

Half-sandwich bi-, tetra-, hexa- and octanuclear complexes were prepared via C–H-activation-directed assembly based on three aromatic ligands. A series of tunnel architectures were observed in the complexes, with guest molecules in certain parts.

From double-shelled grids to supramolecular frameworks

Double-shelled 4f and 3d–4f supramolecular grids were assembled by the combination of two different tritopic hydrazone ligands, and further stacked into supramolecular HOFs through sharing the hydrogen bonding donors of halide ions. This study provides the first lanthanide-based double-shelled supramolecular grids and functionalized HOFs.

Structural reorganization in a hydrogen-bonded organic framework

Self-recognition of 3,3′,5,5′-azobenzenetetracarboxylic acid yields a grid-like anionic hydrogen-bonded framework capable of undergoing structural reorganization by recrystallization in the presence of guanidinium cations.

The trans-Bis(p-thioetherphenylacetynyl)bis(phosphine)platinum(II) Ligands: A Step towards Predictability and Crystal Design

Two organometallic ligands L1 (trans-[p-MeSC₆H₄C≡C-Pt(PR₃)₂-C≡CC₆H₄SMe; R = Me]) and L2 (R = Et) react with CuX salts (X = Cl, Br, I) in MeCN to form one-dimensional (1D) or two-dimensional (2D) coordination polymers (CPs). The clusters formed with copper halide can either be step cubane Cu₄I₄, rhomboids Cu₂X₂, or simply CuI. The formed CPs with L1, which is less sterically demanding than L2, exhibit a crystallization solvent molecule (MeCN), whereas those formed with L2 do not incorporate MeCN molecules in the lattice. These CPs were characterized by X-ray crystallography, thermogravimetric analysis, IR, Raman, absorption, and emission spectra as well as photophysical measurements in the presence and absence of crystallization MeCN molecules for those CPs with the solvent in the lattice (i.e., [(Cu₄I₄)L1·MeCN] _n (CP1), [(Cu₂Br₂)L1·2MeCN] _n (CP3), and [(Cu₂Cl₂)L1·MeCN] _n (CP5)). The crystallization molecules were removed under vacuum to evaluate the porosity of the materials by Brunauer-Emmett-Teller (N₂ at 77 K). The 2D CP shows a reversible type 1 adsorption isotherm for both CO₂ and N₂, indicative of microporosity, whereas the 1D CPs do not capture more solvent molecules or CO₂.

Second sphere coordination of hybrid metal–organic materials: solid state reactivity

An overview of early work and current developments focussing on the solid-state chemistry of hybrid metal–organic complexes assembled by outer sphere coordination involving is presented.

Supramolecular organic network assembled from quadruple hydrogen-bonding motifs

A rigid triptycene derivative with three 2-ureido-4[1H]-pyrimidinone (UPy) terminals was employed to construct a supramolecular hydrogen-bonded organic polymer (HOP-1).

Supramolecular open-framework architectures based on dicarboxylate H-bond acceptors and polytopic cations with three/four N–H+donor units

Supramolecular assemblages based on cationic H-donors and anionic H-acceptors have been envisioned to elaborate organic open frameworks.