Closed-pore crystal capable of adsorbing CO2 onto isolated cavities generated by disorderly mixing of substituents on host skeleton

Long Time CO2 Storage Under Ambient Conditions in Isolated Voids of a Porous Coordination Network Facilitated by the "Magic Door" Mechanism

A coordination network containing isolated pores without interconnecting channels is prepared from a tetrahedral ligand and copper(I) iodide. Despite the lack of accessibility, CO2 is selectively adsorbed into these pores at 298 K and then retained for more than one week while exposed to the atmosphere. The CO2 adsorption energy and diffusion mechanism throughout the network are simulated using Matlantis, which helps to rationalize the experimental results. CO2 enters the isolated voids through transient channels, termed "magic doors", which can momentarily appear within the structure. Once inside the voids, CO2 remains locked in limiting its escape. This mechanism is facilitated by the flexibility of organic ligands and the pivot motion of cluster units. In situ powder X-ray diffraction revealed that the crystal structure change is negligible before and after CO2 capture, unlike gate-opening coordination networks. The uncovered CO2 sorption and retention ability paves the way for the design of sorbents based on isolated voids.

Adsorption under nanoconfinement: a theoretical-computational study revealing significant enhancement beyond the Langmuirian levels

The principal goal of this work is to predict characteristics unique to equilibrated adsorption of a small number of molecules on atomic sites located inside a closed nanoscale space. Compared to the thermodynamic limit of macroscopic systems, significantly enlarged adsorbate coverage under nanoconfinement constitutes a major finding of the modeling. Concomitantly, nanoconfined adsorbates are expected to exhibit extra thermal stability against desorption. These effects on adsorption are explored using canonical partition-functions as well as an original relationship between coverage variations and the Langmuir constant, both in the frameworks of the ideal gas and lattice-gas models. With reported DFT adsorption-energies as input, adsorption isotherms are derived numerically for H2 on Ti-doped graphene-like nanostructures. Remarkable deviations from the classical Langmuir isotherm are predicted for the first time, namely, system-size dependent enhanced H2 adsorbate coverage. The effects are computed also for CO2 inside MOF single-molecule traps, including their relationships to adsorption-energy, specific-heat and to coverage fluctuations. According to preliminary modeling, nanoconfinement effects are anticipated also for adsorption in nanopores undergoing molecular exchange with the external environment, and for impurity segregation in nanoparticle and nanocrystalline solids. The entropic origin of the nanoconfinement effect on equilibrium adsorption (NCEEA) is demonstrated analogously to the nanoconfinement effect on equilibrated chemical reactions studied by us previously. Besides unraveling some basic theoretical issues in physical nanochemistry, this study is expected to be pertinent to nanotechnological applications, such as gas storage and separation in nanoporous materials and other solid adsorbents.

Defect-Engineered Metal-Organic Frameworks

Defect engineering in metal-organic frameworks (MOFs) is an exciting concept for tailoring material properties, which opens up novel opportunities not only in sorption and catalysis, but also in controlling more challenging physical characteristics such as band gap as well as magnetic and electrical/conductive properties. It is challenging to structurally characterize the inherent or intentionally created defects of various types, and there have so far been few efforts to comprehensively discuss these issues. Based on selected reports spanning the last decades, this Review closes that gap by providing both a concise overview of defects in MOFs, or more broadly coordination network compounds (CNCs), including their classification and characterization, together with the (potential) applications of defective CNCs/MOFs. Moreover, we will highlight important aspects of "defect-engineering" concepts applied for CNCs, also in comparison with relevant solid materials such as zeolites or COFs. Finally, we discuss the future potential of defect-engineered CNCs.

Structurally simple complexes of CO2

A wide range of structurally characterized adducts of CO₂are discussed in this review, from the strongly bound, charge assisted carbamate complexes through the weaker halide and pseudo-halide complexes to the weakest possible inclusion complexes.

Selective CO2 gas adsorption in the narrow crystalline cavities of flexible peptide metallo-macrocycles

The BF₄⁻ salt of peptide Ni(ii)-macrocycle demonstrated selective CO₂ gas adsorption (ca. 6–7 molecules per macrocycle) into its narrow cavities.

High-pressure studies of palladium and platinum thioether macrocyclic dihalide complexes

The mononuclear macrocyclic Pd(II) complex cis-[PdCl2([9]aneS3)] ([9]aneS3 = 1,4,7-trithiacyclo-nonane) converts at 44 kbar into an intensely coloured chain polymer exhibiting distorted octahedral coordination at the metal centre and an unprecedented [1233] conformation for the thioether ligand. The evolution of an intramolecular axial sulfur-metal interaction and an intermolecular equatorial sulfur-metal interaction is central to these changes. High-pressure crystallographic experiments have also been undertaken on the related complexes [PtCl2([9]aneS3)], [PdBr2([9]aneS3)], [PtBr2([9]aneS3)], [PdI2([9]aneS3)] and [PtI2([9]aneS3)] in order to establish the effects of changing the halide ligands and the metal centre on the behaviour of these complexes under pressure. While all complexes undergo contraction of the various interaction distances with increasing pressure, only [PdCl2([9]aneS3)] undergoes a phase change. Pressure-induced I...I interactions were observed for [PdI2([9]aneS3)] and [PtI2([9]aneS3)] at 19 kbar, but the corresponding Br...Br interactions in [PdBr2([9]aneS3)] and [PtBr2([9]aneS3)] only become significant at much higher pressure (58 kbar). Accompanying density functional theory (DFT) calculations have yielded interaction energies and bond orders for the sulfur-metal interactions.

Single-crystal X-ray diffraction studies on structural transformations of porous coordination polymers

This review gives a brief overview of single-crystal X-ray diffraction studies and single-crystal to single-crystal transformations of porous coordination polymers.

Single-crystal membrane for anisotropic and efficient gas permeation

Development of gas separation materials has been one of the basic requirements of industry. Microporous materials have adequate pores for gas separation and have contributed to the advancement of gas purification techniques. Because the simplest and most economical method would be membrane separation, various microporous membranes have been prepared and explored for their separation properties. However, a key issue remains as to how to generate defect-free membranes with practical gas permeance. Here we report the preparation of a well-oriented single-crystal membrane with high permeance by using a flexible single crystal of [Cu(2)(bza)(4)(pyz)](n) possessing one-dimensional (1D) penetration channels; this membrane exhibits anisotropic gas permeation through the 1D channels with high permselectivity for H(2) and CO(2). Although the diameter of the neck of the narrow channels is smaller than the kinetic diameters of the sample gases, various gases pass through the 1D channels. This report provides a new way of developing gas permeation membranes as sophisticated crystal devices for gas purification techniques.