The chemical formula of the “blue crystalline” CP is Structure of Two-Dimensional Layer-Stacking Coordination Polymer It is noteworthy that the “blue crystalline” CP/MOF also shows a gate response to supercritical CH 4 at 303 K that usually shows very small interaction to adsorbent ( Figure 2). Subsequent studies revealed that the “blue crystalline” CP/MOF shows the gate phenomena not only to CO 2 but also N 2, O 2, and Ar. In this context, gate adsorption was an unprecedented phenomenon. In other words, before the Li-Kaneko report, all of the gas adsorption phenomena on PCPs/MOFs were classified into representative physisorption by porous materials and resembled such properties, which were shown by traditional adsorbents. Nevertheless, all of the PCPs/MOFs show traditional adsorption isotherms, which are classified by the six types of adsorption isotherms. In the old example, although adsorption isotherms were not disclosed, Mori and Takamizawa reported the gas adsorption phenomena on copper complexes. There were a number of reports on gas adsorption phenomena on PCPs/MOFs before the Li-Kaneko report in 2001. Therefore, the nil gas adsorption in the low-pressure region and the sudden gas uptake profile of the “blue crystalline” CP/MOF cannot be classified by IUPAC categories. Discovery of Gate Phenomena of Coordination Polymerĭespite the difference of the detail profile, all of the six types of adsorption isotherms show a gradual increase of the amount of gas adsorption dependent on gas pressure. Gas Adsorptivity of Elastic Layer-Structured Metal-Organic Frameworks (ELMs) 2.1. We also discuss the advantages of flexible ELMs for practical applications. In this review, we introduce the structures and functions of flexible two dimensional PCPs/MOFs, which are constructed with simple, rigid, and linear ligands, 4,4′-bipyridine (bpy), and are named “elastic layer-structured metal-organic frameworks (ELMs)”. Although such an interesting phenomenon has been extensively studied in the case of crystals of small organic molecules or a discrete complex, the detailed mechanism of non-linear responses of PCPs/MOFs in gas adsorption is still unclear. However, flexible PCPs/MOFs, in some cases, show non-linear responses between the adsorbed amount and the gas pressure. In the case of gas adsorption phenomena on robust traditional porous materials, the adsorbed amount tends to increase gradually with the increment of gas pressure. The flexible PCPs/MOFs interact with guest molecules, showing nonporous/porous structural transformations or change the pore structures in response to external stimuli. On the other hand, some kinds of PCPs/MOFs show structural flexibility. Since traditional porous materials such as zeolite or activated carbon are ordinarily robust, adsorbed guest molecules are accommodated into the steadily constructed pores. Atomic radius patterns are observed throughout the periodic table.One of the characteristics of PCPs/MOFs is a softness derived from the weak interactions between counter ions and ligands, or ligands and ligands. The covalent radii of these molecules are often referred to as atomic radii. Nevertheless, it is possible for a vast majority of elements to form covalent molecules in which two like atoms are held together by a single covalent bond. Some are bound by covalent bonds in molecules, some are attracted to each other in ionic crystals, and others are held in metallic crystals. However, this idea is complicated by the fact that not all atoms are normally bound together in the same way. The atomic radius is one-half the distance between the nuclei of two atoms (just like a radius is half the diameter of a circle). This causes the electron to move closer to the nucleus, thus increasing the electron affinity from left to right across a period. Moving from left to right across a period, atoms become smaller as the forces of attraction become stronger. With a larger distance between the negatively-charged electron and the positively-charged nucleus, the force of attraction is relatively weaker. This means that an added electron is further away from the atom's nucleus compared with its position in the smaller atom. \( \newcommand\): Periodic Table showing Electron Affinity TrendĮlectron affinity generally decreases down a group of elements because each atom is larger than the atom above it (this is the atomic radius trend, discussed below).
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