Atsushi Kondo

Elastic layer-structured metal organic frameworks (ELMs)

Elastic layer-structured metal organic frameworks (ELMs) having flexible two-dimensional structure show a gate phenomenon in sorption/desorption of simple gas molecules. The gate phenomenon is accompanied by expansion/shrinkage of the layers. The gas sorption/desorption is not based on a physical adsorption, but on a chemical reaction, which includes high cooperativity. The cooperative reaction could be analyzed thermodynamically. The gate phenomenon showed advantages in separation of CO2 from mixed gases and in storage of CH4 owing to easy release of absorbed molecules.

Flexible Two-Dimensional Square-Grid Coordination Polymers: Structures and Functions

Coordination polymers (CPs) or metal-organic frameworks (MOFs) have attracted considerable attention because of the tunable diversity of structures and functions. A 4,4′-bipyridine molecule, which is a simple, linear, exobidentate, and rigid ligand molecule, can construct two-dimensional (2D) square grid type CPs. Only the 2D-CPs with appropriate metal cations and counter anions exhibit flexibility and adsorb gas with a gate mechanism and these 2D-CPs are called elastic layer-structured metal-organic frameworks (ELMs). Such a unique property can make it possible to overcome the dilemma of strong adsorption and easy desorption, which is one of the ideal properties for practical adsorbents.

Microporous Brookite-Phase Titania Made by Replication of a Metal–Organic Framework

Metal-organic frameworks (MOFs) provide access to structures with nanoscale pores, the size and connectivity of which can be controlled by combining the appropriate metals and linkers. To date, there have been no reports of using MOFs as templates to make porous, crystalline metal oxides. Microporous titania replicas were made from the MOF template HKUST-1 by dehydration, infiltration with titanium isopropoxide, and subsequent hydrothermal treatment at 200 °C. Etching of the MOF with 1 M aqueous HCl followed by 5% H2O2 yielded a titania replica that retained the morphology of the parent HKUST-1 crystals and contained partially ordered micropores as well as disordered mesopores. Interestingly, the synthesis of porous titania from the HKUST-1 template stabilized the formation of brookite, a rare titania polymorph.

Tuning of Gate Opening of an Elastic Layered Structure MOF in CO2 Sorption with a Trace of Alcohol Molecules

It is important to tune the sorption behavior of metal-organic framework (MOF) materials. Ethanol treatment on the hydrated form of [Cu(bpy)(2)(BF(4))(2)], which is a representative flexible MOF showing the fascinating gate phenomenon on CO(2) sorption, induces an easier dehydration and a significant decrease in the CO(2) gate pressure. The results of IR, X-ray diffraction (XRD), and X-ray absorption fine structure (XAFS) measurements indicated that water molecules in the lattice of the hydrated form can be removed even at room temperature after the ethanol treatment and the basic 2D layered structure remains with a slight interlayer expansion. The results of thermogravimetric (TG) and gas chromatograph/mass spectrometry (GC/MS) analyses and of CO(2) sorptions indicated that the change of the gate phenomenon was caused by a trace of residual ethanol molecules included in the structure. Similar phenomena were observed on alcohols with different polarity and molecular size.

Dynamic Changes in Dimensional Structures of Co-Complex Crystals

A two-dimensional flexible porous coordination polymer (2D-PCP) that shows expansion/shrinkage structural transformation accompanied by molecular accommodation was synthesized by control of dimensionality in zero-dimensional and one-dimensional PCPs: The dynamic structural transformation cooperatively proceeds in the solid state with a drastic molecular rearrangement. Kinetics of the structural transformation was investigated.

New insight into mesoporous silica for nano metal-organic framework.

A micropore- and mesopore-integrated material was synthesized by using a mesoporous silica and a metal-organic framework (MOF). The composite was composed of nano MOF crystals and mesoporous silica showing high porosity based on the intrinsic micropores of MOF and mesopores of mesoporous silica and additional pore spaces that should be from the void between nano MOF crystals. The composite shows higher adsorption rate of ethanol at 303 K than that of the bulk MOF.

Mesoporous Zirconium Phenylenesiliconate-phosphonate Hybrids with Ordered Lamellar Nanostructures

Novel ordered lamellar mesostructure pZrPS-2 was hydrothermally prepared by using zirconium propoxide and 4-(EtO)2OPC6H4Si(OEt)3 (pPPS-E), which was hydrolyzed to organic building units substituted with both siliconate and phosphonate groups, in the presence of Cn TAB and TMAOH. The pZrPS-2 materials were obtained at a Zr/PPS ratio of 2 or higher and the basal spacing was increased by using a longer-chain surfactant (n = 12-18). Removal of the occluded surfactants at 300 °C resulted in retention of the lamellar structure with negligible shrinkage of the interlayer distance. Nitrogen adsorption studies revealed the ordered mesoporous nature of pZrPS-2 with a pore diameter of approximately 2 to 3 nm. The lamellar structure is assumed to be composed of layers that include zirconia-based crystalline nanodomains and interlayer pillars mainly based on PPS units. Although lamellar structures with the same crystalline phase also formed when no surfactant was added or when the meta isomer of PPS was used, no mesoporous materials were obtained except pZrPS-2. A possible schematic model to elucidate these results is also proposed.

A New Synthetic Route to Microporous Silica with Well‐Defined Pores by Replication of a Metal–Organic Framework

Microporous amorphous hydrophobic silica materials with well-defined pores were synthesized by replication of the metal-organic framework (MOF) [Cu3 (1,3,5-benzenetricarboxylate)2 ] (HKUST-1). The silica replicas were obtained by using tetramethoxysilane or tetraethoxysilane as silica precursors and have a micro-meso binary pore system. The BET surface area, the micropore volume, and the mesopore volume of the silica replica, obtained by means of hydrothermal treatment at 423 K with tetraethoxysilane, are 620 m(2) g(-1) , 0.18 mL g(-1) , and 0.55 mL g(-1) , respectively. Interestingly, the silica has micropores with a pore size of 0.55 nm that corresponds to the pore-wall thickness of the template MOF. The silica replica is hydrophobic, as confirmed by adsorption analyses, although the replica has a certain amount of silanol groups. This hydrophobicity is due to the unique condensation environment of the silica precursors in the template MOF.

Ordered Microporous Layered Lanthanide 1,3,5-Benzenetriphosphonates Pillared with Cationic Organic Molecules

Novel isomorphous pillared-layer-type crystalline lanthanide 1,3,5-benzenetriphosphonates were prepared with bpy and dbo as organic pillars (LnBP-bpy and LnBP-dbo; Ln: Ce, Pr, and Nd). Ab initio crystal structure solution using synchrotron X-ray powder diffraction data revealed that the organic pillars do not exist as neutral coordinating ligands but as cationic molecules. Especially the LnBP-dbo phases have ordered interlayer space filled with water molecules between the dbo pillars, and the interlayer water is successfully removed by heating under vacuum with slightly distorted but basically retained pillared layer structures. Microporosity of the materials is confirmed by adsorption of nitrogen, carbon dioxide, and hydrogen gases. Such microporous layered metal phosphonates pillared with cationic molecules should be unprecedented and should offer new strategies to design ordered microporous materials.

GCMC simulations of dynamic structural change of Cu–organic crystals with N2 adsorption

N2 adsorption on Cu–organic crystals [Cu(bpy)2(BF4)2] (bpy = bipyridine) at 77 K begins suddenly at P/P 0 = 0.1. This unique adsorption is named gate adsorption. Gate adsorption is associated with the change of crystal structure from GCMC and dynamic GCMC simulations. An expansion of 10% opens internal pore spaces in the crystal, giving rise to gate adsorption. The complete filling of the internal spaces with N2 molecules induces an expansion of 30%.