Step-by-Step Fabrication of a Highly Oriented Crystalline Three-Dimensional Pillared-Layer-Type Metal–Organic Framework Thin Film Confirmed by Synchrotron X-ray Diffraction

Fabrication of a crystalline ordered thin film based on the porous metal–organic frameworks (MOFs) is one of the practical applications of the future functional nanomaterials. Here, we report the creation of a highly oriented three-dimensional (3-D) porous pillared-layer-type MOF thin film on a metal substrate using a step-by-step approach based on liquid-phase epitaxy. Synchrotron X-ray diffraction (XRD) study clearly indicates that the thin film is crystalline and its orientation is highly controlled in both horizontal and vertical directions relative to the substrate. This report provides the first confirmation of details of not only the crystallinity but also the orientation of 3-D MOF thin film using synchrotron XRD. Moreover, we also demonstrate its guest adsorption/desorption behavior by using <i>in situ</i> XRD measurements. The results presented here would promise useful insights for fabrication of MOF-based nanodevices in the future

Remarkable Lattice Shrinkage in Highly Oriented Crystalline Three-Dimensional Metal–Organic Framework Thin Films

Highly oriented crystalline thin films of metal–organic frameworks (MOFs) have promising practical applications, such as in gas separation, catalysis, and sensing. We report on the successful fabrication of highly oriented crystalline thin films of three-dimensional porous MOFs, Fe­(pz)­[M­(CN)₄] (M = Ni, Pd; pz = pyrazine). Synchrotron X-ray diffraction studies reveal not only the highly oriented crystalline nature but also the remarkable shrunken structure of the thin films (∼3–7% volume shrinkage) compared with bulk samples. Furthermore, because of lattice shrinkage, these films exhibit large lattice expansions upon guest adsorption, in marked contrast to the almost unchanged lattice in the bulk samples

Guest-Induced Two-Way Structural Transformation in a Layered Metal–Organic Framework Thin Film

Fabrication of thin films made of metal–organic frameworks (MOFs) has been intensively pursued for practical applications that use the structural response of MOFs. However, to date, only physisorption-induced structural response has been studied in these films. Chemisorption can be expected to provide a remarkable structural response because of the formation of bonds between guest molecules and reactive metal sites in host MOFs. Here, we report that chemisorption-induced two-way structural transformation in a nanometer-sized MOF thin film. We prepared a two-dimensional layered-type MOF Fe­[Pt­(CN)₄] thin film using a step-by-step approach. Although the as-synthesized film showed poor crystallinity, the dehydrated form of this thin film had a highly oriented crystalline nature (<b>Film-D</b>) as confirmed by synchrotron X-ray diffraction (XRD). Surprisingly, under water and pyridine vapors, <b>Film-D</b> showed chemisorption-induced dynamic structural transformations to Fe­(L)₂[Pt­(CN)₄] thin films [L = H₂O (<b>Film-H</b>), pyridine (<b>Film-P</b>)], where water and pyridine coordinated to the open Fe²⁺ site. Dynamic structural transformations were also confirmed by in situ XRD, sorption measurement, and infrared reflection absorption spectroscopy. This is the first report of chemisorption-induced dynamic structural response in a MOF thin film, and it provides useful insights, which would lead to future practical applications of MOFs utilizing chemisorption-induced structural responses

Fabrication and Structural Characterization of an Ultrathin Film of a Two-Dimensional-Layered Metal–Organic Framework, {Fe(py)₂[Ni(CN)₄]} (py = pyridine)

We report the fabrication and characterization of the first example of a tetracyanonickelate-based two-dimensional-layered metal–organic framework, {Fe­(py)₂Ni­(CN)₄} (py = pyridine), thin film. To fabricate a nanometer-sized thin film, we utilized the layer-by-layer method, whereby a substrate was alternately soaked in solutions of the structural components. Surface X-ray studies revealed that the fabricated film was crystalline with well-controlled growth directions both parallel and perpendicular to the substrate. In addition, lattice parameter analysis indicated that the crystal system is found to be close to higher symmetry by being downsized to a thin film