Design of Frameworks and Spaces for the Control of Physical Properties

Metal complexes (coordination compounds) are composed of metal ions and organic (and inorganic) molecules as ligands around metal ions. Metal ions in complexes flexibly change their oxidation states and spin states strongly dependent on types of ligands (i.e., ligand-field) and the coordination geometry around a metal ion: This situation is just due to the ligand-field theory. Some ligands can bridge metal ions, and consequently, its repeating motifs may construct infinite frameworks as Metal-Organic Frameworks (MOFs). This bridging feature of frameworks promises short- and long-range magnetic correlation and electronic transport via d-p superexchange. Namely, controlling the dimensionality of structures and frameworks on the molecular nano-sized level, and simultaneously, tuning dynamically their oxidation states and spin states spreading over the framework, we would design strong molecular magnets and unique conductive materials, even if they were “soft” molecular materials. On the other hand, the porous structures of MOFs have attracted much attention for a decade. Like a jungle gym, as children gain entry into it, small molecules can enter nano-sized pores of molecular jungle gyms. Sometimes inserted molecules provide electronic interactions (perturbations) to MOFs involving the storage of molecules in pores. By the use of this idea, we might well be able to create unique systems at which chemical perturbations are altered to physical responses. Thus, metal complexes that possess diversity, flexibility, nano-/meso-controllable high design performance create a new platform for molecular materials.

In-situ measurements under gas atmosphere

"Changing electronic and spin properties of materials by molecular adsorption" is one of the important research themes in our laboratory. By using "flexible" porous molecular lattice materials, many phenomena can be controlled by molecular adsorption. For example, 1) structural changes upon molecular adsorption, 2) chemical interactions between MOFs and inserted molecules, and 3) magnetic effects of paramagnetic guest molecules. They may occur synergistically. Naturally, not only the host lattice but also the inserted guest molecule itself can be expected to be activated. Thus, it is possible to transform the electronic and spin states (physical signals) of guest molecules and MOFs based on the physical structural changes and chemical perturbations and reactions (chemical signals) that accompany the adsorption and desorption of molecules.
However, how to capture the "changes" associated with the adsorption and desorption of these molecules is an important research issue to be addressed. To solve these problems, technical aspects involving special equipment setups are required. Molecular adsorption depends on temperature and pressure (partial pressure). Physical properties are also related to external fields such as temperature, magnetic field, electric field, light, and so on. Therefore, we aim to capture the above chemical and physical signals by using a cryo-equipment that can vary these multiple parameters. In our laboratory, we can control the pressure and temperature of various gas molecules (N2, O2, CO2, H2, Ar, NO, CO, CH4, C2H4, C2H2...etc.) and solvent vapor to make the following measurements. These instruments are supported by the Collaboration Research Center on Energy Materials (E-IMR) and the GIMRT program in IMR, Tohoku University, and are used to study various porous compounds and materials through domestic and international collaborations. At the same time, we position these measurement techniques and equipment groups as a Platform for the Project on "Control of Physical Properties Based on Molecular Sponges" and aim to create a base for understanding changes in physical properties due to molecular adsorption from multiple perspectives.
Please contact us if you are interested in our measurement services and collaborations.

• Magnetic measurements (Quantum Design Ltd. MPMS SQUID) (T = 1.8-400 K, H ≤ 7 T)
• Physical measurements (conductivity, dielectric measurements) (Quantum Design Ltd. PPMS) (T = 1.8-400 K, H ≤ 9 T)
• IR spectroscopy (T = 4-300 K)
• Raman spectroscopy (T = 4-300 K)
• UV-Vis spectroscopy (thin-film pellet transmission and solid-state reflection spectroscopy) (T = 4-300 K)
• Circular dichroism/magnetic circular dichroism (CD/MCD) spectra (transmission spectrum measurements) (T = 4-300 K)
• Emission spectra (T = 4-300 K)
• TG-DTA-DSC measurement (atmospheric pressure gas flow type)
• Single crystal X-ray diffraction (nitrogen gas blow, T = 100-300 K)
• Powder X-ray diffraction (nitrogen gas blow, T = 100-300 K)