Munehiro Inukai, Satoshi Horike, Tomoya Itakura, Ryota Shinozaki, Naoki Ogiwara, Daiki Umeyama, Sanjog Nagarkar, Yusuke Nishiyama, Michal Malon, Akari Hayashi, Takashi Ohhara, Ryoji KiyanagiandSusumu Kitagawa : Encapsulating Mobile Proton Carriers into Structural Defects in Coordination Polymer Crystals: High Anhydrous Proton Conduction and Fuel Cell Application, Journal of the American Chemical Society, Vol.138, No.27, 8505-8511, 2016.
(Summary)
We describe the encapsulation of mobile proton carriers into defect sites in nonporous coordination polymers (CPs). The proton carriers were encapsulated with high mobility and provided high proton conductivity at 150 °C under anhydrous conditions. The high proton conductivity and nonporous nature of the CP allowed its application as an electrolyte in a fuel cell. The defects and mobile proton carriers were investigated using solid-state NMR, XAFS, XRD, and ICP-AES/EA. On the basis of these analyses, we concluded that the defect sites provide space for mobile uncoordinated H3PO4, H2PO4(-), and H2O. These mobile carriers play a key role in expanding the proton-hopping path and promoting the mobility of protons in the coordination framework, leading to high proton conductivity and fuel cell power generation.
Ritesh Haldar, Munehiro Inukai, Satoshi Horike, Kazuhiro Uemura, Susumu KitagawaandKumar Tapas Maji : 113Cd Nuclear Magnetic Resonance as a Probe of Structural Dynamics in a Flexible Porous Framework Showing Selective O2/N2 and CO2/N2 Adsorption, Inorganic Chemistry, Vol.55, No.9, 4166-4172, 2016.
T. Itakura, S. Horike, Munehiro InukaiandS. Kitagawa : Freeze-drying synthesis of an amorphous Zn2+ complex and its transformation to a 2-D coordination framework in the solid state, Dalton Transactions, Vol.45, No.10, 4127-4131, 2016.
(Summary)
An amorphous and metastable precursor for a Zn two-dimensional coordination framework was synthesised via freeze drying. The precursor comprises randomly packed discrete clusters of a Zn complex. The amorphous-to-crystalline framework transformation, which was triggered by the gentle application of heat or pressure, was accompanied by a change in the coordination geometry of the Zn2+ ions from tetrahedral to octahedral symmetry.
Munehiro Inukai, Tomohiro Fukushima, Yuh Hijikata, Naoki Ogiwara, Satoshi HorikeandSusumu Kitagawa : Control of Molecular Rotor Rotational Frequencies in Porous Coordination Polymers Using a Solid-Solution Approach, Journal of the American Chemical Society, Vol.137, No.38, 12183-12186, 2015.
(Summary)
Rational design to control the dynamics of molecular rotors in crystalline solids is of interest because it offers advanced materials with precisely tuned functionality. Herein, we describe the control of the rotational frequency of rotors in flexible porous coordination polymers (PCPs) using a solid-solution approach. Solid-solutions of the flexible PCPs [{Zn(5-nitroisophthalate)x(5-methoxyisophthalate)1-x(deuterated 4,4'-bipyridyl)}(DMF·MeOH)]n allow continuous modulation of cell volume by changing the solid-solution ratio x. Variation of the isostructures provides continuous changes in the local environment around the molecular rotors (pyridyl rings of the 4,4'-bipyridyl group), leading to the control of the rotational frequency without the need to vary the temperature.
The establishment of methodologies for the mixing of immiscible substances is highly desirable to facilitate the development of fundamental science and materials technology. Herein we describe a new protocol for the compatibilization of immiscible polymers at the molecular level using porous coordination polymers (PCPs) as removable templates. In this process, the typical immiscible polymer pair of polystyrene (PSt) and poly(methyl methacrylate) (PMMA) was prepared via the successive homopolymerizations of their monomers in a PCP to distribute the polymers inside the PCP particles. Subsequent dissolution of the PCP frameworks in a chelator solution affords a PSt/PMMA blend that is homogeneous in the range of several nanometers. Due to the unusual compatibilization, the thermal properties of the polymer blend are remarkably improved compared with the conventional solvent-cast blend. This method is also applicable to the compatibilization of PSt and polyacrylonitrile, which have very different solubility parameters.
Daiki Umeyama, Satoshi Horike, Munehiro Inukai, Tomoya ItakuraandSusumu Kitagawa : Reversible Solid-to-Liquid Phase Transition of Coordination Polymer Crystals, Journal of the American Chemical Society, Vol.137, No.2, 864-870, 2015.
(Summary)
The solid-to-liquid phase transition, a fundamental process commonly observed for various types of substances with significant potential for application, has been given little attention in the field of coordination polymers (CPs) despite the rich functionality of these compounds. In this article, we report the reversible solid-to-liquid phase transition of crystalline CPs. These CPs are composed of zinc ions, phosphate, and azoles, and a well-balanced composition, ionicity, and bond strength afford "melting" CPs. We examined the structure of one such melting framework in the liquid and glass states and found that the coordination bonds are not fully preserved in the liquid state but are re-formed in the glass state. As a demonstration, we fabricated, via phase transition, a thin film with an aligned crystal orientation and a monolith crystal of the CP.
Novel organic-inorganic hybrid liposomes, so-called coordination polymersomes (CPsomes), with artificial domains that exhibit strong lateral cohesion were prepared by a three-step procedure that formed a coordinative interaction leading to a lipid bilayer. First, the lipophilic complex (dabco-C18)[Mn(N)(CN)4(dabco-C18)] (1; dabco-C18(+)=1,4-diazabicyclo[2,2,2]octane-(CH2)17-CH3 cation), was synthesized. 1 has a lipophilic alkyl tail part and a tetracyanometallate head group, which can be used for an expansion to two-dimensional coordination networks. Second, 1 and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine were mixed to prepare the liposomes. Finally, CPsomes were obtained by the addition of transition-metal ions (M) to form unilamellar faceted liposomes with plain CP raft domains with Mn-CN-M linkages. The concentration of 1 influences the size of the CP raft domains and the shape of the CPsomes. The synthesis of coordination polymers in lipid bilayers is a novel approach for the construction of artificial architectures as raft domains, for example, in cell membranes.
S. Horike, K. Kadota, T. Itakura, Munehiro InukaiandS. Kitagawa : Synthesis of magnesium ZIF-8 from Mg(BH4)2, Dalton Transactions, Vol.44, No.34, 15107-15110, 2015.
(Summary)
Porous Mg(2-methyl imidazolate)2 (Mg-ZIF-8) was synthesised from Mg(BH4)2 as a precursor under an Ar atmosphere. It possesses an uncommon tetrahedral Mg2+-N coordination geometry that is stabilised by the formation of a framework, and it exhibits a Brunauer-Emmett-Teller surface area greater than 1800 m2 g-1.
Satoshi Horike, Wenqian Chen, Tomoya Itakura, Munehiro Inukai, Daiki Umeyama, Hiroyuki AsakuraandSusumu Kitagawa : Order-to-disorder structural transformation of a coordination polymer and its influence on proton conduction, Chemical Communications, Vol.50, No.71, 10241-10243, 2014.
(Summary)
We observed an ordered-to-disordered structural transformation in a Cu(2+) coordination polymer and investigated its influence on the proton conductivity. The transformation generated highly mobile proton carriers in the structure. The resulting material exhibited a conductivity greater than 10(-2) S cm(-1) at 130 °C. The structural transformation and the conduction mechanism were investigated by EXAFS, TPD-MS and NMR.
Munehiro Inukai, Satoshi Horike, Wenqian Chen, Daiki Umeyama, Tomoya ItakuraandSusumu Kitagawa : Template-directed proton conduction pathways in a coordination framework, Journal of Materials Chemistry. A, Materials for Energy and Sustainability, Vol.2, No.27, 10404-10409, 2014.
D. Umeyama, S. Horike, Munehiro InukaiandS. Kitagawa : Integration of intrinsic proton conduction and guest-accessible nanospace into a coordination polymer, Journal of the American Chemical Society, Vol.135, No.30, 11345-11350, 2013.
(Summary)
We report the synthesis and characterization of a coordination polymer that exhibits both intrinsic proton conductivity and gas adsorption. The coordination polymer, consisting of zinc ions, benzimidazole, and orthophosphate, exhibits a degree of flexibility in that it adopts different structures before and after dehydration. The dehydrated form shows higher intrinsic proton conductivity than the original form, reaching as high as 1.3 x 10(-3) S cm(-1) at 120 degrees C. We found that the rearranged conduction path and liquid-like behavior of benzimidazole molecules in the channel of the framework afforded the high proton conductivity. Of the two forms of the framework, only the dehydrated form is porous to methanol and demonstrates guest-accessible space in the structure. The proton conductivity of the dehydrated form increases by 24 times as a result of the in situ adsorption of methanol molecules, demonstrating the dual functionality of the framework. NMR studies revealed a hydrogen-bond interaction between the framework and methanol, which enables the modulation of proton conductivity within the framework.
Y. Hijikata, S. Horike, M. Sugimoto, Munehiro Inukai, T. FukushimaandS. Kitagawa : Pore design of two-dimensional coordination polymers toward selective adsorption, Inorganic Chemistry, Vol.52, No.7, 3634-3642, 2013.
(Summary)
We have synthesized four porous coordination polymers (PCPs) using Zn(2+), 4,4'-sulfonyldibenzoate (sdb), and four types of dinitrogen linker ligands, 1,4-diazabicyclo[2,2,2]octane (dabco), 1,4-bis(4-pyridyl)benzene (bpb), 3,6-bis(4-pyridyl)-1,2,4,5-tetrazine (bpt), and 4,4'-bipyridyl (bpy). The bent sdb ligands form a rhombic space connected by zinc paddle-wheel units to form a one-dimensional double chain, and each dinitrogen ligand linked the one-dimensional double chains. There are different assembled structures of two-dimensional sheets with the same connectivities between Zn(2+) and the organic ligands. [Zn2(sdb)2(dabco)]n (1) has a noninterpenetrated and noninterdigitated structure, [Zn2(sdb)2(bpb)]n (2) and [Zn2(sdb)2(bpt)]n (3) have interdigitated structures, and [Zn2(sdb)2(bpy)]n (4) has an interpenetrated structure. The length of the dinitrogen ligands dominated their assembled structures and flexibility, which influence the adsorption properties. The flexible frameworks of 2 and 3 provide different stepwise adsorption behaviors for CO2, CH4, C2H6, and C2H4 affected by their pore diameters and the properties of the gases. Their different adsorption properties were revealed by IR spectroscopy and X-ray analysis under a gas atmosphere. The framework of 4 possesses less flexibility and a smaller void space than the others and a negligible amount of CH4 was adsorbed; however, 4 can adsorb either C2H6 or C2H4 through the gate-opening phenomenon. Measurement of the solid-state (2)H NMR was also carried out to investigate the relationship between the framework structure and the dynamics of bpy with regard to the lower flexibility of 4. We have demonstrated a strategy to control the pore size and assembled structures toward selective adsorption properties of PCPs.
S. Horike, Y. Kamitsubo, Munehiro Inukai, T. Fukushima, D. Umeyama, T. ItakuraandS. Kitagawa : Postsynthesis modification of a porous coordination polymer by LiCl To enhance H+ transport, Journal of the American Chemical Society, Vol.135, No.12, 4612-4615, 2013.
(Summary)
A Ca(2+) porous coordination polymer with 1D channels was functionalized by the postsynthesis addition of LiCl to enhance the H(+) conductivity. The compound showed over 10(-2) S cm(-1) at 25 degrees C and 20
S. Noro, Y. Hijikata, Munehiro Inukai, T. Fukushima, S. Horike, M. Higuchi, S. Kitagawa, T. AkutagawaandT. Nakamura : Highly selective CO2 adsorption accompanied with low-energy regeneration in a two-dimensional Cu(II) porous coordination polymer with inorganic fluorinated PF6(-) anions, Inorganic Chemistry, Vol.52, No.1, 280-285, 2013.
(Summary)
High selectivity and low-energy regeneration for adsorption of CO(2) gas were achieved concurrently in a two-dimensional Cu(II) porous coordination polymer, [Cu(PF(6))(2)(4,4'-bpy)(2)](n) (4,4'-bpy = 4,4'-bipyridine), containing inorganic fluorinated PF(6)(-) anions that can act as moderate interaction sites for CO(2) molecules.
Munehiro Inukai, S. Horike, D. Umeyama, Y. HijikataandS. Kitagawa : Investigation of post-grafted groups of a porous coordination polymer and its proton conduction behavior, Dalton Transactions, Vol.41, No.43, 13261-13263, 2012.
(Summary)
We investigated the configuration of substituent groups that are post-synthetically bound to the pore surface in a porous coordination polymer. This study demonstrates the observations of orientation and coordination fashions of the grafted groups, which contribute towards improved proton conductivity in porous frameworks.
D. Umeyama, S. Horike, Munehiro Inukai, T. ItakuraandS. Kitagawa : Inherent proton conduction in a 2D coordination framework, Journal of the American Chemical Society, Vol.134, No.30, 12780-12785, 2012.
(Summary)
We synthesized a coordination polymer consisting of Zn(2+), 1,2,4-triazole, and orthophosphates, and demonstrated for the first time intrinsic proton conduction by a coordination network. The compound has a two-dimensional layered structure with extended hydrogen bonds between the layers. It shows intrinsic proton conductivity along the direction parallel to the layers, as elucidated by impedance studies of powder and single crystals. From the low activation energy for proton hopping, the conduction mechanism was found to be of the Grotthuss fashion. The hopping is promoted by rotation of phosphate ligands, which are aligned on the layers at appropriate intervals.
S. Horike, K. Kishida, Y. Watanabe, Y. Inubushi, D. Umeyama, M. Sugimoto, T. Fukushima, Munehiro InukaiandS. Kitagawa : Dense coordination network capable of selective CO2 capture from C1 and C2 hydrocarbons, Journal of the American Chemical Society, Vol.134, No.24, 9852-9855, 2012.
(Summary)
We elucidated the specific adsorption property of CO(2) for a densely interpenetrated coordination polymer which was a nonporous structure and observed gas separation properties of CO(2) over CH(4), C(2)H(4), and C(2)H(6), studied under both equilibrium and kinetic conditions of gases at ambient temperature and pressure.
S. Horike, D. Umeyama, Munehiro Inukai, T. ItakuraandS. Kitagawa : Coordination-network-based ionic plastic crystal for anhydrous proton conductivity, Journal of the American Chemical Society, Vol.134, No.18, 7612-7615, 2012.
(Summary)
An ionic coordination network consisting of protonated imidazole and anionic one-dimensional chains of Zn(2+) phosphate was synthesized. The compound possesses highly mobile ions in the crystal lattice and behaves as an ionic plastic crystal. The dynamic behavior provides a proton conductivity of 2.6 x 10(-4) S cm(-1) at 130 degrees C without humidity.
D. Umeyama, S. Horike, Munehiro Inukai, Y. HijikataandS. Kitagawa : Confinement of mobile histamine in coordination nanochannels for fast proton transfer, Angewandte Chemie International Edition, Vol.50, No.49, 11706-11709, 2011.
(Keyword)
Anisotropy Histamine/*chemistry Magnetic Resonance Spectroscopy Nanostructures/*chemistry/ultrastructure Polymers/*chemistry Porosity *Protons
Munehiro Inukai, Y. NodaandK. Takeda : Nondestructive high-resolution solid-state NMR of rotating thin films at the magic-angle, Journal of Magnetic Resonance, Vol.213, No.1, 192-195, 2011.
(Summary)
We present a new approach to nondestructive magic-angle spinning (MAS) nuclear magnetic resonance (NMR) for thin films. In this scheme, the sample put on the top of a rotor is spun using the conventional MAS system, and the NMR signals are detected with an additional coil. Stable spinning of disk-shaped samples with diameters of 7 mm and 12 mm at 14.2 and 7 kHz are feasible. We present 7Li MAS NMR experiments of a thin-film sample of LiCoO2 with a thickness of 200 nm. Taking advantage of the nondestructive feature of the experiment, we also demonstrate ex situ experiments, by tracing conformation change upon annealing for various durations. This approach opens the door for in situ MAS NMR of thin-film devices as well.
(Keyword)
Electrodes Lithium/chemistry Lithium Carbonate/chemistry Magnetic Resonance Spectroscopy/instrumentation/*methods
Munehiro InukaiandK. Takeda : Double-resonance magic angle coil spinning, Journal of Magnetic Resonance, Vol.202, No.2, 274-278, 2010.
(Summary)
We present an extension of magic angle coil spinning (MACS) solid-state NMR spectroscopy to double-resonance experiments, enabling implementation of powerful double-resonance solid-state NMR methodologies including cross polarization, proton decoupling, and two-dimensional correlation spectroscopy etc., while still enjoying the merits that are intrinsic to MACS, such as high concentration sensitivity, eliminated magnetic susceptibility-induced field distortion, and an easy-to-use approach with the conventional and widespread hardware.
(Keyword)
Carbon Isotopes Magnetic Resonance Spectroscopy/*methods Nitrogen Isotopes Protons Signal Processing, Computer-Assisted Silicon Sodium Isotopes
M. Fukuchi, Munehiro Inukai, K. TakedaandK. Takegoshi : Double-acquisition: utilization of discarded coherences in a 2D separation experiment using the States method, Journal of Magnetic Resonance, Vol.194, No.2, 300-302, 2008.
(Summary)
We propose a new data-acquisition scheme for 2D separation experiments to save the spectrometer time by 1/2. This scheme, referred to as a double-acquisition scheme, is applicable to most of separation experiments with the hypercomplex time-domain data-acquisition scheme (the States method) for data collection.
(Keyword)
*Algorithms Information Storage and Retrieval/*methods Magnetic Resonance Spectroscopy/*methods Sample Size *Signal Processing, Computer-Assisted
Munehiro InukaiandKazuyuki Takeda : Studies on multiple-quantum magic-angle-spinning NMR of half-integer quadrupolar nuclei under strong rf pulses with a microcoil, Concepts in Magnetic Resonance. Part B, Magnetic Resonance Engineering, Vol.33B, No.2, 115-123, 2008.
Layered oxides such as NaxMO2 (M = Co, Cr) have been studied as electrodes for replacing the lithium ion batteries. The relaxation time T1 of 23Na nucleus in Na0.8CoO2 decreased in the range from 180 K to 300 K and increased above 300 K. Temperature dependence of Electrical conductivity NaxCoO2 and NaxCrO2 shows that electric conduction of NaxCoO2 becomes larger than that of NaxCrO2.These results suggest that the crystal structure of NaxCoO2 becomes locally disordered. It is considered that the crystal structure of NaxCoO2 is unstable, and related to the improvement Na+ ion diffusion.
Koichi Nakamura, Hiroaki Ito, Munehiro Inukai, Toshihiro Moriga, 岩井 良樹, 桑田 直明and河村 純一 : Changes of local structure and Li+ ion motion in LiMPO4 (M=Fe, Mn), 第20回超イオン導電体物性研究会講演要旨集, 71-74, Jul. 2017.
(Summary)
Olivine-type LiMPO4 (M=Fe and Mn) has been studied as a cathode material for lithium ion secondary batteries. The XRD peak broadening and peak shift of LiFePO4 at high temperatures suggest that the crystal structure around Li sites becomes locally disordered. The NMR line width and the spin-lattice relaxation time, T1, for 7Li nucleus of LiFePO4 depended on temperature from 550K to 700K, while those of LiMnPO4 did not show a remarkable temperature dependence up to 700K. The results imply that a local structural change of LiFePO4 at high temperatures is related to the motion of a part of Li+ ions.
Olivine type lithium iron phosphates have been studied as a cathode material for lithium ion secondary batteries. The NMR line widths and spin-lattice relaxation time T1 of 7Li nucleus in LiFePO4 changed from 550K to 700K, while those of LiMnPO4 and LiCoPO4 did not show the remarkable temperature dependence. The peak broadening of XRD pattern of LiFePO4 at high temperatures suggests that the crystal structure around Li sites becomes locally disordered. It is considered that these situations would stimulate Li+ ion dynamics related to changes of the NMR line width and T1 at high temperatures.
23Na NMR and electrical conductivity measurements have been performed to study milling effects on ion conducting behavior and local structure of NaNbO3 exposed to milling. A complex MAS NMR spectrum attributed to Na(1) and Na(2) sites was dependent on milling time as well as XRD patterns. It was found that inequivalent local structures around Na sites of NaNbO3 are disturbed severely by milling. This structural change is considered to be connected with the Na+ ion conductivity with the activation energy of 0.3~0.4 eV because narrowing in the NMR line widths and changes in electrical conductivity were observed at high temperatures.
NMR spectra and spin-lattice relaxation time, T-1, for 7Li nucleus have been probed to study the local structure and Li+ ion dynamics in olivine-type LiMPO4 (M=Fe, Mn). Antimagnetic spin correlation was dominant at low temperatures in the NMR spectrum and relaxation time of both samples, while changes in the line width and relaxation time were observed in LiFePO4 above 550K. This would be related with the Li+ ion motion in LiFePO4 at high temperatures.
Non-linear ultrasonic resonance measurement with acoustic echo (phonon echo) has been applied to detect indirectly ion motion in solids. The relaxation time, T2, of SiO2 particles with a small amount of LiNbO3 particles was different from that of SiO2 particles above 600K. The T2 values were significantly dependent on temperature. A simple Debye model was applied to interpret its temperature dependence, and derived thermal activation energy would be related to an activation energy for the Li+ ion motion These results suggest that the indirect measurement is available to detect the Li+ ion motion in solids.