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Understanding the adsorption and diffusional dynamics of CO

Magnesium borohydride ammonia borane, Mg(BH4)2(NH3BH3)2, was electrochemically investigated. Impedance measurements of the mechanochemically synthesized Mg(BH4)2(NH3BH3)2 exhibited an ionic conduct...

The application of high-resolution NMR analysis for CO2 adsorbed in a MOF under high pressure is reported for the first time. The results showed that CO2 adsorbed in MOF-74 had an unusually slow mobility (τ ∼ 10-8 s). CO2-CO2 interactions suppressed the mobility of CO2 under high pressure, which, in turn, would have contributed to the stability of CO2 at the adsorption sites.

We describe the preparation of the crystalline and glassy state of a coordination polymer displaying proton conduction and guest-accessible porosity. EXAFS and solid-state NMR analyses indicated that pyrophosphate and phosphate ions are the main proton transporters in the glass and that homogeneously distributed 5-chloro-1H-benzimidazole in the glass provides the porosity.

Design to store gas molecules, such as CO2 , H2 , and CH4 , under low pressure is one of the most important challenges in chemistry and materials science. Herein, we describe the storage of CO2 in the cavities of a porous coordination polymer (PCP) using molecular rotor dynamics. Owing to the narrow pore windows of PCP, CO2 was not adsorbed at 195 K. As the temperature increased, the rotors exhibited rotational modes; such rotations dynamically expanded the size of the windows, leading to CO2 adsorption. The rotational frequencies of the rotors (k≈10-6 s) and correlation times of adsorbed CO2 (τ≈10-8 s) were elucidated via solid-state NMR studies, which suggest that the slow rotation of the rotors sterically restricts CO2 diffusion in the pores. This restriction results in an unusually slow CO2 mobility close to solid state (τ≥10-8 s). Once adsorbed at room temperature, CO2 is robustly stored in the PCP under vacuum at 195-233 K because of the steric hindrance of the rotors. We also demonstrate that this mechanism can be applied to the storage of CH4 .

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.

We demonstrated a new method of synthesizing crystalline organic cation conductors. The conductivities of various organic cations involved in a one-dimensional zinc sulfate framework were studied. The optimized structure (EMIm)2[Zn(SO4)2] exhibited an ionic conductivity of 3.8 × 10–3 S cm–1 at 210 °C, which is comparable to that of highly conductive organic ionic plastic crystals. The high ionic conductivity is attributable to the defect structures of the organic cations in the inorganic frameworks. The pulsed-field gradient solid-state NMR technique revealed that the self-diffusion coefficient of organic cations in the zinc sulfate at 80 °C is comparable to that of the popular ionic liquid EMIm-BF4 at 30 °C, which indicates that liquid-like fast transporting of organic cation is achieved in the robust crystal structure.

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 Zn(2+) ions from tetrahedral to octahedral symmetry.

Design to store gas molecules, such as CO

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 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.

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.

Zn-based two-dimensional layer coordination framework was synthesized by ionothermal synthesis and its solid-to-solid phase transition was studied by X-ray diffraction, solid state nuclear magnetic resonance and impedance spectroscopy. The phase transition is originated from the order-to-disorder behavior of accommodated ammonium cations in the structure. It occurs rapidly and reversibly, and little volume change and high thermal stability were observed.

We present a strategy for creating coordination frameworks exhibiting proton conduction with thermal stability. The coordination framework, where template cations link 1-D chains via hydrogen bonds, has dynamic hydrogen bond networks where protons move without water support. Solid-state NMR and X-ray studies visualized the proton hopping mechanism, and revealed that the templates provide the bridging of the 1-D chains to attain proton conduction. The templates also enable the proton conductive networks to be maintained at 190 °C through multiple interactions between the templates and the 1-D chains.

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 × 10(-3) S cm(-1) at 120 °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.

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 °C and 20% relative humidity. Pulse-field gradient NMR elucidated that the fast H(+) conductivity was achieved by the support of Li(+) ion movements in the channel.

Two new isomorphous three-dimensional porous coordination polymers, {[Cd(bpe)0.5(bdc)(H2O)]·EtOH}n (1) and {[Cd(bpe)0.5(bdc)(H2O)]·2H2O}n (2) [bpe = 1,2-bis(4-pyridyl)ethane, and H2bdc = 1,4-benzenedicarboxylic acid], have been synthesized by altering the solvent media. Both structures contain one-dimensional channels filled with metal-bound water and guest solvent molecules, and desolvated frameworks show significant changes in structure. However, exposure to the solvent vapors (water and methanol) reverts the structure back to the as-synthesized structure, and thus, the reversible flexible nature of the structure was elucidated. The flexibility and permanent porosity were further reinforced from the CO2 adsorption profiles (195 and 273 K) that show stepwise uptake. Moreover, a high selectivity for O2 over N2 at 77 K was realized. The framework exhibits interesting solvent vapor adsorption behavior with dynamic structural transformation depending upon the size, polarity, and coordination ability of the solvent molecules. Further investigation was conducted by solid state (113)Cd nuclear magnetic resonance (NMR) spectroscopy that unambiguously advocates the reversible transformation "pentagonal-bipyramidal CdO6N → octahedral CdO5N" geometry in the desolvated state. For the first time, (113)Cd NMR has been used as a probe of structural flexibility in a porous coordination polymer system.

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.

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 × 10(-4) S cm(-1) at 130 °C without humidity.

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.

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.

In multiple-quantum magic-angle-spinning (MQMAS) NMR experiments, it has been argued that one should use as strong rf irradiation as possible in most situations so as to attain the better sensitivity. In this work, we theoretically derive formulas for the efficiency of MQMAS experiments for spin nuclei under strong rf irradiation, and experimentally examine the validity of the derived formulas. For this purpose, a microcoil was accommodated to magic-angle-spinning (MAS) experiments by developing a microcoil-based, coin-sized probe, which is attachable to an existing MAS module. The rf intensity of up to ∼1 MHz was realized, and the efficiencies of multiple-quantum (MQ)-excitation and conversion were studied for the 23Na (I = 3/2) nucleus in a polycrystalline sample of sodium sulfite, from which the theoretical formulas were confirmed. Moreover, it was found that the effect of rf inhomogeneity is significant for MQ-excitation when rf irradiation is strong, while it is not appreciable for MQ to single-quantum conversion. From the insight into the MQ-excitation and conversion processes, the optimal set of rf intensity and pulse width is proposed for a given quadrupolar coupling constant. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 33B: 115–123, 2008

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., The intimate mixing of immiscible polymers is desirable both to aid understanding of the fundamental science and for the development of new materials. Here, the authors successfully compatibilize polystyrene and poly(methyl methacrylate) using a porous coordination polymer as a removable template.

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.

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.

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.

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.

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.

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.

2-D layer type porous coordination polymers containing redox active Fe2+ centers were synthesized. One of the compounds [Fe(isophthalate)(4,4′-bipyridyl)] showed structural flexibility via guest adsorption, and we observed reversible Fe2+ and Fe3+ switching by iodine insertion. The composite showed electric conductivity.

Porous substances, including crystalline coordination materials and an amorphous organic polymer, were studied for their selective adsorption of siloxane D4. The investigated materials demonstrated a level of uptake comparable to that of conventional activated carbon.