High ionic conduction in a robust anionic metal-organic framework containing Mg2+ under guest vapors.

We report on the synthesis and high ionic conductivity of a highly crystalline Mg2+-containing metal-organic framework (MOF) with Type A feature (i.e., anionic framework having Mg2+ as a counter cation). We synthesized Mg[Zr(C14H3O8)2] (SU-102-Mg) through ion exchange reaction. SU-102-Mg showed a high ionic conductivity of 3.6 × 10-5 S cm-1 (25 °C, under MeCN vapor).

Ethidium benzoate methanol monosolvate.

In the title salt solvate (systematic name: 8-amino-5-ethyl-6-phenyl-phenanthridin-5-ium benzoate methanol monosolvate), C21H20N3 +·C6H5CO2 -·CH3OH, two ethidium cations, C21H20N3 +, dimerize about a twofold axis through π-π inter-actions [inter-centroid separation = 3.6137 (4) Å]. The benzoate anions are connected through hydrogen bonding with the -NH2 groups of the ethidium cations and the -OH group of the MeOH mol-ecule. The MeOH mol-ecule also accepts a hydrogen bond from the -NH2 group of the ethidium cation. The result is a one-dimensional hydrogen-bonded chain along the b-axis direction.

(2E,2'E)-1,1'-([1,1'-Biphen-yl]-4,4'-di-yl)bis-[3-(di-meth-yl-amino)-prop-2-en-1-one].

The title compound, C22H24N2O2, crystallizes in space group P21/n. The mol-ecular structure is almost planar except for a tilt of the phenyl rings. The allyl groups on both ends exhibit the trans-form and the connected N atoms show sp 2 character. The mol-ecules are stacked and assembled along the c-axis direction by C-H⋯π inter-actions.

A novel threefold interpenetrated zirconium metal-organic framework exhibiting separation ability for strong acids.

We report on the synthesis and selective adsorption property of a novel threefold interpenetrated Zr-based metal-organic framework (MOF), [Zr12O8(OH)8(HCOO)15(BPT)3] (BPT3- = [1,1'-biphenyl]-3,4',5-tricarboxylate) (abbreviated as Zr-BPT). This MOF shows a high tolerance to acidic conditions and has permanent pores, the size of which (approx. <5.6 Å) is the smallest ever reported among porous Zr-based MOFs with high acid tolerance. Zr-BPT selectively adsorbs aryl acids due to its strong affinity for them and exhibits separation ability, even between strong acid molecules, such as sulfonic and phosphonic acids. This is the first demonstration of a MOF exhibiting selective adsorption and separation ability for strong acids.

Design of a robust and strong-acid MOF platform for selective ammonium recovery and proton conductivity.

Metal-organic frameworks (MOFs) are potential candidates for the platform of the solid acid; however, no MOF has been reported that has both aqueous ammonium stability and a strong acid site. This manuscript reports a highly stable MOF with a cation exchange site synthesized by the reaction between zirconium and mellitic acid under a high concentration of ammonium cations (NH4+). Single-crystal XRD analysis of the MOF revealed the presence of four free carboxyl groups of the mellitic acid ligand, and the high first association constant (pKa1) of one of the carboxyl groups acts as a monovalent ion-exchanging site. NH4+ in the MOF can be reversibly exchanged with proton (H+), sodium (Na+), and potassium (K+) cations in an aqueous solution. Moreover, the uniform nanospace of the MOF provides the acid site for selective NH4+ recovery from the aqueous mixture of NH4+ and Na+, which could solve the global nitrogen cycle problem. The solid acid nature of the MOF also results in the proton conductivity reaching 1.34 × 10-3 S cm-1 at 55 °C by ion exchange from NH4+ to H+.

High Mg2+ conduction in three-dimensional pores of a metal-organic framework under organic vapors.

We report on high Mg2+ conduction in a metal-organic framework (MOF), UiO-66, under organic vapors. We prepared a Mg2+-containing MOF, UiO-66⊃{Mg(TFSI)2}1.0 (TFSI- = bis(trifluoromethanesulfonyl)imide), including Mg2+ carriers in three-dimensional pores. The compound showed a superionic conductivity above 10-4 S cm-1 under MeCN and MeOH vapors.

Ethidium hepta-fluoro-butyrate.

In the title compound (systematic name: 3,8-diamino-5-ethyl-6-phenylphenanthridin-5-ium 2,2,3,3,4,4,4-heptafluorobutyrate), C21H20N3 +·C4F7O2 -, two ethidium ions, C21H20N3 + form a dimerized structure due to π-π inter-actions, even though they are positively charged. The hepta-fluoro-butyrate anions are connected to neighbouring cation dimers via hydrogen-bonding inter-actions, the hydrogen-bonding donor sites of the -NH2 groups of the ethidium ions connecting to the hydrogen-bonding acceptor sites of the -COO- groups of the hepta-fluoro-butyrate anions.

Ethidium tetra-phenyl-borate aceto-nitrile disolvate.

In the title solvated salt, (C21H20N3){B(C6H5)4}·2CH3CN (systematic name 3,8-di-amino-5-ethyl-6-phenyl-phenanthridin-5-ium tetra-phenyl-borate aceto-nitrile disolvate), the dihedral angle between the tricyclic fused ring system (r.m.s. deviation = 0.021 Å) and the pendant phenyl group of the ethidium cation is 84.91 (7)°. The {B(C6H5)4}- anion has a typical tetra-hedral structure. The aceto-nitrile solvent mol-ecules do not accept hydrogen bonds from the -NH2 groups of the ethidium ions.

Preparation of a Mg2+-containing MOF through ion exchange and its high ionic conductivity.

We report, for the first time, the preparation and ionic conductivity of a Mg2+-containing metal-organic framework (MOF) having type A features, i.e., an anionic framework containing Mg2+ as the counter cation. We prepared Mg3[(MnMo6O18)2L] (L12- = C{C6H4CHNC(CH2O)3}412-) (MOF-688-Mg) through a simple ion exchange reaction, and it showed high ionic conductivity above 10-5 S cm-1 at 25 °C under MeCN vapor.

Super Mg2+ Conductivity around 10-3 S cm-1 Observed in a Porous Metal-Organic Framework.

We first report a solid-state crystalline "Mg2+ conductor" showing a superionic conductivity of around 10-3 S cm-1 at ambient temperature, which was obtained using the pores of a metal-organic framework (MOF), MIL-101, as ion-conducting pathways. The MOF, MIL-101⊃{Mg(TFSI)2}1.6 (TFSI- = bis(trifluoromethanesulfonyl)imide), containing Mg2+ inside its pores, showed a superionic conductivity of 1.9 × 10-3 S cm-1 at room temperature (RT) (25 °C) under the optimal guest vapor (MeCN), which is the highest value among all Mg2+-containing crystalline compounds. The Mg2+ conductivity in the MOF was estimated to be 0.8 × 10-3 S cm-1 at RT, by determining the transport number of Mg2+ (tMg2+ = 0.41), which is the level as high as practical use for secondary battery. Measurements of adsorption isotherms, pressure dependence of ionic conductivity, and in situ Fourier transform infrared measurements revealed that the "super Mg2+ conductivity" is caused by the efficient migration of the Mg2+ carrier with the help of adsorbed guest molecules.

Support effects of metal-organic frameworks in heterogeneous catalysis.

Catalytic support effects have been widely studied as a key factor for creating highly active heterogeneous catalysts with limited amounts of rare metal elements. Recently, support effects of metal-organic frameworks (MOFs) started to be investigated using their wide variety in pore size, electronic state, and selective adsorption property. Three types of support effects, namely molecular sieving, charge transfer, and substrate adsorption effects, have been reported on composite catalysts of metal nanoparticles supported on MOFs (M/MOFs). The current reports on heterogeneous catalysis in M/MOFs clearly demonstrated that both catalytic activity and product selectivity can be drastically enhanced and modulated by MOF supports through these support effects, and that application of MOFs as the supports is beneficial for creating novel high performance catalysts with metal nanoparticles. This minireview summarizes the catalytic properties and support effects observed on M/MOFs.

Flexibility Control of Two-Dimensional Coordination Polymers by Crystal Morphology: Water Adsorption and Thermal Expansion.

Layer flexibility in two-dimensional coordination polymers (2D-CPs) contributes to several functional materials as it results in anisotropic structural response to external stimuli. Chemical modification is a common technique for modifying layer structures. This study demonstrates that crystal morphology of a cyanide-bridged 2D-CP of type [Mn(salen)]2 [ReN(CN)4 ] (1) consisting of flexible undulating layers significantly impacts the layer configuration and assembly. Nanoplates of 1 showed an in-plane contraction of layers with a longer interlayer distance compared to the micrometer-sized rod-type particles. These effects by crystal morphology on the structure of the 2D-CP impacted the structural flexibility, resulting in dual-functional changes: the enhancement of the sensitivity of structural transformation to water adsorption and modification of anisotropic thermal expansion of 1. Moreover, the nanoplates incorporated new adsorption sites within the layers, resulting in the uptake of an additional water molecule compared to the micrometer-sized rods.

Ion-conductive metal-organic frameworks.

Metal-organic frameworks (MOFs) have emerged as a new class of ionic conductors because of their tuneable and highly ordered microporous structures. The ionic conduction of various ionic carriers, such as a proton (H+), hydroxide ion (OH-), lithium ion (Li+), sodium ion (Na+), and magnesium ion (Mg2+), in the pores of MOFs has been widely investigated over the past decade. Reports reveal that the porous or channel structures of MOFs are fundamentally suitable as ion-conducting pathways. There are clear differences in the basic designs of ion-conductive MOFs, i.e., the introduction of ionic carriers and construction of efficient ion-conducting pathways, depending on the ionic carriers. We summarize the examples and fundamental design of highly ion-conductive MOFs with various types of ionic carriers.

Support Effect of Metal-Organic Frameworks on Ethanol Production through Acetic Acid Hydrogenation.

We present a systematic study on the support effect of metal-organic frameworks (MOFs), regarding substrate adsorption. A remarkable enhancement of both catalytic activity and selectivity for the ethanol (EtOH) production reaction through acetic acid (AcOH) hydrogenation (AH) was observed on Pt nanoparticles supported on MOFs. The systematic study on catalysis using homogeneously loaded Pt catalysts, in direct contact with seven different MOF supports (MIL-125-NH2, UiO-66-NH2, HKUST-1, MIL-101, Zn-MOF-74, Mg-MOF-74, and MIL-121) (abbreviated as Pt/MOFs), found that MOFs having a high affinity for the AcOH substrate (UiO-66-NH2 and MIL-125-NH2) showed high catalytic activity for AH. This is the first demonstration indicating that the adsorption ability of MOFs directly accelerates catalytic performance using the direct contact between the metal and the MOF. In addition, Pt/MIL-125-NH2 showed a remarkably high EtOH yield (31% at 200 °C) in a fixed-bed flow reactor, which was higher by a factor of more than 8 over that observed for Pt/TiO2, which was the best Pt-based catalyst for this reaction. Infrared spectroscopy and a theoretical study suggested that the MIL-125-NH2 support plays an important role in high EtOH selectivity by suppressing the formation of the byproduct, ethyl acetate (AcOEt), due to its relatively weak adsorption behavior for EtOH rather than AcOH.

Electrochemical hydrogenation of non-aromatic carboxylic acid derivatives as a sustainable synthesis process: from catalyst design to device construction.

Electrochemical hydrogenation of a carboxylic acid using water as a hydrogen source is an environmentally friendly synthetic process for upgrading bio-based chemicals. We systematically studied electrochemical hydrogenation of non-aromatic carboxylic acid derivatives on anatase TiO2 by a combination of experimental analyses and density functional theory calculations, which for the first time shed light on mechanistic insights for the electrochemical hydrogenation of carboxylic acids. Development of a substrate permeable TiO2 cathode enabled construction of a flow-type electrolyser, i.e., a so-called polymer electrode alcohol synthesis cell (PEAEC) for the continuous synthesis of an alcoholic compound from a carboxylic acid. We demonstrated the highly efficient and selective conversion of oxalic acid to produce glycolic acid, which can be regarded as direct electric power storage into an easily treatable alcoholic compound.

Proton transfer in hydrogen-bonded degenerate systems of water and ammonia in metal-organic frameworks.

Porous crystalline metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) are emerging as a new class of proton conductors with numerous investigations. Some of the MOFs exhibit an excellent proton-conducting performance (higher than 10-2 S cm-1) originating from the interesting hydrogen(H)-bonding networks with guest molecules, where the conducting medium plays a crucial role. In the overwhelming majority of MOFs, the conducting medium is H2O because of its degenerate conjugate acid-base system (H3O+ + H2O ⇔ H2O + H3O+ or OH- + H2O ⇔ H2O + OH-) and the efficient H-bonding ability through two proton donor and two acceptor sites with a tetrahedral geometry. Considering the systematic molecular similarity to water, ammonia (NH3; NH4 + + NH3 ⇔ NH3 + NH4 +) is promising as the next proton-conducting medium. In addition, there are few reports on NH3-mediated proton conductivity in MOFs. In this perspective, we provide overviews of the degenerate water (hydronium or hydroxide)- or ammonia (ammonium)-mediated proton conduction system, the design strategies for proton-conductive MOFs, and the conduction mechanisms.

Tailoring widely used ammonia synthesis catalysts for H and N poisoning resistance.

Despite many advancements, an inexpensive ammonia synthesis catalyst free from hydrogen and nitrogen poisoning, and capable of synthesizing ammonia under mild conditions is still unknown and is long sought-after. Here we present an active nanoalloy catalyst, RuFe, formed by alloying highly active Ru and inexpensive Fe, capable of activating both N2 and H2 without blocking the surface active sites and thereby overcoming the major hurdle faced by the current best performing pure metal catalysts. This novel RuFe nanoalloy catalyst operates under milder conditions than the conventional Fe catalyst and is less expensive than the so far best performing Ru-based catalysts providing additional advantages. Most importantly, by integrating theory and experiments, we identified the underlying mechanisms responsible for lower surface poisoning of this catalyst, which will provide directions for fabricating poison-free efficient NH3 synthesis catalysts in future.

Consecutive oxidative additions of iodine on undulating 2D coordination polymers: formation of I-Pt-I chains and inhomogeneous layers.

The 2D coordination polymers, [Mn(salen)]2[PtII(CN)4]1-x[PtIV(CN)4(I2)]x (salen = N,N'-ethylenebis(salicylideneaminato), x = 0.18 (1), 0.45 (2), 0.85 (3)), have been synthesized via consecutive oxidative additions of iodine to the 2D undulating layers in [Mn(salen)]2[PtII(CN)4]. The presence of I-Pt-I chains perpendicular to the layers and the inhomogeneity of individual I-Pt-I sites were demonstrated. The I-Pt-I chains in 3 give rise to an absorption band involving the excitation that arises from an antibonding nature orbital to the corresponding bonding nature orbital between iodides in the I-Pt-I bridging units. Moreover, variable-temperature X-ray powder diffraction patterns and Raman spectra for 1 and 2 indicate that some I-Pt-I sites display different vibrational energies that are associated with the contraction of the zigzag 2D layers.

Electrochemical Production of Glycolic Acid from Oxalic Acid Using a Polymer Electrolyte Alcohol Electrosynthesis Cell Containing a Porous TiO2 Catalyst.

A liquid flow-type electrolyser that continuously produces an alcohol from a carboxylic acid was constructed by employing a polymer electrolyte, named a polymer electrolyte alcohol electrosynthesis cell (PEAEC). Glycolic acid (GC, an alcoholic compound) is generated on anatase TiO2 catalysts via four-electron reduction of oxalic acid (OX, a divalent carboxylic acid), accompanied with water oxidation, which achieves continuous electric power storage in easily stored GC. Porous anatase TiO2 directly grown on Ti mesh (TiO2/Ti-M) or Ti felt (TiO2/Ti-F) was newly fabricated as a cathode having favourable substrate diffusivity. A membrane-electrode assembly composed of the TiO2/Ti-M, Nafion 117, and an IrO2 supported on a gas-diffusion carbon electrode (IrO2/C) was applied to the PEAEC. We achieved a maximum energy conversion efficiency of 49.6% and a continuous 99.8% conversion of 1 M OX, which is an almost saturated aqueous solution at room temperature.

Modulation of the catalytic activity of Pt nanoparticles through charge-transfer interactions with metal-organic frameworks.

We employed metal-organic framework (MOF) supports to modulate the electronic states of loaded Pt nanoparticles (NPs) in their composite catalysts (Pt/MOFs). Pt NPs were homogenously deposited on four MOFs characterized with different electronic states (Zn-MOF-74, Mg-MOF-74, HKUST-1, and UiO-66-NH2). Theoretical and experimental studies demonstrated that a charge-transfer interaction between Pt NPs and MOFs is a critical factor for controlling the catalytic activity of Pt NPs supported on MOFs.