A Preinstalled Protic Cation as a Switch for Superprotonic Conduction in a Metal–Organic Framework

Metal–organic frameworks (MOFs), made from various metal nodes and organic linkers, provide diverse research platforms for proton conduction. Here, we report on the superprotonic conduction of a Pt dimer based MOF, [Pt₂(MPC)₄Cl₂Co(DMA)(HDMA)·guest] (H₂MPC, 6-mercaptopyridine-3-carboxylic acid; DMA, dimethylamine). In this framework, a protic dimethylammonium cation (HDMA⁺) is trapped inside a pore through hydrogen bonding with an MPC ligand. Proton conductivity and X-ray measurements revealed that trapped HDMA⁺ works as a preinstalled switch, where HDMA⁺ changes its relative position and forms an effective proton-conducting pathway upon hydration, resulting in more than 105 times higher proton conductivity in comparison to that of the dehydrated form. Moreover, the anisotropy of single-crystal proton conductivity reveals the proton-conducting direction within the crystal. The present results offer insights into functional materials having a strong coupling of molecular dynamic motion and transport properties

Ni@onion-like carbon and Co@amorphous carbon: control of carbon structures by metal ion species in MOFs

We first report the facile synthesis of metal-carbon composites consisting of metal nanoparticles (NPs) and different types of carbon species: onion-like and amorphous carbon, Ni@onion-like carbon and Co@amorphous carbon. By simply changing the metal species in an isostructural metal-organic framework, thermal decompositions of MOF-74 directly afforded different types of metal NPs and carbon composites, which exhibited good electrical conductivity. In particular, the Ni@onion-like carbon, having a well-ordered carbon structure, had high electrical conductivity (sigma = 5.3 omega(-1) cm(-1) at 295 K), explained by a modified model of the Efros-Shklovskii variable range hopping

A mixed-valent metal–organic ladder linked by pyrazine

We report the synthesis, characterization, and electronic state of a novel mixed-valent metal-organic ladder (MOL) linked by pyrazine (pz). Single-crystal x-ray studies revealed that the MOL has a two-legged ladder-shaped framework, which is composed of a pz-connected Pt dimer with bridging Br ions. The electronic state of the MOL was investigated using x-ray and spectroscopic techniques; the MOL was found to have an electronic state that corresponds to the mixed-valence state of Pt(II)and Pt-IV. Furthermore, the intervalence charge transfer energy of the MOL has lower than that expected from the tendency of a similar halogen-bridged mixed-valence MOL owing to its unique 'zig-zag'-shaped legs. These results provide a new insight into the physical and electronic properties of MOL systems

Metal–organic framework thin films with well-controlled growth directions confirmed by x-ray study

Metal–organic frameworks (MOFs) have attracted the attention of a variety of researchers because of their structural diversity and designability, and their varied physical properties based on their uniform microporosity. While MOFs are interesting as bulk materials, future applications in functional nanomaterials will require the use of MOFs as thin films, and to achieve this, several thin-film fabrication techniques have been developed. These techniques have provided rational design of a variety of MOF thin films; however, oriented crystal growth of a MOF thin film, which is mainly confirmed by X-ray diffraction, remains a challenge that should be addressed. In this article, we review thin-film fabrications and characterizations, and structural features of MOF thin films with perfect crystalline orientation

Low temperature ionic conductor: Ionic liquid incorporated within a metal-organic framework

Ionic liquids (ILs) show promise as safe electrolytes for electrochemical devices. However, the conductivity of ILs decreases markedly at low temperatures because of strong interactions arising between the component ions. Metal-organic frameworks (MOFs) are appropriate microporous host materials that can control the dynamics of ILs via the nanosizing of ILs and tunable interactions of MOFs with the guest ILs. Here, for the first time, we report on the ionic conductivity of an IL incorporated within a MOF. The system studied consisted of EMI-TFSA (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide) and ZIF-8 (Zn(MeIM)2, H(MeIM) = 2-methylimidazole) as the IL and the MOF, respectively. While the ionic conductivity of bulk EMI-TFSA showed a sharp decrease arising from freezing, the EMI-TFSA@ZIF-8 showed no marked decrease because there was no phase transition. The ionic conductivity of EMI-TFSA@ZIF-8 was higher than that of bulk EMI-TFSA below 250 K. This result points towards a novel method by which to design electrolytes for electrochemical devices such as batteries that can operate at low temperatures

A compact planar low-energy-gap molecule with a donor-acceptor-donor nature based on a bimetal dithiolene complex.

Accepted 04 Sep 2015We present the first report of a compact, planar and low-energy-gap molecule based on a π-conjugated bimetal system comprising a tetrathiooxalate (tto) skeleton. The observed low HOMO-LUMO energy gap (1.19 eV) is attributed to its donor-acceptor-donor (D-A-D) nature because the skeleton acts as an electron acceptor as well as a tiny and noninnocent bridging moiety

Compression of a Flapping Mechanophore Accompanied by Thermal Void Collapse in a Crystalline Phase

Mechanical control of the molecular energy landscape is an important issue in modern materials science. Mechano­phores play a unique role in that the mechanical responses are induced against the activation barrier for intramolecular transformation with the aid of external forces. Here we report an unprecedented activation process of a flexible flapping mechano­phore. Namely, thermal void collapse in a crystalline phase triggers mechano­phore compression in a definite proportion. Unfavored conformational planarization of the flapping mechano­phore is compulsorily induced by packing force, leading to a total energy gain in crystal packing. Fluorescence chromism indicates extended π conjugation resulting from the mechano­phore compression, giving rise to an energy transfer from the unpressed to compressed conformers

Compression of a Flapping Mechanophore Accompanied by Thermal Void Collapse in a Crystalline Phase

Mechanical control of the molecular energy landscape is an important issue in modern materials science. Mechano­phores play a unique role in that the mechanical responses are induced against the activation barrier for intramolecular transformation with the aid of external forces. Here we report an unprecedented activation process of a flexible flapping mechano­phore. Namely, thermal void collapse in a crystalline phase triggers mechano­phore compression in a definite proportion. Unfavored conformational planarization of the flapping mechano­phore is compulsorily induced by packing force, leading to a total energy gain in crystal packing. Fluorescence chromism indicates extended π conjugation resulting from the mechano­phore compression, giving rise to an energy transfer from the unpressed to compressed conformers

Compression of a Flapping Mechanophore Accompanied by Thermal Void Collapse in a Crystalline Phase

Mechanical control of the molecular energy landscape is an important issue in modern materials science. Mechano­phores play a unique role in that the mechanical responses are induced against the activation barrier for intramolecular transformation with the aid of external forces. Here we report an unprecedented activation process of a flexible flapping mechano­phore. Namely, thermal void collapse in a crystalline phase triggers mechano­phore compression in a definite proportion. Unfavored conformational planarization of the flapping mechano­phore is compulsorily induced by packing force, leading to a total energy gain in crystal packing. Fluorescence chromism indicates extended π conjugation resulting from the mechano­phore compression, giving rise to an energy transfer from the unpressed to compressed conformers