The tetratopic ligand tetrathiafulvalene-tetrabenzoate (H4TTFTB) is used to synthesize Zn2(TTFTB), a new metal-organic framework that contains columnar stacks of tetrathiafulvalene and benzoate-lined infinite one-dimensional channels. The new MOF remains porous upon desolvation and exhibits charge mobility commensurate with some of the best organic semiconductors, confirmed by flash-photolysis-time-resolved microwave conductivity measurements. Zn2(TTFTB) represents the first example of a permanently porous MOF with high charge mobility and may inspire further exploration of the electronic properties of these materials.

Many energy- and information-storage processes rely on phase changes of nanomaterials in reactive environments. Compared to their bulk counterparts, nanostructured materials seem to exhibit faster charging and discharging kinetics, extended life cycles, and size-tunable thermodynamics. However, in ensemble studies of these materials, it is often difficult to discriminate between intrinsic size-dependent properties and effects due to sample size and shape dispersity. Here, we detect the phase transitions of individual palladium nanocrystals during hydrogen absorption and desorption, using in situ electron energy-loss spectroscopy in an environmental transmission electron microscope. In contrast to ensemble measurements, we find that palladium nanocrystals undergo sharp transitions between the α and β phases, and that surface effects dictate the size dependence of the hydrogen absorption pressures. Our results provide a general framework for monitoring phase transitions in individual nanocrystals in a reactive environment and highlight the importance of single-particle approaches for the characterization of nanostructured materials.

Many energy storage materials undergo large volume changes during charging and discharging. The resulting stresses often lead to defect formation in the bulk, but less so in nanosized systems. Here, we capture in real time the mechanism of one such transformation—the hydrogenation of single-crystalline palladium nanocubes from 15 to 80 nm—to better understand the reason for this durability. First, using environmental scanning transmission electron microscopy, we monitor the hydrogen absorption process in real time with 3 nm resolution. Then, using dark-field imaging, we structurally examine the reaction intermediates with 1 nm resolution. The reaction proceeds through nucleation and growth of the new phase in corners of the nanocubes. As the hydrogenated phase propagates across the particles, portions of the lattice misorient by 1.5%, diminishing crystal quality. Once transformed, all the particles explored return to a pristine state. The nanoparticles' ability to remove crystallographic imperfections renders them more durable than their bulk counterparts.

Metal-organic frameworks (MOFs) have attracted interest as adsorbents in water-based adsorption heat pumps owing to their potential for increased water loading capacities and structural and functional tunability versus traditionally used materials such as zeolites and silica. Although pyrazolate-based MOFs exhibit exceptional hydrolytic stability, the water adsorption characteristics of this class of frameworks have remained unexplored in this context. In this report, we describe the modular synthesis of novel dipyrazole ligands containing naphthalenediimide cores functionalized with -H (H 2 NDI-H), -NHEt (H 2 NDI-NHEt), or -SEt (H 2 NDI-SEt) groups. Reaction of these ligands with Zn(NO 3 ) 2 afforded an isostructural series of MOFs, Zn(NDI-X), featuring infinite chains of tetrahedral Zn 2+ ions bridged by pyrazolate groups and $16 Å-wide channels with functionalized naphthalenediimide linkers lining the channel surface. The Type V water adsorption isotherms measured for these materials show water uptake in the 40-50% relative humidity range, suggesting hydrophobic channel interiors. Postsynthetic oxidation of Zn(NDI-SEt) with dimethyldioxirane was used to generate ethyl sulfoxide and ethyl sulfone groups, thereby rendering the channels more hydrophilic, as evidenced by shifts in water uptake to the 30-40% relative humidity range. Such tunability in water adsorption characteristics may find utility in the design of new adsorbents for adsorption-based heat transfer processes. An original MATLAB script, MOF-FIT, which allows for visual modeling of breathing and other structural deformations in MOFs is also presented. Broader contextThe transfer of heat via adsorption/desorption of various gases or vapors by porous materials has long been recognized for potential applications in heat storage and transformation. The possible benets of adsorption-based heat pump systems include the ability to utilize low temperature waste heat and/or solar thermal energy and use of environmentally benign working uids such as water. Porous materials such as silica and zeolites have traditionally been studied as adsorbents in water-based adsorption heat pump applications. However, these materials suffer from a lack of structural and functional tunability, hindering modulation of hydrophilicity and water exchange capacity which directly correlate to their efficiency in water adsorption-based applications. Recently, a new class of porous hybrid materials, metal-organic frameworks (MOFs), has emerged which allow for unprecedented control over structure and chemical functionality. In this study, we describe the use of a simple postsynthetic modication strategy to control the hydrophilicity and water vapor adsorption properties of a new set of water stable Zn 2+ -pyrazolate MOFs. This postsynthetic modication strategy, along with a scalable, modular ligand synthesis, represent promising new approaches for the design of water sorption materials with tunable hydrophilicity and applications in energy efficient and environmentally friendly a...

Metal hydrides often display dramatic changes in optical properties upon hydrogenation. These shifts make them prime candidates for many tunable optical devices, such as optical hydrogen sensors and switchable mirrors. While some of these metals, such as palladium, have been well studied, many other promising materials have only been characterized over a limited optical range and lack direct in situ measurements of hydrogen loading, limiting their potential applications. Further, there have been no systematic studies that allow for a clear comparison between these metals. In this work, we present such a systematic study of the dynamically tunable optical properties of Pd, Mg, Zr, Ti, and V throughout hydrogenation with a wavelength range of 250 -1690 nm. These measurements were performed in an environmental chamber, which combines mass measurements via a quartz crystal microbalance with ellipsometric measurements in up to 7 bar of hydrogen gas, allowing us to determine the optical properties during hydrogen loading. In addition, we demonstrate a further tunability of the optical properties of titanium and its hydride by altering annealing conditions, and we investigate the optical and gravimetric hysteresis that occurs during hydrogenation cycling of palladium. Finally, we demonstrate several nanoscale optical and plasmonic structures based on these dynamic properties. We show structures that, upon hydrogenation, demonstrate five orders of magnitude change in reflectivity, resonance shifts of >200 nm, and relative transmission switching of >3000%, suggesting a wide range of applications.