The Front Cover shows the crystal packings of a zwitterionic triarylmethylium salt and Japanese maple leaves. The zwitterion was easily synthesized by one-pot and two-step reactions from potassium 4-bromophenyltris(pentafluorophenyl)borate and exhibits vivid color change in the solid state from green to yellow and then to red by dissolution/evaporation and grinding, respectively. In addition, single crystals of the zwitterionic salts with green, yellow, and red colors could be obtained with different crystal systems, and thus the crystal packings are highlighted with the corresponding colors. Japanese maple leaves turn from green to red, heralding the arrival of autumn. The cover design also reflects a wish for the arrival of the harvest season in chemical research. More information can be found in the Research Article by Y. Mizuhata, N. Tokitoh and co-workers.

This review summarizes five kinds of POM-based active materials in new molecular nonvolatile memristors, whose device parameters and resistive switching mechanisms relative to their structures are introduced.

Abstract

The coming big-data era has created a huge demand for next-generation memory technologies with characters of higher data-storage densities, faster access speeds, lower power consumption and better environmental compatibility. In this field, the design of resistive switching active materials is pivotal but challengeable. Polyoxometalates (POMs) are promising candidates for next-generation molecular memristors due to their versatile redox characters, excellent electron reservoirs and good compatibility/convenience in microelectronics processing. In this review, five kinds of POM-based active materials in nonvolatile memories (inorganic POMs, crystalline organic-inorganic hybrid POMOFs, polymer modified POMs, POM/transition metal oxides composites and the deposition of POM on metal surfaces) were described. The components of POMs active materials, device fabrications, device parameters, and resistive switching mechanisms relative to their structures were summarized. Finally, challenges and future perspectives of POMs-based memristors were also presented.

A dibismuthane, R₂Bi−BiR₂, with olefin functional groups has been isolated (top right in the graphic). Reactivity studies furnished two series of compounds with Bi-chalcogen bonds, R₂Bi−EPh and R₂Bi−E−BiR₂ (E=O−Te). The properties of compounds R₂Bi−E−BiR₂ (top left in the graphic) as tridentate chalcogen/olefin ligands towards transition metals have been investigated by DFT calculations.

Abstract

Bis[dibenzobismepine], a dibismuthane composed of two bismepine units (R₂Bi−BiR₂), was synthesized and fully characterized (R₂=(C₆H₄CH)₂). Reactions of this dibismuthane with diphenyl dichalcogenides, dibenzoylperoxide, and elemental chalcogens have been investigated. All products of these reactions have been isolated and fully characterized, including a series of compounds R₂Bi−E−BiR₂ (E=O−Te). These species contain two olefin units of the bismepine moieties and a chalcogen atom as potential coordination sites. The potential of these species to act as hybrid tridentate chalcogen/olefin ligands with bismuth atoms as structure-determining elements in the backbone has been investigated by theoretical approaches, aiming at the complexation of Co^I, Rh^I, Ir^I and Ni⁰, Pd⁰, Pt⁰. The analytical techniques applied in this work include heteronuclear and 2D NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction analysis, and DFT calculations.

Cu-nanosphere film with a high surface area and dominant (200) facet was fabricated by a simple electrodeposition method. The Cu-nanosphere achieved excellent nitrate reduction reaction (NO₃RR), and nitrogen reduction reaction (NRR) performance. The dominance of the Cu (200) facet of the Cu-nanosphere electrocatalyst suppresses the competing hydrogen evolution reaction (HER) and thus exhibits better electrochemical NO₃RR and NRR selectivity.

Abstract

The electrochemical reduction reaction of nitrogenous species such as NO₃ ⁻ (NO₃RR) and N₂ (NRR) is a promising strategy for producing ammonia under ambient conditions. However, low activity and poor selectivity of both NO₃RR and NRR remain the biggest problem of all current electrocatalysts. In this work, we fabricated Cu-nanosphere film with a high surface area and dominant with a Cu(200) facet by simple electrodeposition method. The Cu-nanosphere film exhibits high electrocatalytic activity for NO₃RR and NRR to ammonia under ambient conditions. In the nitrate environment, the Cu-nanosphere electrode reduced NO₃ ⁻ to yield NH₃ at a rate of 5.2 mg/h cm², with a Faradaic efficiency of 85 % at −1.3 V. In the N₂-saturated environment, the Cu-nanosphere electrode reduced N₂ to yield NH₃ with the highest yield rate of 16.2 μg/h cm² at −0.5 V, and the highest NH₃ Faradaic efficiency of 41.6 % at −0.4 V. Furthermore, the Cu-nanosphere exhibits excellent stability with the NH₃ yield rate, and the Faradaic efficiency remains stable after 10 consecutive cycles. Such high levels of NH₃ yield, selectivity, and stability at low applied potential are among the best values currently reported in the literature.

The Front Cover shows the structural unit of the newly discovered [Co(terpy)₂]₃[W(CN)₈]₂ ⋅12H₂O compound, terpy=2,2′:6′,2′′-terpyridine. This material can adopt diverse states: low-spin Co^II and W^V, S=1/2; high-spin Co^II, S=3/2; and low-spin Co^III and W^IV, S=0 (blue, purple, red, light blue, and pink polyhedra), depending on the treatment history of the sample. The fresh complex at 10 K has low-spin Co^II and W^V centers. Above 300 K, the material demonstrates thermal desolvation-assisted spin-crossover (DASCO), reaching complete high-spin Co^II and W^V states at 400 K. Next, Co₃W₂ , upon cooling, exhibits SCO on Co^II. Interestingly, a humidity treatment of Co₃W₂ initiates a new effect of isothermal humidity-activated charge-transfer-induced spin transition (HACTIST) leading to the partial conversion of Co^II…W^V to Co^III…W^IV pairs, which can be reversed by desolvation. More information can be found in the Research Article by O. Stefanczyk, S.-i. Ohkoshi and co-workers.

A zwitterionic triarylmethylium salt exhibits solid-state chromism by dissolution & evaporation or evaporation, which shows green, yellow and red. The same color crystalls were obtained from different recrystallization connditions. Correlation between the chromism and molecular structure were studied by using diffuse reflectance measurement, single crystal x-ray analysis and powder x-ray diffraction.

Abstract

Zwitterionic triarylmethylium dyes 1 and 2 were synthesized by using a synthetic unit of a tetraarylborate. The zwitterionic structure of 1 and 2 exhibits varied molecular assembly and induces charge transfer transition. These properties gave them specific optical features such as solvatochromism and mechanochromism in the solid state, that is, the green solid of 2 changes to yellow or red solid by dissolution & evaporation or grinding, respectively. The three colors were reproduced independently in different crystal forms, which were prepared from different recrystallization conditions. The diffuse reflectance measurement and powder X-ray diffraction demonstrated the correlation between the colors and the solid-state structures. The single crystal X-ray analysis revealed face-to-face dimeric assembly in each crystal. Among the crystal structures, the intermolecular distances and packing patterns were notable differences. Based on these results, it can be suggested that unique color change of zwitterionic triarylmethylium dyes originates from the alternation of intermolecular interactions.