The synthesis of artificial ion channels is one of the core areas of biomimetics and is aimed at achieving control over channel functionality by careful design and selection of the constituent components. However, the optimization of ionic conductivity in the channel in the crystalline state is challenging because of crystal strain, polymorphism, and potentially limited stability. In this study, the pore size of cylindrical channels was controlled with the aim of optimizing ionic conductivity. We prepared two isomorphic salts, Li2([18]­crown-6)3[Ni­(dmit)2]2(H2O)4 (1) and Li2([15]­crown-5)3[Ni­(dmit)2]2(H2O)2 (2), both of which possess ion channels formed by a one-dimensional array of crown ethers, Li+ ions, and crystalline water molecules. Meanwhile, [Ni­(dmit)2]− (S = 1/2) molecules formed a ladder configuration with J rung/k B = −631(5) K, J leg/k B = −185(5) K for 1, and J rung/k B = −517(4) K, J leg/k B = −109(5) K for 2. For 1, the Li+ ionic conductivity at 293 K in the crystalline state was enhanced from 1.89(18) × 10–8 S·cm–1 to 2.46(6) × 10–7 S·cm–1 via dehydration. Furthermore, analysis of Li+ ionic conductivities of 2, which incorporated a crown ether with a smaller cavity (the cavity diameters of [18]­crown-6 and [15]­crown-5 are 2.60–3.20 Å and 1.70–2.20 Å, respectively) at the same temperature both before and after dehydration revealed conductivities of 1.93(31) × 10–8 S·cm–1 and 7.01(21) × 10–7 S·cm–1, respectively. This molecular design approach can contribute to increasing the ionic conductivity as well as the development of all-solid-state lithium ion batteries and other electronic device fabrications.

A mono-potassium cation-encapsulated Preyssler-type phosphotungstate, [P 5 W 30 O 110 K] 14– ( 1 ), was prepared as a potassium salt, K 14 [P 5 W 30 O 110 K] ( 1a ), by heating mono-bismuth- or mono-calcium-encapsulated Preyssler-type phosphotungstates (K 12 [P 5 W 30 O 110 Bi(H 2 O)] or K 13 [P 5 W 30 O 110 Ca(H 2 O)]) in acetate buffer. Characterization of the potassium salt 1a by single-crystal X-ray structure analysis, 31 P and 183 W nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared spectroscopy, high-resolution electrospray ionization mass spectroscopy, and elemental analysis revealed that one potassium cation is encapsulated in the central cavity of the Preyssler-type phosphotungstate molecule with a formal D 5 h symmetry. Density functional theory calculations have confirmed that the potassium cation prefers the central position of the cavity over a side position, in which no water molecules are coordinated to the encapsulated potassium cation. 31 P NMR and cyclic voltammetry analyses revealed the rapid protonation–deprotonation of the oxygens in the cavity compared to that of other Preyssler-type compounds. Heating of 1a in the solid state afforded a di-K + -encapsulated compound, K 13 [P 5 W 30 O 110 K 2 ] ( 2a ), indicating that a potassium counter-cation is introduced in one of the side cavities, concomitantly displacing the internal potassium ion from the center to a second side cavity, thus providing a new method to encapsulate an additional cation in Preyssler compounds.

In a mixed-valence polyoxometalate, electrons are usually delocalized within the cluster anion because of low level of inter-cluster interaction. Herein, we report the structure and electrical properties of a single crystal in which mixed-valence polyoxometalates were electrically wired by cationic π-molecules of tetrathiafulvalene substituted with pyridinium. Electron-transport characteristics are suggested to represent electron hopping through strong interactions between cluster and cationic π-molecules.

Herein we report two pentanuclear Mn-substituted sandwich-type polyoxotungstate complexes, [{Mn(bpy)}Na(HO)(MnCl){Mn(HO)}(AsWO)] and [{Mn(bpy)}Na(HO)(MnCl){Mn(HO)}(SbWO)] (bpy = 2,2'-bipyridine), whose structures have been obtained by single-crystal X-ray diffraction (SCXRD), complemented by results obtained from elemental analysis, electrospray ionization mass spectrometry, Fourier transform infrared spectroscopy, and thermogravimetric analysis. They consist of two [B-α-XWO] subunits sandwiching a cyclic assembly of the hexagonal [{Mn(bpy)}Na(HO)(MnCl){Mn(HO)}] and [{Mn(bpy)}Na(HO)(MnCl){Mn(HO)}] moieties, respectively, and represent the first pentanuclear Mn-substituted sandwich-type polyoxometalates (POMs). Both compounds have been synthesized by reacting MnCl·4HO with trilacunary Na[XWO]·27HO (X = As and Sb) POM precursors in the presence of bpy in a 1 M aqueous sodium chloride solution under mild reaction conditions. SCXRD showed that the alternate arrangement of three five-coordinated Mn ions and two six-coordinated Mn ions with an internal Na cation formed a coplanar six-membered ring that was sandwiched between two [B-α-XWO] (X = As and Sb) subunits. The results of temperature-dependent direct-current (dc) magnetic susceptibility data indicated ferromagnetic interactions between Mn ions in the cluster. Moreover, alternating-current magnetic susceptibility measurements with a dc-biased magnetic field showed the existence of a ferromagnetic order for both samples. Electrochemistry studies revealed the presence of redox processes assigned to the Mn centers. They are associated with the deposition of material on the working electrode surface, possibly MnO, as demonstrated by electrochemical quartz crystal microbalance experiments.

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