Anion-π interaction inside the polyanionic Mo132O372 cage with hydrophobic inner space

Synthesis of Hollowed Polyoxometalate with a Flipped VO5 Unit by the Elimination of a Centered Organic Molecule

Mechanistic understanding of the formation of clusters plays a role in designing the structure-dependent properties. Based on the fact that anions act as templates to form spherical polyoxovanadates, various structures were reported by changing anions in the synthetic solution. In this work, another factor in the formation of spherical polyoxometalates was demonstrated. By the reaction of [V10O26]4- in acetonitrile with a reductant to increase the number of tetravalent V4+ and p-toluene sulfonic acid to convert tetrahedral VO4 units to square-pyramidal VO5, acetonitrile-containing polyoxovanadate [V24O60(CH3CN)]6- (ICH3CN) was synthesized. The bulky and hydrophobic aromatic rings prevented the formed anions from acting as a template. By changing the synthetic solvent, encapsulated moieties were controlled. Nitromethane was also encapsulated to afford [V24O60(CH3NO2)]6- (ICH3NO2). When acetone was used as the solvent, the contaminated water was encapsulated to form [V24O60(H2O)]6- (IH2O). The encapsulated acetonitrile molecule was eliminated by heating ICH3CN up to 230 °C under N2 flow conditions to give hollowed polyoxovanadate [V24O60]6- (II), even though ICH3CN possesses no pores for acetonitrile to pass. From the X-ray crystallographic analysis of II, one of the 24 VO5 units was flipped. The electrochemical properties and catalytic performances between ICH3CN and II were also investigated.

Keplerate {Mo132}-Stearic Acid Conjugates: Supramolecular Synthons for the Design of Dye-Loaded Nanovesicles, Langmuir-Schaefer Films, and Infochemical Applications

Self-assembly gives rise to the versatile strategies of smart material design but requires precise control on the supramolecular level. Here, inorganic-organic synthons (conjugates) are produced by covalently grafting stearic acid tails to giant polyoxometalate (POM) Keplerate-type {Mo132} through an organosilicon linker (3-aminopropyltrimethoxysilane, APTMS). Using the liposome production approach, the synthons self-assemble to form hollow nanosized vesicles (100-200 nm in diameter), which can be loaded with organic dyes─eriochrome black T (ErChB) and fluorescein (FL)─where the POM layer serves as a membrane with subnanopores for cell-like communication. The dye structure plays an essential role in embedding dyes into the vesicle's shell, which opens the way to control the colloidal stability of the system. The produced vesicles are moved by an electric field and used for the creation of an infochemistry scheme with three types of logic gates (AND, OR, and IMP). To design 2D materials, synthons can form spread films, from simple addition on the water-air interface to lateral compression in the Langmuir bath, and highly ordered structures appear, demonstrating electron diffraction in Langmuir-Schaefer (LS) films. These results show the significant potential of POM-based synthons and nanosized vesicles to supramolecular design the diversity of smart materials.

Collective Effects of Multiple Fluorine Atoms Causing π-philic Characteristic within a Caged Polyoxometalate Framework

Perfluorination brings about distinctive properties arising from the unusual nature of the F element, which have been extensively developed in materials science and chemistry. Herein we report that the construction of F-rich inner space within a hollowed Mo132 O372 cage ([Mo132 O372 (OCOR)30 (H2 O)72 ]42- ) leads to the emergence of unique guest binding activities in encapsulation. Prominently, the trifluoroacetate-modified cage (R=CF3 , 2) having as many as 90 F groups inside favors trapping cyclopentadiene (Cp), which is hardly trapped by the non-fluorinated counterpart (R=CH3 , 1). Systematic studies using related hydrocarbons show that the amount of the encapsulated guest is correlated with the unsaturation degree of the guests, implying the involvement of the attractive interaction of the CF3 -modified interior wall with the guest π-electron clouds. Control experiments using the semi-fluorinated analogues (R=CF2 H, CFH2 ) reveal that the perfluorination is a critical factor to facilitate the Cp encapsulation by 2, indicating that collective effects of polar C-F bonds spreading over the interior surface, rather than the polarity of the individual C-F bonds, are responsible. We also provide a successful example of the physical molecular confinement within the cage through the "ship-in-a-bottle" Diels-Alder reaction between trapped diene and dienophile.

An anomalous anion transfer order in graphene oxide membranes induced by anion-π interactions

Selective transport of anions across membranes has become an important goal in chemistry and biology. Here, we found an anomalous anion transfer order within the graphene oxide membrane: Cl^- > Br^- > F^- > I^-. This is at odds with the conventional ranking of the transfer order, which usually decreases as the radii of the anions increase, i.e., F^- > Cl^- > Br^- > I^-. The abnormal transportation of F^- can be ascribed to the strong anion-π interactions between F^- and graphene oxide sheets. Such unexpectedly strong anion-π interaction resulted in the lower movement of F^- in the graphene oxide membrane and caused the anomalous anion transfer order. Our findings not only provide experimental evidence of anion-π interactions, but also improve our understanding of anion-π interactions in the selective transport of anions across a two-dimensional membrane.