Synchronous Switching of Dielectric Constant and Photoluminescence in Cyanidonitridorhenate-Based Crystals

Switching of multiple physical properties by external stimuli in dynamic materials enables applications in, e.g., smart sensors, biomedical tools, as well as data-storage devices. Among stimuli-responsive materials, inorganic-organic molecular hybrids exhibiting thermal order-disorder phase transitions were tested as promising molecular switches of electrical characteristics, including dielectric constant. We aimed at broadening the multifunctional potential of such hybrid materials towards the switching of not only electrical but also other physical properties, e.g., light emission. We report two ionic salts based on luminescent tetracyanidonitridorhenate(V) anions bearing two different diamine ligands, 1,2-diaminoethane ( 1 ) and 1,3-diaminopropane ( 2 ), both crystallizing with polar N-methyl-dabconium cations. They exhibit an order-disorder phase transition related to the heating-induced turning-on of the rotation of polar cations. This leads to a unique synchronous switching of the dielectric constant as well as metal-complex-centered photoluminescence, as demonstrated by changes in, e.g., emission lifetime. The roles of organic cations, non-trivial Re(V) complexes, and their interaction in achieving the coupled thermal switching of electrical and optical properties are discussed utilizing experimental and theoretical approaches.     

Reactions of benzopinacol with group 13 alkyl metals:: Crystal structure of Me6In4[OC(C6H5)2C(C6H5)2O]2(OCH3)2, a new alkylalkoxo indium diolate

Reactions of Me₅Al₃[OC(C₆H₅)₂C(C₆H₅)₂O]₂ (1) with alcohols ROH (R = Me, Et, ^tBu) in a 1:1 molar ratio afforded the compound Me₂Al₂[OC(C₆H₅)₂C(C₆H₅)₂O]₂(C₄H₈O) (2) and a mixture of methylaluminum alkoxides. The alcohols acted as the factor formally eliminating a molecule of Me₃Al (as a methylaluminum alkoxide) from compound 1. ^tBu₃Al reacted with an equimolar amount of benzopinacol to form the monomeric complex ^tBuAl[OC(C₆H₅)₂C(C₆H₅)₂O](C₄H₈O) (3). Reactions of Me₃Ga and Me₃In with benzopinacol yielded trinuclear complexes Me₅M₃[OC(C₆H₅)₂C(C₆H₅)₂O]₂ (4 (M = Ga), 5 (M = In)), isostructural to compound 1. In the presence of water and alcohols, compounds 4 and 5 underwent a decomposition reaction to benzopinacol and a mixture of metalloxanes and alkoxides. An unusual methylmethoxo indium benzopinacolate Me₆In₄[OC(C₆H₅)₂C(C₆H₅)₂O]₂(OCH₃)₂ (6) was obtained in the reaction of benzopinacol with Me₃In and Me₂InOMe in a 1:1:1 molar ratio. Molecular structures of the compounds 3, 4 and 6 were determined by X-ray crystallography.     

Mesoporous Carbons of Well-Organized Structure in the Removal of Dyes from Aqueous Solutions

Mesoporous carbons with differentiated properties were synthesized by using the method of impregnation of mesoporous well-organized silicas. The obtained carbonaceous materials and microporous activated carbon were investigated by applying different methods in order to determine their structural, surface and adsorption properties towards selected dyes from aqueous solutions. In order to verify applicability of adsorbents for removing dyes the equilibrium and kinetic experimental data were measured and analyzed by applying various equations and models. The structural and acid-base properties of the investigated carbons were evaluated by Small-Angle X-ray Scattering (SAXS) technique, adsorption/desorption of nitrogen, potentiometric titration, and Transmission Electron Microscopy (TEM). The results of these techniques are complementary, indicating the type of porosity and structural ordering, e.g., the pore sizes determined from the SAXS data are in good agreement with those obtained from nitrogen sorption data. The SAXS and TEM data confirm the regularity of mesoporous carbon structure. The adsorption experiment, especially kinetic measurements, reveals the utility of mesoporous carbons in dye removing, taking into account not only the adsorption uptake but also the adsorption rate.     

Structure,Physicochemical and Biological Properties of an Aqua (2,2′,2′′‐Nitrilotriacetato)‐oxidovanadium(IV) Salt with 4‐Methylpyridinium Cation

The crystal structure of a nitrilotriacetate (nta) oxidovanadium(IV) salt with 4‐methylpyridinium cation, [4‐Me(Py)H]⁺, of [4‐Me(Py)H][VO(nta)(H₂O)] stoichiometry was determined. The complex comprises a discrete mononuclear [VO(nta)(H₂O)]^– coordination entity that can be rarely found among other known compounds containing nitrilotriacetate oxidovanadium(IV) moieties. The complex was characterized by spectroscopic (IR and EPR) methods, magnetic measurements, and thermogravimetry (TG‐FTIR). The stability of the title compound in aqueous solutions was investigated by using the potentiometric titration method. Furthermore, spectrophotometric (UV/Vis) studies have revealed that the compound is capable to scavenge the superoxide free radicals (O₂ ^{? –}) as well as stable organic radicals i.e. 2,2′‐azinobis(3‐ethylbenzothiazoline‐6 sulfonic acid) cation radical (ABTS^{+ ?} ) and 2,2‐diphenyl‐1‐picrylhydrazyl radical (DPPH ^? ). Finally, biological properties of the complex studied were investigated in relation to its cytoprotective activity against the oxidative damage generated exogenously by using hydrogen peroxide in the HT22 hippocampal neuronal cell line (the MTT assay). Additionally, the biological action of the compound towards two human osteosarcoma HOS and MG‐63 cell lines (the MTT and BrdU tests) as well as the untransformed human osteoblast hFOB 1.19 cell line was tested.     

Influence of the charge distribution on the stationary phases zeta potential

A set of seven home‐made silica based bonded phases with different functional groups was investigated. Their zeta potential data in methanol and acetonitrile as well as in methanol/water and acetonitrile/water solution were obtained by using a Zetasizer. The influence of polar functional groups on a zeta potential was investigated. The results show that the amines incorporated in the structure of chemically bonded phases of reversed‐phase materials are protonated during chromatographic analysis, resulting in changes of the zeta potential from negative to positive values. Acetonitrile causes more negative values and methanol provides positive (or less negative) values of the zeta potential.     

Innovative Syntheses of Cyano(fluoro)borates: Catalytic Cyanation,Electrochemical and Electrophilic Fluorination

Different types of high-yield, easily scalable syntheses for cyano(fluoro)borates Kt[BF_n(CN)_4−n] (n=0–2) (Kt=cation), which are versatile building blocks for materials applications and chemical synthesis, have been developed. Tetrafluoroborates react with trimethylsilyl cyanide in the presence of metal-free Brønsted or Lewis acid catalysts under unprecedentedly mild conditions to give tricyanofluoroborates or tetracyanoborates. Analogously, pentafluoroethyltrifluoroborates are converted into pentafluoroethyltricyanoborates. Boron trifluoride etherate, alkali metal salts, and trimethylsilyl cyanide selectively yield dicyanodifluoroborates or tricyanofluoroborates. Fluorination of cyanohydridoborates is the third reaction type that includes direct fluorination with, for example, elemental fluorine, stepwise halogenation/fluorination reactions, and electrochemical fluorination (ECF) according to the Simons process. In addition, fluorination of [BH(CN)₂{OC(O)Et}]⁻ to result in [BF(CN)₂{OC(O)Et}]⁻ is described.     

Ramsey’s theorem for colors from a metric space

The Ramsey theorem says that for any countably infinite undirected clique whose edges are colored by a finite number of colors, there is an infinite subclique whose edges are colored by a single color. In this note, we generalize the theorem to a situation where the colors form a compact metric space.