Resorcarene-based receptor: versatile behavior in its interaction with heavy and soft metal cations

Standard solution Gibbs energies, DeltasG degrees, of the resorcarene-based receptor 5,11,17,23-ethylthiomethylated calix[4]resorcarene, (characterized by 1H NMR and X-ray diffraction studies) in its monomeric state (established through partition experiments) in various solvents are for the first time reported in the area of resorcarene chemistry. Transfer Gibbs energies of from hexane (reference solvent) to other medium are calculated. Agreement between DeltatG degrees (referred to the pure solvents) and standard partition Gibbs energies, DeltapG degrees (solvent mutually saturated) is found. Cation-ligand interactions were investigated through 1H NMR (CD3CN and CD3OD) and conductometric titrations in acetonitrile and methanol. 1H NMR data revealed the sites of interaction of with the metal cation. The composition of the metal-ion complexes (Ag+ and Pb2+ in acetonitrile and Ag+ and Cu2+ in methanol) was established through conductometric titrations. Thus, complexes of 1:1 stoichiometry were formed between and Ag+ and Pb2+ in acetonitrile and Cu2+ in methanol. However, in moving from acetonitrile to methanol, the composition of the silver complex was altered. Thus, two metal cations are hosted by a unit of the ligand. As far as Cu2+ and in acetonitrile is concerned, conductance data suggest that metalates are formed in which up to four units of Cu2+ are taken up per unit of resorcarene. The contrasting behavior of with Cu2+ in acetonitrile relative to methanol is discussed. As far as mercury (II) is concerned, the unusual jump in conductance observed in the titration of Hg2+ with in acetonitrile and methanol after the formation of a multicharged complex (undefined composition) is attributed to the presence of highly charged smaller units (higher mobility) resulting from the departure of pendant arms from the resorcarene backbone. Isolation of these species followed by X-ray diffraction studies corroborated this statement. The thermodynamic characterization of metal-ion complexes of Ag+ and Pb2+ in acetonitrile and Cu2+ and Ag+ in methanol is reported. Final conclusions are given.     

Investigation of the influence of gradual substitution K ? Rb on the structure and phase transition in K x Rb1 ? x Pb2Br5 solid solutions

Single crystals of K _x Rb_{1 − x} Pb₂Br₅ solid solutions have been grown and investigated using X-ray diffraction and polarized light microscopy in the temperature range 270–640 K. The regions of existence of the tetragonal (I4/mcm) and monoclinic (P2₁/c) phases have been determined. It has been demonstrated that the partial introduction of rubidium into KPb₂Br₅ leads to an increase in the temperature of the ferroelastic phase transition (P2₁/c↔mmm), so that it approaches the melting temperature. In the solid solutions with x ≈ 0.4−0.5, the temperature region of existence of the orthorhombic phase is narrowed to ≈ 1−2 K. It has been revealed that an increase in the potassium content in the material results in a considerable increase in the incorporation coefficient of Er³⁺ ions. Original Russian Text ? L.I. Isaenko, S.V. Mel’nikova, A.A. Merkulov, V.M. Pashkov, A.Yu. Tarasova, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 3, pp. 554–557.     

Photoluminescence kinetics of structures with InAs quantum dots for IR photodetectors

The experimental results of a photoluminescence kinetics study of InAs/GaAs structures with quantum dots grown by metal-organic vapor-phase epitaxy are shown. The measurements have revealed the fast capture of excited carriers from the GaAs barrier to quantum dots and slow interlevel relaxation inside the quantum dots.     

Microporous manganese formate: a simple metal-organic porous material with high framework stability and highly selective gas sorption properties

Novel microporous metal-organic framework material composed of Mn(II) and formate ions displays permanent porosity, high thermal stability, and size-selective gas sorption behavior. The framework is stable enough to maintain single crystallinity after the complete guest removal at 150 degrees C under a reduced pressure. Most importantly, it selectively adsorbs H2 and CO2 but not N2 and other gases with larger kinetic diameters, which appears to be due to the small aperture of the channels. Despite a moderate H2 storage capacity, which is however still higher than that of any zeolite, its H2 surface coverage is one of the highest among the known microporous materials. Thus this new zeolite-like material made of a simple organic building block may find useful applications in gas separation and sensor.     

Pyrrhotite Electrooxidation in Acid Solutions

The electrooxidation of pyrrhotite, including that preliminarily etched in acid solutions, is studied by voltammetry, scanning electron microscopy, and X-ray electron spectroscopy. The oxidation mechanism includes the formation; reversible oxidation (which predominantly involves an increase in the amount of polysulfide ions) of a near-surface nonequilibrium metal-deficient layer (NL); and the layer destruction. The pyrrhotite passivation is caused not by a thick NL, but rather by a thin layer that contains oxidized iron, probably by a top, oxygen-containing zone of NL.     

Synthesis and Tautomeric Equilibrium of Polyfluoroacyl-Containing 1,5-Benzodiazepines

Summary. The reaction of bis(polyfluoroalkyl)-containing 1,3,5-triketones with o-phenylenediamine yielded 2-polyfluoroacylmethylene-4-polyfluoroalkyl-1,3- or 1,5-dihydro-1,5-benzodiazepines. The tautomeric equilibrium of the obtained benzodiazepines in CDCl₃, CD₃CN, DMSO, and DMF solution was studied.     

Synthesis and Tautomeric Equilibrium of Polyfluoroacyl-Containing 1,5-Benzodiazepines

The reaction of bis(polyfluoroalkyl)-containing 1,3,5-triketones with o-phenylenediamine yielded 2-polyfluoroacylmethylene-4-polyfluoroalkyl-1,3- or 1,5-dihydro-1,5-benzodiazepines. The tautomeric equilibrium of the obtained benzodiazepines in CDCl₃, CD₃CN, DMSO, and DMF solution was studied.     

A partially substituted calix[4]resorcarene receptor and its selective recognition for soft metal cations (silver and mercury)

A partially substituted calix[4]resorcarene receptor, namely, 5,17-ethylthiomethylated calix[4]resorcarene, 1, has been synthesized and characterized by 1H NMR in CD3OD, CDCl3, and CD3CN and 13C NMR in CD3OD, as well as by 2D NMR. Partition data in the methanol-hexane and acetonitrile-hexane solvent systems show that the monomeric species are predominant in these solvents. The solubility of 1 in various solvents was determined at 298.15 K. These data were used to calculate the standard solution Gibbs energy of 1 in these solvents. Taking hexane as the reference solvent, the standard transfer Gibbs energy of 1 to various solvents was calculated. Good agreement is found between the DeltatG(o) values in the hexane-methanol and hexane-acetonitrile and the DeltapG(o) values of this ligand in these solvent systems. The higher partition constant of 1 in the hexane-methanol relative to the hexane-acetonitrile solvent system contrasts with corresponding data for the fully functionalized receptor, 2. This is explained in terms of the solvation differences of these receptors in these solvents as reflected in the DeltatG(o) values. The cation complexing properties of this receptor were investigated through 1H NMR, conductance, calorimetric, and potentiometric methods. Among the metal cations (alkali, alkaline earth, heavy, and transition), 1 interacts only with Ag+ in methanol and Hg2+ in propylene carbonate, acetonitrile, methanol, and N,N-dimethylformamide. While 1 forms a 1:1 complex with Ag+ in methanol, the hosting ability of the receptor for the mercury cation is enhanced in methanol, acetonitrile, and N,N-diethylformamide. Thus, Hg2+ complexes of 1:2 (ligand:metal cation) stoichiometry are found in these solvents. In moving to propylene carbonate, the composition of the mercury complex is altered from 1:2 to 1:1. The results are compared with corresponding data for 2 and these metal cations in the appropriate solvents. The lack of stability observed for 2 and Hg2+ in acetonitrile resulting from the departure of pendant arms from the resorcarene backbone greatly contrasts with the high stability observed for 1 and this metal cation in the various solvents. Preliminary results on the extraction of silver picrate by this ligand in the water-dichloromethane solvent system are reported. Final conclusions are given.