Porous crystals such as metal–organic framework (MOF), porous coordination polymer (PCP), and porous organic crystals have shown promise as solid materials in terms of their great potentials for catalysis, separation and refinement techniques, environmental protection, nanoengineering, and pharmaceutical applications. Here we discuss cavity-assembled porous solids (CAPSs) formed as the result of self-assembly of macrocycles or cage compounds possessing well-defined binding cavities for guest molecules. In addition to conventional macrocycles such as cyclodextrin, crown ether, cucurbituril, calixarene, cyclotriveratrylene, pillararene, and organic cages, we have recently reported a novel crystalline nanochannel (metal–macrocycle framework: MMF) composed of macrocyclic trinuclear PdII complexes with tris(o-phenylenediamine)cyclophane. This account focuses on how cavities with guest-binding capability assemble to form porous structures taking recent examples.
We discuss cavity-assembled porous solids (CAPSs) composed of macrocycles or cages possessing cavities along with our recent example of a crystalline nanochannel (metal–macrocycle framework: MMF). This account focuses on how cavities assemble to form porous structures taking recent examples.
Rhodium(I)-catalyzed borylation of nitriles is investigated theoretically, using the density functional theory method, to clarify the reaction mechanism, including the formation process of the catalytically active species, carbon–carbon bond cleavage, and the effect of an amine additive. The initial step in this reaction is the formation of a borylrhodium(I) species, in which the rhodium center carries a significant negative charge. The most energetically favorable pathway for carbon–carbon bond cleavage involves the insertion of a cyano group into borylrhodium(I) to form an iminoacyl intermediate, followed by extrusion of boryl isocyanide (iminoacyl mechanism). The calculation suggests that DABCO can react with coproduced reactive boron species, such as boryl chloride and boryl isocyanide, to form stable adducts, lowering the energy of the entire reaction system. In addition, the chemoselectivities among C–CN, C–Br, and C–Cl bonds observed in experimental studies are in good agreement with the calculated activation energies required for these bond activation processes.
Rhodium(I)-catalyzed borylation of nitriles is investigated theoretically, using the density functional theory method, to clarify the reaction mechanism, including the formation process of the catalytically active species, carbon–carbon bond cleavage, and the effect of an amine additive.
The collision dynamics of deuterium molecule with excited-state nitrogen atom has been investigated at a state-to-state dynamic level by using the real wave packet method. The energy-dependent behavior of the differential and integral cross sections, especially from the reactant quantum states of v = 0, j = 0 to the product quantum states of j′ = 0–7, v′ = 0–5, is presented and discussed for total energies up to 0.4 eV. The present study predicted noninverted vibrational populations and inverted rotational populations in product rovibrational distributions. Comparison of the theoretical total differential cross section with the previous experimental measurement has also been presented and discussed.
To systematically elucidate molecular and electronic structures of aromatic selenoic acid salts and their heavier congeners, they were synthesized by reacting selenoic, selenothioic, and diselenoic acid Se-[2-(trimethylsilyl)ethyl] esters with ammonium fluorides. The resulting salts were characterized by 13C and 77Se NMR spectra, and some of their molecular structures were disclosed by X-ray analyses. These results were compared with spectroscopic properties and molecular structures of selenoic and selenothioic acid Se-methyl esters. As a result, in the resonance hybrids of selenoic and selenothioic acid ammonium salts, the resonance structures involving carbon–selenium double bonds also contribute to the resonance hybrids, and the importance of these resonance structures appears to increase on going from selenoic to selenothioic acid salts on the basis of the results of the coupling constants of carbon–selenium bonds and UV–visible spectra. The results were well supported by the optimized structures and evaluated NMR parameters for the species.
DFT (density functional theory) computations of the chemical fixation of copper ions on the naturally functionalized surface of nanodiamond crystallites bound by (111) planes revealed exothermic formation of chelate Cu complexes with two appropriately located carboxylic groups on the (111) surface. The irreversible strict fixation of copper ions is achieved via removing acetic acid in low-pressure conditions yields the corresponding chelate complexes not bearing any other ligands except for the surface carboxylic groups. Optimization of positional isomers of the chelating complexes showed that complexation is more likely to take place near the edges (linear ribs) of the nanoparticle. Nearby functional groups like –F, –Cl, or –OH substituents on the surface strongly affect the structures and stabilities of the resulting chelate complexes. Some of the copper atoms may be incorporated into unusual Cu(III) complexes with Cu–C covalent bonds.
The perturbation effect of various antioxidants viz. ascorbic acid, glutathione, inosine, and N-acetylcysteine is monitored at 30 °C under stirred batch conditions and has a good sensitivity for the determination of these antioxidants. The addition of these antioxidants to the BZ mixture influences the oscillatory parameters to an extent that depends on the concentration of the antioxidant and higher concentrations as such were found to quench the oscillations. The experimental results have shown that the number of oscillations decreases on increasing the concentration of antioxidant. The detection limit is found to be less than 1.0 × 10−7 mol L−1. In the case of glutathione, ascorbic acid, and N-acetylcysteine, a linear relationship (R2 = 0.99) between time period and the [antioxidant] has been obtained over a concentration range of 0.025–0.6, 0.0125–1.0, and 0.00625–0.8 mol L−1 with detection limits 6.925 × 10−5, 3.462 × 10−5, and 1.371 × 10−5 mol L−1 respectively whereas that for inosine a linear relationship (R2 = 0.98) between amplitude and [antioxidant] has been obtained over a concentration range of 0.05–0.7 mol L−1 and the detection limit is 1.385 × 10−4 mol L−1. Further, interactions of these antioxidants with BZ reagents were confirmed by cyclic voltammetry, which paved the way for explaining the mechanisms involved.
Ultrasonic absorption coefficients in aqueous solutions of surfactants, octyltrimethylammonium bromide, dodecyltrimethylammonium bromide, and tetradecyltrimethylammonium bromide have been measured in the presence of 2-propanol or ethanol in the frequency range from 0.8 to 220 MHz at 25 °C. The frequency dependence of the observed absorption in solution of octyltrimethylammonium bromide has been characterized by a Debye-type relaxation equation with one single relaxation frequency which decreases with the surfactant concentration. On the other hand, the dependences in solutions of dodecyltrimethylammonium bromide and cetyltrimethylammonium bromide have been well fitted to the equation with two relaxation frequencies. One relaxation frequency decreases with the surfactant concentrations, and the other relaxation frequency shows concentration independence trend. The relaxation mechanisms have been considered on the basis of interaction between surfactant monomer and alcohol aggregate and of a conformational change of the surfactants with long hydrophobic groups to which plural alcohol molecules (dumpling cake) attract. The rate and thermodynamic parameters have been determined for aqueous solutions of octyltrimethylammonium bromide coexisting with 2.00 mol dm−3 2-propanol and 3.00 mol dm−3 ethanol. It has been speculated from the analysis that the dumpling cake of alcohols attaches and detaches on and from the alkyl chains of the surfactants. The number of alcohols in the aggregate is dependent on size of alcohol molecule although the forward and backward rate constants are not very dependent on coexisting alcohols. However, only the orders of the rate constants for the systems of dodecyltrimethylammonium bromide solution with 2.00 mol dm−3 2-propanol have been speculated because of too many parameters which should be determined. Following the proposed reaction model, the relation between the surfactant concentration dependence of adiabatic compressibility and the solution characteristics has been discussed.
Change of the emission spectrum of anisaldehyde vapor has been investigated as a function of irradiation time by exposing a sample to UV light for different times. It is shown that there is a new photochemical channel for anisaldehyde (p-methoxybenzaldehyde) vapor to form benzaldehyde vapor upon the photoexcitation into the S2(π, π*) state.
A potentially hexadentate N2O4 donor Schiff base ligand N,N′-bis(5-bromo-3-methoxysalicylideneimino)-1,3-diaminopropane (H2L1) has been used to synthesize two mononuclear coordination complexes [Cu(L1)]·H2O (1) and [Co(L1)(HL2)]ClO4·CH3CN (2). The cobalt complex is a unique mixed-ligand species comprising both the di- and mono-condensed ligands; the latter (HL2) resulted from in situ hydrolytic cleavage of H2L1. Ligand L1 assumes a planar arrangement in 1 and a folded β-cis configuration in 2, induced in this case by the chelating HL2 ligand. The complexes are characterized by elemental analyses, FT-IR, and UV–vis spectral methods, and their structures are established by single-crystal X-ray diffraction study. Both the complexes are proven to be efficient catalysts for the epoxidation of alkenes by H2O2 or PhIO. The efficiency of alkene epoxidation is however somewhat superior with PhIO, and in each case, 2 appears to be a slightly better catalyst than 1.
Synthetic todorokite-type manganese oxides containing magnesium (todorokite(Mg)), calcium (todorokite(Ca)), and iron-doped todorokite containing magnesium (Fe-todorokite(Mg)) were treated with acid solutions to obtain protonated todorokite(Mg-H), todorokite(Ca-H), and Fe-todorokite(Mg-H), respectively, and studied for cesium adsorption from the aqueous solutions. The cesium adsorption rate was slow to attain equilibrium in 24 h at pH 4.4–5.5 (uncontrolled); the adsorptive capacities were 0.50 mmol g−1 for todorokite(Mg-H), 0.49 mmol g−1 for todorokite(Ca-H), and 0.27 mmol g−1 for Fe-todorokite(Mg-H). The cesium adsorptive capacity was significantly dependent on pH, increasing with increase in pH. A partial substitution of Mn by Fe (7.2 wt %) in the framework of todorokite greatly decreased the cesium adsorptive capacity compared to metal-undoped todorokite. The distribution coefficient Kd values of the protonated materials for Na+, K+, Cs+, Mg2+, and Ca2+ at 1.0 mmol dm−3 in acidic pH showed that the materials preferred Cs+ over other cations. Both todorokite(Mg-H) and todorokite(Ca-H) were effective for cesium adsorption completely (ca. 100%) from drinking water intentionally contaminated with 0.1 mmol dm−3 CsCl at solution-to-solid ratio of 0.1–1.0 dm3 g−1.
A hydrophobic porous coordination polymer, [Zn9(MeBTZ)12(BPDC)3] where MeBTZ is 5-methylbenzotriazolate and BPDC is 4,4′-biphenyldicarboxylate, was obtained through a one-pot solvothermal reaction of zinc nitrate hexahydrate, 5-methyl-1H-benzotriazole and 4,4′-biphenyldicarboxylic acid in N,N-dimethylacetamide. The structure of [Zn9(MeBTZ)12(BPDC)3] was built from trigonal antiprismatic [Zn9(MeBTZ)12]6+ nodes connected with linear BPDC linkers, having 4669 net topology. The working capacity for CO2 adsorption on [Zn9(MeBTZ)12(BPDC)3] over the pressure range between 0.1 and 1.6 MPa at 40 °C was 3.4 mol kg−1 after the preintroduction of high humidity.
We successfully synthesized perovskite-type (Na1−xKx)NbO3 materials from a Na3NbO4 precursor at low temperature by dissolution–precipitation method. The Nb6O198− cluster was formed as an intermediate by the dissolution of Na3NbO4 into a buffer solution (pH 7). White powders were precipitated by the addition of 1 M NaOH/KOH mixed aqueous solution. We found that the morphology and crystal structure depended on the NaOH/KOH ratio. When the concentration of KOH [CKOH = KOH/(NaOH + KOH)] was low (0 ≤ CKOH ≤ 0.3), rod-like (Na,K,H3O)8Nb6O19·14H2O was precipitated. In the case of high CKOH (0.5 ≤ CKOH ≤ 0.9), (Na0.5K0.5)8Nb6O19·9H2O, whose morphologies changed from hexagonal plate-like to truncated hexagonal bipyramidal structures with the increase in the CKOH, was formed. The (Na,K,H3O)8Nb6O19·14H2O and (Na0.5K0.5)8Nb6O19·9H2O mixture was precipitated using a NaOH/KOH solution with CKOH = 0.4. No precipitation was obtained by the addition of the KOH solution. These precipitations transformed into perovskite-type (Na,K)NbO3 while maintaining their morphology by calcination at 500 °C. The excess Na and/or K were washed out with water. From the lattice constants, the rod-like (Na1−xKx)NbO3 with 0 ≤ x ≤ 0.2 and the hexagonal plate-like or the truncated hexagonal bipyramidal (Na0.5K0.5)NbO3 were synthesized from the rod-like (Na,K,H3O)8Nb6O19·14H2O (0 ≤ CKOH ≤ 0.3) and the hexagonal plate-like or the truncated hexagonal bipyramidal (Na0.5K0.5)8Nb6O19·9H2O (0.5 ≤ CKOH ≤ 0.9), respectively.