Potassium Counterions Research Articles

Is the Hexacyanoferrate(II) Anion Stable in Aqueous Solution? A Combined Theoretical and Experimental Study.

A combined theoretical and experimental study was performed to elucidate the structural and dynamical properties of the isolated aqueous hexacyanoferrate(II) ion as well as in the presence of potassium counterions. It is shown that in absence of counterions, the highly negatively charged hexacyanoferrate(II) complex is not stable in aqueous solution. However, if the high negative charge is compensated by potassium counterions, a stable complex is observed, which is proven by theoretical simulations as well as by extended X-ray absorption fine structure (EXAFS) experiments. From the simulation it is found that potassium ions surrounding the complex are highly mobile and thus cannot be observed via EXAFS experiments. The structure of aqueous hexacyanoferrate(II) in the presence of potassium ions is identical to that of the solid-state structure, but the mobility of potassium ions is significantly increased in the liquid. These highly mobile potassium ions circulating the complex are the reason for the very short lifetime of hydrogen bonds between solvent water molecules and cyanide ligands being on the femtosecond scale.

Syn-Selective Synthesis of β-Branched α-Amino Acids by Alkylation of Glycine-Derived Imines with Secondary Sulfonates

A syn-selective synthesis of β-branched α-amino acids has been developed based on the alkylation of glycine imine esters with secondary sulfonates. The potassium counterion for the enolate, the solvent, and the leaving group on the electrophile were key levers to maximize the diasteroselectivity of the alkylation. The optimized conditions enabled a straightforward preparation of a number of β-branched α-amino acids that can be challenging to obtain.

K2Hg2Se3: Large-Scale Synthesis of a Photoconductor Material Prototype with a Columnar Polyanionic Substructure

K2Hg2Se3, a new photoconducting material with a direct band gap around 1.4 eV, was obtained in nearly quantitative yields and large scale (50 g per batch) by means of solvothermal treatment of a corresponding solid. The compound comprises covalently linked selenidomercurate columns that accommodate potassium counterions. Composition and structure allow for a specific combination of optoelectronic, photophysical, and thermoelectric properties, which initiates a systematic material development within this family of compounds.

Base promoted successive dealkylation steps of molybdenum alkoxides leading to a row of novel 1D and 2D polymeric frameworks of potassium–molybdenum oxomethoxides

The MoCl5 methanolysis reaction, in the presence of basic agents providing weakly alkaline media, leads to the formation of a Mo–Mo triply bridged anionic dimeric complex with a solvated potassium counter-ion, [K(CH3OH)2Mo2O2(μ2-OCH3)3(OCH3)4] (1), that represents the first structurally characterized Mo–K oxoalkoxide. Here we describe its further reactivity, i.e. the MoCl5 methanolysis reaction in the presence of an additional equivalent of base which leads to demethylation of the one of μ2-bridging alkoxides, thus giving an unusual oxo-, dimethoxo-bridged cluster, [K2(CH3OH)Mo2O2(μ2-OCH3)2(μ2-O)(OCH3)4] (2). Subsequent transformation with the generation of the formally {Mo–Mo}4− species in [K4(CH3OH)6Mo2O2(μ2-O)2(OCH3)2(CO3)2] (3) was achieved via addition of an extra amount of base in the presence of potassium carbonate along with providing more vigorous reaction conditions.

Synthesis and crystal structure of an unexpected anionic trinuclear cobalt(III) complex with ferrocenyl-containing tridentate ONO donor Schiff base ligands

The tridentate ONO-donor Schiff base ligand derived from the condensation of 1-ferrocenyl-1,3-butanedione and 2-aminophenol, generated in situ and treated further with potassium tert-butoxide, reacted in THF with Co(NO3)2·6H2O in the presence of pyridine to afford the ionic complex [{(η5-C5H5)Fe(η5-C5H4)-C(O)CH=C(CH3)N-C6H4-2-O}2Co(III)]-[K(HOCH2CH3)2]+ (1, 50% yield). Compound 1 was characterized by elemental analysis, FT-IR, and multidimensional 1H and 13C NMR spectroscopy. Single-crystal X-ray diffraction reveals that the two metalloligands are meridionally coordinated to a Co(III) ion that adopts a slightly distorted octahedral geometry. The doubly solvated potassium counter-ion is asymmetrically positioned with respect to the two metalloligands. Such an arrangement allows the observation by 1H NMR of restricted rotation of the ferrocenyl units and the splitting of both carbonyl and imine carbons, thus suggesting that the structure observed in the solid state is retained in solution. Complex 1 exhibits in its cyclic voltammetry curve two anodic reversible waves attributed to the oxidation of Co(III)-phenolates into Co(III)-phenoxyl radical and that of the ferrocenyl fragment into its ferrocenium counterpart.

Molecular dynamics simulations of uranyl adsorption and structure on the basal surface of muscovite

Anthropogenic activities have led to an increased concentration of uranium on the Earth's surface and potentially in the subsurface with the development of nuclear waste repositories. Uranium is soluble in groundwater, and its mobility is strongly affected by the presence of clay minerals in soils and in subsurface sediments. We use molecular dynamics simulations to probe the adsorption of aqueous uranyl () ions onto the basal surface of muscovite, a suitable proxy for typically ultrafine-grained clay phases. Model systems include the competitive adsorption between potassium counterions and aqueous ions (0.1 M and 1.0 M UO2Cl2, 0.1 M NaCl). We find that for systems with the presence of potassium and uranyl ions, potassium ions dominate the adsorption phenomenon. Potassium ions adsorb entirely as inner sphere complexes associated with the ditrigonal cavity of the basal surface. Uranyl ions adsorb in two configurations when it is the only ion species present, and in a single configuration in the presence of potassium. The majority of adsorbed uranyl ions are tilted < 45° relative to the muscovite surface, and are associated with the Si4Al2 rings near the aluminium substitution sites.

Insights into the Metalation of Benzene and Toluene by Schlosser’s Base: A Superbasic Cluster Comprising PhK, PhLi, and tBuOLi

The metalation of benzene by Schlosser's base (nBuLi/tBuOK) occurs smoothly in THF at low temperatures to afford a discrete mixed-metal Li2 K4 cluster that contains phenyl anions and tert-butoxide. The aggregate itself exhibits superbasic behavior by metalating toluene. The delocalized benzyl anion obtained this way π bonds to potassium counterions, thereby creating a 2D coordination polymer.

The roles of counterion and water in a stereoselective cysteine-catalyzed Rauhut-Currier reaction: a challenge for computational chemistry.

The stereoselective Rauhut-Currier (RC) reaction catalyzed by a cysteine derivative has been explored computationally with density functional theory (M06-2X). Both methanethiol and a chiral cysteine derivative were studied as nucleophiles. The complete reaction pathway involves rate-determining elimination of the thiol catalyst from the Michael addition product. The stereoselective Rauhut-Currier reaction, catalyzed by a cysteine derivative as a nucleophile, has also been studied in detail. This reaction was experimentally found to be extremely sensitive to the reaction conditions, such as the number of water equivalents and the effect of potassium counterion. The E1cB process for catalyst elimination has been explored computationally for the eight possible stereoisomers. The effect of explicit water solvation and the presence of counterion (either K(+) or Na(+) ) has been studied for the lowest energy enantiomer pair (1S, 2R, 3S)/(1R, 2S, 3R).

The effect of the borate/boric acid buffer on the transfer of potassium counter-ion through a cation-exchange membrane: current-voltage characteristics

In this study, we compare the current–voltage (I–V) curves of the same counter-ion with and without buffer coions. We compare the polarization curves of the counter-ion K+ without and with borate coions which results from boric acid dissociation. The boric acid was added progressively from 0.005 to 0.1 N. The role of the mixture (borate coions/boric acid) is to buffer the solution at pH = 9.23, the protons, whatever their origin, do not contribute to the over-limiting current transport. We have a later onset of the over-limiting current and an increase in the plateau length of the membrane’s polarization curves. On the other hand, the addition of boric acid to a potassium sulfate solution does not affect the limiting current density, also the plateau length decreases and its slop increase with increasing boric acid concentration, this unexpected results helps us to better understand the classical electrochemical concentration polarization phenomena in electrodialysis process.

Impact of long-range van der Waals forces on chiral recognition in a Cinchona alkaloid chiral selector system

Singly-charged complexes of (8S,9R)-tert-butylcarbamoylquinine (tBuCQN), N-3,5-dinitrobenzoyl-(S,R)-leucine (DNB-S/R-leucine), and alkali metal counter ions (Li(+), Na(+), K(+)) were investigated by density-functional theory. It is shown that the cations prefer formation of an ionic pair with the carboxylate group of DNB-Leu over the formation of a cation-π interaction. The [tBuCQN·DNB-S/R-Leu·Na](+) complex is bound by a coulombic attraction, a hydrogen bond, a π-π interaction and van der Waals forces. The tBuCQN chiral selector preferentially complexes with the DNB-S-Leu enantiomer, because the favourable stereochemistry allows the stabilization of the complex by at least one binding mode more compared to the complex containing the DNB-R-Leu molecule. Weakening of the binding modes is observed using the lithium counter ion compared to the sodium one. The weakening is more pronounced in [tBuCQN·DNB-R-Leu·Li](+) than in [tBuCQN·DNB-S-Leu·Li](+). The exact opposite effect is observed using the potassium counter ion. Hence, the lithium counter ion enhances the enantioselectivity of tBuCQN while the potassium counter ion reduces the enantioselectivity of tBuCQN.

Inimer Mediated Synthesis of Hyperbranched Polyglycerol via Self-Condensing Ring-Opening Polymerization

A series of hyperbranched polyglycerols (HPGs) have been synthesized using glycol as an initiator in the presence of potassium counterion ([K+]0/[−OH]0 = 0.75) and employing batch monomer addition (BMA) to obtain insight into the kinetics of the polymerization. The first-order time–conversion plots show that the polymerization is fast up to ∼200 min, and the rate decreases substantially with increasing reaction time. Size exclusion chromatography of the HPGs during the polymerization indicates the presence of two living species in the reaction: a large fraction that grows into oligomers ( 140 000 g/mol). 13C NMR of the oligomer HPG shows signals corresponding to epoxy ring headgroup at 45.1 and 52.0 ppm and confirms the formation of epoxy anion, an inimer, via intermolecular proton transfer from glycidol. Self-condensing ring-opening polymerization of epoxy i...

Activity of counterions in hydrogels based on poly(acrylic acid) and poly(methacrylic acid): Potentiometric measurements

The behavior of partially ionized weakly crosslinked gels based on poly(acrylic acid) and poly(methacrylic acid) undergoing contraction in the presence of a low-molecular-mass salt is studied experimentally. The concentration dependences of the enthalpies of swelling of gels in water and aqueous solutions with potassium chloride concentrations of 1, 10, and 100 mmol/L are determined via the method of isothermal calorimetry. On the basis of the obtained data, the enthalpy parameter of interaction between a polymer network and a medium is estimated as a function of the amount of the salt. This parameter does not exceed 0.3 and monotonically decreases with an increase in the concentration of the salt. The Donnan potential of gels depending on the concentration of KCl in the external solution is measured via the method of potentiometry with the use of capillary electrodes, and the activity of potassium counterions in the medium of hydrogel is calculated. The main factor that causes contraction of polyelectrolyte gels in a solution of a low-molecular-mass salt is a decline in the activity of counterions that leads to a decrease in the osmotic pressure inside the gel. A decline in activity may be associated with both a reduction in the activity coefficient and ionic association processes in the hydrogel.

Free energies of absorption of alkali ions onto beidellite and montmorillonite surfaces from constrained molecular dynamics simulations

Ab initio Molecular dynamics have been performed to study the free energy of adsorption of alkali atoms onto smectite clay surfaces and to identify the most favourable region in the interlayer for the cations. This is achieved by potential of mean force calculations using a constraint method to determine the lowest free energy configurations of lithium, potassium and sodium beidellite and sodium montmorillonite clays with a monolayer and bilayer of water present in the interlayer region. The constraint method has allowed us to examine the changes in the lowest free energy configuration for each ion with increasing hydration. From this, we can interpret the likelihood of clay swelling from the monolayer to bilayer coverage and compare with experimental observations. We find, that with a bilayer of water present, both lithium beidellite and sodium montmorillonite have their free energy minimum in the centre of the interlayer. For monolayer coverage, the free energy minimum for lithium, sodium and potassium beidellite is approximately the mid-point of the interlayer. Na-beidellite has a lowest free energy region at 6.1Å from the centre of the clay layer for both mono- and bi-layer coverage, while for the potassium counter-ion, commonly used as swelling inhibitor, the free energy profile for K-beidellite shows peaks close to both surfaces at approximately 6.2 and 8.6Å. We find that for systems where the free energy minimum remains in the middle of the interlayer when the hydration levels increase from monolayer to bilayer, it is known experimentally that these systems will swell in contact with water. The move to the middle of the interlayer with increasing hydration is associated with the full hydration sphere of the ion being composed purely of water oxygen atoms, and no clay surface oxygen atoms.

How Charging Corannulene with One and Two Electrons Affects Its Geometry and Aggregation with Sodium and Potassium Cations

Bowl-shaped mono- and dianions are prepared by reduction of corannulene (C(20)H(10), 1) with sodium and potassium metals in the presence of [18]crown-6 ether. Single-crystal X-ray diffraction studies of two sodium salts, [Na(THF)(2)([18]crown-6)](+)[1(-)] (2a) and [Na([18]crown-6)](+)[1(-)] (2b), reveal the presence of naked corannulene monoanions 1(-) in both cases. In contrast, the potassium adduct, [K([18]crown-6)](+)[1(-)] (3), shows an η(2)-binding of the K(+) ion to the convex face of 1(-). For the first time, corannulene dianions have been isolated as salts with sodium, [Na(2)([18]crown-6)](2+)[1(2-)] (4a) and [Na(THF)(2)([18]crown-6)](+)[Na([18]crown-6)](+)[1(2-)] (4b), and potassium counterions, [K([18]crown-6)](2)(+)[1(2-)] (5). Their structural characterization reveals geometry perturbations upon addition of two electrons to a bowl-shaped polyarene. It also demonstrates η(5)- or η(6)-binding of metals to the curved carbon surface of 1(2-), depending on the crystallization conditions. Both mono- and doubly-charged corannulene bowls show the preferential exo binding of Na(+) and K(+) ions in all investigated compounds. Various types of C-H···π interactions are found in the crystals of 2-5. The UV/Vis, ESR, and (1)H NMR spectroscopic studies of 2-5 indicate different coordination environment of corannulene anions in solution, depending on the metal ion.

Influence of processing history on water and salt transport properties of disulfonated polysulfone random copolymers

Disulfonated poly(arylene ether sulfone)s are high glass transition temperature polymers, and their water and salt transport properties depend sensitively on thermal processing history. In this study, films of a 32 mol% disulfonated poly(arylene ether sulfone) random copolymer (BPS-32), polymerized in the potassium counter-ion form, were acidified using solid state and solution routes. The resulting acid counter-ion form materials were then converted to sodium, potassium, and calcium counter-ion forms via ion exchange. Additionally, several films were subjected to various thermal treatments in the solid state. Water uptake as well as water and NaCl permeability of these BPS-32 films were measured. Acidification via immersion of BPS-32 films in boiling sulfuric acid solution increased water uptake, and water and salt permeability increased. Exposure of samples to elevated temperature also influenced transport properties. For example, immersing BPS-32 films in boiling water for 4 h increased water sorption by 50%, water permeability by 2.3 times, and NaCl permeability by 8 times. The counter-ion form of the sulfonated polymer influenced the polymer’s transport properties, but these effects were weaker than the effect of thermal treatment. Generally, the BPS-32 samples prepared with different processing histories followed a trade-off between water/salt permeability selectivity and water permeability. These results suggest that, like many other glassy polymers, thermal processing history influences small molecule transport in these materials.

The intramolecular Diels–Alder reaction of tryptamine-derived Zincke aldehydes is a stepwise process

Computational studies show that the base-mediated intramolecular Diels-Alder of tryptamine-derived Zincke aldehydes, used as a key step in the synthesis of the Strychnos alkaloids norfluorocurarine and strychnine, proceeds via a stepwise pathway. The experimentally determined importance of a potassium counterion in the base is explained by its ability to preorganize the Zincke aldehyde diene in an s-cis conformation suitable to bicyclization. Computation also supports the thermodynamic importance of the generation of a stable enolate in the final reaction step. The thermal cycloreversion reaction of the Diels-Alder products is also found to proceed in a stepwise manner.

Supramolecular Coordination Assemblies Using 2-Aminodiacetic Terephthalic Acid Ligands: K[NiII(Hadta)(H2O)2]·H2O and K[Cu 1.5 II (adta)(H2O)1.5]·H2O

Two new network structures, K[NiII(Hadta)(H2O)2]·H2O (1) and K[Cu 1.5 II (adta)(H2O)1.5]·H2O (2) which are stabilized by 2-aminodiacetic terephthalic acid ligands have been synthesized and structurally characterized. Supplemental analyses include infrared spectroscopy and CHN analysis. 1 contains mononuclear secondary building units that are linked through potassium counterions and H-bonds to form a 3D network structure. 2 contains a 1D coordination polymer containing CuII ions with two different coordination environments. Potassium counterions further network these 1D chain structures.

Two dinuclear iron(ii) complexes K[Fe2(L1)(SCN)4]·2(C3H8O) and [Fe2(L1)(SeCN)3(C5H5N)]·H2O are stabilised in the ‘[HS–LS]’ state by a bis-tetradentate pyrazolate-based ligand

Two air-sensitive dinuclear iron(II) complexes, K[Fe(II)(2)(L(1))(SCN)(4)]·2(C(3)H(8)O) (1) and [Fe(II)(2)(L(1))(SeCN)(3)(C(5)H(5)N)]·H(2)O (2), of 3,5-bis[N,N-bis(2-pyridylmethyl)aminomethyl]-1H-pyrazolate [(L(1))(-)] have been prepared. Interestingly, complex 1 is anionic, featuring four coordinated SCN(-) anions and a potassium counterion whereas complex 2 is neutral, containing a coordinated pyridine molecule and only three coordinated SeCN(-) anions. These are the first iron complexes reported for this type of ligand. Magnetic measurements and Mössbauer spectra show that both 1 and 2 are in a '[HS-LS]' mixed spin state between 300 and 2 K.

Anionic polymerization of N ,N -dialkyl-2-methylenebut-3-enamide: Effect of alkyl substituents on polymerization behavior

Anionic polymerizations of three 1,3-butadiene derivatives containing different N,N-dialkyl amide functions, N,N-diisopropylamide (DiPA), piperidineamide (PiA), and cis-2,6-dimethylpiperidineamide (DMPA) were performed under various conditions, and their polymerization behavior was compared with that of N,N-diethylamide analogue (DEA), which was previously reported. When polymerization of DiPA was performed at −78 °C with potassium counter ion, only trace amounts of oligomers were formed, whereas polymers with a narrow molecular weight distribution were obtained in moderate yield when DiPA was polymerized at 0 °C in the presence of LiCl. Decrease in molecular weight and broadening of molecular weight distribution were observed when polymerization was performed at a higher temperature of 20 °C, presumably because of the effect of ceiling temperature. In the case of DMPA, no polymer was formed at 0 °C and polymers with relatively broad molecular weight distributions (Mw/Mn = 1.2) were obtained at 20 °C. The polymerization rate of PiA was much faster than that of the other monomers, and poly(PiA) was obtained in high yield even at −78 °C in 24 h. The microstructure of the resulting polymers were exclusively 1,4- for poly(DMPA), whereas 20–30% of the 1,2-structure was contained in poly(DiPA) and poly(PiA). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3714–3721, 2010

Enhanced luminescence properties of highly threaded conjugated polyelectrolytes with potassium counter-ions upon blending with poly(ethylene oxide)

The photophysics and electroluminescence (EL) of thin films of unthreaded and cyclodextrin-encapsulated poly(4,4′-diphenylenevinylene) (PDV) with potassium countercations, blended with poly(ethylene oxide) (PEO) are investigated as a function of the PEO concentration. We show that three main factors contribute to increasing the photoluminescence (PL) quantum efficiency as a result of suppressed intermolecular interactions, namely: the high degree of encapsulation of the polyrotaxanes, the relatively large countercation (e.g., compared to lithium), and the complexation of the rotaxanes with PEO. By facilitating cationic transport to the negative electrodes, PEO also leads to devices with enhanced electron injection and improved charge balance, whose operation therefore resembles that of “virtually unipolar” light-emitting electrochemical cells. This effect, together with the enhanced PL efficiency, leads to higher EL efficiency for both polyrotaxanes and unthreaded polymers, upon addition of the PEO. We show that the concurrent exploitation of the various strategies above lead to an overall EL efficiency that is approximately twice the value previously reported for Li-based PDV. A blueshift of the EL spectrum during the devices turn-on is also reported and analyzed in terms of interference and doping effects.