Ionic Association and Mobility IV. Ionophores in Dimethylsulfoxide at 25°C

The results of conductance measurements on pyridinium picrate, tetraphenylo-sonium picrate, potassium picrate, tetraphenylantimony picrate, tetrapropylam-monium, tetrafluoroborate, tetramethylammonium hexafluorophosphate ion association noncoulombic interaction in dimethyl sulfoxide (DMSO) at 25°C in the concentration range 1–15×10^–4 M are reported. The data were analyzed by the Justice modification of the Fuoss–Hsia equation. Except for pyridinium picrate all salts studied were found to be associated.Application of the Justice Barthel–Bjerrum model of ion association permitted calculation of the noncoulombic portion of the potential of mean force, W _±. Ionic limiting conductances were calculated for six ions using known values of previously determined transport numbers. A table of most current limiting ionic conductances for a variety of ions in DMSO at 25°C has been established.     

Ion association of lithium and sodium picrate in 2-propanol at 25°C. II. Spectrophotometric measurements

The molar absorptivities of lithium picrate and of sodium picrate have been measured as a function of salt concentration (in the 0.1–1 mmol-dm^–3 concentration range) in 2-propanol at 25°C. Values of the molar absorptivities of the free picrate ion _i, of the ion pair _p, and of the ion pair association constant K_a have been calculated for each salt. The K_a values for these two salts in this solvent calculated from spectrophotometric measurements were found to be the same within experimental uncertainty as the values of K_a calculated from conductance measurements.     

Transference numbers of potassium picrate in water at 25°C and the dimerization of picrate ions

The cation- and anion-constituent transference numbers of aqueous 0.02M potassium picrate have been measured at 25°C by the moving-boundary method. The large difference (0.014) between the results and the predictions of the Debye-Hückel-Onsager theory, and similar anomalies in the literature, are consistent with the existence of picrate ion dimers (Pi ₂ ^2– ) with a formation constant of 4(±2) liter-mole^–1.This work was carried out at Imperial College while P. G. N. Moseley was on leave of absence from the University of Khartoum.     

Influence of the dielectric constant on ion-pair and ion-ligand complex formation

The effect of dielectric constant on ion association of triethylammonium picrate and methylimidazolium picrate and on ion-ligand complex formation between the cations Et₃NH⁺ and MeImH⁺ and 1-methylimidazole was investigated from conductance data carried out in nitrobenzene-benzene mixtures (34.8K _A satisfy in first approximation the relation logK _A 1/D. The center-to-center distance å has been calculated and compared to the value obtained for nonhydrogenbonded ion pairs. The ion-ligand association constantK ₁ ⁺ increases as the dielectric constant of the medium decreases. Plots of logK ₁ ⁺ against 1/D give straight lines, the slopes of which are consistent with the predictions of a theory that interprets the effect of the dielectric constant in terms of changes in the polarization energy of the solvent around the complexed and the uncomplexed ions. For these interactions, the complexed ions can be approximated as charged spheres, the volume of which is equal to that of the bare ion plus the volume of the ligand.     

Stabilization of a K+-(bis-Cage-Annulated 20-Crown-6) Complex by Bidentate Picrate

Bis-cage-annulated 18-crown-6 and 20-crown-6 macrocyclic ethers (i.e., 1 and 2, respectively) have been synthesized, and their alkali metal picrate extraction profiles have been determined. Host system 1 proved to be a significantly more avid alkali metal cation complexant than 2 and somewhat more avid than 18-crown-6. Both 1 and 18-crown-6 display modest selectivity toward K⁺ and Rb⁺. A stable host–guest complex was prepared by slow evaporation of a CH₂Cl₂–hexane solution of an equimolar mixture of 2 and potassium picrate. The X-ray crystal structure of this complex reveals that picrate anion functions as a bidentate ligand therein. The gas-phase interaction energy between the 2 K⁺ complex and picrate anion was calculated to be ca. –64.9 kcal mol^–1, thereby indicating that participation of picrate anion as an additional bidentate ligand results in significant stabilization of complex 10.     

Interactions in water-alcohol mixtures: Conductance of lithium picrate in solutions of water and isomeric pentanols at 25°C

Conductance measurements of lithium picrate in solutions of water in n-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol and 3-methyl-1-butanol have been carried out at 25°C. Ionic association and conductance were found to change with water content and with the molecular structure of the alcohols (i.e. position of the OH group and degree of branching of the alkyl chain). These results indicate that both conductance and ion pair formation are not the consequence of the simple motion of ions in the electrical field as required by the continuum model. A more realistic approach, involving the internal structure of the solvent mixtures, has been considered.     

Electroconduction,Association, and Ion–Molecular Interactions in Nickel Chloride Solutions in Methanol at 5–55°C

Results of a conductimetric investigation of nickel chloride in methanol at 5–55°C and electrolyte concentrations of 0.1–5 mM are presented. Limiting equivalent conductivities by Ni²⁺ and Cl^– and constants of ionic association in the first step with the formation of ionic pair NiCl⁺ are determined for asymmetric electrolytes using an extended Lee–Wheaton equation. In dilute nickel chloride solutions in methanol the association of ions in the second step is inessential. The size of dynamic solvation sheaths of the ions and the short-range non-coulombic interion potential suggest that the Ni²⁺ ion forms a kinetically and energetically stable solvated complex with the nearest solvation layer being 400 pm thick and virtually temperature-independent. The nearest kinetically stable solvation sheath of the Cl^– ion comprises mostly hydroxyl groups of methanol molecules and its stability is severely dependent on temperature.     

Electric dipole moments in polar solvents. II. Tetraisoamylammonium nitrate ion pairs in chlorobenzene. Effect of mutual polarization of the ions

The dielectric constant and conductivity of dilute solutions of tetraisoamylammonium nitrate in chlorobenzene are measured between –34.6° and 99.0°C to give association constants for the formation of ion pairs (K _A) and triple ions, and electric dipole moments. The quantityK _A as a function of temperature is reproduced by the Denison-Ramsey-Fuoss treatment for unolarized ion pairs [Eq. (2)] with a distance of closest approach of 4.90 Å. The dielectric data are reproduced by Onsager's equation with an inherent (gas-phase) dipole moment of the ion pairs of 14.2±0.3 D. Other methods of calculation lead to consistent dipole moments, confirming that the mutual polarization of the ions is important. The energetics of ionic association is considered on the basis that the ion pair may be treated as a polarizable dipole in a spherical cavity.     

New ditopic receptors for alkylammonium ion complexation

New receptor molecules have been synthesized in which ,-bis-(4-hydroxyphenyl)-1,4-diisopropylbenzene is linked to 1,10-diaza-18-crown-6, 1,10-diaza-21-crown-7 or 1,13-diaza-24-crown-8 units by ethylene or 1,4-butylene bridges. Binding abilities of the new receptors and the model compoundN,N-didecyl-1,10-diaza-18-crown-6 toward alkali metal cations and alkylammonium ions were assessed by picrate extraction. Spectral evidence for inclusion of alkylammonium ions within the receptor cavity was obtained by¹H NMR spectroscopy. From a¹H NMR titration experiment conducted in CDCL₃–CD₃OD (91), a relatively strong inclusion complex (K _a 900M^–1) of the receptor having a 1,10-diaza-18-crown-6 subunit and ethylene spacers with propylammonium picrate was observed.     

Study of the stoichiometry and the kinetics of the Jaffé reaction with a picrate ion-selective electrode

Potentiometric studies with the picrate ion-selective electrode indicate that the species formed as the product of reaction between alkaline picrate and creatinine in the Jaffé reaction is a 1:1 complex. Kinetic studies indicate that the forward reaction is first order with respect to picrate, creatinine, and hydroxide concentration. The second-order rate constant k was found to be in the range 9.1–10.4 M⁻² sec⁻¹ at 27 °C and μ = 1.00, with creatinine or picrate in excess, k increases with increasing μ and temperature. An activation energy of 10.1 kcal/mol was calculated for the Jaffé reaction, with creatinine in excess.     

Conductance of tetraalkylammonium salts in 2-butanone from −45 to 25°C

Interactions of three types of tetraalkylammonium cations (tetrapropyltetrabutyl-and tri-isoamylbutyl- ammonium) with perchlorate and tetraphenylborate anions were studied by the conductivity method in 2-butanone from –45°C to 25°C. Conductance data obtained for diluted solutions (5×10^–5 – 2×10^–3 mol-dm^–3) were used to calculate the limiting molar conductivities and associationconstants. The conductance equation of Fuoss-Hsia including the Chen term and the chemical model assumption were applied. Limiting ion conductivities were calculated assuming equal limiting conductivities of the i-Am₃BuN⁺ and BPh ₄ ^– ions at all temperatures. Gibbs energies and entropies of ion pair formation, calculated from the dependence of association constants on temperature, are presented including the contributions due to short-range forces.     

The effect of high pressure on the ion pair equilibrium constant of alkali metal fluorides: A spectrophotometric study

Bromophenol blue indicator was used in UV-visible spectrophotometric measurements to study ion association constants of alkali metal fluorides. The equilibrium constants for the ion pair formation of the alkali metal fluorides were determined as a function of ionic strength at one atmosphere pressure and 25°C. The effect of pressure on these association constants was measured at a constant total ionic strength of 1.0 mol-kg^–1 over a pressure range of 1 to 2000 atmospheres at 25°C. The pressure dependences of the stoichiometric association constants of the alkali metal fluorides are given by: lnK _LiF ^* =0.77–2.47×10^–4P–2.12×10^–8P²; lnK _NaF ^* =0.53–1.08×10^–4P–1.66×10^–8P²; lnK _KF ^* =0.24–4.41×10^–5P–7.15×10^–8P²; lnK _RbF ^* =–0.17–8.65×10^–5P–4.51×10^–8P²; and lnK _CsF ^* = –0.37–1.14×10^–4P–6.82×10^–8P², where P is the pressure in atmospheres. The stoichiometric molar volume and compressibility changes for ion pair formation of the alkali metal fluorides were evaluated from the pressure dependence of K _MF ^* data. The thermodynamic association constants were also calculated making use of activity coefficient data from the Pitzer equations. The partial molal volume and compressibility changes for ion pair formation of each alkali metal fluoride are reported.     

Amiloride Conformation: The Effect of Different Crystalline Environments

The crystal structure of (3,5-diamino-6-chloro-pyrazine-2-carbonyl)-guanidine picrate has been determined with the use of X-ray diffraction method. The crystals are triclinic, space group PI with a = 10.2980(4) Å, b = 12.4322(4) Å, c = 14.4310(5) Å, = 66.317(2), = 70.077(2), = 72.462(2), Z = 2. The asymmetric unit consists of one amiloride cation, picrate anion, and three DMSO molecules from the solvent, two of which are disordered. The molecules of amiloride and picrate are almost planar. The guanidine group of amiloride is protonated and makes a kind of a salt bridge with phenolate and forms hydrogen bonds with ortho-nitro oxygen atoms of picrate. The pairs of amiloride cation–picrate anion, transformed by the inversion center and translated by 2 a and c, are mutually parallel and are connected by molecules of DMSO. The conformation of amiloride picrate is compared with those in other crystal structures.     

Transport properties and electroanalytical response characteristics of drotaverine ion-selective sensors

The construction and electroanalytical response characteristics of poly(vinyl chloride) matrix ion-selective sensors (ISSs) for drotaverine hydrochloride are described. The membranes incorporate ion-association complexes of drotaverine with tetraphenylborate, picrate, tetraiodomercurate, tetraiodobismuthate, Reinecke salt, and heteropolycompounds of Keggin structure—molybdophosphoric acid, tungstophosphoric acid, molybdosiliconic acid and tungstosiliconic acid as electroactive materials for ionometric sensor controls. These ISSs have a linear response to drotaverine hydrochloride over the range 8×10^–6 to 5×10^–2 mol L^–1 with cationic slopes from 51 to 58 mV per concentration decade. These ISSs have a fast response time (up to 1 min), a low determination limit (down to 4.3×10^–6 mol L^–1), good stability (3–5 weeks), and reasonable selectivity. Permeabilities and ion fluxes through a membrane were calculated for major and interfering ions. Dependences of the transport properties of the membranes on the concentrations of the ion exchanger and near-membrane solution and their electrochemical characteristics are presented. The ISSs were used for direct potentiometry and potentiometric titration (sodium tetraphenylborate) of drotaverine hydrochloride. Results with mean accuracy of 99.1±1.0% of nominal were obtained which corresponded well to data obtained by use of high-performance liquid chromatography.     

Raman and infrared spectroscopic investigation of contact ion pair formation in aqueous cadmium sulfate solutions

Raman and IR data for aqueous CdSO₄ and (NH₄)₂SO₄ solutions have been recorded over broad concentration and temperature ranges. Whereas the v₁-SO ₄ ^2– band profile is symmetrical in (NH₄)₂SO₄ solutions, in CdSO₄ solutions a shoulder appears on the high frequency side which increases in intensity with increasing concentration and temperature. The molar scattering coefficient of the v₁-SO ₄ ^2– band is the same for all forms of sulfate in (NH₄)₂SO₄ and CdSO₄ solutions and is independent of temperature up to 99°C. The high frequency shoulder is attributed to the formation of a contact ion pair [Cd²⁺OSO ₃ ^2– ] (11 associate). Also the v₃-SO ₄ ^2– antisymmetric stretching mode shows a splitting in the CdSO₄ solution. Further spectroscopic evidence for contact ion pair formation is provided by IR spectroscopy. No higher associates or anionic complexes are required to interpret the spectroscopic data. The degree of association has been measured as a function of concentration and temperature. The thermodynamic association constant, K_A=0.15±0.05 kg-mol^–1 at 25°C is estimated from the Raman data by an extrapolation procedure by taking account of the activity coefficients. Values are reported for the activity coefficient of the ion pair. From the Raman temperature dependence studies, the enthalpy of formation for the contact ion pair is estimated to be 10±1 kJ-mol^–1.     

Anion dependence of crown ether selectivities for alkali picrates and sulfonates in dioxane and toluene. A synergistic effect

The binding constants,K _N, of sodium and potassium 8-anilinonaphthalene-1-sulfonate (ANS) and of sodium 5-dimethylamino-1-naphthalenesulfonate (DNS) to benzo-18-crown-6 bound to a 2% cross-linked polystyrene network (RN18C6) were measured spectrophotometrically in dioxane and the results compared with those obtained for picrate salts. The network RN18C6 was then used to measure in dioxane and toluene by a competition method the equilibrium constant,K, of the reaction A^–M⁺N+CrA^–M⁺Cr+N.A^–M⁺N denotes the ionic solute (ANS, DNS, methyl orange or picrate salt) bound to the network RN18C6 (N) and A^–M⁺Cr is the solute bound to a soluble ligand Cr, where Cr represents a series of 18-crown-6 and 15-crown-5 compounds. Combining theK _N andK values the formation constants,K _L, of the crown ether complexes of the respective salts were obtained in dioxane. The data show a reversal in the complexation strength of the 18-crown-6 compounds in dioxane when sodium picrate is replaced by sodium ANS. The results were rationalized in terms of a synergistic effect exerted by dioxane, with dioxane forming a 1:1 dioxanate with the crown ion pair complex. This effect is especially strong with ANS and with a rigid planar crown ether like dibenzo-18-crown-6. The binding constants,K _N, of NaANS and NaDNS to RN18C6 in dioxane are nearly three times larger than for sodium picrate, and the same holds for the potassium salts. Differences in anion interactions with the network appear to be a plausible cause for the anion dependence ofK _N.     

Conductance in isodielectric mixtures. I.n-butyronitrile with dioxane,benzene, and carbon tetrachloride

The conductance of tetrabutylammonium tetraphenylboride, picrate, nitrate, and bromide has been measured at 25°C inn-butyronitrile and in mixtures of this solvent with dioxane, benzene, and carbon tetrachloride covering the range of dielectric constants from 10–24.26. For the picrate, nitrate, and bromide, the association constants at a given dielectric constant are independent of the chemical composition of the solvent. The changes of Walden products with solvent composition, however, are different, depending on which other solvent is mixed with the butyronitrile.     

Specific ion-molecule interactions of imidazole and 1-methylimidazole in nitrobenzene

We have studied, by conductivity measurements, the formation of hydrogenbonded complexes between imidazoles and ions in the three systems triethylammonium picrate (Et₃NHPic)+imidazole (Im), triethylammonium bromide (Et₃NHBr)+Im, and Et₃NHPic+1-methylimidazole (1-MeIm) in nitrobenzene in order to specify the importance of the two functions of the imidazole molecule, the tertiary nitrogen N₃, and the imino group N₁-H. While 1-MelIm forms only a single complex with the cationic species Et₃NH⁺, imidazole enters into specific interactions as well with the cations through its basic site N₃ and with the anions through its imino group. The complexing of the anions by imidazole, always weaker than the complexing of the cations, is more effective for Br^– than for Pic^–. Moreover, if imidazole is used as ligand, a 1:2 complex is formed between the cation and the imidazole, in which the second molecule of imidazole is bonded to the N-H group of the first by a hydrogen bond at the tertiary N atom. We did not observe a correlation between the equilibrium constants K ₁ ⁺ for the complexing of the cation Et₃NH⁺ by imidazole and pyridines (k ₁ ⁺ for pyridine, 3–4 dimethylpyridine, and imidazole are 8, 24, and 165, respectively) and the pK _a values of these ligands due to the fundamental difference in the structure of the imidazole and pyridine molecules, although both are considered as aromatic nitrogen bases.     

Solvent Extraction–Photometric Determination of Palladium Using Complexation with 1-(2-Pyridylazo)-2-Naphthol

Palladium(II) complexation with 1-(2-pyridylazo)-2-naphthol (PAN) in aqueous solutions followed by extraction with chloroform and photometric detection was studied. The best conditions were found for the formation of the complex in an aqueous solution and for its extraction with chloroform that provided a sufficient degree of binding palladium ions. The stability constant of the complex cation PdX⁺, which is extracted by chloroform as an ion pair [PdX]⁺[An^–] (An^–– CH₃COO^–), was calculated using the methods proposed by Rossotti (log K _stab= 18.73) and Komar' (log K _stab= 18.82). The equilibrium constant of the complexation reaction was also calculated (5.45 × 10⁴). It was shown that components of nonferrous alloys affect the determination of palladium by photometry as its complex or ion pair with PAN in chloroform.     

Synthesis and alkali metal cation complexation ofN-aryl [3.2.2] cryptands

Two novel three-nitrogen cryptands withN-aryl substituents are prepared by cyclization of 1, 10-diaza-18-crown-6 with mixed anhydrides of 6-arylaza-3,9-dioxadecanedioic acid followed by borane reduction of the resultant bicyclic diamides. For the alkali metal cations, theN-phenyl [3.2.2] cryptand exhibits strongest complexation for Rb⁺ in picrate extractions.Presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986.