Univalent Ions

Univalent Ions.— The technique of pulse radiolysis has been used to measure the kinetics of the formation of the Cu+ complexes (3) of maleic and fumaric acids. 

Comparatively little work has been done on the kinetics of complex formation between the alkali metal ions and simple ligands in view of the high rate constants and low stability constants involved. Atkinson has recently studied the ultrasonic absorption of the five alkali metal sulfates in water in the frequency range 25-250 MHz, where he found only one relaxation for each salt. The results are analyzed in terms of the normal two-step mechanism (the fast formation of an outer-sphere complex followed by rapid conversion to the inner-sphere complex) in which the rates of the two steps approach each other as the concentration of the solution decreases. (The concentrations were in the range 0.3-1.0 mol dm . ) As expected, the reactions are nearly diffusion controlled the rate constants for inner-sphere complex formation at 0.5 mol dm and 25°C are 1.0 x 10 s for Li, Na, Rb, and Cs sulfates but 2.0 x 10 s for the potassium salt. 

Merbach and co-workers have provided high-pressure nmr evidence that the same gradual change in mechanism from L to la occurs for water exchange at the bivalent cations [M(H20)6] (for the series Ni, Co, Fe, Mn) as has 

The kinetics of complex formation between Ni(II) and ortho-phosphate, ribose monophosphate and cytidine monophosphate (CMP) in water have been reported.The results are consistent with an/ mechanism involving protonated (HL ) and unprotonated (L ) ligands, and rate constants for reaction with L and HL are about 1.5 x 10 dm mol s and 2.3 x 10 dm mol s respectively, for all three systems. The cytidine ring appears to exert no effect on the binding of Ni(II) to CMP. The rate parameters have also been reported for the reaction of nickel(II) with 4-phenylpyridine and isoquinoline in water-r-butanol mixtures. Rate parameters for the dissociation of the isoquinoline and thiocyanate complexes of Ni(II) in 1-propanol, and of the former in ethanol and in water, are accommodated within an Id mechanism, and Tanaka has commented further on the relationships between the activation enthalpies for the dissociation of the same two complexes and the Gutmann donor number of the solvent. 

Rorabacher and co-workers have summarized the very considerable problems associated with the measurement of the water-exchange parameters at [Cu(H20)6] and have used the kinetics of this ion reacting with NH3 to form the monoammine complex [Cu(NH3)(H20)5] to estimate them. For the formation and dissociation of the monoammine complex the kinetic parameters are, respectively, k (25 C) = 2.3 x 10 dm moP s and 2.0 x 10 s HH = 4.5 and 9.5 kcal mol and A5 = — 5 and —7 cal K rnoPP On the basis of these data and evidence that the reaction proceeds by a dissociative mechanism, the best kinetic parameters for the inner-sphere solvent exchange at the aquo-copper(II) ion are calculated to be (25°C) = 2.0 x 10 s , Af/fx = 4.5 kcal mol and A5 = - 1 cal K moPP 

Lincoln has reported the rate of ligand exchange at [ZnL4] in CD2CI2, where L = tetramethylthiourea and hexamethylphosphoramide. 

The kinetic deuterium solvent isotope effects on the acid-catalyzed dissociation of Li(2,l,l) and Ag(2,2,2) have been reported, as have the exchange kinetics of cryptand (2,2,1) on Tl(2,2,2) and T1(2b,2,2) . The kinetics of complex formation between Li and 18-crown-6 ether in 1,3-dioxalane and 1,2-dimethoxyethane solvents have also been reported.  

Kinetics of the formation and dissociation of the cryptates Ag(2,2,2) and K(2,2,in acetonitrile/water mixtures have been reported. The 

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Electrical properties of liquids and solids are sometimes crucially influenced by H bonding. The ionic mobility and conductance of H30 and OH in aqueous solutions are substantially greater than those of other univalent ions due to a proton-switch mechanism in the H-bonded associated solvent, water. For example, at 25°C the conductance of H3O+ and OH are 350 and 192ohm cm mol , whereas for other (viscosity-controlled) ions the values fall... 

As a postscript to this chapter we may return to the values for ions in aqueous solution given in Tables 25 and 26. We recall that each value contains the conventional cratic quantity R In M that is to say, 8.0 e.u. per uni-univalent ion. Subtracting 8.0 e.u. from each of the values in Table 26, we obtain those given in Table 30, assigning —13.5 e.u. to... 

For cases of univalent ions, the magnitude of this quantity was found to be small however, for large macromolecnles with high surface charge, there could be significant electric-field-indnced dispersion. 

Group (1) Cations and anions which are incapable of donor-acceptor interactions. These are the large univalent ions. Bonding is purely by Coulomb and Madelung electrostatic interactions. From the Lewis point of view these are not acids or bases. They have no cement-forming potential. 

Equations (4.5) and (4.8), which were developed for univalent ions, can be rewritten, thus ... 

Phenols are weak acids and hence can be present in the forms of neutral molecule (AH) and univalent anion (A ). We consider the transfer of acid across the interface between an organic solvent (O) and water (W) in the forms of a neutral molecule and a univalent ion, respectively. 

Finally, consider a metal (ar)-solid electrolyte ( )-electrolyte solution (y) system where the solid electrolyte and the electrolyte solution contain a common anion A- and the metal and the solid electrolyte contain a common cation B+ (for simplicity, only univalent ions are considered). The potential difference between phase a (metal) and phase y (solution) is... 

The procedure described in the preceding section can form a basis for unambiguous determination of the Galvani potential difference between two immiscible electrolyte solutions (the Nernst potential) considering Eqs (3.1.22) and (1.4.34), e.g. for univalent ions,... 

Consider a system of two solvents in contact in which a single electrolyte BA is dissolved, consisting of univalent ions. A distribution equilibrium is established between the two solutions. Because, in general, the solvation energies of the anion and cation in the two phases are different so that the ion with a certain charge has a greater tendency to pass into the second phase than the ion of opposite charge, an electrical double layer appears at... 

The behavior that we observed for the iodide ion is typical for the transfer of a univalent ion. For multivalent ions the situation is more complicated. Depending on the system under consideration and on the electrode potential a multivalent ion can either be transferred in one step, or its charge is first reduced by an electron-transfer reaction. Table 9.1 summarizes the different behavior of ion-transfer and electron-transfer reactions. 

Table 11.1 lists the resulting low-temperature phases calculated for this set of compounds. Where experimental data are available (marked with a star) the predicted structures are those observed at low temperatures. Inverse denotes a perovskite structure in which a large divalent ion is 12-coordinate and a smaller univalent ion 6-coordinate. Unit cell dimensions are predicted to within 1% of the measured values. 

If A X (SbF6 ), as explained above, we can estimate it from the Stokes-Einstein equation for univalent ions... 

Bangham AD, Standish MM, Watkins JC. Diffusion of univalent ions across the lamellae of swollen phospholipids. J Mol Biol 1965 13 238. 

Sherry, H.S. (1966) The ion-exchange properties of zeolites. I. Univalent ion exchange in synthetic faujasite. f Phys. Chem., 70 (4), 1158-1168. 

Membrane Properties. The performance range of ammonia-modified membranes in low pressure operation is indicated in Figure 6 along with the performance of the reference membrane (I, reference membrane IV, ammonia-modified membrane). The lower boundary of the performance range refers to a solvent-to-polymer ratio of 3, the upper boundary to a ratio of 4. While the salt rejection towards univalent ions of the ammonia-modified membrane is limited to below 80 %, the maximum low pressure flux is over 15 m /m d (approaching 400 gfd) at a sodium chloride rejection of the order of 10 %. This membrane thus exhibits the flux capability of an ultrafiltration membrane while retaining the features of reverse osmosis membranes, viz. asymmetry and pressure resistance. 

The ionic concentration necessary to produce coagulation varies with increasing concentration of the suspension, with univalent ions the ratio of electrolyte to suspension necessary increases, with trivalent ions it decreases, with divalent ions the ratio appears to be independent of the concentration. 

Effects of Complexing. For complexes of the univalent ions (Ag+ and Cu+) the catalytic activity generally increases with the basicity of the ligand or solvent. This has been attributed to increased stabilization of the proton which is released in the splitting of hydrogen or, in one instance... 

Most commonly, metal ions M2+ and M3+ (M = a first transition series metal), Li+, Na+, Mg2+, Al3+, Ga3+, In3+, Tl3+, and Sn2+ form octahedral six-coordinate complexes. Linear two coordination is associated with univalent ions of the coinage metal (Cu, Ag, Au), as in Ag(NH3)2+ or AuCL Three and five coordination are not frequently encountered, since close-packing considerations tell us that tetrahedral or octahedral complex formation will normally be favored over five coordination, while three coordination requires an extraordinarily small radius ratio (Section 4.5). Coordination numbers higher than six are found among the larger transition metal ions [i.e., those at the left of the second and third transition series, as exemplified by TaFy2- and Mo(CN)g4 ] and in the lanthanides and actinides [e.g., Nd(H20)93+ as well as UC Fs3- which contains the linear uranyl unit 0=U=02+ and five fluoride ligands coordinated around the uranium(VI) in an equatorial plane]. For most of the metal complexes discussed in this book a coordination number of six may be assumed. 

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