Showing papers on "Aquation published in 1981"

The aquation of hexachlorotechnetate(IV)

Abstract: The photochemical decomposition of (NH4)2TcCl6 in dilute HCl, HClO4 and H2SO4 solutions has been studied. Electrophoresis and spectrophotometry were used to identify TcCl 6 2− , TcCl5 (H2O)−, cationic and uncharged species and TcO 4 − . The yield of each species as a function of the time of uv irradiation was determined. The TcCl 6 2− , yield decreases to zero after 50 h of irradiation. The TcCl5(H2O)−, cationic and uncharged species and TcO 4 − are formed in different proportions in the three acids. After 120 h of irradiation of the HCl solution the principal Tc species was the cationic one (≈70%) followed by the uncharged species (≈24%). In HClO4 solution the cationic species (≈70%) was followed by TcO 4 − , but in H2SO4 solution the uncharged species amounts to ≈90%.

Solution structure of ionic polymers and their catalysis

Abstract: Recent X-ray and neutron scattering studies of dilute solutions of polyelectrolytes show distinct peak in low angle regions. The peak position depends on the degree of polymerization. When two fractions are mixed, not two but a single peak appears, suggesting strongly that the peak is due to inter-molecular ordering of macroions. The Bragg distance (intermacro-ion distance) , 2Dexp, decreases with increasing polymer concentration. With increasing concentration of added salt, the 2Dexp increases (not decreases). The 2Dexp values obtained from the X-ray data and also from the neutron scattering are always smaller than (about one half of) .2Do, an intermacroion distance calculated with the assumption of simple cubic distribution, for fractionated polyacrylates, polystyrenesulfonate (Mw/MN < 1.2) , polymethacrylate and poly-L-lysine. This suggests the presence of a two-state structure in solutions, which is a consequence of unusually intense macroion-gegenion interaction. On the basis of this interaction, polyelectrolytes are known to show remarkable catalytic influence on various interionic reactions. Our explanation of the polyelectrolyte catalysis is based on the Bronsted-Bjerrum equation, k/k* = fA. fB/fX (k, k* : rate constants with and without polyelectrolyte, f's: activity coefficients of the reactants A and B and of the activated complex X). Besides the electrostatic stabilization or destabilization of the reactants and/or the activated complex, which was pointed out earlier, a new factor responsible for variation of the activity coefficient term is found to be important, namely solvent. The high pressure study indicates clearly that the solvation-desolvation factor is of a substantial importance. The volume of activation (ΔV≠) shows that acceleration caused by polystyrenesulfonate for the Ag+-induced aquation reaction of Co (NH3)5Br2+ is largely due to dehydration of the activated complex by the macroions. Correspondingly the entropy of activation (ΔS≠) is increased so that the free energy of activation (ΔG≠) and hence the fX is lowered. On the other hand, deceleration of the OH−-hydrolysis of the Co complex is found to be due to dehydration of the reactants. In this case, addition of macroions lowers ΔV≠, ΔS≠, and accordingly the reactant activity and hence increases ΔG≠.

Pressure-dependent aquation of the Tris(2,2'-bipyridyl)iron(II) cation

Abstract: The aquation of Fe(bpy)32+ (bpy = 2,2'-bipyridyl) was studied in aqueous hydrochloric acid at a range of pressures between 1 and 2070 bar. Activation volumes (ΔV‡) in 1.0 M HCl (+ 12.3 cm3 mol-1), 0.01 M HCl (+14.8cm3 mol-1), 1.0 M DCl (+13.3 cm3 mol-1) and 0.01 M DCl (+16.3 cm3 mol-1) were determined. A mechanism involving a significant positive contribution to ΔV‡ arising from a low-spin ↔ high-spin preequilibrium is proposed. The minor effect of the deuterium solvent isotope on ΔV‡ is consistent with this proposal.

Kinetics of reactions of the tris-(4-methyl-1,10-phenanthroline)iron(II) cation

Abstract: Kinetic parameters are reported for aquation of the tris-(4-methyl-1,10-phenanthroline) iron(II) [Fe(4-Mephen)3]2+, cation and for its reactions with hydroxide, cyanide, and peroxodisulphate. Activation volumes have been determined for the two last-named reactions; they reflect the importance of solvation changes in transition state formation.

The Aluminium(III) Ion-assisted Aquation of the Pentaammine fluorochromium(III) Ion

Abstract: The aquation of the pentaamminefluorochromium(III) complex was found to be assisted by the aluminium ion. The observed pseudo-first-order rate constant, kobsd, can be written approximately as: kobsd=kAl[Al3+] (kAl=7.5×10−4 dm3 mol−1 s−1 at 35 °C, pH 3.0, I=2.0 mol dm−3). The rate constant decreased with an increase in the hydrogen-ion concentration, and this hydrogen-ion dependence was explained by assuming that the attack of aluminium ions on CrF(NH3)52+ was blocked by the protonation of the fluoro ligand. The analysis of the experimental results gave 3.0±0.1 for the logarithm of the protonation constant. The effects of ClO4− and Co(CN)63− on the reaction rate were explained by considering the formation of ion-pairs between the anions and the reacting cations.

The aluminium ion-assisted aquation of (CoF(NH3)5)2+.

Abstract: A kinetic study of the aluminium ion-assisted aquation of CoF(NH3)52+ was carried out. The pseudo-first order rate constant obtained can be expressed as kobsd=kAl[Al3+], where kAl=(1.6±0.2)×10−3 dm3 mol−1 s−1(I=2.0 mol dm−3, 25 °C). The reaction rate is independent of the pH in the (pH)obsd<3.3 range, in contrast with the pH-dependent rate for the CrF(NH3)52+-Al3+ system. The different behavior between CoF(NH3)52+ and CrF(NH3)52+ in aquation can be explained in terms of their electronic structures, as calculated on the basis of the CNDO/2 method.

KINETICS AND MECHANISM OF THE METAL ION CATALYSED AQUATION OF cis-DIAQUOBIS(MALONATO) CHROMATE(III) ION IN AQUEOUS-ACID MEDIA

Abstract: The Cu(II), Ni(II), Co(II) and Zn(II) catalysed dissociation of the cis-diaquobis(malonato)chromate(III) ion has been studied kinetically in perchloric acid solution over a temperature range. Under these conditions k obs = kH[H+] + k cat[M2+] where k obs is the observed first order rate constants and k H and k cat are the appropriate rate constants for the proton and metal ion catalysed pathways respectively. The metal ion exert marked catalytic effects with k cat following the sequence Cu(II) > Ni(II) > Co(II) > Zn(II). A possible mechanism for the metal promoted reaction is proposed and the relevance of these results to the mechanism of the trans → cis isomerisation of [Cr(mal)2(H2O)2]− considered.

Preparation and kinetics of acid, base and Hg(II)-induced hydrolysis of cis β

Abstract: The kinetics of aquation and base hydrolysis of cisgb 2 [CoCl(benzimidazole)(trien)] 2+ cation are described. In the range [H + ]=0.001-0.1 M (I=0.1 M) chloride is released from the complex via aquation and base hydrolysis paths. At 50°C k H 2 O = 3.4 × 10 -5 sec -1 , δH * =104±5 kJ mol -1 , δS * =-11±16 JK -1 mol -1 and k OH =2.19×10 7 M -1 sec -1 , δH * =66.4±4.3 kJ mol -1 , δS * =101±13 JK -1 mol -1 . The site of deprotonation in the base hydrolysis path, generating the reactive conjugate base, is believed to be the planar secondary NH of the trien ligand trans to benzimidazole; chloride dissociation from the conjugate base is rate limiting (SN 1 cb). The rate and activation parameters for the acid independent Hg(II)-induced aquation are 0.103 ± 0.002 M -1 sec -1 (35°C), 72.4± 5.5 kJ mol -1 , and -29 ± 18 JK -1 mol -1 (I = 0.3 M) respectively. There is no evidence of release of benzimidazole from the chloro complex, but the OH group of cisβ 2 [CoOH(BzmH)(trien)] 2+ is found to labilise benzimidazole from the Co(III) centre to yield the corresponding aquo product.