AN EQUILIBRIUM IN THE COBALTAMMINES.¹

Kinetics of aquation of the fluoropentaamminecobalt(III) ion

“…The equilibrium quotient Q for reaction [2] cannot be determined with any certainty from our measurements, and we have been unable to devise an accurate method for the direct measurement of the rate coefficient for anation of Co(NH3),OHZ3+ by F-. Nevertheless, it appears that Q is not less than 100 M -' at 25" and I = 0.1 M , even if the reaction [2] is strongly endothermic, so that the value 20 < Q < 30 M-' which can be obtained from Chan's data (1) is probably incorrect.…”

“…Nevertheless, it appears that Q is not less than 100 M -' at 25" and I = 0.1 M , even if the reaction [2] is strongly endothermic, so that the value 20 < Q < 30 M-' which can be obtained from Chan's data (1) is probably incorrect. Thus, CO(NH,),F~+ may not fit the Langford linear free-energy relationship (L.f.e.r.)…”

“…However, the values of the aquation rate coefficient, k,,, so obtained were close to those obtained by following only the first 8 % of reaction either with buffer or without (see below), so the actual aquation process is not directly affected by the presence of buffer. The equilibrium quotient for the reaction [2] (i.e., the "stability constant" of CO(NH,),F~+) in pyridinelpyridinium perchlorate buffer of I = 0.1 M and p H 4.5 was determined by direct equilibrium measurements and from eq. [3] as 170 k 30 M-' in the range 45-75"; in view of the apparent interaction of CO(NH,),OH,~+ with the buffer, this value represents a lower limit.…”

Stereochemistry and Reaction Mechanisms of Hexacovalent Inorganic Complexes.

“…Therefore, the kinetic data collected in aqueous solutions have shed no light on the role played by water in such reactions. Although rates of acid hydrolysis are for the most part independent of ionic strength (2, 123,124), Garrick (74) has shown that the rate with [Co(NH3)&l]f2 is definitely accelerated in the presence of nitrate or sulfate ions. He observed a specific catalytic effect, the sulfate ion being a much better catalyst for the reaction than the nitrate ion.…”

“…In addition, the rate of acid hydrolysis of ammine complexes in an acid medium (pH range of approximately 0.5 to 3) is independent of the hydrogenion concentration (124). However, the rate of aquation of an acidoaquoammine complex varies inversely with the concentration of hydrogen ion (31).…”