Cobalt, pentaammine reduction

This experiment begins a series of analytical investigations that will be used to confirm the product composition of your cobalt ammine coordination compound. We begin by determining the percentage composition by mass of cobalt in the coordination compound synthesized in Experiment 2.1. The first step involves quantitative decomposition and reduction of the cobalt(III) complex into the cobalt(II) ion. The decomposition of pentaammine-chlorocobalt(III)chloride [Co(NH3)5Cl]Cl2 is shown as an example in equation (2.6). 

Table I lists some rate constants at room temperature for the chromium(Il) reduction of pentaammine cobalt (III) complexes containing monocarboxylic ligands. The tetraammineglycinate is a complex with a minimum of steric hindrance. The rate of reaction is very similar to that of the acetato complex, indicating that inductomeric effects are of little importance in these redox processes, so that the observed decreases in the reaction rates may be related to the steric hindrance of the ligand. As the bulk of the carbon ring increases the rate decreases, although this decrease is accompanied by an increase in activation entropy (4) (from -38 e,u, for the cyclopropane complex to -23...

The rates of electron transfer to a series of pentaammine(pyridine)-cobalt(III) complexes, [Co (NH3)5(NC5H4X)]- + (X = 3-CN, 3-Cl, H, 4-CH3, 4-C(CH3)3, and 4-N(CH3)2) were determined using the mentioned competition method. The homolytic scission of the chromium-carbon bond in [(H20)5CrC(CH3)20H] was used to estimate the rate constants for the reducing agent C(CH3)20H, whereas direct measurements were carried out for the reductions by V(H20)6 " and Ru(NH3)6. Arguments have been put forward that in each case the reactions proceed by a direct outer-sphere... 

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