Aquation Chromium in Complexes

Recently c/ -activation has been recognized as playing an important part in chromium(m) substitutions whenever potentially chelating co-ordinated oxoanions are present e.g. NOs , SOa, AcO, S04 ). This makes it important that the correct counterion is chosen in studies of substitution reactions of cationic complexes. For example, replacing nitrate ion by perchlorate ion makes a significant difference to the rates of acid hydrolysis of some chromium(m) ammines.  

Another feature of chromium(m) substitutions which distinguishes them from analogous cobalt(m) reactions is the dominance of stereoretentive pathways, trans-Complexes of cobalt(m), in particular, often undergo stereochemical change, but this is rarely the case for chromium(in). Despite these characteristics which distinguish chromium(m) and cobalt(m) substitutions, there are still many features which make the chemistries of these two metal ions comparable. For example, the relative labilities of analogous complexes is similar, and acid- and base-catalysed reactions oftra occur for related compounds. These similarities will be apparent in the following sections. 

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