Substitution Reactions of Linear Complexes

The symmetrization of methylmercury(ii) chloride in non-aqueous media is a rather slow process.  

An ultrasonic absorption study of the kinetics for the formation of the second acetate complex of mercury(ii) in acidic aqueous solution, reaction (1), gives rate 

Another ultrasonic absorption study of the rates of complexation-decom-plexation of 15-crown-5 and 18-crown-6 complexes for a series of bivalent cations in aqueous solution shows that non-spherically co-ordinated Hg + (similarly to the previously studied - Ag+) reacts faster with the crown ethers than spherically co-ordinated metal ions, which gives additional evidence for water loss as the rate-determining step. The more rigid crown ethers have to undergo considerable conformational strain to accommodate themselves to the linear geometry of silver(i) and mercury(ii), so the rigidity of the ligand is especially important for the rate of complexation with these metal ions.  

Substitutions at linear Ag in aqueous solution are very fast and involve displacement of water as the rate-determining step. Reaction between silver(i) ions and diphenylmethylenebismercaptoethanol is reported to be seven orders of magnitude slower, and can be followed using stopped-flow techniques. The experiments give further support to the associative mechanism. 

Satchell and T. J. Weil, Inorg. Chim. Acta, 1978, 29, L239. 

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