Mechanistic Studies on the Formation of a Trinuclear Ruthenium(III) Complex [Ru_3(NH_3)_(13)(SCN)Cl_2]Cl_6 by the Reaction of NH_4SCN and [Ru(NH_3)_5Cl]~(2+) in the Temperature Range 30°- 45℃

摘要

Reaction between the species Ru(NH_3)_5Cl~(2+) and SCN~- in aqueous solution was investigated spectrophotometrically in the temperature range 31.5°to 41.5℃. Direct replacement of chloride by thiocyanate ion takes place in which the later species acts as the centre for ion-aggregation. Thiocyanate ion acts as the bridging ligand between the two complex ions. Ion-pair formation does not take place at any stage of the reaction. Activation parameters are : △H = 102 ± 4 and 59 ± 2 kJ mol~(-1) and △S = -25 ± 14 and -138 ± 8 JK~(-1) mol~(-1) for the acid - free and acid-dependent paths respectively. An associative mechanism has been invoked for the process.