Kinetics and Mechanism of Formation of Monothiocyanato and Mononitrilotriacetato Complexes of Iron(III)

Kinetics of the formation of monothiocyanato and mononitrilotriacetato complexes of iron(III) in aqueous solution have been studed by using a stopped-flow technique:Fe3++SGN−\oversetk1\undersetk−1\ightleftharpoonsFeNCS2+FeOH2++SCN−\oversetk2\undersetk−2\ightleftharpoonsFeNCS2++OH−FeOH2++H2nta−\oversetk→Fe(nta)+H+Rate constants at 25°C and μ=0.5 (NaClO4) are as follows: k=90 M−1 sec−1, k−1=1.6 sec−1, k2=5.1×103M−1sec−1, k−2=10×1013 M−1 sec−1, k=1.0×105 M−1 sec−1. Some discussions are made on the effect of hydroxide ion on the complex formation reactions.