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The aquation of the cis-bis(iminodiacetato)chronlate(III) ion and the ti.cLns(Sac)-bis(meth3.liminodiacetato)chr~~nate(IlI) ion in acidic aqueous medium has been studied spectrophotometrically. The products of the aquation are the iminodiacetatotriaquochromium(II1) cation and the methyliminodiacetatotriaquochromium( 111) cation, respectively. In the reaction involving the cis-bis(imiiiodiacetato)chromate(III) ion, two distinct aquation steps were observed. The first observable step showed the rate lawThe second step gave the rate lawl'alues of k ' , k". and k"' a t 25.0" and ionic strength 0.9 are 7.08 X 10-3 JI-1 sec-1, 1.71 X 10-' sec-1, and 1.28 X M-' sec-1, respectively. The activation parameters for k', k", and k'" are AH+' = 15.3 f 0.4 kcal mol-', ASF = -17.0 f 1.5 cal deg-1 mol-'; AH& = 17.0 i : 0.6 kcal mol-', AS* = -18.7 ik 2.1 cal deg-1 mol-'; and AH* = 24.3 i : 0.4 kcal mol-', AS* = 5.1 i 1.4 cal deg-' mol-', respectively. In the aquation of the tuans(fac)-bis(metliyliminodiacetato)chromate(III) ion, an aquation step was observed with the rate law = (k'[H10+] + k"[H30]2)[complex] d [complex] dt ~ I-alues of k' and k" at 25.0" and ionic strength 0.9 are 1.88 X 10-4 36-1 sec-1 and 5.74 X J k -2 sec-l, respectively. The activation parameters for k' and k" are AH* = 17.0 i 0.3 kcal mol-1, AS* = -18.6 i 1.1 cal deg-l mol-'; and AH+' = 15.6 It 0.2 kcal mol-', AS'? = -21.2 i . 0.7 cal deg-l mol-', respectively. Reaction mechanisms for both systems, which are in agreement with the experimental data, are proposed.

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