The reaction of CrCl3 with liquid NH3 to give yellow [Cr(NH3)6]Cl3 often has a low yield,

since the reaction tends to stop with the production of pink [Cr(NH3)5Cl]Cl2. However,

adding a small piece of Na metal to the liquid NH3 results in complete conversion of the

CrCl3 to [Cr(NH3)6]Cl3. Offer two plausible explanations of this rate enhancement for the

final step of the substitution process

2- Write a hypothetical inner-sphere redox mechanism for the reaction of [Cr(OH2)6]2+ with cis-

[Co(en)2I2]+ in acid solution to give (ultimately) cis-[Cr(OH2)4I2]+, Co2+

(aq) and en. What

evidence could support this mechanism and why?

3-Consider reduction of the following cobalt complexes [Co(NH3)5(L)]3+ (L = pyridine (I),

NC5H4-p-CH2NH2 (II), NC5H4-p-CONH2 (III)) by labile [Cr(OH2)6]2+

.

a). Which cobalt complex is least likely to be reduced by an inner-sphere mechanism?

b). The reduction of III proceeds with a rate constant of k = 17.4, while the reduction of I

proceeds with a rate constant of k = 4.0 × 10-3

. What is a likely explanation of the difference?

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