Summary
The ammoniation ofcis-[Rh(en)2Cl2] · (ClO4) in liquid NH3 was studied at constant ionic medium of 0.20 m perchlorate in the 0 to 35° range. The complex reacts in two distinct steps to givecis-[Rh(en)2(NH3)2] · (ClO4)3, with the intermediate formation ofcis-[Rh(en)2(NH3)Cl] · (ClO4)2. Both steps follow a conjugate-base mechanism. Activation parameters were obtained for the acid-base preequilibrium and the rate-determining step. The entropies of activation for the rate-determining step are 0 and −42 JK−1mol−1 for the first and second ammoniations respectively. These values are considerably lower than those found for the cobalt(III) analogues. The entropy changes for the acid-base equilibria are −84 and −36 JK−1mol−1 respectively, which is less negative than those values found for the cobalt(III) analogues.
Trans-[Rh(en)2I2] · (ClO4) ammoniates totrans-[Rh(en)2(NH3)I] · (ClO4)2. The contribution of spontaneous ammoniation to the overall reaction oftrans-[Rh(en)2I2] · (ClO4) is negligible, so the uniqueness oftrans-[Co(en)2Cl2] · (ClO4) among cobalt(III) complexes in this respect is not reproduced for thetrans-dihalotetraamine structure in rhodium(III) complexes. A comparison of cobalt(III) and rhodium(III) amines with respect to activation parameters and the influence of formal charge of the metal complex on reactivity indicates a more associative type of activation for rhodium(III).
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Balt, S., Jelsma, A. Kinetics of ammoniation of some halobis(ethylenediamine)-rhodium(III) perchlorates in liquid ammonia. Transition Met Chem 6, 119–122 (1981). https://doi.org/10.1007/BF00626121
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DOI: https://doi.org/10.1007/BF00626121