Iron Hexaaqua species

Harris and co-workers have extensively studied the kinetics of water substitutions in [Rh(H20)6] + (equation 281 X = HjO," Cl, " Br " ). A two-term rate law was found in all three cases, as was an inverse [H" ] effect. Reaction of the substituting ligand with either [Rh(H20)6], or its conjugate base [Rh(H20)50H], accounts for the two-term rate law, while the inverse [H ] effect occurs because the [Rh(H20)0H] is several orders of magnitude more reactive than the hexaaqua ion, making the base-catalyzed path the dominant route in all but the most acidic solutions. For Cl and Br anations, the monohalo-substituted species were not isolated, as rapid substitution of a second halide leads to the (presumably trans) [Rh(H20)4X2] ions. The kinetic irons effect was also cited to explain the reactivity of the [Rh(H20)50Hp ion for the [Rh(H30)5X] series, the order of the kinetic trans effect induced by X was shown to be OH > Br > Cl." Kinetic studies of the anation of [Rh(H20)4] by NCS (equation 281 X = NCS ) have been presented by Filipenko and co-workers at 80 °C, = 0.104 M s ,... 

---