3. The water exchange rate constants for metal(III) aquo ions, [M(H2O)6]3+, are

Question

3. The water exchange rate constants for metal(III) aquo ions, [M(H2O)6]3+, are observed to increase as the pH of the solution is increased due to faster water exchange in the conjugate base, [M(H20)50H12+. The rate constants and activation parameters for M = Cr(III), Fe(III), Ru(III), and Ga(III) are given in the table below. (a) Explain the trends in the rate constants and activation parameters for the four [M(H20)6]3+ complexes. (b) Explain why deprotonating one of the water ligands causes an increase in the rate constants for water exchange. (c) Explain the changes in the activation parameters when going from [M(H2O)6]3+ to [M(H2O)5OH]2+ as the species undergoing water exchange.

Explanation / Answer

Answer:

The rate constant for the formation of [Ga(H2O)6]3+ is the highest of all complexes. Followed by [Ru(H2O)6]3+, [Cr(H2O)6]3+ and [Fe(H2O)6]3+.

Deprotonating one of the water ligands cause increases in rate constants due to negative charge on hydroxyl which allowing complex molecule to reduce positive charge.

The activation energy while moving [M(H2O)6] to [M(H2O)5(OH)] will be on lesser side, as the molecule tends to get neutrality.

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