The structure of H 5 DTPA (see Box 4 3) is shown below (a) Write equilibria to show the stepwise acid dissociation of H 5 DTPA Which step do you expect to have the largest value of K a (b) In the complex Gd(DTPA)(OH 2 ) 2 , the Gd 3 ion is 9 coordinate Draw a diagram that illustrates how the DTPA 5...

a The structure of H5DTPA provided in the images indicates that it contains five protonatable sites that can undergo stepwise acid dissociation The st ...

The structure of H 5 DTPA (see Box 4.3) is shown below: (a) Write equilibria to show

Question:

The structure of H₅DTPA (see Box 4.3) is shown below:

(a) Write equilibria to show the stepwise acid dissociation of H₅DTPA. Which step do you expect to have the largest value of K_a?

(b) In the complex [Gd(DTPA)(OH₂)]²⁻, the Gd³⁺ ion is 9-coordinate. Draw a diagram that illustrates how the DTPA⁵⁻ ion binds to the metal centre in this complex. How many chelate rings are formed?

(c) Values of log K for the formation of [M(DTPA)]ⁿ⁺ complexes in aqueous media are as follows: Gd³⁺, 22.5; Fe³⁺, 27.3; Ag⁺, 8.7. Comment on these data.

Box 4.3.