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Chem20018: Reactions and Synthesis.

Coordination chemistry (Prof Donnelly): Tutorial 1

1. a) Write a reaction scheme (using chemical structure diagrams) for a ligand substitution reaction where the hexaaquacobalt(II) chloride reacts with three equivalents of sodium cyanide to form product ‘X’ (assume cyanide acts a N-donor monodentate ligand).

b) Draw any possible isomers of product ‘X’.

c) Write an expression for the equilibrium constant b3 which applies to reaction in part (a).

d) Suggest a reason for the well-known toxicity of cyanide.

2. a) Write a reaction scheme (using chemical structure diagrams) for a ligand substitution reaction where the hexaaquacobalt(II) chloride reacts with three equivalent of sodium oxalate to form product ‘Y’.

b) Draw any possible isomers of product ‘Y’.

c) Write an expression for the equilibrium constant b3 which applies to reaction in part (a).

d) Oxalate is formed by normal metabolism but excessive concentrations in the urine can lead to hyperoxaluria. What is the cause of hyperoxaluria?

3. a) Use the stepwise stability constants K_f1 = 5 x 107, K_f2 = 2.2 x 106, K_f3 = 3.64 x 104 to calculate the b₃ for the reaction of ethylenediamine (en) with [Ni(OH₂)₆]²⁺.

b) Specify the coordination geometry of the product formed.

c) Rationalise the observation that K_f1 > K_f2 >K_f3.

4. Define the term ‘dissociation constant’.

5. a) Draw the reaction scheme for the reaction of [Cu(OH₂)₆]²⁺ with two equivalents of ethylenediamine to form the square planar complex [Cu(en)₂]²⁺. The DSo for this reaction is 22 J K–1 mol–1.

b) Draw the reaction scheme for the reaction of [Cu(OH₂)₆]²⁺ with triethylenetetramine, NH2(CH2)2NH(CH2)2NH(CH2)2NH2 (ligand ‘3’ in question 6), to form a 1:1 square planar complex. Use the following data to calculate DS⁰ for the reaction at 298 K: log10b1 = 20.7; DHo = –90.0 kJ.mol–1 

c) Suggest a reason difference in DSo for parts (a) and (b).

6. The ordering of values of logb_n for metal complexes with high spin 2+ cations with a variety of ligands follows the order:

Mn²⁺ < Fe²⁺ < Co²⁺ < Ni²⁺  < Cu²⁺ > Zn²⁺

Discuss this series (your answer should be ~ ½ page in length)

7.   Consider the reaction of the ligands shown below with [Ni(OH₂)₆]²⁺. List the ligands in order of increasing K_f1 and explain your order.