2. The [Ni(en)]+ complex contains the bidentate ligand ethylenediamine (en), HNCHCHNH2. (a) Chelating ligands are commonly...

 

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2. The [Ni(en)]²+ complex contains the bidentate ligand ethylenediamine (en), H₂NCH₂CH₂NH2. (a) Chelating ligands are commonly used in inorganic chemistry, including trace metal detection. (i) Explain the meaning of the term "chelating ligand". (ii) Explain the term "chelate effect". [2 marks] [3 marks] (iii) Explain the origin of the chelate effect by reference to the following reaction, with equilibrium constant K = 109.7 at 298 K. Calculate the change in Gibbs free energy during this reaction [Ni(NH3)]2+ (aq) + 3en(aq) = [Ni(en)]2+ (aq) + 6NH³(aq) [4 marks] (b) Crystal field effects play a key role in the stability and physical properties of transition-metal complexes. (i) Determine the oxidation state and d electron count of nickel in [Ni(en)]²+. [2 marks] (ii) Sketch the crystal field splitting diagram for the nickel ion in [Ni(en)]²+ and calculate the crystal field stabilisation energy in terms of Ao and P. [6 marks] (iii) Given they adopt the same coordination geometry why does [Ni(en)]²+ have higher energy d-d transitions than [Ni(acac)2(H₂O)2]? ("acac" refers to the bidentate ligand acetylacetonate, (CH3COCHCOCH3)'"). [3 marks] 2. The [Ni(en)]²+ complex contains the bidentate ligand ethylenediamine (en), H₂NCH₂CH₂NH2. (a) Chelating ligands are commonly used in inorganic chemistry, including trace metal detection. (i) Explain the meaning of the term "chelating ligand". (ii) Explain the term "chelate effect". [2 marks] [3 marks] (iii) Explain the origin of the chelate effect by reference to the following reaction, with equilibrium constant K = 109.7 at 298 K. Calculate the change in Gibbs free energy during this reaction [Ni(NH3)]2+ (aq) + 3en(aq) = [Ni(en)]2+ (aq) + 6NH³(aq) [4 marks] (b) Crystal field effects play a key role in the stability and physical properties of transition-metal complexes. (i) Determine the oxidation state and d electron count of nickel in [Ni(en)]²+. [2 marks] (ii) Sketch the crystal field splitting diagram for the nickel ion in [Ni(en)]²+ and calculate the crystal field stabilisation energy in terms of Ao and P. [6 marks] (iii) Given they adopt the same coordination geometry why does [Ni(en)]²+ have higher energy d-d transitions than [Ni(acac)2(H₂O)2]? ("acac" refers to the bidentate ligand acetylacetonate, (CH3COCHCOCH3)'"). [3 marks]