2. The [Ni(en)]+ complex contains the bidentate ligand ethylenediamine (en), HNCHCHNH2. (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) + 6NH(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 marks] (ii) Sketch the crystal field splitting diagram for the nickel ion in [Ni(en)]+ 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)]+ have higher energy d-d transitions than [Ni(acac)2(HO)2]? ("acac" refers to the bidentate ligand acetylacetonate, (CH3COCHCOCH3)'"). [3 marks]