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Account for the following: [2 5] a. the highest oxidation states usually occur with f as a ligand but the lowest oxidation states can occur with co as a ligand. b. [ni(nh3)6]2+ is less stable than [ni(en)3]2+ in terms of entropy
Accepted Answer
a. Fluorine's high electronegativity: Fluorine is the most electronegative element, leading to a strong withdrawal of electron density from the central metal atom. This results in the highest possible oxidation states for the metal.
Carbon monoxide's pi-backbonding: Carbon monoxide acts as a strong pi-acceptor ligand. This pi-backbonding (donation of electron density from the metal d-orbitals to the antibonding orbitals of CO) leads to a decrease in the effective nuclear charge on the metal, favoring lower oxidation states.
b. Chelate effect: The stability of a complex is enhanced by the chelate effect. [Ni(en)3]2+ has three ethylenediamine (en) ligands, each of which forms a chelate ring, whereas [Ni(NH3)6]2+ has six individual ammonia ligands. The chelate effect arises from the increased entropy change upon formation of the chelate complex compared to a complex with monodentate ligands. This increased entropy favors the formation of the more stable [Ni(en)3]2+ complex.
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