Oxalate anions, C₂O₄²⁻, added to a solution of [Fe(H₂O)₆]³⁺ displace water molecules within the complex ion to form [Fe(C₂O₄)₃]³⁻, as shown in the reaction below:[Fe(H₂O)₆]³⁺(aq) + 3 C₂O₄²⁻(aq) → [Fe(C₂O₄)₃]³⁻(aq) + 6 H₂O(l)Which of the following does NOT explain why C₂O₄²⁻ displaces H₂O in the formation of [Fe(C₂O₄)₃]³⁻ ?

Question

Quizplus · Accepted Answer

11ecba2d_11f5_8389_a3bf_1fb1aaf0de7a_MD0008_00 Coordination complexes consist of a central metal ion surrounded by one or more ions or molecules called ligands that are bound to the metal center by coordinate bonds. The ligands act as a Lewis base, and the metal center acts as a Lewis acid. Stronger Lewis bases can displace weaker Lewis bases as ligands within a complex. Stronger Lewis bases tend to be those that have lone pair electrons on atoms with a net charge and/or a lower electronegativity. Charged species tend to be less stable (more reactive) than uncharged species because forming a bond produces a more stable, lower energy state. Likewise, atoms with a lower electronegativity tend to be better Lewis bases because the electrons are held more loosely and any net charge is less stabilized. Both C₂O₄²⁻ and H₂O have available lone pair electrons on an oxygen atom (same electronegativity aspect), but C₂O₄²⁻ is a stronger Lewis base because it also has a negative charge on each of two of the oxygen atoms. This charge comes from the presence of an extra lone pair of electrons on each. Therefore, C₂O₄²⁻ does not have fewer lone pair electrons per oxygen atom than H₂O, and this choice does NOT explain why C₂O₄²⁻ displaces H₂O. (Choice B) This statement explains the formation of [Fe(C₂O₄)₃]³⁻ because weaker Lewis bases tend to form weaker coordinate bonds. C₂O₄²⁻ is a stronger Lewis base, which can displace H₂O and form a stronger coordinate bond than H₂O. (Choices C and D) These choices explain the reaction because charged species tend to be stronger Lewis bases and more reactive than uncharged species. The two additional lone pairs of electrons on two oxygen atoms in C₂O₄²⁻ give C₂O₄²⁻ its net charge and a greater tendency to donate electrons for coordinate bond formation. Educational objective: Stronger Lewis bases (electron pair donors) can displace weaker Lewis bases as ligands within a coordination complex. Lone pair electrons on atoms with a lower electronegativity tend be stronger Lewis bases than those with a higher electronegativity, and charged atoms with lone pair electrons tend to be stronger Lewis bases than comparable uncharged atoms.

Oxalate Anions, C2O42−, Added to a Solution of [Fe(H2O)6]3+ Displace

Oxalate Anions, C₂O₄²⁻, Added to a Solution of [Fe(H₂O)₆]³⁺ Displace