Problem 87 - Chemistry The Central Science

Question

Generally speaking, for a given metal and ligand, the stability of a coordination compound is greater for the metal in the +3 rather than in the +2 oxidation state (for metals that form stable +3 ions in the first place). Suggest an explanation, keeping in mind the Lewis acid-base nature of the metal-ligand bond.

Step-by-Step Solution

Answer

In summary, the stability of a coordination compound is generally greater for a metal in the +3 oxidation state than in the +2 oxidation state due to the stronger positive charge and charge density of the metal in the +3 state. This leads to a stronger Lewis acid-base interaction between the metal ion and the ligand, contributing to a more stable coordination compound.

Step 1: Understanding Lewis acid-base interaction

In a metal-ligand bond, the metal acts as a Lewis acid, and the ligand acts as a Lewis base. A Lewis acid is an electron pair acceptor, while a Lewis base is an electron pair donor. The formation of a coordination compound involves the interaction of metal ions with ligands, and the strength of this interaction determines the stability of the compound.

Step 2: Comparing the +2 and +3 oxidation states

A metal in the +3 oxidation state has one more positive charge compared to a metal in the +2 oxidation state. This means that a metal in the +3 oxidation state has a stronger positive charge, which can attract electron pairs more effectively from a ligand. As a result, the metal-ligand interaction is stronger in the +3 oxidation state, contributing to greater stability for the coordination compound.

Step 3: Relating the oxidation state to the stability of the metal-ligand bond

When a metal is in a higher oxidation state, it has a greater charge density and an increased ability to accept electron pairs from ligands, resulting in stronger metal-ligand bonds and higher stability of the coordination compound. Since the +3 oxidation state has a higher positive charge and charge density compared to the +2 oxidation state, the Lewis acid-base interaction is generally stronger for metals in the +3 oxidation state.

Step 4: Conclusion

The stability of a coordination compound with a metal in the +3 oxidation state is generally greater compared to the same metal in the +2 oxidation state. This is because a metal in the +3 oxidation state has a stronger positive charge and charge density, which results in a stronger Lewis acid-base interaction between the metal ion and the ligand. This stronger interaction leads to a more stable coordination compound.