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.

Coordination compounds are formed when a central metal atom or ion is bonded to one or more ligands. These ligands are usually Lewis bases, which are molecules or ions that have lone pairs of electrons. The central metal atom or ion, on the other hand, acts as a Lewis acid. The metal atom/ion accepts the electron pairs from the ligands, which then form coordinate covalent bonds.

We are given that the stability of coordination compounds is generally greater when the metal is in the +3 oxidation state rather than in the +2 oxidation state. When a metal ion has a higher oxidation state, it has a higher positive charge, which means it has a greater ability to attract electron pairs from the ligands.

The charge density of an ion is the ratio of its charge to its size, or the charge per unit volume. In general, a higher charge density indicates a stronger electrostatic attraction between the ion and the surrounding atoms or ions. Therefore, metal ions with higher charge densities will form stronger bonds with the ligands.

For a given metal ion, when the oxidation state increases from +2 to +3, its charge density also increases, since its charge increases while its size remains relatively constant. This results in stronger electrostatic interactions between the metal ion and the ligands, leading to greater stability of the coordination compound.

As mentioned earlier, the central metal atom/ion in a coordination compound acts as a Lewis acid, while the ligands act as Lewis bases. In this case, an increase in the metal's oxidation state from +2 to +3 increases its Lewis acidity, making it a stronger Lewis acid. This results in the formation of stronger bonds with the ligands, which in turn increases the stability of the coordination compound. In conclusion, the greater stability of coordination compounds for metals in the +3 oxidation state compared to the +2 oxidation state can be explained by the increased charge density and Lewis acidity of the metal ion, leading to stronger electrostatic interactions and Lewis acid-base bonding with the ligands, respectively.