The formation of Sn2+ ions (tin ions with a charge of +2) is not commonly observed because the most stable oxidation state of tin is +4.
Tin (Sn) is a metal that can exhibit multiple oxidation states, including +2 and +4. However, the +4 oxidation state is more energetically favorable for tin due to its electron configuration and the stability of the filled 5s and 5p orbitals. In the +4 oxidation state, tin forms a stable ion known as Sn4+ by losing all its valence electrons.
In contrast, the +2 oxidation state of tin (Sn2+) requires the loss of only two electrons. However, the resulting configuration does not involve completely filled orbitals, making it energetically less stable compared to Sn4+. As a result, Sn2+ is relatively unstable and tends to be easily oxidized to Sn4+.
That being said, there are some compounds and complexes where Sn2+ can be stabilized under certain conditions, such as in the presence of ligands that provide stability to the ion. However, in general, the +2 oxidation state of tin is less common than the +4 oxidation state.