Carbon typically does not form C4- or C4+ ions because of its relatively high ionization energy. Ionization energy is the energy required to remove an electron from an atom or molecule. The ionization energy of carbon is 1086 kJ/mol, which is higher compared to other elements in group 14 (also known as the carbon group).

This high ionization energy means that it is relatively difficult to remove an electron from a carbon atom, making it less likely to form positive ions with a charge of 4 or higher. Additionally, carbon has a small atomic radius and a high electronegativity, which further contribute to its stability and resistance to forming high-charge positive ions.

While carbon typically does not form C4- or C4+ ions, it can form other types of ions, such as carbocations (positive ions with a carbon atom bearing a positive charge) or carbanions (negative ions with a carbon atom bearing a negative charge).