In order to form ionic bond carbon either should loose 4${{e}^{-}}$ or gain 4${{e}^{-}}$ to form C${{4}^{+}}$ or C${{4}^{-}}$ ion. Loosing 4${{e}^{-}}$ needs large amount of energy and by gaining 4${{e}^{-}}$, it will have 10${{e}^{-}}$. It is difficult for 6 protons to hold 10${{e}^{-}}$. So C${{4}^{+}}$ and C${{4}^{-}}$is not possible.