What are the possible resonance structures for $\ce{ClO_2^-}$? Assigning one double bond to the structure makes for formal charges of $\ce{O (-1) - Cl (0) = O (0) <-> O (-1) = Cl (0) - O (-1)}$. It appears that the same set of formal charges can be achieved with two double bonds (expanding the octet on $\ce{Cl}$ to 12 electron capacity, using the d orbital). That is, $\ce{O (0) = Cl (-1) = O (0)}$.

Is this feasible, and if not, why not?