# why do the complex [Cu(NH3)5NO2]SO4 show ionisation isomerism?

In ionisation isomerism, secondary valencies can be replaced by primary valencies on the condition that net charge going outside the coordination sphere must be equal to net charge coming inside it . Here NO2 ligand has charge - 1 on it . So how can it be replaced by SO4 which has -2 charge? Thanks!

• $\ce{[Cu(NH3)5(NO2)]SO4^{-1}}$
• $\ce{[Cu(NH3)5(SO4)]NO2^{-1}}$
Both $\ce{NO2^-}$ and $\ce{SO4^{2-}}$ are necessary for the overall complex to have a -1 charge overall. It just depends on which is attached directly to the copper ion.