I was doing a question which asked about the nature of $\pi$ bonds between the $\ce{Mn}$ and $\ce{O}$ atoms in $\ce{MnO4-}$. According to the answer all the three $\pi$ bonds were formed by $p\pi-d\pi$ overlap. However, I know that the hybridisation of $\ce{MnO4-}$ is $d^3s$. Which means three of the $\mathrm{3d}$ orbitals are involved in hybridisation and only two are left for making $\pi$ bonds. Which means that all the three $\pi$ bonds cannot be formed by $p\pi-d\pi$ overlap. According to me two of the three $\pi$ bonds are formed by $p\pi-d\pi$ overlap and the third is formed by $p\pi-p\pi$ overlap using the unhybridised $\mathrm{4p}$ orbital (to which the electron from $\mathrm{4s}$ gets excited from the ground state).
Where is the flaw in my reasoning?
