I am not sure I completely understand the bonding in coordination compounds formed by donation of pi electron cloud by the ligands to the central atom.
For example, consider Ziese's salt:
I came across a question which asked the total number of sigma bonds in the salt. I expected the bond between ethene and platinum to be a sigma bond too because it appears as if it is formed by overlap of the orbitals along the axis and hence my answer was 9. But the answer given was 8 and the answer key didn't consider that bond as a sigma bond.
So is the bond between platinum and ethene a $\pi$ bond? If yes, then how?
What orbitals are actually involved in that bond?