p-d combination of orbitals

Question

In JD Lee Concise Inorganic Chemistry, Page 83, p-d combination of orbitals it is written,

" A p orbital on one atom may overlap with d orbital on another atom. Since the orbitals do not point along the line joining the two nuclei, overlap must be of pi type."

Why do we not consider the overlap of a p_x orbital with d_x²-y² or p_y with d_x²-y² or p_z with d_z² which can form a sigma Mo and ABMO if brougt close along a particular axis. Why always these orbitals are considerd in p-d combination which form a pi overlap.

Answer 1

You can form sigma bonds with $p$ and $d$ orbitals as described in the question. However, the symmetry in that case also allow $s$ orbitals to mix in with the sigma-bonding (also sigma-antibonding) molecular orbitals. Apparently the textbook was referring to pure $p$-$d$ interactions.