Which d orbitals can form sigma, pi, delta bonds?

If two $\ce{d_{xy}}$ orbitals approach each other on $x=y, z=0$, would a sigma bond be formed? I would think so.

Can $\ce{d_{z^2}}$ form pi bond with another $\ce{d_{z^2}}$? (as all others can on $x$ or $y$ or $z$ as internuclear axis?) I am not sure but overlapping similar to p could be observed.

I would assume all except $\ce{d_{z^2}-d_{z^2}}$ form delta bond. (both of same type like $\ce{d_{xy}}$ with $\ce{d_{xy}}$)

What are the faults in my logic?

Answer

Sigma, pi and delta denote how many planar nodes are in the bond. Sigma bonds have no node, pi bonds have one and delta bonds have two. You can tell what kind of bond forms by how the orbitals overlap. Two single lobes form a sigma bond, two pairs of lobes form a pi bond and two quartets form a delta bond.