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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?

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    $\begingroup$ Atomic orbitals forming molecular orbitals are a way of thinking about chemical bonding. Neither atomic orbitals nor molecular orbitals really exist so they cannot be observed either. Do you have an example? One can then maybe tell you what "kinds of bonds" the d-Orbitals could form there. The concepts you are referring to have been given up by most people a long time ago and are mainly used today as a tool to teach people wrong things. They can, however, be relevant under very specific circumstances, hence an example would be great. $\endgroup$ – AMT Jan 18 '17 at 16:00
  • $\begingroup$ sigma bond is overlapping on the internuclear axis and pi is perpendicular to it. LCAO, doesn't have mathematical problems to me, I am a novice though. I would just ask what stops from a sigma or pi bond to be formed, if two lobes of same phase overlap, theoretically, some sort of bonding molecular orbital would be formed right and with it a abmo? unless there is +,+ and +,- interference equally, then it would be non bonding. $\endgroup$ – Mrigank Jan 18 '17 at 16:14
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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.

This is how a delta bond is formed.

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    $\begingroup$ goldbook.iupac.org/S05434.html I was wrong $\endgroup$ – Mrigank Jan 18 '17 at 18:09
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    $\begingroup$ The image makes it seem as if d orbitals were only capable of forming delta bonds which is definitely not the case (they can form pi and sigma bonds too, of course). Please be more explicit. $\endgroup$ – Jan Oct 30 '17 at 10:50
  • $\begingroup$ @Jan Do you know a source which discusses this topic in greater detail? Thanks a lot! And yes I think this is a better representation of different bonding situations: commons.wikimedia.org $\endgroup$ – samjoe Oct 31 '17 at 14:24
  • $\begingroup$ @samjoe I am one of the worst people you could ask for sources because all my sources boil down to my lecture notes ^^' $\endgroup$ – Jan Nov 1 '17 at 8:47

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