d orbitals overlapping [closed]








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I have two questions.


1. Why can't dx2-y2 orbitals only make sigma bonds? If there is another dx2-y2 coming through z axis, can't they possibly make delta bonds since 4 overlappings seem possible?
2. Is there a reason why there is no dz2-y2 or dz2-x2 orbitals except experimental results?


[![enter image description here](https://i.stack.imgur.com/k3cRu.png)](https://i.stack.imgur.com/k3cRu.png)


[![enter image description here](https://i.stack.imgur.com/8thxk.png)](https://i.stack.imgur.com/8thxk.png)




1. d orbitals can make different types of bonds depending on the orientation and the other orbital. All cases are possible.
2. the other orbitals are possible but they can combine giving an orbital with S-symmetry. You can have only 5 orbitals with l = 2 so there is an extra combination which is not linearly independent. Cartesian d orbitals in certain electronic structure programs come in groups of six.


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