Orthogonal geometry, acceptor orbitals

Donor-acceptor interactions also lead to strangely bent geometries in heavier F— M—F alkaline earth fluorides. Such bending can occur when strong ionic attractions force a filled fluoride pz orbital into proximity with an orthogonal metal pj orbital, for in this case symmetry-forbidden (pz)p —(p l)m interactions can turn on only when the strict a/n symmetry of a linear F—M—F arrangement is broken. 

There are many other systems where two acceptors interact with orthogonal donors. One way to viewallene is by the union of two carbenes with a central carbon atom, 15.32. The four electrons in the central carbon will artificially be placed in the two p orbitals. The D2d geometry then maximizes it bonding if the two carbene... 

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