Alkaline earth bent ionic

Bent ionic compounds of heavy alkaline earths... 

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. 

Fuentealba and Savin " looked at the electronic structure of the ground state of monoxides MO and carbides MC2 with M an alkaline-earth metal atom. From their ELF study they learn that in the monoxides, and not in the carbides, a change in the type of bonding occurrs in going fi om Be to Ba. BeO is the only compound presenting some covalent bond character while the other oxides are clearly ionic. All carbides are ionic and bent. 

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