Polymerization

The trend of many molecules to aggregate and form dimers (example Al₂Cl₆  2), larger oligomers or expanded polymeric structures can be regarded  as a donor-acceptor interaction. So in the reaction

To one AlCl₃, a chlorine atom bound uses nonbonding electrons to complex with the other aluminum atom; like in most other instances of this kind of the bridging atoms are symmetrically disposed with the same bonds to each aluminum. Polymerization of AX_n molecules  is more likely to take place when n is small and when the atom A has vacant orbitals and is sufficiently large to increase its coordination  number.  Several oxides and halides of stoichiometry AB₂  and AB₃  form structures  that may be considered  as polymeric, even though the distinction between this (polar covalent) explanation and an ionic one is not clear-cut.

Hydrogen bonding  can also be considered as as a donor-acceptor interaction in which the acceptor LUMO is the (unoccupied) antibonding orbital of hydrogen bonded to an electronegative element.