Factors controlling extremely strong AAA-DDD triply hydrogen-bonded complexes

Triply hydrogen-bonded complexes of the form AAA-DDD are shown to have the strongest interaction when the complex is substituted with electron withdrawing groups on the donor molecule (DDD) and electron donating groups on the acceptor molecule (AAA). In particular, the largest effects are observed when the withdrawing groups act through resonance. This serves to flatten the entire system resulting in more linear, and consequently stronger, hydrogen bonds. Furthermore, the present calculations show that the binding energy correlates with the electron density at the bond critical points and inversely with the hydrogen bond lengths.