Theoretical study of β- and γ-cyclodextrin complexes with ferrocene-containing azoles

The interaction between cyclodextrins (β- and γ-CD) and ferrocenyl azoles (i.e., pyrazole ferrocenes (I, III–V) and benzimidazole ferrocenes (VI, VII)), along with 1-ferrocenylethanol (II), each in the form of (R)- and (S)-enantiomers, in forming inclusion complexes is studied for the first time using detailed quantum chemical calculations. Compounds are calculated in terms of the density functional theory (DFT), using the Becke–Lee–Yang–Parr (B3LYP) approach in the 6-31G* basis sets. For the considered CD complexes with enantiomers of I–VII, structures in which a guest partially enters a host cavity from the side of the heterocyclic substituent (pyrazole or benzimidazole) are found to be energetically advantageous. It is shown that for successful resolution of (R,S)-enantiomers on chiral phases containing cyclodextrins, we must consider the interaction between outer hydroxyl groups on the CD cone’s surface, in addition to the correspondence of geometric dimensions. The calculated data correlate well with the data from the chromatographic separation of guest enantiomers on cyclodextrin sorbents.