DFT studies of the electronic structure and geometry of 18-crown-6, hexaaza[18]annulene, and their complexes with cations of the heavier alkali and alkaline earth metals

DFT calculations for M@C12H12N6 and M@C12H24O6 (where M = Rb+, Cs+, Sr2+, and Ba2+, C12H12N6 = hexaaza[18]annulene, and C12H24O6 = 18-crown-6) were performed using the recently developed model core potential parametrization. Results show that the ions bind more strongly to C12H12N6 than to 18-crown-6 moiety; the difference is more pronounced for cations with smaller radii.

Graphical abstractThe geometrical structures of 18-crown6 (on the left) and hexaaza[18]annulene (on the right) are very similar. The nitrogen atoms of the hexaaza[18]annulene molecule point towards the centre of the molecule and their lone electron pairs create an electron-rich environment that may effectively capture metal ions.Figure optionsDownload full-size imageDownload as PowerPoint slide