Theoretical investigation on the structural and electronic properties of complexes formed by N7,N9-dimethylguaninium and different anions

The interactions of N7,N9-dimethylguaninium with different anions (fluoride, bromide or tetrafluoroborate) and the related electronic properties are reported. The calculations show that the cation interactions with one to three different anion(s) give 31 stable structures. Among these structures, the cation interactions with two anions, especially with N1H (or/and N2Ha) and C8H of guanine, are the most favorable, while with one anion are the least favorable. Moreover, with the increase of the anionic radius, the interaction energies are decreased. NBO analyses reveal that the interactions between the F anion(s) with the cation mainly occur through the formation of FH/C covalent bond besides Flp→σC/NH∗ or/and Flp→πC8N7∗ interaction(s). However, with the increase of the anionic radius, the designed pairs are more favorable for the ionic bond, which may suggest that N7,N9-dimethylguaninium fluoride is not suitable to be selected as an ionic liquid.