In this manuscript we report a high-level ab initio study of anion-pi interactions involving N9-methyl-adenine, N6-methyl-adenine, N9-methyl-hypoxanthine, a dimer of N9-methyl-adenine, and N9,N9'-trimethylene-bisadenine. DNA bases like adenine are electron-deficient arenes that are well suited for interacting favorably with anions. We demonstrate that these compounds are able to interact favorably with anions. N9-Methyl-adenine, N6-methyl-adenine, and the dimer of N9-methyl-adenine interact with the anion via the six-membered ring more strongly than adenine due to cooperativity effects between the noncovalent pi-pi and anion-pi interactions. This pattern, i.e., coexistence of pi-pi and anion-pi bonding, is observed experimentally in the solid state. Finally, we report the solid-state characterization of two new compounds N6,N6'-dimethylene-bisadenine hydrochloride and an outer-sphere complex of protonated N9,N9'-trimethylene-bishypoxanthine with zinc tetrachloride anion, that exhibit interesting anion-pi interactions. They are in strong agreement with high-level theoretical calculations.

In this manuscript, we report the synthesis and the solid-state characterization of five new compounds based on the 2-aminopyrimidine building block. Some of them exhibit interesting anion-π interactions. In addition, we report a high level ab initio study of anion-π interactions involving 2-methylaminopyrimidine and its dimer. We demonstrate that these compounds are able to interact favorably with anions. The dimer of 2-methylaminopyrimidine interacts with the anion more strongly than the monomer due to cooperativity effects between the noncovalent hydrogen bonding and anion-π interactions. This pattern, that is, coexistence of hydrogen bonding and anion-π bonding, is observed experimentally in the solid state.

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