Cyameluric Acid as Anion-π Type Receptor for ClO4(-) and NO3(-): π-Stacked and Edge-to-Face Structures.

Based on the binding energies at high levels of ab initio theory including coupled cluster theory at the complete basis limit, we show that cyameluric acid (C6N7O3H3) is a potent receptor for ClO4(-) and NO3(-) anions through the anion-π interactions. In contrast, cyanuric acid (C3N3O3H3) binds Cl(-), NO3(-), and ClO4(-) with the hydrogen bonding type structures, while their anion-π type structures show slightly weaker binding. Consequently, the cyameluric acid having the C3h symmetric C6N7 nucleus with electron withdrawing oxygen atoms is a novel anion-π type receptor for trigonal-planar and tetrahedral anions. The structures of the cyameluric acid interacting with Cl(-) and ClO4(-) are considered as the π stacking type. For the cyameluric acid interacting with NO3(-), the π(edge) type complex is only slightly more favored over the π(stack) type in the gas phase, but the π(stack) type is likely to be as stable as the π(edge) type in the solvent phase.