Stabilization of the non-canonical adenine–adeninium base pair by N(7) coordination of Zn(II)

A new zinc (II) compound with 9-ethyladenine (9-EtA) of formula [Zn(9-EtA–N7)Cl3](9-EtAH) has been synthesized and characterized by X-ray diffraction. Its X-structure consists of an Zn(II) anionic complex and 9-ethyladeninium as counteranion. The Zn(II) complex shows a distorted tetrahedral geometry in which three Cl and an 9-EtA coordinates through N(7) position are the ligands. An indirect chelation via intramolecular H-bond between N(6)H and an Cl ligand is present in the complex. The network of [Zn(9-EtA–N7)Cl3](9-EtAH) shows interesting features. Thus, self-association of coordinated adenine–adeninium takes place by H-bonding of N(6)–H⋯N(1) and N(6)–H⋯N(7), leading to a polymeric ribbon-like 1D supramolecular arrangement. Ab initio calculations have been applied in order to study the stability of the adenine–adeninium interaction due to the coordination of the Zn(II) to the N(7) position and to compare experimental and theoretical structural data.