Restricting the versatile metal-binding behaviour of adenine by using deaza-purine ligands in mixed-ligand copper(II) complexes

In order to deepen our understanding of the versatile behaviour of adenine (Hade) as ligand, we have synthesized four novel ternary copper(II) complexes having two deazaadenine ligands, namely 4-azabenzimidazole (H4abim) or 7-azaindole (H7azain) as N1,N6-dideazaadenine or N1,N6,N7-trideazaadenine, respectively. The related compounds were studied by thermal, spectral and single crystal X-ray diffraction methods. In [Cu(NBzIDA)(H4abim)]n (1) the recognition between H4abim and the (N-benzyliminodiacetate)-copper(II) chelate only displays the formation of the Cu–N7(purine-like) bond, in contrast to Hade behaviour in [Cu(NBzIDA-like)(Hade)(H2O)]·H2O (Cu–N3(Hade) bond reinforced by N9–H···O(IDA-like) interaction). In [Cu(EIDA)(H7azain)(H2O)] (2, EIDA = N-ethyliminodiacetate ligand), [Cu(NBzIDA)(H7azain)(H2O)] (3) and [Cu(μ2-SO4)(H7azain)2(H2O)2]n (4), H7azain binds Cu(II) centre by the Cu–N3(purine-like) bond, reinforced by a N9–H···O(IDA-like or sulfate) intra-molecular interligand interaction.

Graphical abstractThe crystal structures of four novel ternary copper(II) compounds having 4-azabenzimidazole or 7-azaindole (as N1,N6-dideazaadenine or N1,N6,N7-trideazaadenine, respectively) are reported. Both deaza-adenines partially simulate the role of adenine in related complexes, but the crystal packing of one of these compounds influences on binding mode of the purine-like ligand.Figure optionsDownload full-size imageDownload as PowerPoint slide