Copper(II) polyamine chelates as efficient receptors for acyclovir: syntheses, crystal structures and dft study

In order to further understand the metal-binding patterns (MBP) of acyclovir (acv), copper(II) and zinc(II) oxo salts (nitrate, sulfate or perchlorate) and tridentate or tripodal-tetradentate chelating-polyamines were reacted with acyclovir to obtain the following compounds: [Cu(dien)(acv)(H₂O)]SO₄·1.25MeOH·0.5H₂O (1), [Cu(dien)(acv)(H₂O)]·[Cu(dien)(acv)(H₂O)(NO₃)](NO₃)₃]·H₂O (2), {[Cu(dien)(µ₂-acv)](ClO₄)₂}_n (3), [Zn(dien)(acv)(SO₄)] (4), [Cu(pmdta)(acv)](ClO₄)₂·H₂O (5), [Cu(bpa)(acv)(SO₄)]·6H₂O (6), [Cu(tren)(acv)](NO₃)₂ (7) and [Cu(tren)(acv)](ClO₄)₂ (8) (dien = diethylenetriamine, pmdta = N,N,N′,N′,N″-pentamethyl-diethylenetriamine, bpa = bis-(2-picolyl)amine and tren = tris(2-aminoethyl)amine). All the compounds were studied by spectroscopic techniques and single-crystal X-ray diffraction methods. The metal binding pattern of copper(II) compounds 1–3, 7 and 8 consists of the cooperation of the Cu–N7(acv) bond with an intramolecular interligand (primary/terminal amino)N-H⋯O6(acv) interaction (which is ‘bifurcated’ in 8). Note that in 3 this MBP is embedded within the unusual bridging µ₂-N7,O(ol, N9-side chain) mode. On the other hand, the Zn-N7(acv) bond in compound 4 is reinforced with the intramolecular (secondary amino)N-H⋯O6(acv) H-bond. This latest interaction is indeed possible but not displayed in compounds 5 or 6, which feature an asymmetric chelating-N7,O6-acv MBP with O6 acting as an apical/distal Cu(II) donor atom. Remarkably, in compounds 7 and 8, an intricate combination of anion⋯π/π⋯π/π⋯anion interactions generates interesting supramolecular networks that have also been studied theoretically by means of DFT calculations. In addition, these assemblies have been characterized using Bader’s theory of “atoms-in-molecules”.