Molecular recognition between adenine or 2,6-diaminopurine and copper(II) chelates with N,O2,S-tripodal tetradentate chelators having thioether or disulfide donor groups

• N,O2,S-tripodal Cu(II) chelates bind adenine (Hade) or 2,6-diaminopurine (Hdap).
• The N-branched topology of the chelators strongly favors the formation of Cu–S bonds.
• The S(thioether or disulfide) donor occupies a distal site in Cu(II) coordination.
• N7-H(N9)ade, μ2-N3,N7-H(N9)ade or μ2-N7,N9-H(N3)dap modes are reported.
• Cu–N(purine) bonds cooperate with intra-molecular N–H⋯O interligand interactions.

Five novel ternary copper(II) complexes with the N,O2,S-tripodal tetradentate chelators N,N-bis(carboxymethyl)-S-benzylcysteaminate(2-) ion (BCBC) or N,N,N′,N′-tetrakis(carboxymethyl)cystaminate(4-) ion (TCC) and adenine (Hade), 2,6-diaminopurine (Hdap), 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) as co-ligand were synthesized and characterized by X-ray diffraction and other physical methods: [Cu2(BCBC)2(μ2-N3,N7-H(N9)ade)(H2O)2]·H2O (1), [Cu2(BCBC)2(μ2-N7,N9-H(N3)dap)(H2O)2]·4H2O (2), [Cu2(μ2-TCC)(H(N9)ade)2(H2O)2]·10H2O (3), [Cu2(μ2-TCC)(bpy)2]·15H2O (4) and [Cu2(μ2-TCC)(phen)2]·14H2O (5). The crystal structure of H4TCC·3H2O was also determined. All ternary Cu(II) complexes have molecular structures. The N-(2-mercaptoethyl)-iminodiacetate moieties of BCBC or TCC ligands play a NO2 + S-tripodal tetradentate role, with the S-(thioether or disulfide) atom as the apical/distal donor of the copper(II) center. In 1–3, the iminodiacetate moiety exhibits a mer-NO2 conformation (two nearly coplanar chelate rings) while in 4 and 5 (with bpy or phen as coligand) it displays a fac-NO + O (apical/distal) conformation. We conclude that the formation of the Cu–S(thioether or disulfide) bonds is strongly favored by the N-branched topology of the S-ligands in the reported compounds.

Copper(II) chelates with mono- or bi-nucleating N,O2,S-tripodal tetradentate ligands bind neutral adenine or 2,6-diaminopurine. The Cu–N(purine) bonds cooperate with intra-molecular (purine)N–H⋯O(carboxylate) interligand interactions.Figure optionsDownload as PowerPoint slide