Three purine-containing metal complexes with discrete binuclear and polymeric chain motifs: Synthesis, crystal structure and luminescence

To investigate the influences of exocyclic substituent of purine base on the coordination and recognition behavior, three new purine-based inner-sphere metal complexes, [Cd2(H2ade)2(H2O)4(btc)2]·4H2O (1), [Cd2(Hhyp)2(H2O)4(Hbtc)2]·4H2O (2), and [Cd(H2dap)(H2O)2(btc)]n (3) (Hade = adenine, Hhyp = hypoxanthine, Hdap = 2,6-diaminopurine, and H3btc = 1,2,4-benzenetricarboxylic acid), were hydrothermally synthesized and structurally characterized. The former two complexes with monodentate H2(N1, N9)ade+ cation (for 1) and H(N1, N7)hyp molecule (for 2) are centrosymmetric binuclear entities aggregated by a pair of tricarboxylate ligand. In contrast, 3 bearing a cationic H2(N1, N9)dap+ ligand has a polymeric one-dimensional helical chain extended by btc3− connectors. The side group of the purine can significantly dominate and stabilize the supramolecular network by different H-bonding recognition patterns. Additionally, these three samples with considerable thermal stability display strong emissions originated from ligand-based electron transfer, suggesting their potential application as luminescent materials.