Crystal Engineering and Self-Assembled Nanoring Formation with Purine-Cd^II/Hg^II Supramolecular Frameworks

We report three complexes of Cd^II and Hg^II with two purine rare tautomers, N9-(pyridin-2-ylmethyl)-N⁶-methoxyadenine, L1 and N7-(pyridin-2-ylmethyl)-N⁶-methoxyadenine, L2, highlighting diverse crystallographic signatures exhibited by them. Influence of substituents, binding sites, steric effects and metal salts on the different modes of binding enabled an insight into metal-nucleobase interactions. L1 interacted with two and three equivalents of Cd(NO₃)₂.4H₂O and HgCl₂, respectively, while L2 interacted with two equivalents of HgCl₂, altogether leading to three different complexes (1 [C₄₈H₄₈Cd₆N₃₄O₅₀], 2 [C₁₂H₁₂Cl₄Hg₂N₆O] and 3 [C₁₂H₁₂Cl₂HgN₆O]) possessing varied dimensionality and stabilising interactions. The photoluminescent properties of these coordination frameworks have also been probed. Notably, nanoring-like structures were obtained, as a result of self-assembly of 3 when investigated by transmission electron microscopy, additionally supported by molecular dynamics simulations.