IntroductionIn past few years supramolecular architectures built by organic or inorganic cations and polyiodides have attracted much attention due to their richness in structural chemistry and supramolecular chemistry in particular.1–14In these architectures, the polyiodide species show not only a wide diversity in their geometrical features, from discrete oligomeric anions to variously extended 1D, 2D and 3D networks, but also an unusually continuous spectrum of I⋯I distances, fromca.2.7 Å of the I2moiety toca.4 Å of the van der Waals radius summation of iodine, indicating the varying strengths of I⋯I interactions.1–3It has also been found that the formation and topology of polyiodide species depends on the nature, such as shape, size and charge, of the counter-cations; thereforethe cations are usually considered as templating agents.1,3Besides the unconventional structural features and supramolecularity of polyiodides, the architectures display rich, complicated and fascinating intermolecular interaction patterns such as hydrogen bonds (both conventional and weak), π–π interactions, embraces, and the complementarity between cations and polyiodide anions.4–9Many types of cations, transition metal complexes,2,5–9macrocyclothiother complexes,1,3,4organometallics10,11and nitrogen bases12,13have been used. Protonated nucleobases such as adenine (Ade)1or cytosine (Cyt)2(Chart 1), however, have never been explored before in this field. Nucleobases can be protonated and thus form various cations.15–22They possess multi­hydrogen­bonding sites and various tautomers15such that they can form an abundance of aggregates through hydrogen bonds, from dimers15(e.g.the well­known Watson–Crick pairs) to infinite extended species.16,17,20–22Molecular structure of adenine1and cytosine2with labeling of atomic sites. For adenine there are three N sites (1, 3 and 7) which can be protonated, and for cytosine only one N site (3) can be protonated.The ability to form hydrogen­bonded networks is obviously the most important and interesting characteristic for nucleobases, because the self­assembly of hydrogen­bonded networks of nucleobases or their derivatives has been used to design or construct highly ordered supramolecular nanostructures, not only in 3D crystals17,18,20but also on 2D solid surfaces,23,24and these ordered nanostructures are of interest for their potential applications as molecular devices.23,25Finally, nucleobases are planar and aromatic, and therefore they should be suitable for intermolecular stacking and π–π interactions, and have complementarity with polyiodide species like other common aromatic nitrogen bases.2,5–9Thus, nucleobases should be expected to act as an interesting and unique class of templatescomparable with other templating agents used in the construction of novel assemblies with polyiodides. As the first result of our systematic investigation on designing and constructing these assemblies, we report here the crystal structures of [AdeH+](I3−)(I2)5/2(H2O)1and [CytH+]2(I5−)2(H2O)32. As far as we are aware, they are the first architectures built by protonated nucleobases and polyiodides, and both contain hydrogen­bonded ribbons of nucleobase and water, and highly unexpected polyiodide species.