Supramolecular architectures based on p-cymene/ruthenium complexes functionalized with nucleobases

The nucleophilic attack of a series of nucleobase derivatives on the [(eta(6)-p-cymene)RuCl(mu-Cl)](2) dinuclear entity has yielded four mononuclear complexes with the general formula [Ru(eta(6)-p-cymene)(L)Cl-2], in which L stands for cytosine (1), 2-thiouracil (2), hypoxanthine (3) and 5-aminouracil (4). Furthermore, the sieving of chlorido from compound 1, assisted by a mild base, has prompted the formation of a tetranuclear ruthenium cationic complex which crystallizes as [(eta(6)-p-cymene)(4)Ru-4(mu-cytosinato-kappa N1:kappa N3,O2)(4)](CF3SO3)(4) (compound 5). The crystal structure analysis of compounds 1-4 reveals that the supramolecular packing is dominated by the self-assembly capabilities provided by the stabilized nucleobase-tautomer, which is at the same time dependent on the Ru/nucleobase coordination mode. In this regard, the assembly of the complex units is conducted through base-pairing interactions, and is also assisted by means of nucleobase/ chloride hydrogen bonding. The stability of these monomeric entities in water and phosphate buffered solution is analysed by means of H-1-and P-31-NMR. The tetranuclear entity of compound 5 presents an available hydrogen-donor set (exocyclic amino group) but it lacks any available acceptor atom, which prevents the nucleobase mediated self-assembly of the complex units. Consequently, a doubly interpenetrated supramolecular network is woven by the hydrogen bonding between the triflate (CF3SO3-) anions and complex cationic entities.