The present paper reports the structures of bis-(adeninium) zoledronate tetra-hydrate {systematic name: bis(6-amino-7H-purin-1-ium) hydrogen [1-hy-droxy-2-(1H-imidazol-3-ium-1-yl)-1-phospho-natoeth-yl]phospho-nate tetra-hydrate}, 2C5H6N5 +·C5H8N2O7P2 2-·4H2O, (I), and bis-(ade-ninium) zoledron-ate hexa-hydrate {systematic name: a 1:1 cocrystal of bis(6-amino-7H-purin-1-ium) -hydrogen [1-hy-droxy-2-(1H-imidazol-3-ium-1-yl)-1-phos-pho-natoeth-yl]phospho-nate hexa-hydrate and 6-amino-7H-purin-1-ium 6-amino-7H-purine di-hydrogen [1-hy-droxy-2-(1H-imidazol-3-ium-1-yl)ethane-1,1-diyl]diphos-pho-nate hexa-hydrate}, 2C5H6N5 +·C5H8N2O7P2 2-·6H2O, (II). One of the adenine mol-e-cules and one of the phospho-nate groups of the zole-dronate anion of (II) are protonated on a 50% basis. The zoledronate group displays its usual zwitterionic character, with a protonated imidazole ring; however, the ionization state of the phospho-nate groups of the anion for (I) and (II) are different. In (I), the anion has both singly and doubly deprotonated phospho-nate groups, while in (II), it has one singly deprotonated phospho-nate group and a partially deprotonated phospho-nate group. In (I), the cations form an R 2 2(10) base pair, while in (II), they form R 2 2(8) and R 2 2(10) base pairs. Two water mol-ecules in (I) and five water mol-ecules in (II) are involved in water-water inter-actions. The presence of an additional two water mol-ecules in the structure of (II) might influence the different ionization state of the anion as well as the different packing mode compared to (I). © 2014 International Union of Crystallography.