Tetra- and hexahydrates of bis(adeninium) zoledronate

The present paper reports the structures of bis(adeninium) zoledronate tetrahydrate {systematic name: bis(6-amino-7H-purin-1-ium) hydrogen [1-hydroxy-2-(1H-imidazol-3-ium-1-yl)-1-phosphonatoethyl]phosphonate tetrahydrate}, 2C5H6N5(+)·C5H8N2O7P2(2-)·4H2O, (I), and bis(adeninium) zoledronate hexahydrate {systematic name: a 1:1 cocrystal of bis(6-amino-7H-purin-1-ium) hydrogen [1-hydroxy-2-(1H-imidazol-3-ium-1-yl)-1-phosphonatoethyl]phosphonate hexahydrate and 6-amino-7H-purin-1-ium 6-amino-7H-purine dihydrogen [1-hydroxy-2-(1H-imidazol-3-ium-1-yl)ethane-1,1-diyl]diphosphonate hexahydrate}, 2C5H6N5(+)·C5H8N2O7P2(2-)·6H2O, (II). One of the adenine molecules and one of the phosphonate groups of the zoledronate 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 phosphonate groups of the anion for (I) and (II) are different. In (I), the anion has both singly and doubly deprotonated phosphonate groups, while in (II), it has one singly deprotonated phosphonate group and a partially deprotonated phosphonate group. In (I), the cations form an R2(2)(10) base pair, while in (II), they form R2(2)(8) and R2(2)(10) base pairs. Two water molecules in (I) and five water molecules in (II) are involved in water-water interactions. The presence of an additional two water molecules in the structure of (II) might influence the different ionization state of the anion as well as the different packing mode compared to (I).