Neutralization of 2-(1-imidazole)-1-hydroxyl-1,1 -ethylidenediphosphonic acid (zoledronic acid) by an excess of ammonia yielded bis(ammonium) zoledronate dihydrate,The product is readily soluble in water and forms monocrystals for which the X-ray structural analysis was carried out. The zoledronic anion is of double negative charge due to deprotonation of three P-OH groups and protonation of the nitrogen in the imidazole ring. The structure is stabilized by extensive network of N-H⋅ ⋅ ⋅ O and O-H⋅ ⋅ ⋅ O hydrogen bonds expanding through the crystal in plane (002). The imidazole ring is involved in -stacking interactions with its symmetry equivalents related by inversion centers at (1 0 0) and (1 1/2 0), with distances between centroids (Cg-Cg) of 3.819 (2) and 3.881 (2)Å, respectively.

The title compound {sys­tematic name: bis(μ2-dihydrogen 4-aza­niumyl-1-hy­droxy­butane-1,1-di­phos­pho­n­ato)bis­[aqua­(dihydrogen 4-aza­nium­yl-1-hy­droxy­butane-1,1-diphospho­n­ato)nickel(II)] dihydrate}, [Ni2(C4H12NO7P2)4(H2O)2]·2H2O, was synthesiized under hydro­thermal conditions. Its structure is isotypic with the CoII analogue. The crystal structure is built up from centrosymmetric dinuclear complex mol­ecules and the structure is reinforced by a net of inter­molecular O—H⋯O and N—H⋯O hydrogen bonds. One water mol­ecule is bound to the NiII atom in the octahedral coordination sphere, while the second is part of the inter­molecular hydrogen-bond system.