Hydronium (cycloheptylammonio)methylene-1,1-bisphosphonate (hydronium incadronate).

The structure of the title compound, H(3)O(+).C(8)H(18)NO(6)P(2)(-), adopts a zwitterionic form containing an alkylammonium group, a hydronium ion, and two negatively charged phosphonate groups. The cycloheptyl side chain adopts a twist-chair conformation.

Three hydrates of the bisphosphonate risedronate, consisting of one molecular and two ionic structures.

Three different hydrates of risedronate were obtained by varying the pH of a solution containing the compound. At the pH values used, the N atom of the pyridine group is protonated and the compounds are zwitterionic. Crystals obtained directly from the synthesis resulted in risedronate monohydrate, or [1-hydroxy-1-phosphono-2-(pyridinium-3-yl)ethyl]phosphonate monohydrate, C(7)H(11)NO(7)P(2).

Monosodium [1-hydroxy-2-(1H-imidazol-3-ium-4-yl)ethane-1,1-diyl]bis(phosphonate) tetrahydrate (monosodium isozoledronate).

The title compound, Na(+).C(5)H(9)N(2)O(7)P(2)(-).4H(2)O, is an isomer of zoledronate, a potent bone antiresorptive bisphosphonate drug having significant activity against several parasitic protozoa.