Monosodium 4-Amino-1-hydroxy-1,1-butanediyldiphosphonate Trihydrate (Alendronate)

The cation in the title compound, Na⁺.C₄H₁₂NO₇P₂^-.3H₂O, has the expected zwitterionic character, with a terminal protonated amine group on one side of the chain and a negatively charged diphosphonate group on the other, the latter interacting with the Na⁺ ion. The structure is stabilized by a complex hydrogen-bonding scheme, which is found to be weaker than that observed in the free acid.

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