Acta Crystallographica Section C

Crystal Structure Communications

Volume 59, Part 2 (February 2003)

metal-organic compounds

 

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

W. L. Gossman, S. R. Wilson and E. Oldfield

Abstract: 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, C₇H₁₁NO₇P₂·H₂O, (I), in which just one phosphonate group is negatively charged. Recrystallizations at pH values of 2 and 4 yielded risedronate dihydrate, or sodium [1-hydroxy-2-(pyridinium-3-yl)ethane-1,2-diyl]bis(phosphonate) dihydrate, Na⁺·C₇H₁₀NO₇P₂^-·2H₂O, (II). Finally, recrystallizations at pH values of 7 and 8 produced risedronate 2.5-hydrate, or sodium [1-hydroxy-2-(pyridinium-3-yl)ethane-1,2-diyl]bis(phosphonate) 2.5-hydrate, Na⁺·C₇H₁₀NO₇P₂^-·2.5H₂O, (III). At these four pH values, both phosphonate groups in (II) and (III) are negatively charged and coordinated to an Na⁺ ion. Crystals of (II), i.e. those grown at pH values of 2 and 4, have isomorphous polymeric ion aggregate structures with geminal phosphonate and alcohol groups coordinated to the same Na⁺ ion. On the other hand, crystals of (III), i.e. those grown at pH values of 7 and 8, have isomorphism polymeric ion aggregate structures with geminal phosphonate and alcohol groups coordinated to different Na⁺ ions.

Formula: C₇H₁₁NO₇P₂·H₂O, Na⁺·C₇H₁₀NO₇P₂^-·2H₂O and Na⁺·C₇H₁₀NO₇P₂^-·2.5H₂O

	Structure factor file (CIF format) (110.0 kbytes) Contains datablock I
	Structure factor file (CIF format) (127.0 kbytes) Contains datablock II
	Structure factor file (CIF format) (119.7 kbytes) Contains datablock III

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