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Key indicators: single-crystal X-ray study; T = 173 K; mean (C-C) = 0.004 Å; R factor = 0.037; wR factor = 0.081; data-to-parameter ratio = 12.3.The title compound, [Zn(C 2 H 8 NO 6 P 2 ) 2 (H 2 O) 4 ]Á4H 2 O, was synthesized by the reaction of ZnCl 2 with 1-aminoethane-1,1-diyldiphosphonic acid in aqueous solution. The asymmetric unit contains one-half of the complex and two water molecules of solvation. The Zn atom occupies a special position on an inversion centre. This results in a slightly distorted octahedral coordination environment, which consists of the O atoms from two phosphonic acids and four water molecules. The crystal structure displays N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonding, which creates a three-dimensional network. Related literature

The title compound, NH4 +·C2H8NO6P2 −·2H2O, was obtained by the reaction between 1-amino­ethane-1,1-diyldiphospho­nic acid and ammonium hydroxide (1:1) in an aqueous solution. The asymmetric unit contains one anion with two H atoms transferred from the phospho­nic acid groups to the amino group of the anion and to an ammonia mol­ecule, giving an ammonium cation. The structure displays N—H⋯O and O—H⋯O hydrogen bonding, which creates a three-dimensional network.

The asymmetric unit of the second polymorph of the title compound, C2H9NO6P2, contains one mol­ecule existing as a zwitterion. The N atom of the ammonio group is protonated and one of the phospho­nic acid groups is deprotonated. Bond lengths and angles are similar in both polymorphs. Besides the differences in cell parameters, the most significant structural difference between this structure and that of the first polymorph [Dudko, Bon, Kozachkova, Tsarik & Pekhno (2008 ▶), Ukr. Khim. Zh. 74, 104–106] is the presence of strong symmetric hydrogen bonds between neighbouring phospho­nate groups. H atoms involved in these hydrogen bonds are located at inversion centres and O⋯O distances are observed in the range 2.458 (5)–2.523 (5) Å. These bonds and additional O—H⋯O and N—H⋯O hydrogen bonds inter­link the mol­ecules, giving a three-dimensional supromolecular network.

Досліджували вплив різних бісфосфонових кислот, а саме етиліденбісфосфонової (ЕБФ),