Crystal structure of bis­[(1-ammonio-1-phosphono­eth­yl)phospho­nato]tetra­aqua­cadmium dihydrate: a powder X-ray diffraction study

In the title compound, [CdL (2)(H(2)O)(4)]·2H(2)O [L = (1-ammonio-1-phosphono­eth­yl)phospho­nate, C(2)H(8)NO(6)P(2) (−)], the Cd(II) ion is situated on an inversion centre being coordinated by four aqua mol­ecules in the equatorial plane and two phosphonate O atoms from two deprotonated L ligands in the axial positions in a distorted octa­hedral geometry. The asymmetric unit contains one-half of the complex mol­ecule and one lattice water mol­ecule. The ligand L exists in a zwitterionic form, with a positive charge on the NH(3) group and a negative charge on the O atom of the non-coordinating phospho­nate group, and with an intra­molecular O—H⋯O inter­action forming an S(6) ring motif and two intra­molecular N—H⋯O inter­actions each generating an S(5) ring motif. In the crystal, N—H⋯O and O—H⋯O hydrogen bonds link the complex mol­ecules into a three-dimensional network in which the voids of 38 Å(3) are filled with ordered lattice water mol­ecules, which are also involved in O—H⋯O hydrogen bonding.