Crystal structure of bis-[(1-ammonio-1-phosphono-eth-yl)phospho-nato]tetra-aqua-cadmium dihydrate: a powder X-ray diffraction study.

In the title compound, [CdL 2(H2O)4]·2H2O [L = (1-ammonio-1-phosphono-eth-yl)phospho-nate, C2H8NO6P2 (-)], the Cd(II) ion is situated on an inversion centre being coordinated by four aqua mol-ecules in the equatorial plane and two phosphonate O atoms from two deprotonated L ligands in the axial positions in a distorted octa-hedral geometry. The asymmetric unit contains one-half of the complex mol-ecule and one lattice water mol-ecule. The ligand L exists in a zwitterionic form, with a positive charge on the NH3 group and a negative charge on the O atom of the non-coordinating phospho-nate group, and with an intra-molecular O-H⋯O inter-action forming an S(6) ring motif and two intra-molecular N-H⋯O inter-actions each generating an S(5) ring motif. In the crystal, N-H⋯O and O-H⋯O hydrogen bonds link the complex mol-ecules into a three-dimensional network in which the voids of 38 Å(3) are filled with ordered lattice water mol-ecules, which are also involved in O-H⋯O hydrogen bonding.