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

Abstract

In the title compound, [CdL2(H2O)4]·2H2O [L= (1-ammonio-1-phosphonoethyl)phosphonate, C2H8NO6P2−], the CdIIion is situated on an inversion centre being coordinated by four aqua molecules in the equatorial plane and two phosphonate O atoms from two deprotonatedLligands 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 ligandLexists in a zwitterionic form, with a positive charge on the NH3group and a negative charge on the O atom of the non-coordinating phosphonate group, and with an intramolecular O—H...O interaction forming anS(6) ring motif and two intramolecular N—H...O interactions each generating anS(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 Å3are filled with ordered lattice water molecules, which are also involved in O—H...O hydrogen bonding.