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 CdII 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 NH3 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 Å3 are filled with ordered lattice water molecules, which are also involved in O—H...O hydrogen bonding.

Keywords

• crystal structure
• bisphosphonate complexes
• complexes
• cadmium
• powder diffraction
• octahedral coordination
• zwitterion
• hydrogen bonding