Poly[[diaquacadmium(II)]-mu4-[N-(phosphonatomethyl)ammonio]acetato].

The title compound, [Cd(C3H6NO5P)(H2O)2]n, is a three-dimensional polymeric complex. The asymmetric unit contains one Cd atom, one N-(phosphonomethyl)glycine zwitterion [(O-)2OPCH2NH2+CH2COO-] and two water molecules. The coordination geometry is a distorted CdO6 octahedron. Each N-(phosphonomethyl)glycine ligand bridges four adjacent water-coordinated Cd cations through three phosphonate O atoms and one carboxylate O atom, like a regular PO(4)3- group in zeolite-type frameworks. One-dimensional zigzag (-O-P-C-N-C-C-O-Cd-)n chains along the [101] direction are linked to one another via Cd-O-P bridges and form a three-dimensional network motif with three types of channel systems. The variety of O-H...O and N-H...O hydrogen bonds is likely to be responsible for stabilizing the three-dimensional network structure and preventing guest molecules from entering into the channels.