1,4-Bis{[hydroxy(phenyl)phosphoryl]methyl}piperazine-1,4-diium tetrachloridocadmate(II) dihydrate and the cobaltate(II) analogue.

The reaction of aminophosphinic acid with CdCl2·2.5H2O or CoCl2·6H2O in concentrated hydrochloric acid yielded the isostructural compounds 1,4-bis{[hydroxy(phenyl)phosphoryl]methyl}piperazine-1,4-diium tetrachloridocadmate(II) dihydrate, (C18H26N2O4P2)[CdCl4]·2H2O, (I), and 1,4-bis{[hydroxy(phenyl)phosphoryl]methyl}piperazine-1,4-diium tetrachloridocobaltate(II) dihydrate, (C18H26N2O4P2)[CoCl4]·2H2O, (II). The asymmetric unit of each contains two half dications, both located on crystallographic centres of inversion, a tetrachloridometallate(II) dianion and two solvent water molecules. The residues are linked into two-dimensional layers in the ab plane by O-H···O hydrogen bonds.