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.