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.