Hexaaqua-cobalt(II) 3-ammonio-naphtha-lene-1,5-disulfonate tetra-hydrate

The title compound, [Co(H2O)6][H3NC10H5(SO3)2]2·4H2O, is part of an isostructural family that includes the nickel(II) and zinc(II) analogues. The salts contain centrosymmetric hexa-aqua-metal cations and protonated ammonio-naphthalene-disulfonate anions arranged in alternating layers. The anions stack so that the charged groups face the cationic layers, maximizing electrostatic inter-actions. The non-coordinated water mol-ecules are located in the cation layers. An extensive network of strong near-linear N - H⋯O and O - H⋯O hydrogen bonds involving the ammonio group, water mol-ecules and sulfonate O atoms further anchors the packing. One of the uncoordinated water mol-ecules is disordered over at least two sites (modelled over two positions with almost equal site occupancies).