Crystal structures of two new divalent transition-metal salts of carb­oxy­benzene­sulfonate anions

Hexa­aqua­nickel(II) bis­(3-carb­oxy-4-hy­droxy­benzene­sulfonate) dihydrate, [Ni(H2O)6][C6H3(CO2H)(OH)SO3]2·2H2O, (I), crystallizes in the triclinic space group PUnlabelled Image with the nickel(II) aqua complexes on centers of inversion. The carboxyl­ate group is protonated and neither it nor the sulfonate group is involved in direct coordination to the metal ions. The structure consists of alternating layers of inorganic cations and organic anions linked by O—H⋯O hydrogen bonds that also include non-coordinated water mol­ecules of crystallization. The first-row divalent transition-metal salts of this anion are reported as both dihydrates and tetra­hydrates, with two distinct structures for the dihydrates that are both layered but differ in the hydrogen-bonding pattern. Compound (I) represents the second known example of one of these structures. Hexa­aqua­cobalt(II) bis­(3-carb­oxy­benzene­sulfonate) dihydrate, [Co(H2O)6][C6H4(CO2H)SO3]2·2H2O, (II), also crystallizes in triclinic PUnlabelled Image with the cobalt(II) aqua complexes on centers of inversion. The structure is also built of alternating layers of complex cations and organic anions without direct coordination to the metal by the protonated carboxyl­ate or unprotonated sulfonate groups. A robust O—H⋯O hydrogen-bonding network involving primarily the coordin­ated and non-coordinated water mol­ecules and sulfonate groups directs the packing. This is the first reported example of a divalent transition-metal salt of the 3-carb­oxy­benzene­sulfonate anion.