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)center dot 2H(2)O, (I), crystallizes in the triclinic space group P (1) over bar 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 center dot center dot center dot 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)center dot 2H(2)O, (II), also crystallizes in triclinic P (1) over bar 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 center dot center dot center dot 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.