Crystal structures of two coordination isomers of copper(II) 4-sulfobenzoic acid hexahydrate and two mixed silver/potassium 4-sulfobenzoic acid salts

A reaction of copper(II) carbonate and potassium 4-sulfobenzoic acid in water acidified with hydrochloric acid yielded two crystalline products. Tetraaquabis(4-carboxybenzenesulfonato)copper(II) dihydrate, [Cu(O₃SC₆H₄CO₂H)₂(H₂O)₄]·₂H₂O, (I), crystallizes in the triclinic space group P with the Cu²⁺ ions located on centers of inversion. Each copper ion is coordinated to four water molecules in a square plane with two sulfonate O atoms in the apical positions of a Jahn-Teller-distorted octahedron. The carboxylate group is protonated and not involved in coordination to the metal ions. The complexes pack so as to create a layered structure with alternating inorganic and organic domains. The packing is reinforced by several O-H..O hydrogen bonds involving coordinated and non-coordinated water molecules, the carboxylic acid group and the sulfonate group. Hexaaquacopper(II) 4-carboxybenzenesulfonate, [Cu(H₂O)₆](O₃SC₆H₄CO₂H)₂, (II), also crystallizes in the triclinic space group P with Jahn-Teller-distorted octahedral copper(II) aqua complexes on the centers of inversion. As in (I), the carboxylate group on the anion is protonated and the structure consists of alternating layers of inorganic cations and organic anions linked by O-H..O hydrogen bonds. A reaction of silver nitrate and potassium 4-sulfobenzoic acid in water also resulted in two distinct products that have been structurally characterized. An anhydrous silver potassium 4-carboxybenzenesulfonate salt, [Ag0.69K0.31](O₃SC₆H₄CO₂H), (III), crystallizes in the monoclinic space group C2/c. There are two independent metal sites, one fully occupied by silver ions and the other showing a 62% K⁺/38% Ag⁺ (fixed) ratio, refined in two slightly different positions. The coordination environments of the metal ions are composed primarily of sulfonate O atoms, with some participation by the non-protonated carboxylate O atoms in the disordered site. As in the copper compounds, the cations and anions cleanly segregate into alternating layers. A hydrated mixed silver potassium 4-carboxybenzenesulfonate salt dihydrate, [Ag0.20K0.80](O3SC6H4CO2H)·2H2O, (IV), crystallizes in the monoclinic space group P21/c with the Ag⁺ and K⁺ ions sharing one unique metal site coordinated by two water molecules and six sulfonate O atoms. The packing in (IV) follows the dominant motif of alternating inorganic and organic layers. The protonated carboxylate groups do not interact with the cations directly, but do participate in hydrogen bonds with the coordinated water molecules. (IV) is isostructural with pure potassium 4-sulfobenzoic acid dihydrate.