Two calcium salts of o-tolidine-6,6′-disulfonate

The dibasic and monobasic calcium salts of o-tolidine-6,6′-disulfonic acid, tetraaqua(4,4′-diamino-5,5′-dimethyl-1,1′- biphenyl-2,2′-disulfonato-O:O′)calcium, [Ca(C₁₄H₁₄N₂O₆S₂)(H ₂O)₄], (I), and hexaaqua (4-amino-4′-ammonio-5,5′-dimethyl-1,1′-biphenyl-2,2′- disulfonato-O)calcium 4-amino-4′-ammonio-5,5′-dimethyl-1,1′-biphenyl-2,2′- disulfonate hexahydrate, [Ca(C₁₄H₁₅N₂O₆S₂)(H ₂O)₆](C₁₄H₁₅N₂O ₆S₂).6H₂O, (II), have structures built upon layers of anions, with the calcium cations and water molecules between these layers. The calcium ions are seven-coordinate. The coordination sphere in compound (I) contains three sulfonate O atoms and four water molecules, while that in (II) contains one sulfonate O atom and six water molecules. Both structures are held together by a network of hydrogen bonds involving the amine, sulfonate and water groups. The biphenyl rings in the anions are approximately 75° out of parallel and the ortho-sulfonate groups are in an anti conformation.