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'-disulfonalo-O:O')calcium, [Ca(C14H14N2O6S2)(H2O)(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)(H2O)(6)](C14H15N2O6S2).6H(2)O, (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 degrees out of parallel and the ortho-sulfonate groups are in an anti conformation.