5-Aminonaphthalene-1-sulfonic acid and its manganese, nickel and cobalt salts.

5-Ammonionaphthalene-1-sulfonate monohydrate, C10H9NO3S x H2O, contains layers of zwitterionic molecules with the acidic sulfonic acid H atom transferred to the amine N atom. Within each layer, the charged groups (NH3(+) and SO3(-)) are directed to the surface of the layer and are inverted on adjacent molecules. The naphthalene rings in a given layer are all parallel. The layers are held together by N-H...O and O-H...O hydrogen bonds involving the ammonium, sulfonate and water atoms. The Mn and Ni salts crystallize as fully aquated trihydrates, namely hexaaquamanagnese(II) bis(5-aminonaphthalene-1-sulfonate) trihydrate, [Mn(H2O)6](C10H8NO3S)2 x 3 H2O, (II), and hexaaquanickel(II) bis(5-aminonaphthalene-1-sulfonate) trihydrate, [Ni(H2O)6](C10H8NO3S)2 x 3 H2O, (III), in which layers of hexaaquametal(II) complexes alternate with layers of 5-aminonaphthalene-1-sulfonate anions. The cations reside on twofold rotation axes and display regular octahedral coordination. The additional water molecules are found in the inorganic layer between the complex cations, one on a twofold axis and one in a general position. The anions are packed in a herring-bone arrangement with the rings of neighboring rows of anions approximately 43 degrees out of parallel. The NH2 and SO3(-) groups line the surface of the layer, where they participate in numerous hydrogen bonds with the water molecules. Whereas the Mn and Ni salts are orthorhombic, the Co salt, hexaaquacobalt(II) bis(5-aminonaphthalene-1-sulfonate) dihydrate, [Co(H2O)6](C10H8NO3S)2 x 2 H2O, (IV), crystallizes in a triclinic cell of similar dimensions, with the cations situated on centers of inversion. The overall packing is very similar to that of the Mn and Ni salts, with the main differences being the absence of the solvent water molecule on the special position and subtle modifications in the positioning of the anions within their layers. This series of salts is compared with those of the same metals with the 5-aminonaphthalene-2-sulfonate and 4-aminonaphthalene-1-sulfonate isomers, allowing for similarities and differences in packing to be discussed on the basis of the differing substitution of the naphthalene ring and, in some cases, differing degrees of hydration.