Supramolecuar motifs in s-block metal-bound sulfonated monoazo dyes: The case of Orange G

Solid-state structures of Mg, Sr, Ba, Na2, Na0.8K1.2, NaRb, and Na1.5Cs0.5 complexes of the disulfonated dye 7-hydroxy-8-(phenylazo)-1,3-naphthalenedisulfonic acid, Orange G, are presented. It is shown that the s-block metal salts of the Orange G dianion (Og) can be categorized into three structural classes related to those previously proposed for simple monosulfonated azo dyes. All of the structures feature alternate organic/inorganic layering, but whereas the Mg, Ca, and Li complexes are solvent-separated ion-pair species, the Sr and Ba complexes form simple discrete molecules based on metal-sulfonate bonding, and the heavy alkali metal complexes utilize a variety of M-O interactions to form 2- and 3-dimensional coordination networks. These structural differences are rationalized in terms of simple properties of the metals (charge, size, and electronegativity) and the steric demands of the arylsulfonate groups. The Ag2 complex of Orange G is also structurally characterized, and in contrast to the s-block salts, it is found to exhibit strong Ag pi bonds. In confirmation of the above, the crystal structures of Mg(H2O)6]Og] . 3.33H2O, Sr(Og)(H2O)7].H2O, Ba(Og)(H2O)7]2 . 2H2O, Na2(Og)(H2O)6.67], Na2(Og)(H2O)2(HOEt)], Na0.8K1.2(Og)(H2O)6] . 1.75H2O, NaRb(Og)(H2O)6.5] . 2.375H2O, Na1.5Cs0.5(Og)(H2O)6] . 0.5H2O, and Ag2(Og)(H2O)4].H2O are presented.