No abstract

The solid-state structures of 43 Li, Na, K, Rb, Mg, Ca and Ba salts of para- and meta-sulfonated azo dyes have been examined and can be categorised into three structural classes. All form alternating organic and inorganic layers, however, the nature of the coordination network that forms these layers differs from class to class. The class of structure formed was found to be primarily governed by metal type, but can also be influenced by the nature and position of the organic substituents. Thus, for the para-sulfonated azo dyes, Mg compounds form solvent-separated ion-pair solids; Ca, Ba and Li compounds form simple coordination networks based on metal-sulfonate bonding; and Na, K and Rb compounds form more complex, higher dimensional coordination networks. Compounds of meta-sulfonated azo dyes follow a similar pattern, but here, Ca species may also form solvent-separated ion-pair solids. Significantly, this first attempt to classify such dyestuffs using the principles of supramolecular chemistry succeeds not only for the simple dyes used here as model compounds, but also for more complex molecules, similar to modern colourants.

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.

Crystallographic studies of monosulfonated azo dyes have concentrated on the salt forms that contain the azo anion. Here we present a study that compares the structures of these anions with protonated free acid forms and with doubly deprotonated dianion forms. To this end, the new single crystal diffraction structures of 13 systematically related free acid forms of monosulfonated azo dyes are presented, together with three new structures of doubly deprotonated forms and two new structures of Na salt forms of azo anions. No structures of dideprotonated monosulfonated azo dyes have previously been reported and this paper also reports the first crystal structure of an azo dye with a hydronium cation. The geometries of the free acid, anion and dianion forms are compared to literature equivalents. It is shown that protonation of the azo bond gives predictable bond lengthening and shortening, which is of a greater magnitude than similar effects caused by azo-hydrazone tautomerisation, or the smaller again effects caused by the resonance electron donation from O or N based substituents. The dianion containing structures have twisted dianion geometries that can be understood based on the resonance effects of the phenoxide groups and upon the needs to bond to a relatively high number of metal cations.