RESUMO
The first solid-state structures of ortho-sulfonated monoazo dyestuffs are reported and compared to those of their para- and meta-sulfonated analogues. The structures of the 16 Na, K, Cs, Mg, Ca, Sr, and Ba ortho-sulfonated salts are found to have fewer M-O(3)S bonds than their isomeric equivalents and this in turn means that the metal type is no longer the prime indicator of which structural type will be adopted. M-O(3)S bonds are replaced by M-OH(2), M-HOR and M-pi interactions, apparently for steric reasons. As well as new bonding motifs, the changed dye shape also leads to new packing motifs. The simple organic/inorganic layering ubiquitous to the para- and meta-sulfonated dye salt structures is replaced by variations (organic bilayers, inorganic channels), each of which correlates with a different degree of molecular planarity in the sulfonated azo dye anion.