Supramolecular structure in s-block metal complexes of sulfonated monoazo dyes: discrepant packing and bonding behavior of ortho-sulfonated azo dyes

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 MO3S 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. MO3S bonds are replaced by MOH2, MHOR and M- 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.