X-RAY CRYSTAL-STRUCTURES AND CHEMICAL-PROPERTIES OF HETEROCYCLIC AZO-COMPOUNDS COUPLED WITH M-ALKOXYPHENOLS

X-Ray crystal structures have been determined for two compounds obtained by the coupling reaction of 2-pyridinediazonium salt and m-methoxyphenol, viz., 3-methoxy-4-(2-pyridylazo)phenol (1) and 5-methoxy-2-(2-pyridylazo)phenol (2). The 2-pyridylazo and 2-thiaaolylazo compounds having o-methoxy and p-hydroxy groups, such as 1, have lower pK(a) values and lower affinities for or higher selectivities to metal ions than corresponding o-hydroxy isomers. The resulting bis complexes with metal ions show molar absorptivities greater than 10(5).