Position isomers, basic properties

Derivatives of a-diaminodihydroxyanthraquinones are the most important disperse dyes with respect to shade and affinity. The dye properties may be optimized by introducing suitable substituents, selecting the positions of the isomers, and blending. Some of these properties can be illustrated with the three basic structures 9-11. 

Substitution at one or more metal sites will generally break the symmetry of the cluster core, and can greatly influence its electronic properties and reactivity. Consider, for example, the possible substitutions of a metal M into an octahedral core of composition MfiX v (x = 8, 12). The first substitution will afford an MsM X core, for which the symmetry has been lowered to C4v. A second substitution generates an M4M 2Xx core with two possible isomers One in which the M atoms are positioned at trans vertices (D4/,) and another where they are positioned at cis vertices (C2v). With a third substitution to give an M3M 3Xx core, fac and mer isomers become possible, while further substitutions simply repeat the pattern with M and M interchanged. Here again, the substitutions can be anticipated to alter the basic electronic properties of the cluster. Moreover, the outer-ligand substitution chemistry could potentially be quite different... 

Based on the above, this chapter is focused on the synthesis and some selected properties of meta-substituted calix[4]arenes known in the state of the art. The review is by no means comprehensive, but rather should be meant as an overview of the most common ways leading to the wta-substituted isomers, showing the synthetic strategies and approaches that can address this least accessible position of a basic calix[4]arene skeleton. 

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