Shape terpyridine based

The single pyridine sites were designed with both a to- and a p-pyridine for varying metal specificity. Upon introduction of an iron(II) salt and subsequent binding of iron into two of the terpyridine-based sites, a square-shaped tetramer results with a metakligand ratio of 1 1 (Fig. 7.14). 

Their activity compared to those of the Cu(II)-terpyridine and Cu(II)-bipyridine complexes indicate notable cooperativity between the metal centers (k mJ2 kmanoaet = 18-26 at pH = 7 and ca. 10 at the pH optimum of the given complex). The pH-rate profile of both complexes shows a bell-shaped structure. Thus, the postulated double general-base catalysis for both complexes is not fully justified. In case of 38 this was explained by possible inhibition by the buffer used. While double Lewis-acid activation is proposed for 37, single Lewis-acid activation is favored for 38. 

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