Self-assembly of the 2-His-1-carboxylate facial triad in mononuclear iron(II) and zinc(II) models of metalloenzyme active sites.

A synthetic strategy involving the use of sterically hindered N-donor and terphenylcarboxylate ligands has been used to prepare complexes of iron(II) and zinc(II) that feature N2(carboxylate) donors. X-ray crystallographic and NMR data show that the 2-His-1-carboxylate facial triad found in metalloenzyme active sites is closely modeled by the mononuclear complexes. In addition, by virtue of the flexibility of the ligands used, the geometries and coordination environments of the complexes display carboxylate binding mode differences such as those seen in the enzymes.