Protonation-induced color change of an amino group functionalized [Fe4(μ3-O)2]8+ cluster

Abstract

Although synthetic efforts to prepare carboxylato-bridged tetranuclear iron(III) clusters have been well preformed, introducing of functional groups on the coordination ligands to tune the structural, spectroscopic and physical properties of the cluster remains unstudied. Using amino functionalized ligands bipy-NH2 and O2CPh-NH2, we have prepared a new cluster 1 ([Fe4O2 (O2CPh-NH2)7(bipy-NH2)2]·HO2CPh-NH2·(CH3CN)3·C2H5OH·OH) via a new precise orientated strategy starting from iron(II) compound. The cluster was characterized by UV–Vis, IR and Mossbauer spectroscopy, X-ray crystallography, cyclic voltammetric and magnetic studies. Results have shown that the [Fe4(μ3-O)2]8+ core was disposed in a bent “butterfly” arrangement, and the adjacent cores were connected into 1-D chain via hydrogen-bonding contacts involving lattice OH− anion, HO2CPh-NH2 and solvent molecules. This 1D chain exhibits strong antiferromagnetic interactions, and irreversible electron reduction of one iron(III) ion to iron(II) at EP.C = −1.77 V vs SCE. Remarkably, color change from reddish violet to bluish green have been observed for this cluster upon protonating the amino functional groups.