Synthesis, characterization and catalytic ATP-hydrolysis of two tetrairon(iii) complexes bridged by succinate/terephthalate with tris(2-benzimidazolylmethyl) amine

Abstract

Two new tetranuclear iron(III) complexes, [Fe₄(TBA)₄(μ-O)₂(μ₄-Suc)](ClO₄)₄(OH)₂·1.5CH₃CN·2C₂H₅OH·6H₂O (1) and [Fe₄(TBA)₄(μ-O)₂(μ₄-Tp)](ClO₄)₆·3C₂H₅OH·6H₂O (2) (Suc = succinate, Tp = terephthalate, TBA = tris(2-benzimidazolylmethyl)amine) have been prepared and characterized by various physicochemical techniques. X-Ray crystallography reveals complex 1 contains equivalent two μ-oxo-μ-carboxylate diiron(III) centers bridged by a succinate acting as a tetradentate ligand linked to four iron atoms, forming a tetranuclear core [Fe₄(TBA)₄(O)₂(Suc)]⁶⁺, in which each iron atom has an N₄O₂ donor set with distorted octahedral geometry and each of the two diiron(III) centers contains two iron atoms with a distinct coordination environment. Magnetic behaviors indicate the presence of a stongly antiferromagnetic coupling in the two complexes with the exchange coupling constants J = −114.27(8) cm⁻¹ for 1 and J = −119.52(6) cm⁻¹ for 2. The NMR spectra imply that the structures in the solid state are retained in solution. The two tetranuclear complexes exhibit similar cyclic voltammograms, i.e. there are three irreversible two-electron redox peaks at E_c = 0.247, −0.233 V; E_a = 0.354 V for 1 and E_c = 0.307, −0.166 V; E_a = 0.526 V for 2. The preliminary study on the hydrolysis of adenosine 5′-triphosphate (ATP) followed by ³¹P NMR spectroscopy shows that the two complexes can catalyze the hydrolysis of ATP.