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

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(µO)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 Ec= 0.247, 0.233 V; Ea= 0.354 V for 1 and Ec= 0.307, -0.166 V; Ea= 0.526 V for 2. The preliminary study on the hydrolysis of adenosine 5triphosphate (ATP) followed by 31P NMR spectroscopy shows that the two complexes can catalyze the hydrolysis of ATP.