Two tetranuclear 3d–4f heterometal complexes Mn2Ln2 (Ln = Dy, Gd): synthesis, structure, magnetism, and electrocatalytic reactivity for water oxidation

Abstract

In this present study, two Mn/Ln clusters, [Mn₂Ln₂(O₂CMe)₆(pdmH)₂L](NO₃)·H₂O (Ln = Dy (1), Gd (2)), have been synthesized and experimentally investigated by X-ray crystallography, PXRD, magneto- and electrochemistry. By X-ray analysis, it is shown that the two complexes are isomorphous, both possessing one [Mn^IIMn^IIILn^III₂(μ₃-O)₂]⁶⁺ core with four metal atoms in one plane arranged in a butterfly conformation. This is the first time that mixed-valent manganese (Mn^II and Mn^III) and Ln^III heterometal tetranuclear complexes have been isolated and characterized. Magnetic susceptibility measurements reveal that compounds 1 and 2 both display overall weak ferromagnetic exchanges between the metal ions within the clusters. The temperature dependencies of the out-of-phase (χ_M′) and in-phase (χ_M′) ac susceptibility signals exhibit no significant frequency-dependency for compounds 1 and 2, which suggests that the two complexes may not be SMMs. Electrochemical studies indicate that compounds 1 and 2 can both catalyze water oxidation at a potential of ∼1.70 V with an overpotential of ∼880 mV vs. NHE, which could be due to a cooperative catalytic effect between the manganese and lanthanide ions.