Two Trinuclear Cu^II Complexes: Effect of Phosphonate Ligand on the Magnetic Property and Electrocatalytic Reactivity for Water Oxidation

Two trinuclear copper phosphonate complexes, [Cu₃ (pda)₃ (tBuPO₃ )]⋅2(Et₃ NH) (1) and [Cu₃ (pda)₃ (PhPO₃ )]⋅2(Et₃ NH) (2), have been synthesized and investigated by a combination of X-ray crystallography, PXRD, magneto- and electrochemistry, EPR, in situ UV-vis spectroelectrochemistry and DLS. The two complexes feature almost identical crystal structures, the anions of which are both supported by pda^2- and tBuPO₃ ^2- /PhPO₃ ^2- groups, bridging three five-coordinated Cu^II atoms to form a crown-like structure. This is the first time that trinuclear copper phosphonate complexes have been isolated and characterized. Magnetic susceptibility measurements reveal that complexes 1 and 2 both display overall ferromagnetic characters, but with different exchange interactions between the metal ions within the two clusters. The electrocatalytic activity for water oxidation of the two complexes was preliminarily investigated, which reveals that both of the two complexes can carry out electrocatalytic water oxidation in a neutral system owing to the introduction of phosphonate ligands into the complexes, with a TOF of about 0.82 s^-1 (1) and 0.58 s^-1 (2), respectively. We propose that the presence of phosphonate ligands may affect the magnetic property and catalytic activity of the complexes.