Copper(II) defect-cubane water oxidation electrocatalysts: from molecular tetramers to oxidic nanostructures.

We report on the synthesis and spectroscopic evidence for a sequence of structural transformations of a new defect-cubane type copper complex, [Cu 4 (pyalk) 4 (OAc) 4 ](ClO 4 )(HNEt 3 ), which acts as a pre-catalyst for water oxidation. In situ and post-catalytic studies showed that the tetrameric complex undergoes a structural transformation into dimeric and monomeric species, induced by water molecules and carbonate anions, respectively. Further, the observed electrocatalytic water oxidation activity has been confirmed to arise from in situ -generated Cu(II) oxidic nanostructures at the electrode interface.