Synthesis of a nanoscale Cu(II) 31 -oxo-carboxylate cluster, and effect of Cu-oxo cluster size on visible-light absorption.

Cu-Cu Cu(II)-oxo-carboxylate clusters are reported, including those with condensed 1.5 nm Cu-O cores supported exclusively by O-donor ligands. A size-colour correlation is observed due to a red-shift of the charge transfer absorption band on increasing size; hence these clusters sit between small molecules and (black) CuO nanostructures.