['It', 'was', 'reported', 'that', 'Fe3', '+', 'and', 'Cu2', '+', 'were', 'grafted', 'as', 'amorphous', 'oxide', 'cluster', '[', '9,10', ']', ',', 'and', 'reduced', 'into', 'Fe2', '+', 'and', 'Cu+', 'by', 'receiving', 'one', 'electron', ',', 'respectively', '[', '11,12', ']', '.']