Photosynthetic water oxidation occurs naturally at a tetranuclear manganese center in the photosystem II protein complex. Synthetically mimicking this tetramanganese center, known as the oxygen-evolving complex (OEC), has been an ongoing challenge of bioinorganic chemistry. Most past efforts have centered on water-oxidation catalysis using chemical oxidants. However, solar energy applications have drawn attention to electrochemical methods. In this paper, we examine the electrochemical behavior of the biomimetic water-oxidation catalyst [(H(2)O)(terpy)Mn(mu-O)(2)Mn(terpy)(H(2)O)](NO(3))(3) [terpy = 2,2':6',2''-terpyridine] (1) in water under a variety of pH and buffered conditions and in the presence of acetate that binds to 1 in place of one of the terminal water ligands. These experiments show that 1 not only exhibits proton-coupled electron-transfer reactivity analogous to the OEC, but also may be capable of electrochemical oxidation of water to oxygen.