The electrochemistry of a large number of transition metal complexes of iron, cobalt, chromium, and ruthenium have been examined regarding their anodic and cathode peak potential, peak separation, and reversibility as a function of a broad pH range. Criteria for reversibility are considered. In addition, absorption and/or color characteristics have been described at a fixed pH. The stability of stored samples in terms of cyclic voltammetry and absorption spectra has been examined for a given period of time. A significant number of redox couples have properties which should make them useful in photoelectrochemistry, and other electrochemical applications, catalysis, redox flow cells, and the like.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.171.57.189 Downloaded on 2015-06-13 to IP