A series of manganese and dimanganese organometallic complexes containing carbonyl ligands were studied by voltammetry, coulometry and IR spectroelectrochemistry. One-electron oxidations to cations were reversible at sub-ambient temperatures in dichloromethane for all complexes incorporating a phosphine ligand, two such processes being observed for the dinuclear complexes. The mono- and dications were characterized by IR spectroelectrochemistry using a thin-layer cell in the transmission mode. Good results were obtained for dichloromethane solutions with temperatures as low as 213 K. All of the mixed-valent monocations of the di-manganese complexes exhibited trapped valency.