A detailed structural and thermodynamic study of a series of cobalt-hydride complexes is reported. This includes structural studies of [H2Co(dppe)(2)](+), HCo(dppe)(2), [HCo(dPPe)(2)(CH3CN)](+), and [Co(dpPe)(2)(CH3CN)](2+), where dppe = bis(diphenylphosphino)ethane. Equilibrium measurements are reported for one hydride- and two proton-transfer reactions. These measurements and the determinations of various electrochemical potentials were used to determine 11 of 12 possible homolytic and heterolytic solution Co-H bond dissociation free energies of [H2Co(dppe)(2)](+) and its monohydride derivatives. These values provide a useful framework for understanding observed and potential reactions of these complexes. These reactions include the disproportionation of [HCo(dppe)(2)](+) to form [Co(dPPe)(2)](+) and [H2Co(dPPe)(2)](+), the reaction of [Co(dppe)(2)](+) with H-2, the protonation and deprotonation reactions of the various hydride species, and the relative ability of the hydride complexes to act as hydride donors.