The possibility of using hydrogenase models based on Fe-2(mu-NRN) complexes was investigated. The use of benzo-[c]-cinnoline (BC = N2C12H8) bridge allows for an unprecedented control of the electron-transfer process in diiron complexes. We were able to modify the potential gap between the two one-electron reduction steps of [Fe-2(BC)(CO)(6)] by changing the solvent properties. The catalyst exhibits modest catalytic activity for proton reduction. However, there is a considerable opportunity for improvement considering the wide range of azo-bridged diiron described in the literature. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.