Mossbauer and UV-vis spectroscopic measurements of the two diazene-bridged Systems [{Fe'NHS4'}(2-)(N2H2)] ('NHS4'(2-) = 2,2)-biS(2-mercaptophenylthio)diethylamine(2-)) and [{Fe'S-4'(PPr3)}(2)(N2H2)] ('S-4'(2-) = 1,2-bis(2-mercaptophenylthio)ethane(2-)) have been combined with self-consistent-field X alpha scattered-wave (SCF-X alpha-SW) calculations in order to describe the electronic properties of diazene coordinated to FE(II)-sulfur centers. For both model systems, the experiments and calculations indicate a Fe(II)-N2H2-Fe(TT) structure with Fe(II low-spin centers. The stabilization of diazene is due to sigma-donation from its highest occupied MO and pi-backbonding into its lowest unoccupied MO (LUMO). The intense absorption band at approximately 600 nm is ascribed to a charge-transfer transition from metal-d orbitals into the diazene LUMO. Importantly, the diazene LUMO also is the LUMO of the complexes and is located between the fully occupied t(2g)* and empty e(g)* orbitals of the iron centers. It is concluded that the Fe(II) high-spin configuration present in a sulfur environment of lower ligand-field strength leads to reduction of diazene. Therefore diazene is likely to be involved in a reduction pathway of dinitrogen bound symmetrically (i.e., with both nitrogen atoms) to the iron-molybdenum cofactor (FeMoCo) of the enzyme nitrogenase.