Two N-functionally substituted diiron azadithiolate complexes, [(µ-SCH2)2NCH2CH2OC(O)C6H4I-p]Fe2(CO)6 (1) and {[(µ-SCH2)2NCH2CH2OC(O)C6H4I-p]Fe2(CO)5Ph2PCH}2 (2) as models for the active site of [FeFe] hydrogenases, have been prepared and fully characterized. Complex 1 was prepared by the reaction of [(µ-SCH2)2NCH2CH2OH]Fe2(CO)6 with p-iodobenzoic acid in the presence of 4-dimethylaminopyridine (DMAP) and N,N'-dicyclohexylcarbodiimide (DCC) in 78% yield. Further treatment of 1 with 1 equiv. of Me3NO · 2H2O followed by 0.5 equiv. of trans-1,2-bis(diphenylphosphino)ethylene (dppe) affords 2 in 60% yield. The new complexes 1 and 2 were characterized by IR and 1H (13C, 31P) NMR spectroscopic techniques and their molecular structures were confirmed by X-ray diffraction analysis. The molecular structure of 1 has two conformational isomers, in one isomer its N-functional substituent is axial to its bridged nitrogen and in the other isomer its N-functional substituent is equatorial. The crystal structure of 2 revealed that its N-functional substituents are equatorial to its nitrogens and dppe occupies the two apical positions of the square-pyramidal irons. [ABSTRACT FROM AUTHOR]