A series of mono- and disubstituted complexes, FeI2(CO)(x)L4-x, x = 2 or 3, is conveniently accessed from simple mixing of N-heterocyclic carbenes, phosphines, and aromatic amines with FeI2(CO)(4), first reported by Hieber in 1928. The highly light sensitive complexes yield to crystallization and X-ray diffraction studies for six complexes showing them to be rudimentary structural models of the monoiron hydrogenase, [Fe]-H(2)ase or Hmd, active site in native (Fe-II(CO)(2)) or CO-inhibited (Fe-II(CO)(3)) states. Diatomic ligand (nu(CO)) vibrational and Mossbauer spectroscopies are related to those reported for the Hind active site. The importance of a serial approach for relating such parameters in model compounds to low spin Fe-II in the diverse ligation of enzyme active sites is stressed.