The preparation and characterization of several {FeNO}(6) porphyrinates ([Fe(OEP)(L)(NO)](+)), where OEP is octaethylporphyrin and L is one of the neutral nitrogen-donating axial ligands 1-methylimidazole (1-MeIm), pyrazole (Pz), indazole (Iz), or pyrazine (Prz), are described. The synthesis and crystallization of these derivatives requires an NO atmosphere and careful attention to conditions. The characterization of these [Fe(OEP)(L)(NO)](+) complexes by IR and UV-vis spectroscopies provides for general distinctions between five- and six-coordination and the two common oxidation states of iron nitrosyl porphyrins. The UV-vis spectra of the [Fe(OEP)(L)(NO)](+) derivatives are all characterized by very distinct alpha and beta bands. The solid-state NO stretching frequencies are found in the narrow range of 1890 to 1921 cm(-1). Six X-ray structure determinations have been completed. The molecular structures of [Fe(OEP)(1-MeIm)(NO)]ClO4, [Fe(OEP)(P-2)(NO)]ClO4(1), [Fe(OEP)(Iz)(NO)]ClO4, and {[Fe(OEP)(NO)](2)Prz}(ClO4)(2) are described in detail. All structural features are consistent with the assignment of a low-spin state to the central iron. The Fe-N-p bond lengths range from 1.995(8) to 2.004(5) Angstrom. The axial Fe-N-NO bond lengths are quite short (range 1.627(2)-1.6465(17) Angstrom). The Fe-N-O groups are essentially linear (Fe-N-O angle range is 176.6(3)-177.6(3)degrees) which is that expected for these {FeNO}(6) species. The Fe-L bond lengths trans to the nitrosyl are normal (range 1.988(2)-2.039(2) Angstrom); there is no nitrosyl structural trans effect. The iron is displaced only slightly out of the plane of the 24-atom core toward the nitrosyl, and with the short Fe-N-NO bond lengths steric interactions cause modest porphyrin core distortions.