Molecular structures of 12 porphyrin analogues, Fe-\\\(EtioP)X(1(a)-1(d)), Fe-\\\(EtioCn)X(2(a)-2(d)), and Fe-\\\(Etio-Pc)X(3(a)-3(d)), where X = F (a), Cl (b), Br (c), and \ (d), are determined on the basis of X-ray crystallography. Combined analyses using Mossbauer, H-1 NMR, and EPR spectroscopy as well as SQUID magnetometry have revealed that 3(d) exhibits a quite pure S = 3/2 spin state with a small amount of an S = 5/2 spin admixture. In contrast, all the other complexes show the S = 5/2 spin state with a small amount of the S = 3/2 spin admixture. The structural and spectroscopic data indicate a strong correlation between the spin states of the complexes and the core geometries such as Fe-N bond lengths, cavity areas, and DeltaFe values.