Iron-containing molecules and ions with various types of bonding were calculated using DFT theory (B3LYP functional) and an energy-adjusted effective core potential for iron (ECP(S)). Examination of calculated geometries, bond dissociation energies, ionization energies, enthalpies of formation, and harmonic frequencies and their comparison with experimental and higher level (CCSD(T), MCPF, CASSCF) computational data show that B3LYP/ECP(S) calculations of iron-containing species are capable of giving reliable results. The dissociation energies were calculated for iron-containing species with various bonding interactions having experimental estimates of bond strengths varying from 5.0 (Fe+-H-2) to 99.5 kcal/mol (Fe+-CH), i.e., within a range of 95 kcal/mol, do not reveal any systematic trends in the errors, The average absolute deviation is 3.6 kcal/mol. The maximum deviation from the experimental D-0 value is +8.0 kcal/mol for Fe+-CH. This experimental estimate, however, has an uncertainty of +/-7 kcal/mol. The B3LYP/ECP(S) calculated enthalpies of formation have an average absolute deviation of 5.7 kcal/mol with the largest deviation of 14+/-7 kcal/mol of the experimental Delta H-f0 value in the case of FeCH+. Geometries and harmonic frequencies calculated using the B3LYP/ECP(S) scheme are generally in good agreement with the available experimental data or with results of higher level calculations.