Iron-carbonyl complex bond length

Further examples of coordinate bonds are found in metal carbonyl complexes. Metal carbon (carbon monoxide) bond distances in a selection of (first-row) transition-metal carbonyls and transition-metal organometallics are examined in Table 5-11. As expected, Hartree-Fock models do not perform well. The 6-3IG model is clearly superior to the STO-3G and 3-2IG models (both of which lead to completely unreasonable geometries for several compounds), but still exhibits unacceptable errors. For example, the model shows markedly different lengths for the axial and equatorial bonds in iron pentacarbonyl, in contrast to experiment where they are nearly the same. Hartree-Fock models cannot be recommended. 

There are a limited number of structures reported for Fe—Pb complexes and these are recorded in Tables 16-18. For a series of iron carbonyl lead clusters, the Fe—Pb bond lengths vary from 2.624 A for an electron-deficient three-coordinate planar Pb cluster [FefCO jjPbl to 2.828 A for a tetrahedral bridging anionic Pb cluster... 

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