Pentacoordinated metals orbitals

Figure 13.6. Valence orbitals of a pentacoordinated metal A (longer gray bracket) is analogous to Asu- The splitting of the upper levels (shorter gray bracket) is a measure of the trans effect.

The pentacoordinate trifluorophosphine complexes behave similarly. Thus the difference in energy between the 2E and 2E" states, Ae e"> increases markedly in going from Fe(PF3)s to Ru(PF3)s. This increase is caused by the change in energy of the 2E state, which, in turn, results from changing from a 3d to a 4d metal orbital. 

Orbital symmetry arguments and EHT calculations have also provided a way of discriminating between axial and apical substitution in the above mentioned case of pentacoordinate phosphorus. This analysis leads the way to more complex problems of coordination around transition metal atoms. 

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