Chapter 2: Basic Concepts Relating to Organometallic Complexes

Just as the octet rule is a basic rule in organic chemistry, the EAN (Effective Atomic Number = 18-electron) rule is fundamental and useful in organometallic chemistry. In discussing a transition metal complex, it is important that the number of valence electrons of the metal and the number of electrons supplied from the ligands around the metal can be counted. This chapter explains how to perform electron counting both from the transition metal side and the ligand side. It would be extremely challenging to attempt to remember how many electrons are donated by each ligand, due to the enormous number and variety of ligands, but using the concepts described in this chapter, a solution is presented and there is no need to remember the details for individual ligands. Once the 18-electron rule is mastered, it is possible to predict the stability and the reasonable structure of any given transition metal complex, as well as the formal oxidation number and d-electron number of the transition metal. Moreover, in a multinuclear complex, the bond order between the metal atoms can be predicted.