Nitric Oxide A Non-Innocent Ligand

3 Bonding in Nitrosyl Complexes 3.1 Nitric Oxide A Non-Innocent Ligand 

The following limitations of the Enemark-Feltham notation have become apparent over the last 40 years  

Enemark and Feltham noted that it is quite misleading to describe all linear complexes as derivatives of NO and all bent complexes as derivatives of NO , but did not provide a notation for indicating the M-N-O geometry and did not connect the notation to the 8 and 18 EAN rules. 

Enemark and Feltham s notation deliberately does not specify the oxidation state of the complex or its coordination number. However, recent studies based on independent spectroscopic and structural data may provide compelling evidence for a specific metal oxidation state, which has implications for the metal-nitrosyl bonding. Some authors therefore see a need to communicate this information. 

The suggestion of antiferromagnetic coupling between nitrosyl unpaired electrons and unpaired electrons on the metal undermines the fundamental assumptions of the Enemark-Feltham model since it implies weaker interactions within the MNO moiety. Furthermore, the antiferromagnetic coupling models require a definition of the oxidation states and spin states of the metal and the nitrosyl ligand. 

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