Review: Some considerations about coordination compounds with end-on dinitrogen

There have been several reviews on dinitrogen coordination compounds but no special attention has been paid to correlate the electron configuration of the metal ions with the main features of the ligands in order to establish an electron configuration-stability relationship. In this article we consi der nearly 200 complexes with terminal dinitrogen to find common characteri stics that lead to the synthesis of other stable dinitrogen compounds. This survey shows that for coordination number 6 there is a strong tendency for a d(6) configuration in the metals, with oxidation states between 1- and 2 . On the basis of quantum chemistry, dinitrogen as a ligand can be compared w ith the isoelectronic species CO, CN-, NO+. The MO and orbital energy diagr ams indicate that N-2 is not a good donor neither a good acceptor, but with the appropriate symmetry and in the presence of a good pi -donor metal it forms an N-2<-- M <pi>-bond strengthened by an N-2--> M sigma -back-bonding .