Metals bound to so-called triply bonded carbyne, imide, nitride (nitrido), and oxide (oxo) ligands are generally assigned to high oxidation states with low d electron counts. The high oxidation state stabilizes the highly reduced ligands. The low d electron count allow for many bonds between ligands and the metal center. A d metal center can accommodate up to 9 bonds without violating the 18 electron rule, whereas a d species can only accommodate 6 bonds.