The ion-molecule reaction chemistry of Co(CO)/sub 3/(NO) and Ni(CO)/sub 4/ is presented. Ionic cluster fragments of the type M/sub x/(CO)/sub y(NO)/sub z//sup +/ are formed from the reaction of the fragment ion M(CO)/sub a/(NO)/sub b//sup +/ with its respective neutral. The relative reaction rate and electron deficiency of the ionic cluster fragments are used to estimate the bond order of the ionic cluster fragments. Comparison of the Cr(CO)/sub 6/, Fe(CO)/sub 5/, Co(CO)/sub 3/(NO), and Ni(CO)/sub 4/ systems shows that the ionic cluster fragments can be divided into two categories: (1) ionic cluster fragments with simple polyhedral structures and (2) ionic cluster fragments which exhibit unusual binding of the ligands and/or metals, resulting in ionic cluster fragments with high bond orders. These two classes of ionic cluster fragments are discussed in terms of the interrelationship of the reactivity/electron deficiency model and the cluster valence molecular orbital model developed by Lauher.