The 18-electron rule is a fundamental rule in chemistry governing the structure and bonding of transition metal compounds. Here we report the observation of a chemically bound Ni(CO)(5)(+) complex, which was characterized by infrared photodissociation spectroscopy and quantum chemical calculations to be a fivefold coordinated trigonal bipyramidal carbonyl compound having 19 valence electrons with the extra electron residing largely on metal center. This finding provides new insight of ligand interactions and coordination for the transition metals. (C) 2012 Elsevier B. V. All rights reserved.