Metal-metal bonds belong. from the topological point of view, to the wide class of the closed shell interactions proposed by Bader. Such a simple classification is. however, not satisfying in the description of these bonds and the nature of the metal-metal bond, in particular in polynuclear complexes, is debated. Using some topological and energy parameters. a comparison is made between polynuclear complexes and bulk metals and indicates the similar nature of these bonds. (C) 2004 Elsevier B.V. All rights reserved.