The room temperature adsorption of a chromium tris-diketonate, i.e., tris-dibenzoylmethanate on Cu(100) was investigated using scanning tunnelling microscopy in ultra high vacuum (UHV-STM). The analysis of the STM images, supported by image calculations demonstrates that the molecule dissociates by loosing one ligand, both products remaining adsorbed on the surface. Attractive interaction between the two species results in a number of different molecular structures that are briefly discussed. (C) 2002 Elsevier Science B.V. All rights reserved.