The sublimation of molecules under ultra-high vacuum conditions becomes critical with increasing molecular complexity as thermal fragmentation comes into play. In this case, scanning tunneling microscopy experiments of large molecules commonly focus on the small portion of the surface displaying intact molecules. In this work, we shed light on the major part of the surface where molecular fragments are observed. Upon the deposition of nanometer-sized wheelbarrows on a Cu(100) surface, only a few intact molecules, but several highly symmetric objects were observed. Using a full range of techniques the chemical structure and a possible formation pathway of these molecules were proposed. (c) 2006 Elsevier B.V. All rights reserved.