Different-smelling molecules. Computer-generated molecular graphics of ferrocene & nickelocene, molecules with a virtually similar structure but which smell very different. The aromatic properties of these and other chemicals suggest that their smell is dependent upon the molecular bond vibrations, rather than the molecules' shape. Ferrocene and nickelocene are types of cyclopentadienylides, having respectively an iron (red) and nickel (white, large) ion sandwiched between two groups that contain 5 carbon (grey) & 5 hydrogen (white, small) atoms each. Ferrocene smells similar to camphor, whilst nickelocene smells like cycloheptatriene or tropilidene.