We propose an investigation in which the crystal structure of Fe2(CO)9 will be studied as a function of pressure. This compound has previously been investigated by high pressure Raman spectroscopy which showed the occurrence of 2 phase transformations. In addition to terminal M-CO units, this system possesses three bridging CO groups. To date only two high pressure study diffraction studies have been performed on a binary metal carbonyl, namely Ru3(CO)12. and a 2012 study on W(CO)6 We intend to pursue this emergent area in organometallic chemistry. The key objectives are: (1) to determine the variation in the bond lengths of a bridged Fe-Fe bond with pressure; (2) how changes in the Fe-Fe distance affect the geometry and bond lengths of the bridging and terminal CO groups; (3) to account for differences between the two types of carbonyl group.