The new iron phosphide with the highest phosphorus content of known ion phosphides, FeP 4, was synthesized by the reaction of elemental components at 60 kbar in a cubic anvil device. Its space group was found to be C 222 1, with four formula units in the unit cell ( a = 0.5005(1), b = 1.0213(3), c = 0.530(1) nm). The structure of FeP 4 was analysed by standard Patterson and Fourier techniques and refined by a block-diagonal least-squares method to a final conventional R value of 0.067 for 546 reflections. The coordination around Fe and P in FeP 4 is very similar to that of Cr, Mn, and P in CrP 4 and MnP 4. The difference in structure between these compounds is discussed and correlated to the electronic configuration.