The four-coordinate iron(II) phosphoraniminato complex PhB(MesIm)(3)Fe-N=PPh3 undergoes an S = 0 to S = 2 spin transition with T-C = 81 K, as determined by variable-temperature magnetic measurements and Mossbauer spectroscopy. Variable-temperature single-crystal X-ray diffraction revealed that the S = 0 to S = 2 transition is associated with an increase in the Fe-C and Fe-N bond distances and a decrease in the N-P bond distance. These structural changes have been interpreted in terms of electronic structure theory.