 Early evidence for its distinctive C2v structure came from Mössbauer spectroscopic measurements that revealed two quadrupole doublets with similar isomer shifts but different (1.13 and 0.13 mm s−1) quadrupolar coupling constants.Fe3(CO)12 consists of a triangle of iron atoms surrounded by 12 CO ligands.Ten of the CO ligands are terminal and two span an Fe---Fe edge, resulting in C2v point group symmetry.