The geometry/shape of the Fe₄ core of the cluster [Fe₄C(CO)₁₂]^2- is

Concept:

• The polyhedral skeletal electron pair theory (PSEPT) provides electron counting rules useful for predicting the structures of clusters such as main group and transition metal polyhedral complexes.

Explanation:

• For the transition metal polyhedral complex [Fe4C(CO)12]2-, Fe contributes 8 electrons, C contributes 4 electrons, the 12 carbonyl group will contribute 24 electrons and two negative charges will contribute 2 electrons to the polyhedral electron count.
• The total polyhedral electron counts for the cluster compound [Fe4C(CO)12]2- is

​

.

• Hence, according to the PSEPT, The geometry/shape of the Fe4 core of the cluster [Fe4C(CO)12]2- is butterfly.