Geometry parameters (in Å and degrees) of singlet and triplet Fe(CO)₄, and ¹Fe(CO)₄^2− a.

	Fe–Cax	Fe–Ceq	C–Oax	C–Oeq	Cax–Fe–Cax	Ceq–Fe–Ceq	Fe–Cax–Oax	Fe–Ceq–Oeq
1Fe(CO)4	1.777	1.732	1.151	1.158	181.7	126.6	178.2	170.5
3Fe(CO)4	1.810	1.761	1.151	1.154	154.5	96.0	175.8	178.8
1Fe(CO)42−	1.727	1.727	1.201	1.201	109.7	109.7	179.8	179.8

^aComputed at ZORA-OPBE/TZ2P.