The most stable geometric structure of a Fe CO 5 complex molecule, as predicted by ab initio calculations, is a trigonal bipyramidal geometry. In this structure, the iron Fe atom is at the center, and the five carbonyl CO ligands are arranged with three in the equatorial plane and two in the axial positions.The electronic configuration of the Fe CO 5 complex can be determined by considering the 18-electron rule, which states that a stable transition metal complex will have a total of 18 valence electrons when counting both the metal and the ligands. In the case of Fe CO 5, the iron atom has 8 valence electrons as it is in the +2 oxidation state , and each carbonyl ligand contributes 2 electrons, resulting in a total of 18 valence electrons.The electronic configuration of the Fe CO 5 complex can be represented as follows:Fe: [Ar] 3d6 4s0CO: [He] 2s2 2p4When the carbonyl ligands form a bond with the iron atom, they donate a pair of electrons to the metal, forming a metal-to-ligand -backbonding. This results in the following electronic configuration for the Fe CO 5 complex:Fe CO 5: [Ar] 3d8 4s0This electronic configuration and the trigonal bipyramidal geometry contribute to the stability of the Fe CO 5 complex.