Fe CO 5, also known as iron pentacarbonyl, is a complex molecule with an iron Fe atom at the center, surrounded by five carbonyl CO ligands. To determine its electronic structure and bond order, we need to consider the molecular orbital MO theory.1. Electronic structure:Iron Fe is in the 3d transition series and has an electron configuration of [Ar] 3d^6 4s^2. In Fe CO 5, the iron atom loses its 4s electrons and forms a complex with five CO ligands, which act as -donor and -acceptor ligands. The CO ligands have a total of 10 valence electrons 5 pairs . The electron configuration of Fe in the complex becomes [Ar] 3d^6.The CO ligands donate a pair of electrons to the Fe atom through -bonding, and the Fe atom donates electrons back to the CO ligands through -backbonding. This results in the formation of 5 metal-to-ligand -bonds and 5 ligand-to-metal -bonds.2. Bond order:Bond order is defined as the number of bonding electrons minus the number of antibonding electrons, divided by 2. In Fe CO 5, there are 5 -bonds and 5 -bonds, making a total of 10 bonds. The bond order for each Fe-CO bond can be calculated as follows:Bond order = Number of bonding electrons - Number of antibonding electrons / 2Bond order = 10 - 0 / 2Bond order = 5So, the bond order for each Fe-CO bond in Fe CO 5 is 5.3. Vibrational modes and infrared spectrum:Fe CO 5 has a trigonal bipyramidal structure, with the Fe atom at the center and the CO ligands occupying the axial and equatorial positions. This molecule has 4N-5 vibrational modes N = number of atoms , which means it has 15 vibrational modes. These vibrational modes can be divided into two categories: stretching and bending modes.The stretching modes involve the Fe-C and C-O bonds, while the bending modes involve the deformation of the Fe-C-O angle. The stretching modes are typically observed in the infrared spectrum, while the bending modes are not observed due to their low intensity.In the infrared spectrum of Fe CO 5, there are two main bands observed, corresponding to the symmetric and asymmetric stretching modes of the Fe-C and C-O bonds. The symmetric stretching mode is observed at around 2000 cm^-1, while the asymmetric stretching mode is observed at around 2100 cm^-1. These bands provide information about the strength and nature of the Fe-CO bonds in the complex.In summary, the electronic structure of Fe CO 5 involves -donation and -backbonding between the Fe atom and the CO ligands, resulting in a bond order of 5 for each Fe-CO bond. The vibrational modes and infrared spectrum of the molecule provide information about the strength and nature of these bonds.