Around the manganese atom, there are five CO ligands and one Mn occupying octahedron vertices. For octahedral geometry, the more appropriate hybridization is d2sp3 that produces six hybrid orbitals pointing towards CO and Mn.
The octahedral shape of molecules is the shape of molecules where six atoms or ligands or groups of atoms are arranged in a systematic way around a central dogma or atom. The Octahedral Shape of Molecules molecules has eight faces.
