The coordination number of a transition metal ion in a complex compound refers to the number of ligands atoms, ions, or molecules that are directly bonded to the central metal ion. It indicates the number of donor atoms surrounding the central metal ion in a complex.An example of a complex with a coordination number of 6 is hexaaquairon III ion, [Fe H2O 6]3+. In this complex, the central metal ion is iron Fe3+ , and it is surrounded by six water molecules H2O acting as ligands.The octahedral geometry that results from a coordination number of 6 can be visualized as an octahedron, a polyhedron with eight faces, twelve edges, and six vertices. In this geometry, the central metal ion is at the center of the octahedron, and the six ligands are located at the vertices. The ligands are arranged in such a way that they are equidistant from the central metal ion, and the angles between any two adjacent ligands are 90 degrees. This arrangement minimizes the repulsion between the electron pairs of the ligands, resulting in a stable complex.