The number and nature of ligands in coordination complexes play a crucial role in determining the crystal field splitting, which in turn affects their color and magnetic properties. Crystal field splitting refers to the splitting of d-orbitals in a metal ion when it forms a coordination complex with ligands. This splitting occurs due to the electrostatic interaction between the metal ion and the ligands.1. Number of ligands: The coordination number number of ligands surrounding the metal ion influences the geometry of the complex, which in turn affects the crystal field splitting. For example, a complex with a coordination number of 4 can have either a tetrahedral or a square planar geometry, while a complex with a coordination number of 6 usually has an octahedral geometry. The crystal field splitting is different for each geometry, with octahedral complexes having the largest splitting, followed by square planar and tetrahedral complexes.2. Nature of ligands: The nature of ligands also plays a significant role in determining the crystal field splitting. Ligands can be classified according to their ability to split the d-orbitals, known as the spectrochemical series. Strong-field ligands e.g., CN-, CO cause a larger splitting, while weak-field ligands e.g., I-, Br- cause a smaller splitting. This is because strong-field ligands have a greater ability to accept electron density from the metal ion, leading to a more significant electrostatic interaction and a larger splitting.The crystal field splitting affects the color and magnetic properties of coordination complexes in the following ways:1. Color: The color of a coordination complex is determined by the absorption of light, which promotes an electron from a lower-energy d-orbital to a higher-energy d-orbital. The energy difference between these orbitals corresponds to the energy of the absorbed light, which is related to its wavelength and color. A larger crystal field splitting results in the absorption of higher-energy shorter wavelength light, while a smaller splitting results in the absorption of lower-energy longer wavelength light. Consequently, the color of the complex depends on the number and nature of ligands.2. Magnetic properties: The magnetic properties of coordination complexes are determined by the presence of unpaired electrons in the d-orbitals. A larger crystal field splitting can lead to a low-spin complex, where electrons are paired up in the lower-energy orbitals, resulting in a diamagnetic or weakly paramagnetic complex. In contrast, a smaller splitting can lead to a high-spin complex, where electrons occupy the higher-energy orbitals, resulting in a strongly paramagnetic complex. Thus, the number and nature of ligands can significantly impact the magnetic properties of coordination complexes.