The presence of different ligands can significantly affect the electronic and magnetic properties of transition metal complexes. This is mainly due to the ligand field theory, which is an extension of the crystal field theory, and the molecular orbital theory. These theories help explain the behavior of transition metal complexes in terms of their electronic structure, magnetic properties, and spectroscopy.1. Ligand Field Theory: When ligands approach a transition metal ion, they create a ligand field that interacts with the d-orbitals of the metal ion. The strength of this interaction depends on the nature of the ligand, which can be classified as strong-field or weak-field ligands. Strong-field ligands cause a larger splitting of the d-orbitals, while weak-field ligands cause a smaller splitting. This splitting of d-orbitals is known as the crystal field splitting or ligand field splitting, and it affects the electronic configuration of the metal ion.2. Electronic Properties: The electronic properties of a transition metal complex are determined by the distribution of electrons in the d-orbitals. The ligand field splitting causes the d-orbitals to split into two groups: the lower energy t2g orbitals and the higher energy eg orbitals. Depending on the strength of the ligand field, electrons will either occupy the lower energy orbitals first strong-field ligands or distribute evenly between the two sets of orbitals weak-field ligands . This difference in electron distribution affects the complex's color, reactivity, and stability.For example, in the octahedral complex [Fe H2O 6]3+, the water ligands are weak-field ligands, and the electron configuration is t2g^3eg^2. This complex is light violet in color. However, when the water ligands are replaced by strong-field ligands like cyanide CN- , the complex [Fe CN 6]3- forms, with an electron configuration of t2g^6eg^0. This complex is deep red in color.3. Magnetic Properties: The magnetic properties of a transition metal complex are determined by the presence of unpaired electrons in the d-orbitals. Complexes with unpaired electrons exhibit paramagnetism, while those with all paired electrons exhibit diamagnetism. The ligand field strength affects the distribution of electrons in the d-orbitals, which in turn influences the magnetic properties of the complex.For example, the octahedral complex [Fe CN 6]3- mentioned earlier has an electron configuration of t2g^6eg^0, with all electrons paired. This complex is diamagnetic. On the other hand, the complex [Fe H2O 6]3+ has an electron configuration of t2g^3eg^2, with five unpaired electrons, making it paramagnetic.In summary, the presence of different ligands affects the electronic and magnetic properties of transition metal complexes through their influence on the ligand field strength and the resulting splitting of d-orbitals. This, in turn, affects the distribution of electrons in the d-orbitals, which determines the complex's color, reactivity, stability, and magnetic properties.