Discuss the structural effects of crystal field splitting.

In the study of transition metal chemistry, octahedral complexes occupy a central position. These complexes feature a metal atom surrounded by six ligands positioned at the corners of an octahedron.

This geometric arrangement results in crystal field splitting where the d-orbitals divide into two sets: the higher energy e_g orbitals (d_z^2 and d_x^2-y^2) and the lower energy t_2g orbitals (d_xy, d_xz, and d_yz). The energy difference between these two sets is denoted by the symbol Δ_o, where 'o' stands for octahedral. The magnitude of Δ_o influences the electronic distribution and is a determining factor in properties like color and magnetic behavior of the complex.

Tetrahedral complexes are less common than octahedral, but they provide an interesting contrast in terms of crystal field theory. Here, a central metal ion is surrounded by four ligands at the corners of a tetrahedron.

Unlike in octahedral complexes, the crystal field splitting in tetrahedral complexes sees the e orbitals (d_xy, d_xz, and d_yz) lower in energy while the t₂ orbitals (d_z^2 and d_x^2-y^2) are raised, denoted as Δ_t, with 't' indicating tetrahedral. The splitting is also generally smaller in magnitude compared to octahedral splitting. The differences in geometry and energy splitting have direct implications on the complex’s electronic configuration and thus its physical and chemical properties.

The arrangement of electrons in the d-orbitals after crystalline field splitting is crucial for understanding the magnetic properties of metal complexes. These properties are primarily linked to whether electrons are paired or unpaired.

A complex with unpaired electrons exhibits paramagnetism; such complexes are attracted to magnetic fields. On the other hand, complexes with all paired electrons exhibit diamagnetism and are not attracted to magnetic fields. The number of unpaired electrons and the extent of crystal field splitting dictate the strength of the paramagnetism. Greater the number of unpaired electrons, stronger the magnetic attraction.

The electronic distribution in metal complexes is significantly influenced by crystal field splitting. When ligands approach the central metal ion, they create an electrostatic environment that causes the degeneracy of the d-orbitals to be lifted.

The resulting split of orbitals into different energy levels requires an electronic reorganization, which depends on the electron count of the metal and the strength of the field produced by the ligands. The low-spin or high-spin configurations arise based on whether electrons prefer to occupy the lower energy orbitals first, pairing up only after these are filled, or if they remain unpaired as much as possible, influenced by the energy gap created by the crystal field. This distribution governs the properties such as magnetism, optical absorption, and potential chemical reactivity of the complex.