Draw the crystal-field energy-level diagrams and show the placement of electrons for each of the following complexes:
d. [NiCl₄]²⁺ (tetrahedral),

Crystal Field Theory (CFT) explains the electronic structure of transition metal complexes by considering the interaction between the metal ion's d-orbitals and the electric fields produced by surrounding ligands. In this theory, the degeneracy of d-orbitals is lifted, leading to different energy levels based on the geometry of the complex, such as octahedral or tetrahedral arrangements.

In tetrahedral complexes, the arrangement of ligands around the central metal ion creates a specific geometry where the d-orbitals split into two sets: the lower-energy e set (dxy, dyz, dzx) and the higher-energy t2 set (dx2-y2, dz2). This splitting is less pronounced than in octahedral complexes, resulting in a smaller energy difference between the orbitals, which influences electron placement and the overall stability of the complex.

The electron configuration of a transition metal ion determines how electrons are distributed among the available d-orbitals. For [NiCl4]2+, nickel is in the +2 oxidation state, leading to a d8 configuration. In a tetrahedral field, the electrons will fill the lower-energy e orbitals first, followed by the higher-energy t2 orbitals, which is crucial for accurately drawing the crystal-field energy-level diagram.