text: A general d-orbital splitting diagram for square planar (D) transition metal complexes can be derived from the general octahedral (O) splitting diagram, in which the d−y, d and d orbitals. When the two axial ligands are removed to generate a square planar geometry, the d, d and d orbitals because of the torus shaped lobe of the d, d and d orbitals are generally presented as degenerate but they have to split into two different energy levels with respect to the irreducible representations of the point group D. Their relative ordering depends on the nature of the particular complex. Furthermore, the splitting of d-orbitals is perturbed by π-donating ligands in contrast to octahedral complexes. In the square planar case strongly π-donating ligands can cause the d and d orbitals to be higher in energy than the d</sub> orbital, whereas in the octahedral case π-donating ligands only affect the magnitude of the d-orbital splitting and the relative ordering of the orbitals is conserved.