Factors affecting Crystal Field Splitting parameter (Delta-o)

Two separate factors control how large the crystal field splitting parameter, Delta-o, turns out to be for a given octahedral complex. (a) Ligand strength: ligands that sit further along the spectrochemical series toward the strong-field end (Table 9.6) are able to approach the central metal ion more closely, and this closer approach is what produces a LARGER Delta-o -- ligand strength and Delta-o size go hand in hand. (b) Oxidation state of the metal ion: a metal ion carrying a HIGHER positive charge exerts a stronger electrostatic pull, drawing the surrounding ligands in closer than a metal ion with a lower charge would, and this closer approach again means a LARGER separation between the t2g and eg energy levels. As a direct consequence, a trivalent (3+) metal ion always produces a larger crystal field splitting than …