INVESTIGATION OF THE EFFECT OF NATURE OF LIGAND ON THE CRYSTAL FIELD SPLITTING PARAMETER OF OCTAHEDRAL CHROMIUM(III) COMPLEXES

Transition metal complexes are mostly coloured. These colors are known to be resulted from the energy difference between the sperated d-shells. The amount of seperation of d-shells depends on many factors, such as the size of metal ion, oxidation number of metal ion, complex geometry, nature of metal ion, and the nature of the ligand. As the nature of the ligand is is easy to change and there are lots of ligands, effect of the nature of ligands on \ncrystal field splitting parameter of a metal is selected as the question. As chromium(III) is common metal ion, easy to find and it forms d3 complexes, which have spectrums relatively easy to interpret; the scope of the investigation is limited to chromium(III) complexes. So, the objective of this study to investigate the effect of the nature of ligand on the Octahedral Crystal Field Splitting Parameter(Δo) of chromium(III) complexes. \nA variety of chromium (III) complexes with different ligands were synthesised; and characterized with UV-visible spectrometer. Then complexes’ crystal field splitting parameters are calculated from the transition band with the longest wavelength. Also another method, involving Tanabe-Sugano diagrams, was used to calculate crystal field splitting parameters for comparison. It was found that there is no significant difference between the calculate crystal field splitting parameter values calculated from the transition band with the longest wavelength and values calculated from Tanabe-Sugano diagram.Overall, the crystal field splitting parameter values are found to be as 199442 J/mole for Cr(acac)3, 258805 J/mole for [Cr(en)3]Cl3, 203020 J/mole for [Cr(H2O)6](NO3)3, 209766 J/mole for K3[Cr(ox)3], 212761 J/mole for K3[Cr(NCS)6]. The order of the ligands in increasing order is found to be acac <H2O< C2O42- (ox)<NCS<en which matches mostly with the spectrochemical series, which shows the order as C2O42-(ox) < H2O < NCS- < en.