Comparing Nickel Complexes: UV-VIS Spectra Analysis and Absorbance Differences

The difference in absorbance between Ni(SCN)2(PPh3)2 and Ni(NO3)2(PPh3)2 might be explained by several factors. 1. Difference in Concentration: The concentrations of the two solutions you are comparing are different. Ni(NO3)2(PPh3)2 is at a concentration of 5x10^-3 M, while Ni(SCN)2(PPh3)2 is at a concentration of 1x10^-3 M. According to Beer's Law, a higher concentration would lead to a higher absorbance. Therefore, the higher concentration of Ni(NO3)2(PPh3)2 could be the reason why its absorbance is higher. 2. Difference in Solvent: The choice of solvent can also be a factor altering the absorbance values. Each compound may have different interactions with their respective solvents (nitromethane for Ni(NO3)2(PPh3)2 and acetonitrile for Ni(SCN)2(PPh3)2), potentially impacting the stability of the compounds and the resulting spectra. 3. Difference in Ligand and Metal Orbital Interactions: Different ligands can lead to different splitting of the d-orbitals of the nickel complexes, leading to absorptions at different wavelengths and intensities. The SCN- ligand has different spectral properties compared to the NO3- ligand leading to variations in the UV-VIS spectra. 4. Difference in Coordination Geometry and/or Spin States: Differences in coordination geometry (tetrahedral, square planar etc.) or spin state (low spin or high spin) between the two complexes could also contribute to differing absorbances. To gain a comprehensive understanding, a more detailed study on the spectral characteristics of each compound along with a look at factors like the molar absorptivity of each compound, and the effects of solvent on the complexes may provide additional insights.