Absorbance of light of wavelength 470 nm at different concentrations of iron (II
ID: 493837 • Letter: A
Question
Absorbance of light of wavelength 470 nm at different concentrations of iron (III) thiocyanate [Source of both figures: Chan et al., Chemical Education Journal (CEJ), Vol. 7, No. 2, Registration No. 7-18, received October 27, 2003, http://chem.sci.utsunomiya- u.ac.jp/v7n2/choilchoi.html. Figure 2 was re-plotted based on the data in the source.] Figure 1 shows that a solution of iron (III) thiocyanate has maximum absorbance at a wavelength of 470 nm. State three factors that affect the wavelength of radiation absorbed by a transition metal complex carefully explaining the reasons for your choiceExplanation / Answer
The wavelength of the absorption depends on the energy difference between the t2g and eg orbitals i.e Delta(o) or crystal field stabilisation energy, wherein the wavelength is inversely prorportional to the energy difference.
1. The nature of the ligand, whether it is a strong field or weak field ligand. For strong field ligand the energy difference will be high and hence the wavelength of the absorption decreases for it, whereas for the weak field ligand it is the reverse case.
2. The oxidation state of the metal ion also plays an important role in the wavelength absorption. With the increase in the oxidation state of the metal ion, the crystal field splitting energy increases as a result the wavelength decreases.
3. The wavelength of the absorption also depends on the geometry of the complex. With respect to the octahedral. tetrahedral and square planar geometries.
The energy differences among the three will be in the order of
square planar > octahedral > tetrahedral
Hence reverse will be the case of wavelength absorption in these complexes.