Compound Max Wave length Absorbance CuSo4 (0.05M) = 800nm CuSO4 + EdTA = 732nm C
ID: 539209 • Letter: C
Question
Compound Max Wave length Absorbance
CuSo4 (0.05M) = 800nm
CuSO4 + EdTA = 732nm
CuSO4 + Sodium nitrate (0.05M) = 780nm
CuSO4 + Ethylenediamine (0.05) = 550nm
CuSO4 + Ethylenediamine (16.5M) = 571nm
Please help on how to figure out these questions.
1) Calculate the corresponding crystal field splitting energy values for each of the copper (II) complexes with the different ligands used above.
2) Based upon the information above, created a spectrochemical series for the copper (II) ligands.
Please help and explain!!
Explanation / Answer
1) crystal field splitting energy values calculation
The CFSE of an octahedral complex can be calculated using the following formula
CFSE = -nt2g*0.4+neg*0.6
-nt2g = no. of electrons present in the t2g level
neg = no. of electrons present in the eg level
For the reaction between CuSO4 and NaNO2 we get [Cu(NO2)6]^4-
CuSO4(aq) + NaNO2(aq) -------> Cu(NO2)6(aq) + Na2SO4(aq)
In Cu(NO2)6, Cu is in +2 oxidation state and it contain 9 electrons. These 9 electrons can be arranged in the 5 d-orbitals as t2g^6 eg^3. Thus its CFSE is
CFSE = -6*0.4+3*0.6 = -0.6 = 6Dq
For the reaction between CuSO4 and Ethylenediamine(En) we get [Cu(En)3]^2+
CuSO4(aq) + H2N-CH2-CH2-NH2(aq) -------> Cu(En)3(aq)
In [Cu(EN)3]^2+, Cu is in +2 oxidation state and it contain 9 electrons. These 9 electrons can be arranged in the 5 d-orbitals as t2g^6 eg^3. Thus its CFSE is
CFSE = -6*0.4+3*0.6 = -0.6 = 6Dq
The CFSE value is same for all given ligand irrespective of their field strengths i.e., 0.6 or 6Dq
2) Based upon the information above, a spectrochemical series for the copper (II) ligands can be predicted
The wavelengths of absorption is given that
CuSo4 (0.05M) = 800nm
CuSO4 + EdTA = 732nm
CuSO4 + Sodium nitrate (0.05M) = 780nm
CuSO4 + Ethylenediamine (0.05) = 550nm
CuSO4 + Ethylenediamine (16.5M) = 571nm
The wavelength of radiation is directly proportional to the energy gap between t2g and eg levels in the octahedral field. This energy gap is depends upon the field strength of the ligand
As field strength increases the frequency of radiation absorbed by the complex increases or as field strength increases the wavelength of radation absorbed decreases.
Thus, En(0.05 M) > En(16.5 M) > EDTA > NO2- > SO4^2-
En (0.05 M) showing shortest wavelength and hence its field strength is strong while SO4^2- showing longer wavelength and hence its field strength is weak
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