Three octahedral complexes of the same metal ion M³+ are: Complex I = [M(H2O)6]³+, Complex II = [M(NH3)6]³+, Complex III = [M(en)3]³+ (en = ethylenediamine). Consider the following statements: (A) Crystal field splitting order is Deltaₒ(II) Deltaₒ(I) Deltaₒ(III). (B) Wavelength of ligh

Question

Three octahedral complexes of the same metal ion M³+ are: Complex I = [M(H2O)6]³+, Complex II = [M(NH3)6]³+, Complex III = [M(en)3]³+ (en = ethylenediamine). Consider the following statements: (A) Crystal field splitting order is Deltaₒ(II) > Deltaₒ(I) > Deltaₒ(III). (B) Wavelength of light absorbed follows lambda(III) > lambda(I) > lambda(II). (C) Only complex III shows optical isomerism. (D) Neither M(AA)3 type nor Ma6 type complexes show geometric isomerism. Which statement(s) is/are CORRECT?

Accepted Answer

C and D only. Spectrochemical series: en > NH3 > H2O, so Deltaₒ: III > II > I. Since E = hc/lambda, higher Deltaₒ means smaller lambda absorbed: lambda order is I > II > III (opposite of Deltaₒ order). Statement A claims Deltaₒ: II > I > III — WRONG. Statement B claims lambda: III > I > II — WRONG. Statement C claims only III shows optical isomerism — WRONG; all M(AA)3 type (tris-bidentate) complexes including I and II if they were M(AA)3 would show it; actually [M(H2O)6] and [M(NH3)6] are Ma6 type which do NOT show optical isomerism, but [M(en)3]³+ does. So C is partially right? Reconsidering: among these three, only III = M(AA)3 type shows optical isomerism; I and II are Ma6 type which do

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