For each series of octahedral complexes, predict which will have the largest and
ID: 923584 • Letter: F
Question
For each series of octahedral complexes, predict which will have the largest and which will have the smallest value for Do. Briefly explain your answers. (Do not compare actual experimental values).
a) [Fe(H2O)6]3+ [Fe(ox)3]3– [Fe(CN)6]3– [Fe(NO2)6]3–
b) [Cr(SCN)6]3– [Cr(NH3)6]2+ [Cr(NH3)6]3+ [Cr(SCN)6]4–
c) [Ir(H2O)6]3+ [Rh(H2O)6]3+ [Co(H2O)6]2+ [Co(H2O)6]3+
d) [MoCl6]3– [MoF6]3– [MoCl6]2– [MoF6]2–
e) [V(en)3]4+ [Nb(en)3]4+ [V(CN)6]3– [Nb(CN)6]3–
Explanation / Answer
a) [Fe(H2O)6]3+
Ans: Largest ( Reason: Fe3+ free ion is a d5 ion. Two complexes are 6-coordinate and octahedral). high-spin complex.
[Fe(CN)6]3–
Ans : Smallest (Reason : We have 5 d-electrons. But only one unpaired electron. The 4th and 5th electrons must pair with electrons already in t2g orbitals). low-spin complex.
b) [Cr(NH3)6]3+ : Ans : Largest (High spin complex), Strong field ligands.
[Cr(SCN)6]4– : Smallest (Low spin complex), Weak field ligands.
c) [Ir(H2O)6]3+ : Ans : Largest
[Co(H2O)6]2+ Ans : Smallest
d) [MoCl6]3– : Ans : 3 spin allowed (Largest)
[MoCl6]2– : Ans : 2 spin allowed (Smallest)
e) [V(en)3]4+ : Ans : LArgest (High spin)
[Nb(CN)6]3– : Ans : Smallest (Low spin)
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