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Question
The hexaquo manganese (II) ion contains five unpaired electrons, while the hexacyanoion contains only one unpaired electron. Explain using Crystal Field Theory.
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Solution
The configuration of Mn in oxidation state +2 is 3d5. In the presence of H2O (weak field ligand) as ligand, the distribution of these five electrons is \[\ce{t^3_{2{g}} e^2_{{g}}}\] i.e. all the electrons remain unpaired. In the presence of CN– (strong field ligand) as ligand, the distribution is \[\ce{t^5_{2{g}} e^0_{{g}}}\] i.e. two t2g orbitals have paired electrons while the third t2g orbital has one unpaired electron.
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