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Question
Discuss the nature of bonding in the following coordination entity on the basis of valence bond theory:
[CoF6]3−
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Solution
Co(27) = [Ar] 3d74s2
Co3+ = [Ar] 3d64s0
F− being a weak field ligand cannot pair electrons.
The oxidation state of cobalt in the complex is +3. Its electronic configuration is [Ar] 3d6. F− ion provides a weak ligand field and is unable to pair up the unpaired electrons of the 3d orbitals.
Hence, six equivalent hybrid orbitals are obtained by mixing of one 4s, three 4p and two 4d orbitals. Six empty sp3d2 hybrid orbitals are filled up by six electron pairs provided by F− ion. The highly paramagnetic nature of the complex further confirms the presence of four unpaired electrons.
As d-orbitals of the outermost shell participate in hybridisation, the complexes thus formed are called outer orbital complexes.
Hence, [CoF6]3− is a paramagnetic and octahedral complex.
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