This document discusses evidence for covalent bonding in metal complexes from three perspectives: 1. The nephelauxetic effect shows that electron-electron repulsion is less in complexes than free metal ions due to delocalization of electrons over ligand orbitals. 2. Nephelauxetic parameters (β) quantify this effect, with softer ligands having smaller β values. 3. Electron paramagnetic resonance (EPR) spectroscopy reveals hyperfine splitting in complex spectra, showing interaction between ligand nuclear spins and metal electron spins, further indicating covalent bonding.

1. Ligand orbital
Evidences for Covalent
bonding in complexes
Dr. Mithil Fal Desai
Shree Mallikarjun and Shri Chetan
Manju Desai College Canacona Goa
metal orbital

2. Nephelauxetic effect
Electron-electron repulsion in the complexes is less
than that of free metal ion due to expansion of
electron cloud. This is caused by delocalisation of
electron over ligand orbitals.
metal orbital
Free metal ion
Complex ion
Ligand orbital

3. Nephelauxetic parameter (β or h)
𝜷 =
𝑩(𝒄𝒐𝒎𝒑𝒍𝒆𝒙)
𝑩(𝒇𝒓𝒆𝒆 𝒊𝒐𝒏)
B= Racah parameter (repulsion energies between individual
d electron).
β is in order
Br-< CN-,Cl < NH3 < H2O < F-
Softer the ligand smaller will be the nephelauxetic
parameter

4. Electron paramagnetic resonance
(EPR)
ms = -½
ms = +½
B0

5. Hyperfine splitting in EPR spectra
of the complexes
ms = +½
ms = -½
ml = -½
ml = -½
ml = +½
ml = +½
External
magnetic
field
With
magnetic
nucleus
Energy
The EPR spectra of the complexes show there is interaction of nuclear spin of
ligand with free electrons metal ion.
Free metal ion
Complex ion
Signal
Magnetic field
strength

6. Hyperfine splitting in EPR spectra
of the complexes
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