This document discusses evidence for covalent bonding in metal complexes. It explains that electron-electron repulsion is less in complexes than free metal ions due to delocalization of electrons over ligand orbitals. This is known as the nephelauxetic effect. The nephelauxetic parameter (β) quantifies this effect, with softer ligands having a smaller β value. Electron paramagnetic resonance (EPR) spectroscopy provides further evidence, as the spectra of complexes show interaction between the ligand nuclear spin and electrons of the metal ion.

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
Externalmagneticfield
Withmagneticnucleus
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