Crystal-field theory
In crystal-field theory, a ligand lone pair is modelled as a point negative charge (or as the partial negative charge of an electric dipole) that repels electrons in the d orbitals of the central metal ion. The theory concentrates on the resulting splitting of the d orbitals into groups with different energies, and uses that splitting to rationalize and correlate the optical spectra, thermodynamic stability, and magnetic properties of complexes.
Weak/strong field ligands
A spectrochemical series is a list of ligands ordered by ligand “strength”, and a list of metal ions based on oxidation number, group and element. For a metal ion, the ligands modify the difference in energy Δ between the d orbitals, called the ligand-field splitting parameter in ligand field theory, or the crystal-field splitting parameter in crystal field theory. The splitting parameter is reflected in the ion's electronic and magnetic properties such as its spin state, and optical properties such as its color and absorption spectrum.
TO READ:
- Shriver and Atkins' Inorganic Chemistry, Fifth Edition
- J. E. Huheey, E. A. Keiter, and R. L. Keiter, Inorganic chemistry: principles of structure and reactivity (Harper Collins College Publishers, New York, 1993).
- Savina, A. A., Boev, A. O., Orlova, E. D., Morozov, A. V., & Abakumov, A. M. (2023). Nickel as a key element in the future energy. Russ. Chem. Rev., 92.