Strong Field Ligand
A ligand that produces a large crystal field splitting, favouring electron pairing over occupation of upper orbitals.
Formula / equation
Δ > P
Unit
cm⁻¹
In depth
When the splitting exceeds the pairing energy, electrons pair up in the lower set rather than occupying the upper one, giving a low spin complex. Strong field ligands are typically good pi acceptors that stabilise the t₂g orbitals through back-bonding.
Examples in the real world
CN⁻, CO and NO₂⁻; hexacyanoferrate(II) is diamagnetic where the aqua complex has four unpaired electrons.