`CN^(-)` is a strong field ligand. This is due to the fact that

Options

A. it carries a negative charge
B. it is a pseudohalide
C. it can accept electrons form metal species
D. it form high spin complexes with metal species

Answer

C

Explanation

Ligands such as CO, `CN^(-)` and `NO^(+)` have empty `pi` orbitals with the sorrect symmetry to overlap with the metal `t_(2g)` orbitals, forming `pi` bonds. This is often described as back bonding. Normally the `pi` orbitals on the ligands are higher energy than th emetal `t_(2g)` orbitals. No more electrons are added to the scheme as the ligand `pi` orbitals are empty, but the `pi` interaction increases the value of `Delta_(o)` . This accounts for th eposition of these ligands as strong field ligands, at the right of the spectrochemical series.