Question

Why CN- is a strong ligand than NC-??Aren't c donor stronger ligands.

Answer 1

(CN) is a strong ligand because of its ligand strength or binding power. CN− can bind to both iron(II) and -(III) hemo-proteins.

One definite factor is the ability of the ligand to stabilize its lone pair. You observe that the cyanide ion is a better ligand than the nitrogen ligand. Let's think about this. The lone pair that reacts on the cyanide ion is the lone pair on the carbon atom. Not the lone pair on the nitrogen atom.

Carbon is less electronegative than nitrogen. Thus carbon is less able to stabilize its valence electron density, which in turns enhances the reactivity of its valence electron density through increased negative charge density.