Ligands and complexes
Ligands and complexes
- A transition ion can be surrounded by ligands to form a complex.
- A ligand donates a lone pair in a dative bond.
- The shape follows the coordination number.
Ligands and denticity
- a ligand has a lone pair that forms a dative covalent bond to the metal.
- monodentate (one bond): $\text{H}_2\text{O}$, $\text{NH}_3$, $\text{Cl}^-$, $\text{CN}^-$.
- bidentate (two): "en", ethanedioate $\text{C}_2\text{O}_4^{2-}$.
- polydentate (many): $\text{EDTA}^{4-}$ (six).
Practice
A ligand bonds to a metal ion by:
A ligand donates a lone pair to the metal's vacant orbital — a dative (coordinate) bond.
Practice
A bidentate ligand forms:
Bidentate ligands (e.g. "en", ethanedioate) form two dative bonds each.
Shape and coordination number
- The coordination number = number of dative bonds to the metal:
- 2 → linear; 4 → tetrahedral or square planar; 6 → octahedral.
- The complex's charge = the metal's charge + all the ligand charges.
Practice
A complex with coordination number 6 is:
6 → octahedral; 4 → tetrahedral or square planar; 2 → linear.
Practice
The overall charge on a complex ion is found by:
Sum the central metal charge with the charges of all the ligands.
You've got it
Key idea
- a ligand donates a lone pair (dative bond); mono-/bi-/poly-dentate = 1/2/many bonds
- coordination number: 2 → linear, 4 → tetrahedral/square planar, 6 → octahedral
- complex charge = metal charge + ligand charges