Question

Polydentate ligands can vary in the number of coordination positions they occupy. In each of the following, identify the polydentate ligand present and indicate the probable number of coordination positions it occupies: (a) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4}(0-\mathrm{phen})\right] \mathrm{Cl}_{3}\) (b) \(\left[\mathrm{Cr}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\right] \mathrm{Br}\) (c) \(\left[\mathrm{Cr}(\mathrm{EDTA})\left(\mathrm{H}_{2} \mathrm{O}\right)\right]^{-}\) (d) \(\left[\mathrm{Zn}(\mathrm{en})_{2}\right]\left(\mathrm{ClO}_{4}\right)_{2}\)

Short answer

(a) The polydentate ligand is orthophenanthroline (0-phen), which is a bidentate ligand and occupies two coordination positions. (b) The polydentate ligand is oxalate ion (\(\mathrm{C}_{2}\mathrm{O}_{4}\)), which is a bidentate ligand and occupies two coordination positions. (c) The polydentate ligand is ethylenediaminetetraacetic acid (EDTA), which is a hexadentate ligand and occupies six coordination positions. (d) The polydentate ligand is ethylenediamine (en), which is a bidentate ligand and occupies two coordination positions. In this complex, there are two ethylenediamine ligands, so there are a total of four occupied positions.

Step-by-step solution

Identify the polydentate ligand

In this complex, the polydentate ligand is 0-phen, which stands for orthophenanthroline.

Determine the number of coordination positions

Orthophenanthroline (0-phen) is a bidentate ligand, meaning it can occupy two coordination positions. (b) $\left[\mathrm{Cr}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\right] \mathrm{Br}$

Identify the polydentate ligand

In this complex, the polydentate ligand is \(\mathrm{C}_{2}\mathrm{O}_{4}\), which represents oxalate ion.

Determine the number of coordination positions

Oxalate ion is a bidentate ligand, meaning it can occupy two coordination positions. (c) $\left[\mathrm{Cr}(\mathrm{EDTA})\left(\mathrm{H}_{2} \mathrm{O}\right)\right]^{-}$

Identify the polydentate ligand

In this complex, the polydentate ligand is EDTA, which stands for ethylenediaminetetraacetic acid.

Determine the number of coordination positions

EDTA is an hexadentate ligand, which means it can occupy six coordination positions. (d) \(\left[\mathrm{Zn}(\mathrm{en})_{2}\right]\left(\mathrm{ClO}_{4}\right)_{2}\)

Identify the polydentate ligand

In this complex, the polydentate ligand is en, which stands for ethylenediamine.

Determine the number of coordination positions

Ethylenediamine (en) is a bidentate ligand, meaning it can occupy two coordination positions. In this complex, there are two ethylenediamine ligands, so there are a total of four occupied positions.