Question

A complex ion is a species in which a central metal ion is attached to a group of surrounding ions or molecules by coordinate covalent bonds. The surrounding species are called ligands. Within a ligand, the atoms that are directly attached to the metal ion (or atom) are called donor atoms. Most ligands contain a single donor atom (monodentate), but some contain two donor atoms (bidentate), six donor atoms (hexadentate), or another combination of donor atoms. A complex ion that is associated with one or more counter ions is called a coordination compound. For example [PdCl4]2− is a complex ion, and Na[PdCl4] is a coordination compound. The following table lists some common ligands.

Ligand	Number of donor atoms
Cl−	1
F−	1
Br−	1
CO32−	2
CN−	1
gly−	2
EDTA4−	6
NH3	1
H2O	1
CO	1

The coordination number for a complex is the total number of donor atoms surrounding the central atom. The overall charge on a complex is the sum of the charges of the metal and all the ligands.

Part A

What is the coordination number for each of the following complexes or compounds?

a) [Co(NH3)4Cl2]+

b) [Pb(EDTA)]2−

c) [Pt(NH3)4]2+

d) [Ag(NH3)2]NO3

Part B

What is the charge on each of the following complex ions?

a) hexaaquachromium(II), [Cr(H2O)6]?

b) tris(carbonato)aluminate(III), [Al(CO3)3]?

c) amminepentachloroplatinate(IV), [Pt(NH3)Cl5]?

Part C

What is the oxidation number of the central metal ion in each of the following complexes or compounds?

a) [NiCl2Br2]2−

b) [Cr(H2O)2(NH3)4]3+

c) Na[Ag(CN)2]