Chemistry, Third edition

208 12 · CHEMICAL FAMILIES

Notice that a transition metal complex ion is written in squarebrackets and the over-

all charge on the ion is written outsidethe brackets. In this example, the copper ion

carries two positive charges and the water molecules are neutral, so the overall

charge on the ion is 2. The number of atoms directly attached to the central metal

atom (in this example, six) is called the coordination number.

Complex ions

Four Clions can act as ligands to form a complex ion with Cu^2 :

(i) What is the overall charge of the complex ion?

(ii)Write the formula for the complex ion.

(iii)What is the coordination number of the complex ion?

(iv)Name the complex.

Exercise 12P

Names of complex ions

Exercise 12Q

1. Name the following ions:
   (i) [Fe(CN) 6 ]^3 
   (ii)[Zn(NH 3 ) 4 ]^2 

(iii)[Ti(H 2 O) 6 ]^3 

(iv)[Cu(NH 3 ) 4 (H 2 O) 2 ]^2 

(v)[Co(NH 3 ) 5 Br]^2 

(vi)[Pt(NH 3 ) 2 Cl 4 ].

2. What are the formulae of the
   following ions?
   (i) hexachloroplatinate(IV)

(ii)tetraaquadichlorochromium(III)

(iii)hexacyanopalladate(IV)

(iv)tetrabromocobaltate(II)

(v)hexaaquairon(III).

BOX 12.9

Understanding the names of complex ions

Cationic (and neutral) complexes

Cationiccomplex ions are named by indicating the name and number of the ligands, followed

by the name and oxidation state of the central metal ion:

[Cu(H 2 O) 6 ]^2  is the hexaaquacopper(II) ion

[Ag(NH 3 ) 2 ]is the diamminesilver(I) ion

[FeCl(H 2 O) 5 ]is the pentaaquachloroiron(II) ion

Notice that water and ammonia produce ‘aqua’ and ‘ammine’ complexes. Negatively charged

ligands, such as Cl(chloro) end in ‘o’. The prefixes ‘di’, ‘tri’, ‘tetra’, ‘penta’ and ‘hexa’ are

used to show the number of ligands present and ligands are named in alphabetical order.

Anionic complexes

If the complex ion is anionic, the rules are followed as for cationic complexes but ‘ate’ is added

to the metal’s name:

[PtCl 4 ]^2  is the tetrachloroplatinate(II) ion

[Ni(CN) 4 ]^2 is the tetracyanonickelate(II) ion

[Zn(OH 4 ]^2 is the tetrahydroxozincate(II) ion

Notice that ‘ate’ is added to the Latin name of a metal, if it exists. Anionic complexes of copper

therefore end in ‘cuprate’ (from cuprum), whereas those of iron end in ‘ferrate’ (from ferrum).