The Foundations of Chemistry

Coordination Isomers

Coordination isomerism can occur in compounds containing both complex cations and
complex anions. Such isomers involve exchange of ligands between cation and anion, that
is, between coordination spheres.

Linkage Isomers

Certain ligands can bind to metal ions in more than one way. Examples of such ligands
are cyano, XCN, and isocyano, XNC; nitro, XNO 2 , and nitrito, XONO. The
donor atoms are on the left in these representations.

Cl

Cl

H 3 N NH 3

H 3 N NH

3

2 
 2 

[Pt(NH 3 ) 4 ][PtCl 6 ],

tetraammineplatinum(II) hexachloroplatinate(IV)

Pt

Cl Cl

Cl Cl

Pt

Cl

Cl

H 3 N NH 3

H 3 N NH

3

2 
 2 

[Pt(NH 3 ) 4 Cl 2 ][PtCl 4 ],

tetraamminedichloroplatinum(IV) tetrachloroplatinate(II)

Pt

Cl Cl

Cl Cl

Pt

25-6 Structural (Constitutional) Isomers 983

OH 2

OH 2

H 2 O OH 2

H 2 O OH

2

3 
 2 

[Cr(OH 2 ) 6 ]Cl 3

hexaaquachromium(III)

chloride

Cr 3 Cl

[Cr(OH 2 ) 4 Cl 2 ]Cl · 2H 2 O

tetraaquadichlorochromium(III)

chloride dihydrate

Cl,

2H 2 O

Cl

Cl

H 2 O OH 2

H 2 O OH

2

Cr

[Cr(OH 2 ) 5 Cl]Cl 2 · H 2 O

pentaaquachlorochromium(III)

chloride hydrate

2 Cl,

H 2 O

Cl

OH 2

H 2 O OH 2

H 2 O OH

Cr^2

violet blue-green green